This is a worldwide forum, and I'll bet the majority of members and guests really don't know everything and more about Jowetts, and are actually grateful to be able to read posts by such knowledgeable Jowetteers. Explanations are necessary, as most of us perhaps haven't had a lifetime of working with motor vehicles, so keep it coming in a light-hearted way. Tony.yes know all that and more
Distributors
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Tony Fearn
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- Your interest in the forum: Early pre-wars. Owner of 1933 'Flying Fox' 'Sarah Jane, and 1934 Short saloon 'Mary Ellen'.
- Given Name: Anthony
- Location: Clayton le Moors, Lancashire, the Premier County in the British Isles!!
Distributors
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Forumadmin
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I copied this from a website, most of it is relevant. I have highlighted some points.
Maybe you've just built up a brand new engine, or upgraded to new heads and a cam, perhaps you're simply trying to dial-in an existing combination. In either scenario, one area of tuning that is highly overlooked and greatly misunderstood is timing. All too often we see people dropping in their distributor, making a quick adjustment with their timing light, and setting off to make another pass.
Timing is everything, and without a proper timing curve, every thing else goes out the window. Jetting changes, fuel pressure adjustments, are all useless if first the timing is not set correctly.
So what is timing? In a nutshell, timing or 'ignition timing' relates to when the sparkplug is fired in relation to piston position. At idle, when engine speeds are the lowest, the plug fires just before the piston reaches the top of its stroke. As engine speeds increase, the time between piston strokes is less, and therefore the plug must fire sooner. In all cases the plug is fired in advance of the piston reaching top dead center. There is a small window of time in which the combustion need to take place in order to produce peak power. Too late and power is lost, too soon and detonation occurs, which can lead to melted pistons.
In reality, ignition timing, is a complex physical process, dealing with multiple variable, including compression ratio, volumetric efficiency, combustion chamber shape, cylinder temperature, etc. Very interesting stuff indeed, but we wont get into it here.
In this article we're going to focus primarily on carburated, non-computer controlled, engines which have fully adjustable distributors. The EEC-IV computer controlled Fords allow for setting initial timing, but the rest is adjusted by the computer. The newer modular engine Fords have distributor-less ignitions which offer no adjustability from the factory, although companies like Steeda have recently developed timing adjusters for these engines. Some Fords, particularly in the 70's and early 80's, had distributors where timing was fixed due to emissions reasons.
When it comes to timing the most common myth is that adjusting the timing simply means moving the distributor clockwise or counterclockwise. While this does affect the timing, it is not the correct way to adjust the timing curve. To explain why, we first we need to define some terms.
Advancing and retarding timing refers to increasing or decreasing the 'time' at which spark is delivered to the cylinders. This 'time' is measured in crankshaft degrees, signified by marks on the harmonic balancer, and a reference pointer on the block or timing chain cover. When the piston is at Top Dead Center (TDC), this is synonymous with zero degrees on the balancer. Ten degrees before that point would mean the piston is ten degrees of rotation from being at TDC.
So how does the crank position relate to the distributor?
The distributor shaft on Ford engines is driven by the camshaft gear, which is turned at half-crank speed by the timing chain connected to the crankshaft. Thus there is a direct correlation between the position of the crank and the position of the distributor. Remember, the distributor is a switch. Regardless of the type of distributor you have, there is a fundamental design common to all of them; the shaft is in a fixed position, spinning in direct relation to the crankshaft. On the shaft sits the trigger which activates the switch. On electronic distributors the trigger may be a magnetic sleeve with eight openings, or in the case of points, its simply an arm that open and closes the points. The distributor housing does not spin and it contains the actual switch, such as the Pertronix box, which is mounted on a breaker plate. By rotating the housing you in effect move the position of the switch, changing when it triggers a spark. When you rotate the distributor to "adjust the timing" you are moving the switch on the housing side in relation to the trigger on the shaft.
Rotating the distributor housing clockwise on a Ford advances the timing (i.e. spark is being fired a greater number of degrees before the piston reaches TDC), and counterclockwise decreases the timing.
When referring to timing, there are really four terms that must be considered; initial timing, mechanical (or centrifugal) timing, total timing, and vacuum advance. There is also cam timing which is more appropriately termed valve timing, since it deals with when the valves open and close in relation to crank position. We won't talk about this since it has no dynamic bearing on ignition timing.
Initial: This is the most common adjustment that people associate with timing. At idle, with the vacuum advance hose disconnected and plugged, this is the timing that you would see if you flashed timing light on the timing marks. On typical stock engines you'd see as low as 0 to as high as 15 degrees. Most Ford shop manuals specify around 6-8 degrees initial timing advance for the 289-351 motors.
Mechanical/Centrifugal: Most V8 distributors contain an internal advance mechanism consisting of two each of weights, springs, and slotted 'reluctor' arms. There is also a stop tab for the arms. On Fords this assembly can only be seen by removing the cap, rotor, and breaker plate; we'll get to removal a bit later. As the distributor shaft spins with increasing rpms, the centrifugal force acts on the weights, which begin to force outwards against the springs. This movement rotates the shaft and thus advances the timing. The slotted arm controls how much the weights can move the assembly, and the springs control how fast the assembly reaches that limit. The reluctor arm on a Ford has two slotted sides, only one side contributes to the timing, the arm can be flipped around if more advance is needed (see pictures.) On Fords each side is stamped with a number, usually 10L and 13L; or some have 15L and 18L. These numbers refer to 1/2 of the total degrees of timing that will be obtained when using that arm. So for example a 15L arm would contribute 15 x 2= 30 degrees of timing when full against the stop.
