Correct Fuel

[JohnBetteridge]

Does anyone have an opinion as to correct fuel for the Jupiter. I was told that the unleaded has 5% ethanol which is affecting the fuel system, this being increased to 10% at a later date ( verification please). Using the Supreme or V power unleaded would be better because no ethanol is present. Having filled up with V power and after a 20 odd miles or so the engine cutting out the AA was called out. I was informed that this fuel is only for high power engines and that it would wash through the system taking any debris with it causing problems in the carbs. Being at various shows talk of additives and tablets were spoken of which leads to the question what is everyone else using?

[Edmund Nankivell]

I have an article on the subject of Ethanol in petrol & classic cars. It say "cork, paper, natural rubber, neoprene rubber and some silicone materials are vulnerable to te ill-effects of ethanol...".
Millers Oils do a product called "EPS" which is said to provide protection when using unleaded fuel, to protect against the corrosion effects of ethanol in modern fuel...recommended for rebuilt classic car engines with hardened valve seats previously requiring leaded fuel - combats the adverse effects of ethanol in fuel. Prevents fuel system corrosion. One 250ml bottle treats 40 litres of fuel. NB 40 litres is virtually 9 gallons

[Nick Webster]

To clarify, the use of a higher octane fuel such as V Power (or any other Premium brand) would not cause a problem in the actual running of your engine. However higher priced fuels tend to be so for a reason and often the motorist benefits from an increase in the various additives that are already included in the fuel available at the pump. The most common of these is a detergent for keeping systems clean. This is now common with varying percentages in all grades of fuel. Ask yourself how long is it since your modern car had a "decoke"? The answer should be "never". In the early days of multi-grade engine oils the inclusion of detergents was thought to be a problem with the same washing of debris around the oil passages. Now we all have remarkably clean engines compared with the carbon encrusted internals of yore. I think you may have been just unlucky that some piece of debris detached and was big enough to affect the fuel flow. I don't know what fuel you have used previously. Perhaps it contained higher ethanol and there has been some degradation to rubber components and bits were floating around anyway.

The use of a premium grade fuel in an engine which does not really warrant it, by way of high compression ratio, will simply mean that in terms of performance you may have wasted your money in paying extra. By performance I mean the most efficient combustion to drive a piston down a bore. However there are some relatively low power classic engines that tend to run more smoothly, probably due to a combination of burn characteristics and combustion chamber design. Unfortunately the number of remaining Jowetts, small mileages covered and driving characteristics means that we are not really well placed to come up with a definitive scientific answer for the likes of a Jupiter.

To conclude - I use V-Power or similar in my 8.5:1 compression ratio Triumph TR2 (never could afford a Jup) and although it will run perfectly well on ordinary fuel, subjectively I find low speed high gear (i.e. high torque) running is smoother. I do not use any supplementary additives.

Nick

[Keith Clements]

Fuel, like lubricating oil, is now a complex mixture of chemicals, rather than the imprecise fraction from distillation in the refinery that was about in the 1950’s. So yes, there will be less muck created on burning it. The detergent added will have more of an effect in the fuel delivery system than the cylinder head, its job being to keep injectors clean, but this might also keep the carb jets clean as well. The detergent effect on the emulsifying block in the Zenith needs investigation.

The presence of ethanol in the fuel might have an effect on the components of the fuel delivery system so may dissolve or dislodge components which might affect the carb and thus cause bad running. The filter just before each carb should catch these, so check to see if they are intact and clean. Also check the filter after the pump and the filter inside the pump. The needle valves in the Zenith float chamber are notorious for flooding the carb, so make sure there is no smell or trace of petrol on the outside of the carb body.

The ethanol may also dissolve the gasket in the emulsifying block and thus cause a problem. It might affect the diaphragm in the petrol pump as well causing loss of pump pressure. Check the gasket around the pump and filter bowls. I have had these start to leak recently.