Total Advance: So far we have looked at initial advance and mechanical advance. Both of these combined gives total advance. Say for example initial was found to be 6 degrees, and we visually verified that the reluctor arm was on the 15L side. Total timing, theoretically, is then the initial + mechanical. In this case 6 + (15 x 2) = 36 degrees. If we shined a timing light on the marks (with vacuum hose disconnected and plugged), at idle we'd see 6 degrees, then as we increased the engine speed, we'd see more and more advance, until at some point the total centrifugal advance would be reached, and we would see 36 degrees. When exactly the total advance occurs is of great importance when it comes to performance, and we discuss this in the section below on "curving."
Vacuum Advance: Most Ford distributors include a vacuum advance mechanism. This consists of a diaphragm vacuum canister, an arm from the canister to the breaker plate, and a hose connected to an engine vacuum source. The purpose of this mechanism is to provide spark advance when the engine is not spinning fast enough to create the centrifugal advance talked about earlier. In other words this is an engine-load dependent advance. This would be a typical situation when climbing a steep hill, or driving at low rpms, light throttle, conditions. In these conditions there is high engine vacuum, so the vacuum signal applied to the diaphragm in the canister, via the hose, will cause a 'pull' effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there is very little engine vacuum, and thus the vacuum advance does not contribute to total advance.
Vacuum advance is tricky to tune because there is no direct measurement like total. In fact, the reason you must measure initial and total timing with the vacuum hose disconnected is because when the engine is in neutral there no load, thus the vacuum is high, and if the hose were connected you'd see as high as 60 degrees advance and think something is really wrong! The only way to tune vacuum advance is on the road, by feel, and AFTER the initial and total are adjusted.
In short, vacuum advance was developed to optimize fuel economy and reduce emissions. It is not a bad thing to have on a car which sees a lot of street driving, and in such conditions the engine will perform better with it properly adjusted. However many factory and aftermarket performance distributors do not even come with a vacuum advance. The reason is simply because race cars do not spend much time at part throttle.
Curving for Performance
A timing curve is simply a plot of how much ignition advance takes place over the rpm range. In other words, when the timing advances is just as critical as how much it advances.
When it comes to performance there are many different engine combinations, buildups, components, and uses….Each requiring slightly different timing curves. On the other hand if you have a stock motor, and do not care for every extra horsepower, you really do not need to do more than follow the shop manual procedures. However even a stock or mild daily driver motor can be made to accelerate faster with a five minute timing curve adjustment.
The rule of thumb is that the higher the compression ratio, the less total timing it can handle before detonation, and also the higher octane rating it needs to control detonation. Low octane fuels ignite faster, thus require less timing advance. Conversely high octane fuel can handle slightly more advance. Dyno testing has shown that most small block Fords with 9:1 to 9.5:1 compression make peak HP with 38-42 degrees total advance. Engines with 9.5:1 - 10.5:1 run best with 35-38 degrees total, and above 11:1, should not go higher than 35 deg. total. When using power adders such as nitrous, super or turbo chargers, the timing should be advanced accordingly.
The first step in curving a distributor is to set you initial and total advance. As detailed above and in the picture captions, the total is determined by the reluctor arm setting plus the initial advance. Ideally you should keep the initial between 10 and 20 degrees, and the total in the ranges listed above for your compression ratio. For example, if you are shooting for 40 degrees total, and your reluctor arm is on the 15L slot, you would have 30 degrees mechanical advance, requiring the initial to be set at 10 degrees.
The second step is to dial-in how fast the distributor achieves the total advance. This is controlled by the springs which hold back the weights, under the breaker plate. A stock distributor usually has one light and one heavy spring, and brings the timing in really slow, such that the distributor may only reach the total timing at very high engine speeds, 4500+ for example. For performance driving, the best acceleration comes when total advance is achieved before 2500 rpm. To adjust this rate, you can replace the stock springs with lighter tension springs. You can also bend the tabs on which the springs connect to change their tension.
Once you've set the initial and mechanical timing, and adjusted the curve, you should be very very close, if not right at, the optimum timing curve for wide-open throttle performance. You should use timing light at this point to confirm that the initial timing is where you set it, and steady, and then check the timing from idle to 3500 in 500rpm increments. The curve should increase a few degrees at every checkpoint until 2500, where it hits the maximum. After 2500 it should not go beyond the total advance.
Final Thoughts
Hopefully we taken some of the mystery out of properly curving a distributor. Keep in mind these are ballpark ranges, and every engine responds differently. Aluminum heads, large overlap cams, differences in cylinder pressures, all affect timing. Optimum timing can really only be determined on a dyno, or under very controlled and repeatable track conditions. When we dynoed Project 11.99 recently on a chassis dyno, we saw first hand a difference of 30 rear wheel horsepower from timing at 30 degrees total and 42 degrees total! We've also seen gains of up to eight tenths due to improper timing. It is a cheap and relatively quick modification that can be worth significant power.
Maybe you've just built up a brand new engine, or upgraded to new heads and a cam, perhaps you're simply trying to dial-in an existing combination. In either scenario, one area of tuning that is highly overlooked and greatly misunderstood is timing. All too often we see people dropping in their distributor, making a quick adjustment with their timing light, and setting off to make another pass.
Timing is everything, and without a proper timing curve, every thing else goes out the window. Jetting changes, fuel pressure adjustments, are all useless if first the timing is not set correctly.
So what is timing? In a nutshell, timing or 'ignition timing' relates to when the sparkplug is fired in relation to piston position. At idle, when engine speeds are the lowest, the plug fires just before the piston reaches the top of its stroke. As engine speeds increase, the time between piston strokes is less, and therefore the plug must fire sooner. In all cases the plug is fired in advance of the piston reaching top dead center. There is a small window of time in which the combustion need to take place in order to produce peak power. Too late and power is lost, too soon and detonation occurs, which can lead to melted pistons.