[Edmund Nankivell]

I have weber carbs on both my Jupiters, hope the carb problems will ne less!

[Jack]

I think that V-Power and Supreme now contain ethanol up to 5%, too - so no benefit if your engine prefers standard fuel to V-Power and other performance fuels.

That said I wouldn't expect any petrol to go as far as to cause a breakdown vs any other, just affect how smooth and perhaps powerful the engine feels when driving. There are detergents etc in all modern fuel, just more of them in high performance fuels, so it sounds like (if it has dislodged crud which has caused it) that you probably would have had the same result on either fuel.

Jack.

[Keith Andrews]

Putting aside compatibility issues of ethanol on rubber etc....
Comments above re matching your octane to your compression is correct... more correct is matching the octane to the dynamic compression ratio of the cam profile of the engine is what is critical....or more accurately the cylinder pressure at point of max explosion of the engine... if timed correctly at a given point between 12 and 18 degs ATDC at a given load and rpm.
Also of note is increase the octane of the fuel the time for the flash across the chamber to max cyclinder press is greater.
Then balance that with higher the dynamic compression ratio the speed of the flame front is faster.

Then throw in another curly.. higher the octane the lower the specific gravity.. add ethanol and goes even lower.
What does this mean? less BTU (energy) per volume but greater BTU per weight.
We buy our fuels by volume, and the carb meters the fuel by volume...
so increase octane or use ethanol fuels u will need to increase the speed of the timing curve (not the intial) by reducing cent counter weight springs, and increase jet sizes to run efficiently.
If real serious , and basically a must, is invest in a data logger like a innovate LM1 or LM2 with min of rpms rpms O2 sensor... ideally also IMAP (engine vaccuum) and Throttle position sensor to re dial in the engine tuning specs.
Once one uses these 21st century , now affordable tuning tools u realise the old school ear/ vaccuum gauge spark plug tools belong to the museum.. anything less is just hit miss
Basically u have a chassis dyno on tarmac...usually with better results.

[Keith Clements]

Keith,
Have you put your datalogger onto the Bradford or any other Jowett? If so, can you share your results? If not, and you have one, can you do it? We would be most interested to learn.

[Forumadmin]

To qualify what Keith A. stated. Flow through carb jets is governed by the pressure difference across the jet and the viscosity of the fluid. Kinematic Viscosity of ethanol is greater than the petrol it replaces (petrol 1.473 versus 15% ethanol 1.760 mmsquared/sec) so less fluid will flow. This probably compensates for any difference in density (petrol 0.752 versus 15% ethanol 0.756 gm/cm cubed) but not the huge difference in calorific value, ethanol contains approximately 34% less energy per unit volume than gasoline. In a E10 mix that equates to about 4% loss in energy. Other fuel qualities such as burn rate and flash temperature (pre-ignition point) would also affect advance timing. So practice rather than theory is more effective! Since ethanol has a higher octane rating, the engine can be made more efficient by raising its compression ratio, but that is not an easy tuning solution.

Note too that fluid temperature is by far the largest variable so make sure the carb is always warm but not hot. Since alcohol doesn't vaporize as easily as does gasoline, cold weather starting can be a problem ... especially if the engine itself is cold.

I should also mention that air is the other component of the fuel and that it's temperature and pressure also affect the ideal mixture, as we experience when traversing mountain passes.

Fuel Type / Quality

Low quality and/or low octane fuel can cause knock which will elevate cylinder temperatures. The increased cylinder temperature will cause the temperature of the combustion chamber components (spark plug, valves, piston, etc.) to rise, and will lead to pre-ignition if the knock is uncontrolled.

When using an ethanol blend fuel with high ethanol content in high performance applications, a colder heat range may be necessary. The spark timing can be advanced further because ethanol blend fuel has a higher resistance to knock (higher octane). Due to the decreased knock, there will be less audible “warning” from knock before the spark plug overheats and pre-ignites.
Some types of fuel additives in lower quality fuels can cause spark plug deposits that can lead to misfires, pre-ignition, etc.

Ignition Timing

Advancing ignition timing by 10° will cause the spark plug tip temperature to increase by approximately 70° to 100°C.

A colder heat range spark plug may be necessary if the ignition timing has been advanced to near the knock level. Higher cylinder temperatures near the knock level will bring the spark plug firing end temperature closer to the pre-ignition range.

Ambient Air Temperature / Humidity

As the air temperature or humidity decreases, the air density increases, requiring a richer air-fuel mixture. If the air-fuel mixture is not properly richened, and the mixture is too lean, higher cylinder pressures / temperatures, knocking, and the subsequent increase in the spark plug tip temperatures can result.
As the air temperature or humidity increases, the air density decreases, requiring a leaner air-fuel mixture. If the air-fuel mixture is too rich, decreased performance and/or carbon fouling can result.

Barometric Pressure / Altitude

Air (atmospheric) pressure and cylinder pressure decrease as altitude increases. As a result, spark plug tip temperature will also decrease.
Fouling can occur more easily if the air-fuel mixture is not adjusted to compensate for the altitude. Higher altitude = less air = less fuel.

[Keith Clements]

Reading Noel's book on Competition Jowetts and the work done by Horace Grimley on tuning the engines with all manner of sensors attached to the car whilst driving over the Yorkshire hills, you realise how they would have benefitted from dataloggers and knock sensors! They had to rely on ears, noses, and eyes to tune their engines.

[Keith Clements]

The discussion about ethanol in fuel will continue not only on the energy efficiency, CO2 balance and tuning front, but also on the damage it causes to car components. Anything plastic (such as fibreglass patches to your tank), washers and seals is likely to be affected and that includes rubber and gasket sealers. So expect to see leaks starting and check frequently all along the fuel line. Smell is the best way to detect. If you smell petrol in the garage, you probably have a leak. I am now coating my petrol tanks with tank sealer if they are taken out.

Ethanol also absorbs water from the air which can settle in the tank and rust it from the inside or can sit in the carb bowl and upset the fuel metering.

Ethanol also forms a brown sludge after standing for a few months so can clog the carb and filters, so check and clean these after any lay-up.

Hopefully it will not eat through the petrol pump diaphragm or the emulsion block seal but, in case it does, carry a spare pump and a spare carb bowl with float and needle valve with washers.

[Srenner]

Here in the USA, we had ethanol foisted upon us some years back. I'm sure the mix differs in the USA, but here is my experience.

The short story is that you will need to adjust the jetting to make things richer.

The higher the ethanol content, the greater the problems. Water absorption can be a real problem, resulting in clots that plug lines and filters. In cold and wet weather, the clots form more rapidly. The fuel sold here has about a two month's life in a car's gas tank, regardless of humidity. After that, it smells, feels and performs like really old gasoline.

On the original Zenith 30VM, I have had to reset the air regulating screw to get a better idle and start. On one car this was minimal, but on another it was about 1 full turn (mmm, air leak at the shaft?). The main and compensating jets remained untouched. It is my opinion that the old Zeniths are not as sensitive to the change since they are sort of crude to start with.

On the Webers, the idle circuit is engaged at almost all points except WOT. The idle jet went up two steps. Using an Innovate LM-1 tail pipe sniffer, I drove around to get readings and installed a larger main jet, but did not change the air compensation jet on the recommendation of my dyno man.

The LM-1 can easily mislead if the set-up is less than perfect. I have not tried the LM-2, which is more sophisticated. These units are not too expensive, but an expense not justified for occasional use.

The ethanol can also swell the "rubber" lines and cause the fuel pump diaphragm to fail. Moss sells a replacement diaphragm for the pump.

[Keith Clements]

Fuel_Property_Comparison_for_Ethanol-Gasoline-No2Diesel.xls

(36.5 KiB) Downloaded 8 times

This should contain all you need to know on the properties of the fuels.