In reality, ignition timing, is a complex physical process, dealing with multiple variable, including compression ratio, volumetric efficiency, combustion chamber shape, cylinder temperature, etc. Very interesting stuff indeed, but we wont get into it here.
In this article we're going to focus primarily on carburated, non-computer controlled, engines which have fully adjustable distributors. The EEC-IV computer controlled Fords allow for setting initial timing, but the rest is adjusted by the computer. The newer modular engine Fords have distributor-less ignitions which offer no adjustability from the factory, although companies like Steeda have recently developed timing adjusters for these engines. Some Fords, particularly in the 70's and early 80's, had distributors where timing was fixed due to emissions reasons.
When it comes to timing the most common myth is that adjusting the timing simply means moving the distributor clockwise or counterclockwise. While this does affect the timing, it is not the correct way to adjust the timing curve. To explain why, we first we need to define some terms.
Advancing and retarding timing refers to increasing or decreasing the 'time' at which spark is delivered to the cylinders. This 'time' is measured in crankshaft degrees, signified by marks on the harmonic balancer, and a reference pointer on the block or timing chain cover. When the piston is at Top Dead Center (TDC), this is synonymous with zero degrees on the balancer. Ten degrees before that point would mean the piston is ten degrees of rotation from being at TDC.
So how does the crank position relate to the distributor?
The distributor shaft on Ford engines is driven by the camshaft gear, which is turned at half-crank speed by the timing chain connected to the crankshaft. Thus there is a direct correlation between the position of the crank and the position of the distributor. Remember, the distributor is a switch. Regardless of the type of distributor you have, there is a fundamental design common to all of them; the shaft is in a fixed position, spinning in direct relation to the crankshaft. On the shaft sits the trigger which activates the switch. On electronic distributors the trigger may be a magnetic sleeve with eight openings, or in the case of points, its simply an arm that open and closes the points. The distributor housing does not spin and it contains the actual switch, such as the Pertronix box, which is mounted on a breaker plate. By rotating the housing you in effect move the position of the switch, changing when it triggers a spark. When you rotate the distributor to "adjust the timing" you are moving the switch on the housing side in relation to the trigger on the shaft.
Rotating the distributor housing clockwise on a Ford advances the timing (i.e. spark is being fired a greater number of degrees before the piston reaches TDC), and counterclockwise decreases the timing.
When referring to timing, there are really four terms that must be considered; initial timing, mechanical (or centrifugal) timing, total timing, and vacuum advance. There is also cam timing which is more appropriately termed valve timing, since it deals with when the valves open and close in relation to crank position. We won't talk about this since it has no dynamic bearing on ignition timing.
Initial: This is the most common adjustment that people associate with timing. At idle, with the vacuum advance hose disconnected and plugged, this is the timing that you would see if you flashed timing light on the timing marks. On typical stock engines you'd see as low as 0 to as high as 15 degrees. Most Ford shop manuals specify around 6-8 degrees initial timing advance for the 289-351 motors.
Mechanical/Centrifugal: Most V8 distributors contain an internal advance mechanism consisting of two each of weights, springs, and slotted 'reluctor' arms. There is also a stop tab for the arms. On Fords this assembly can only be seen by removing the cap, rotor, and breaker plate; we'll get to removal a bit later. As the distributor shaft spins with increasing rpms, the centrifugal force acts on the weights, which begin to force outwards against the springs. This movement rotates the shaft and thus advances the timing. The slotted arm controls how much the weights can move the assembly, and the springs control how fast the assembly reaches that limit. The reluctor arm on a Ford has two slotted sides, only one side contributes to the timing, the arm can be flipped around if more advance is needed (see pictures.) On Fords each side is stamped with a number, usually 10L and 13L; or some have 15L and 18L. These numbers refer to 1/2 of the total degrees of timing that will be obtained when using that arm. So for example a 15L arm would contribute 15 x 2= 30 degrees of timing when full against the stop.
Total Advance: So far we have looked at initial advance and mechanical advance. Both of these combined gives total advance. Say for example initial was found to be 6 degrees, and we visually verified that the reluctor arm was on the 15L side. Total timing, theoretically, is then the initial + mechanical. In this case 6 + (15 x 2) = 36 degrees. If we shined a timing light on the marks (with vacuum hose disconnected and plugged), at idle we'd see 6 degrees, then as we increased the engine speed, we'd see more and more advance, until at some point the total centrifugal advance would be reached, and we would see 36 degrees. When exactly the total advance occurs is of great importance when it comes to performance, and we discuss this in the section below on "curving."
Vacuum Advance: Most Ford distributors include a vacuum advance mechanism. This consists of a diaphragm vacuum canister, an arm from the canister to the breaker plate, and a hose connected to an engine vacuum source. The purpose of this mechanism is to provide spark advance when the engine is not spinning fast enough to create the centrifugal advance talked about earlier. In other words this is an engine-load dependent advance. This would be a typical situation when climbing a steep hill, or driving at low rpms, light throttle, conditions. In these conditions there is high engine vacuum, so the vacuum signal applied to the diaphragm in the canister, via the hose, will cause a 'pull' effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there is very little engine vacuum, and thus the vacuum advance does not contribute to total advance.
Vacuum advance is tricky to tune because there is no direct measurement like total. In fact, the reason you must measure initial and total timing with the vacuum hose disconnected is because when the engine is in neutral there no load, thus the vacuum is high, and if the hose were connected you'd see as high as 60 degrees advance and think something is really wrong! The only way to tune vacuum advance is on the road, by feel, and AFTER the initial and total are adjusted.
In short, vacuum advance was developed to optimize fuel economy and reduce emissions. It is not a bad thing to have on a car which sees a lot of street driving, and in such conditions the engine will perform better with it properly adjusted. However many factory and aftermarket performance distributors do not even come with a vacuum advance. The reason is simply because race cars do not spend much time at part throttle.
Curving for Performance
A timing curve is simply a plot of how much ignition advance takes place over the rpm range. In other words, when the timing advances is just as critical as how much it advances.
When it comes to performance there are many different engine combinations, buildups, components, and uses….Each requiring slightly different timing curves. On the other hand if you have a stock motor, and do not care for every extra horsepower, you really do not need to do more than follow the shop manual procedures. However even a stock or mild daily driver motor can be made to accelerate faster with a five minute timing curve adjustment.
The rule of thumb is that the higher the compression ratio, the less total timing it can handle before detonation, and also the higher octane rating it needs to control detonation. Low octane fuels ignite faster, thus require less timing advance. Conversely high octane fuel can handle slightly more advance. Dyno testing has shown that most small block Fords with 9:1 to 9.5:1 compression make peak HP with 38-42 degrees total advance. Engines with 9.5:1 - 10.5:1 run best with 35-38 degrees total, and above 11:1, should not go higher than 35 deg. total. When using power adders such as nitrous, super or turbo chargers, the timing should be advanced accordingly.
The first step in curving a distributor is to set you initial and total advance. As detailed above and in the picture captions, the total is determined by the reluctor arm setting plus the initial advance. Ideally you should keep the initial between 10 and 20 degrees, and the total in the ranges listed above for your compression ratio. For example, if you are shooting for 40 degrees total, and your reluctor arm is on the 15L slot, you would have 30 degrees mechanical advance, requiring the initial to be set at 10 degrees.
The second step is to dial-in how fast the distributor achieves the total advance. This is controlled by the springs which hold back the weights, under the breaker plate. A stock distributor usually has one light and one heavy spring, and brings the timing in really slow, such that the distributor may only reach the total timing at very high engine speeds, 4500+ for example. For performance driving, the best acceleration comes when total advance is achieved before 2500 rpm. To adjust this rate, you can replace the stock springs with lighter tension springs. You can also bend the tabs on which the springs connect to change their tension.
Once you've set the initial and mechanical timing, and adjusted the curve, you should be very very close, if not right at, the optimum timing curve for wide-open throttle performance. You should use timing light at this point to confirm that the initial timing is where you set it, and steady, and then check the timing from idle to 3500 in 500rpm increments. The curve should increase a few degrees at every checkpoint until 2500, where it hits the maximum. After 2500 it should not go beyond the total advance.
Final Thoughts
Hopefully we taken some of the mystery out of properly curving a distributor. Keep in mind these are ballpark ranges, and every engine responds differently. Aluminum heads, large overlap cams, differences in cylinder pressures, all affect timing. Optimum timing can really only be determined on a dyno, or under very controlled and repeatable track conditions. When we dynoed Project 11.99 recently on a chassis dyno, we saw first hand a difference of 30 rear wheel horsepower from timing at 30 degrees total and 42 degrees total! We've also seen gains of up to eight tenths due to improper timing. It is a cheap and relatively quick modification that can be worth significant power.
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Forumadmin
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And this is for a VW engine, another flat four.
What you want is to set your ignition timing about 4 degrees retarded from the point where detonation begins. This setting means the flame front will meet the piston at the top, maximizing cylinder pressure and the time (crank degrees) to push the piston down, making the most power. If you ignite the charge too late, the pressure doesn't build until the crank has rotated some, and you lose precious crank degrees (HORSEPOWER) of work. If the charge is ignited too early, the flame front will hit the piston ON THE WAY UP, and this is a sure-fire way to destroy your engine very quickly.
What is needed is to find the timing point at EVERY RPM point where you are around 4 degrees retarded from detonation under full throttle, since this is the "ideal" time for our spark to occur. Obviously, you would leave yourself a safety zone of 3-4 degrees of timing at all points to CYA in case of bad gas, clogged main jet, vacuum leak, abnormally hot engine, etc. The power difference between detonation and 3-4 degrees of retarded timing from this point is negligible, so riding the ragged edge of timing is not worth the risk, IMO. Detonation does NOT have to be audible for it to turn your expensive mechanical marvel into junk in short order.
Finding the Advance Curve
Ideally, you would remove all advance from the distributor, and run a locked timing. You then put the engine on a dyno, and play with timing across the RPM band from idle to redline at full throttle (finding the timing where you are 4 degrees from detonation) and then chart it. Then, you remove the locked timing from the distributor, set your initial timing to match what you found was best at idle. Next, match the distributor's curve to match what you found to be best on the dyno by changing weights and springs in the distributor.
If you have the patience and time to set up this custom curve, and have a heavily modified engine, your patience will be rewarded! Get yourself a Mallory/MSD distributor. You will find they are VERY adjustable. The easiest method to follow is very straightforward. Find the MAX advance point your engine tolerates (between 30-40 degrees BTDC) above 3000 RPM. Now find the place where it responds best at idle. It may be 15-24 degrees BTDC. You may find that this much advance causes starting difficulties when the engine is hot, so be sure to check this out! Ignition before top dead center causes "negative torque" and that's what suddenly STOPS your engine from cranking. Avoid this, or use a retard that is activated during cranking.
Now, you know the two critical points in your advance curve. You only need to figure out how FAST you want the advance to come in. I recommend being conservative, and kick the advance in SLOWLY and see how the engine responds. Keep adjusting it (it requires distributor disassembly) so it comes in quicker and quicker, until you detect detonation (problem). Back it to the previous setting, and you are DONE with the centrifugal advance. Now, dial in 10 degrees of vacuum advance, and adjust the advance so the carb(s) will actually activate it and you are done! PHEW!
Frankly, though, finding the advance curve using this method isn't practical for most of us.
What you want is to set your ignition timing about 4 degrees retarded from the point where detonation begins. This setting means the flame front will meet the piston at the top, maximizing cylinder pressure and the time (crank degrees) to push the piston down, making the most power. If you ignite the charge too late, the pressure doesn't build until the crank has rotated some, and you lose precious crank degrees (HORSEPOWER) of work. If the charge is ignited too early, the flame front will hit the piston ON THE WAY UP, and this is a sure-fire way to destroy your engine very quickly.
What is needed is to find the timing point at EVERY RPM point where you are around 4 degrees retarded from detonation under full throttle, since this is the "ideal" time for our spark to occur. Obviously, you would leave yourself a safety zone of 3-4 degrees of timing at all points to CYA in case of bad gas, clogged main jet, vacuum leak, abnormally hot engine, etc. The power difference between detonation and 3-4 degrees of retarded timing from this point is negligible, so riding the ragged edge of timing is not worth the risk, IMO. Detonation does NOT have to be audible for it to turn your expensive mechanical marvel into junk in short order.
Finding the Advance Curve
Ideally, you would remove all advance from the distributor, and run a locked timing. You then put the engine on a dyno, and play with timing across the RPM band from idle to redline at full throttle (finding the timing where you are 4 degrees from detonation) and then chart it. Then, you remove the locked timing from the distributor, set your initial timing to match what you found was best at idle. Next, match the distributor's curve to match what you found to be best on the dyno by changing weights and springs in the distributor.
If you have the patience and time to set up this custom curve, and have a heavily modified engine, your patience will be rewarded! Get yourself a Mallory/MSD distributor. You will find they are VERY adjustable. The easiest method to follow is very straightforward. Find the MAX advance point your engine tolerates (between 30-40 degrees BTDC) above 3000 RPM. Now find the place where it responds best at idle. It may be 15-24 degrees BTDC. You may find that this much advance causes starting difficulties when the engine is hot, so be sure to check this out! Ignition before top dead center causes "negative torque" and that's what suddenly STOPS your engine from cranking. Avoid this, or use a retard that is activated during cranking.
Now, you know the two critical points in your advance curve. You only need to figure out how FAST you want the advance to come in. I recommend being conservative, and kick the advance in SLOWLY and see how the engine responds. Keep adjusting it (it requires distributor disassembly) so it comes in quicker and quicker, until you detect detonation (problem). Back it to the previous setting, and you are DONE with the centrifugal advance. Now, dial in 10 degrees of vacuum advance, and adjust the advance so the carb(s) will actually activate it and you are done! PHEW!
Frankly, though, finding the advance curve using this method isn't practical for most of us.
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Keith Andrews
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Both very good articules...
One thing to watch with remarks like
When I was looking at the Bradford cam/tappet clearances, it would be the only vechile engine I know of that basically the valves close TDC and BTC!!!
A SB chevy/Ford/Dodge whatever modded up for performance with a 10.5:1 or 11:1 static compession ratio is quite street drivable and economic if a high duration cam is put in...reducing the dynamic ratio down as low as 9 or 9.5 :1
Most modern cars run around the 8 to 9.5 :1 Static, but calculate the dynamic one gets 8 to 8.5.
This is pleasing because it doent take much to bring low compression jowetts up to modern stds for modern pump fuels with a little maching and billet custom cam profiles
Add a good timing curve, bit of modern therory and /I recon these things will literially fly like they where never designed to do....Bigger brakes? lol
One thing to watch with remarks like
Yes that is correct, but calculated compression ratio is little morethan a advertsing ploy and means nothing...Due to overlap on a cam, compression starts after the piston rises, therefor REAL or dynamic compession ratio is what should be looked at...The rule of thumb is that the higher the compression ratio, the less total timing it can handle before detonation, and also the higher octane rating it needs to control detonation.
When I was looking at the Bradford cam/tappet clearances, it would be the only vechile engine I know of that basically the valves close TDC and BTC!!!
A SB chevy/Ford/Dodge whatever modded up for performance with a 10.5:1 or 11:1 static compession ratio is quite street drivable and economic if a high duration cam is put in...reducing the dynamic ratio down as low as 9 or 9.5 :1
Most modern cars run around the 8 to 9.5 :1 Static, but calculate the dynamic one gets 8 to 8.5.
This is pleasing because it doent take much to bring low compression jowetts up to modern stds for modern pump fuels with a little maching and billet custom cam profiles
Add a good timing curve, bit of modern therory and /I recon these things will literially fly like they where never designed to do....Bigger brakes? lol
My Spelling is Not Incorrect...It's 'Creative'
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Forumadmin
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The whole point of this discussion to to answer the question ' Is the distributor curve correct for modern fuels?' with a supplementary question ' If you have performed the recommendations in the 'Jowett Tuning Notes' or any other mods ' 'Is the distributor curve correct for my engine in its current state?'
It is not all about power; but also about effecient burning and reducing polution. One day the cars may be subject to polution tests. Keeping the timing on the stochiometric curve or just on the lean side is key to economy AND polution.
Any comment guys?
It is not all about power; but also about effecient burning and reducing polution. One day the cars may be subject to polution tests. Keeping the timing on the stochiometric curve or just on the lean side is key to economy AND polution.
Any comment guys?
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Keith Clements
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No, we do not agree. Getting the curve correct generically for modern conditions and the way in which many Jav/Jups have now been modified since 1947, when they were designed, is important. Showing how to finely tune that generic curve for a particular engine is also important.
Knowing what the curve should be will also help choose or modify a replacement.
It may well be the modifications such as higher compression, better gas flow, and cleaner fuel cancel out the difference in fuel and driving conditions. Please let us discuss logically, technically and scientifically with some anecdotal experience as well.
Those Greens among us may also want to run leaner, cleaner engines, so how do we do that?
Please let us apply our massive collective knowledge to the problem and share it on the forum. Perhaps the timing was not correct on that modified engine of yours, Pat?
Knowing what the curve should be will also help choose or modify a replacement.
It may well be the modifications such as higher compression, better gas flow, and cleaner fuel cancel out the difference in fuel and driving conditions. Please let us discuss logically, technically and scientifically with some anecdotal experience as well.
Those Greens among us may also want to run leaner, cleaner engines, so how do we do that?
Please let us apply our massive collective knowledge to the problem and share it on the forum. Perhaps the timing was not correct on that modified engine of yours, Pat?
skype = keithaclements ;
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Forumadmin
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The kit?
http://www.brdevelopments.com
LAMBDA LINK £85.00
Oxygen Sensors (Lambda Probes) are self generating sensors that produce a small output voltage according to that oxygen content of the exhaust gas
Higher amounts of exhaust oxygen indicate a lean mixture and produce a small output voltage. Rich mixture produces very little oxygen and the output voltage is higher. This voltage range is amplified and scaled by the display unit to drive an LED bar-graph calibrated to both air/fuel ratio and carbon monoxide (CO). Instant O2 Display Check engine fuel mixture Carburetted or EFI engines Factory or after market sensor Optimise Power And Economy Running lean or rich? That is the question. LambdaLink allows you to monitor your O2 and fuel mixture with ease. Comes complete with a tailpipe kit for accurate readings. A must for the enthusiast.
KNOCK LINK £85.00
Most modern engines will already have a knock sensor fitted as standard, but any type of knock sensor may be fitted as required. The sensor is normally screwed into a boss on the engine block although some manufactures fit the sensor in the inlet manifold. In either case, the sensor must be in such a position that block variations are coupled to the sensor. Assuming the engine is operating correctly, the LED’s will show only background noise which will rise in proportion to engine power output. Any abrupt rise in signal level at any time is an indication that detonation is occurring. The immediate remedy is to close the throttle. Severe detonation will destroy any engine in seconds. Knocking is the self detonation of the unburnt fuel in the combustion chamber toward the end of combustion. The flame burns around ten times faster than normal causing high pressures. Possible cures for knocking are: cooler intake air: increased intake humidity; reduce load; increase RPM; enrich or lean engine from lambda stochiometric; improve spark; increase octane level of fuel; reduce total ignition advance etc.
Monitor engine "noise"
Optimise advance
Detect detonation
Mechanical or Electrical Ignition
Toolbox tool or permanent fit
The Knock Sensor in many cars is quite often a sophisticated microphone. These can with engine modifications prove to be unreliable , this is where the KNOCK LINK comes into its own. Being able to isolate abrupt rise in signal level allows one to prevent the damage knocking causes. Keep a finger on your upgrades. Your Knock LINK will not only allow a safer upgrade path but also prevent destruction of an engine that comes as result of knocking or pinging.
LAMBDA LINK £85.00
Oxygen Sensors (Lambda Probes) are self generating sensors that produce a small output voltage according to that oxygen content of the exhaust gas
Higher amounts of exhaust oxygen indicate a lean mixture and produce a small output voltage. Rich mixture produces very little oxygen and the output voltage is higher. This voltage range is amplified and scaled by the display unit to drive an LED bar-graph calibrated to both air/fuel ratio and carbon monoxide (CO). Instant O2 Display Check engine fuel mixture Carburetted or EFI engines Factory or after market sensor Optimise Power And Economy Running lean or rich? That is the question. LambdaLink allows you to monitor your O2 and fuel mixture with ease. Comes complete with a tailpipe kit for accurate readings. A must for the enthusiast.
KNOCK LINK £85.00
Most modern engines will already have a knock sensor fitted as standard, but any type of knock sensor may be fitted as required. The sensor is normally screwed into a boss on the engine block although some manufactures fit the sensor in the inlet manifold. In either case, the sensor must be in such a position that block variations are coupled to the sensor. Assuming the engine is operating correctly, the LED’s will show only background noise which will rise in proportion to engine power output. Any abrupt rise in signal level at any time is an indication that detonation is occurring. The immediate remedy is to close the throttle. Severe detonation will destroy any engine in seconds. Knocking is the self detonation of the unburnt fuel in the combustion chamber toward the end of combustion. The flame burns around ten times faster than normal causing high pressures. Possible cures for knocking are: cooler intake air: increased intake humidity; reduce load; increase RPM; enrich or lean engine from lambda stochiometric; improve spark; increase octane level of fuel; reduce total ignition advance etc.
Monitor engine "noise"
Optimise advance
Detect detonation
Mechanical or Electrical Ignition
Toolbox tool or permanent fit
The Knock Sensor in many cars is quite often a sophisticated microphone. These can with engine modifications prove to be unreliable , this is where the KNOCK LINK comes into its own. Being able to isolate abrupt rise in signal level allows one to prevent the damage knocking causes. Keep a finger on your upgrades. Your Knock LINK will not only allow a safer upgrade path but also prevent destruction of an engine that comes as result of knocking or pinging.
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Keith Andrews
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Some points to note re dizzy models...
In most cases the dizzy and the vac advance are to separate part numbers.
Tale Av delco for example...
There are nearly 1000 model dizzys for the SB chevy all with different curves..
Then there are another several 100 models of Xac canisters.
The car manufactors then take a particular dizzy rhen match a Vac adv to to that dizzy ro siut diff fuels and models of vechile...hence a particular Dizzy set can have 1000s of combinations, to best suit if it is a van, estate, truck, car, heavt, liight, performance, family car, engine size/model etc etc.
So the 1st concept to drop is the old idea a paricular dizzy has interchangable curves between manudactures and models for optimin performance.
To clear up any confusion in ou7r application
"performance." is best defined as
To establish the Cent we need to get beat powr/emissions at a paricular rpm... We dont all have a Dyno in the workshop so have to do it the hard way...Dyno time is expensive.
Lock down the dizzy weights so the is no curve...this canbe be done with tieing in with wire or very heavy springs.
remove/disable the vac advance canister.
Set the dizzy to a known advance at a given rpm
ie 2500 rpm and 10*
Find a long steep hill make 2 points
Hit these point at the known setting and time
Repeat for a range from 500 rpm thru to 4000 rpm in 500 rpm increments
Change the dizzy advance and repeat...
Graph up the resaults from this using the best times a best performace graph canbe established....
Also put a manifold vac gauge in the car... the max vac curve serves as a ssecondary check that u are on the right track.
Another parameter, if u have one, is a portable exhaust anyliser hooked up in car and note the emissions at each piont.
U may very well find the best curve could also cause ping...do not go above a faint ping. This is the ping curve.
If this is the case ,As I mentioned way back, reducing back 3*to 4* off the ping curve should give enough safty margin to have a curve that is far enough back so there is no ping be it audiable or not.
Generally there is not enough advance in the dizzy to run std idle advance.
Do not be suprised if the std idle avance is say 5* and u now have 12 or 15 *..This now causes heavy load on starter motors and hard starting if excessive depending on the engine design (cam/compession/etc)
This canbe fixed 2 ways
1/with vac advance taken off manifold vac and this depends on the opitum vac advance curve
2/Getting out files and nodding the amount of weight throw out distance of the cent advance mechanism...I may also mean changing the cam shape on the weights to achieve this.
With all this done u are now ready to play with different spings to put the opitum curve into the dizzy...This is best done in car rather than a Dizzy machine...the dizzy machine is easier but dosent take into a/c the small tolerances in the cam gear, flex and other 'in engine' variables.
Any way, like the dyno, I doubt if most of use have a Dizzy macine in the workshop...
Once all of this is done one can establish the Vac advance curve.
Since the function of the vac advance is to provide good emissions and economy at off cruise and cruise (from little throttle to 1/4 or 1/3 throttle) and it works on engine vac...the whole exersise on the hill is done again on the flat.
U need full vac advance at highway cruise speed which has a lower engine vac than at lower around town cruise.
Again using the fixed weights in the dizzy and advancing up to find the ping curve at a given rpm, noting the manifold vac reading.
knock this curve back 3* to 4 * and u will now have a TOTAL cruise/ off cruise graphs. Minus the Cenrifical curve and this will be the amount of advance at a given vac of the engine that is to be in the Vac Advance canister.
The degs u end up with the vac advance is not as critical as the centrifical curve, 2 to 5*s each way is ok....dont go overboard u will be wasying your time The vac it works at is.
By closing and opening the distance the arm moves in the slot establishes the degs in in the canister
By changing to postion of the above changes the vac range it works at
U will need a canister that has a operational vac range within the ball park of the graph.
I Then lengthen the arm slot ( chances are to adapt to moern fuel this will be the case) then once I have a movable distance in the req'd vac range, I make up a couple of little adjustable cam stops Tap a hole each end of the arm and attach the cam stops with screws. Now change the length of these so u end up with the required vac and * deg range.
I then (optional) put 3 or 4 little rounded grooves beside the the point that u wish to use, at slightly different depths. Once u have the dizzy runing on the road u may find u wish to fine tune a little over the next yr to real practical application...or u may change a carb or rebuild it, fix a manifold leak, change a cam, change carb jetting...anything that may change the vac of the engine...or find u get a little ping under certain cirumstances.
These optional settings on the stops makes life eaier down the road.
3 opition grooves at each end of the slot will give u 9 opitional settings.
When u put a dizzy into a dyno shop they just opitmise the dizzy u have in the engine this costs 50 or $100s...
If u want them to estabilsh an opitmal curve then recurve, the time machining is huge, u will then run into a bill of many 100s of dollars....get up to a $1000+ could be expected....be warned.
In most cases the dizzy and the vac advance are to separate part numbers.
Tale Av delco for example...
There are nearly 1000 model dizzys for the SB chevy all with different curves..
Then there are another several 100 models of Xac canisters.
The car manufactors then take a particular dizzy rhen match a Vac adv to to that dizzy ro siut diff fuels and models of vechile...hence a particular Dizzy set can have 1000s of combinations, to best suit if it is a van, estate, truck, car, heavt, liight, performance, family car, engine size/model etc etc.
So the 1st concept to drop is the old idea a paricular dizzy has interchangable curves between manudactures and models for optimin performance.
To clear up any confusion in ou7r application
"performance." is best defined as
.It is not all about power; but also about effecient burning and reducing polution
gives good econimy by producing max use of potentual energy (power) at a given RPM and therefore reduced emissions.effecient burning
To establish the Cent we need to get beat powr/emissions at a paricular rpm... We dont all have a Dyno in the workshop so have to do it the hard way...Dyno time is expensive.
Lock down the dizzy weights so the is no curve...this canbe be done with tieing in with wire or very heavy springs.
remove/disable the vac advance canister.
Set the dizzy to a known advance at a given rpm
ie 2500 rpm and 10*
Find a long steep hill make 2 points
Hit these point at the known setting and time
Repeat for a range from 500 rpm thru to 4000 rpm in 500 rpm increments
Change the dizzy advance and repeat...
Graph up the resaults from this using the best times a best performace graph canbe established....
Also put a manifold vac gauge in the car... the max vac curve serves as a ssecondary check that u are on the right track.
Another parameter, if u have one, is a portable exhaust anyliser hooked up in car and note the emissions at each piont.
U may very well find the best curve could also cause ping...do not go above a faint ping. This is the ping curve.
If this is the case ,As I mentioned way back, reducing back 3*to 4* off the ping curve should give enough safty margin to have a curve that is far enough back so there is no ping be it audiable or not.
Generally there is not enough advance in the dizzy to run std idle advance.
Do not be suprised if the std idle avance is say 5* and u now have 12 or 15 *..This now causes heavy load on starter motors and hard starting if excessive depending on the engine design (cam/compession/etc)
This canbe fixed 2 ways
1/with vac advance taken off manifold vac and this depends on the opitum vac advance curve
2/Getting out files and nodding the amount of weight throw out distance of the cent advance mechanism...I may also mean changing the cam shape on the weights to achieve this.
With all this done u are now ready to play with different spings to put the opitum curve into the dizzy...This is best done in car rather than a Dizzy machine...the dizzy machine is easier but dosent take into a/c the small tolerances in the cam gear, flex and other 'in engine' variables.
Any way, like the dyno, I doubt if most of use have a Dizzy macine in the workshop...
Once all of this is done one can establish the Vac advance curve.
Since the function of the vac advance is to provide good emissions and economy at off cruise and cruise (from little throttle to 1/4 or 1/3 throttle) and it works on engine vac...the whole exersise on the hill is done again on the flat.
U need full vac advance at highway cruise speed which has a lower engine vac than at lower around town cruise.
Again using the fixed weights in the dizzy and advancing up to find the ping curve at a given rpm, noting the manifold vac reading.
knock this curve back 3* to 4 * and u will now have a TOTAL cruise/ off cruise graphs. Minus the Cenrifical curve and this will be the amount of advance at a given vac of the engine that is to be in the Vac Advance canister.
The degs u end up with the vac advance is not as critical as the centrifical curve, 2 to 5*s each way is ok....dont go overboard u will be wasying your time The vac it works at is.
By closing and opening the distance the arm moves in the slot establishes the degs in in the canister
By changing to postion of the above changes the vac range it works at
U will need a canister that has a operational vac range within the ball park of the graph.
I Then lengthen the arm slot ( chances are to adapt to moern fuel this will be the case) then once I have a movable distance in the req'd vac range, I make up a couple of little adjustable cam stops Tap a hole each end of the arm and attach the cam stops with screws. Now change the length of these so u end up with the required vac and * deg range.
I then (optional) put 3 or 4 little rounded grooves beside the the point that u wish to use, at slightly different depths. Once u have the dizzy runing on the road u may find u wish to fine tune a little over the next yr to real practical application...or u may change a carb or rebuild it, fix a manifold leak, change a cam, change carb jetting...anything that may change the vac of the engine...or find u get a little ping under certain cirumstances.
These optional settings on the stops makes life eaier down the road.
3 opition grooves at each end of the slot will give u 9 opitional settings.
When u put a dizzy into a dyno shop they just opitmise the dizzy u have in the engine this costs 50 or $100s...
If u want them to estabilsh an opitmal curve then recurve, the time machining is huge, u will then run into a bill of many 100s of dollars....get up to a $1000+ could be expected....be warned.
My Spelling is Not Incorrect...It's 'Creative'
-
Keith Andrews
- Posts: 941
- Joined: Wed Jul 26, 2006 8:11 am
- Location: New Zealand
- Contact:
What can I say to that, either u are not prepared to share your info with other jowetewrs of u havnt a clue
Refer
http://jowett.net/forum/viewtopic.php?p=1409#1409
Refer
http://jowett.net/forum/viewtopic.php?p=1409#1409
My Spelling is Not Incorrect...It's 'Creative'
-
Bryan Walker
- Posts: 114
- Joined: Fri Feb 10, 2006 9:33 am
- Your interest in the forum: Jowett owner
- Given Name: Bryan
- Location: New Zealand
Oxygen sensors - Lambdalink
Not a bad toy but not so easy for use with jav/jup exhaust setup.
IE 2 sensors should be used , one for each side but with 1&3s manifold going into 2&4s manifold the data for the 2nd carb will not be true?.
PS on the Link Engine Management website the tail pipe attachment is an option.
Bryan
IE 2 sensors should be used , one for each side but with 1&3s manifold going into 2&4s manifold the data for the 2nd carb will not be true?.
PS on the Link Engine Management website the tail pipe attachment is an option.
Bryan
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Forumadmin
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Chris Cole
- Posts: 29
- Joined: Tue Feb 21, 2006 1:41 pm
- Location: Near Tewkesbury.
Distributors
Gentlemen. Many thanks to Keith Clements, (who I think is also Forumadmin?), Pat Lockyer, Keith Andrews and Paul Beaumont, plus others, for all you replies to my simple initial request. I am stunned by the number of answers and have saved them to a Word document and find this is 15 pages long.
Your collective wealth of experience has more than answered my initial question, which was only to try to find out if my two distributors were basically the same unit or not.
There is obviously more than one way to skin a cat, or to set up an engine, and I shall try to use a distillation of all this information to help me. Perhaps we could draw a line under this discussion thread now and please accept my grateful thanks for the collective help give.
Your collective wealth of experience has more than answered my initial question, which was only to try to find out if my two distributors were basically the same unit or not.
There is obviously more than one way to skin a cat, or to set up an engine, and I shall try to use a distillation of all this information to help me. Perhaps we could draw a line under this discussion thread now and please accept my grateful thanks for the collective help give.
Chris Cole from sunny (!) north Gloucestershire.