Distributor spring specifications

[Forumadmin]

Fired it up . Vacuum works. RPM works and lights flash. Can't wait to get a dizzie on it.

[Forumadmin]

Tried it out last night and gave Jack a demonstration. Hopefully I will get time to edit the video of the operation.
I also, as I always do , took it apart because it was making a noise. I cleaned it up and then put some shims under the protractor ring as it was rubbing on the display disk. Works beautifully now, so if anyone wants to test a dizzie just contact me.

The tests include checking the dynamic advance curve through the whole rev range, vacuum advance with exact monitoring of vacuum pressure, evenness of the 4 lobes, and dwell angle. No HT tests can be performed.

This was the curve I plotted as a first attempt. Really needs two pairs of eyes as speed wavers slightly.
Static 0deg, 400rpm 1deg, 700rpm 2deg, 1000rpm 3 deg, 1200 rpm 4 deg, 1400 rpm 5 deg, 1500 rpm 6 deg, 1700rpm 7 deg, 2000 rpm 8 deg which was the max. This equates to 16 crank degrees at 4000 engine rpm.
Vacuum advance started at .1 bar with an extra 3 deg, going up to 6 deg at .2 bar.
Thus cruising at above 4000rpm gives 28 degrees of advance which is a tad too much.

[ian Howell]

Keith: -

Glad it is still working OK. When I checked it out it was not rubbing on the display disc so I guess it has moved a bit in its travels! I think it probably had very little use during its working life.

Could the speed wavering possibly be due to wear in the dizzy bearings and not a function of the test set?

Have the 'correct' advance curves ever been published?

Would it be possible to calibrate sets of springs by changing them into a 'standard' dizzy?

Shame my Long Four is manual A and R!

[Keith Andrews]

No HT tests can be performed.

It doesnt take much to hook up a coil

Could the speed wavering possibly be due to wear in the dizzy bearings

yep.

Thus cruising at above 4000rpm gives 28 degrees of advance which is a tad too much.

I have mentioned that these old engines..the cam profiles, compression etc where all built basically to run on british pool fuel
Modern internal combustion engines pre EGR etc as a ball park require a Cent around 36 to 38 degs all in around 3200 to 3600.....the VA usually manifold and the VA specs generally have the VA all in approx 1" either side of of idle vac.
Total intial+cent+ VA can be anyware between 40 and 56 degs
Who u say 58? well think about it...what happens to the engine vac at high speeds..it doesnt remain at the same vac travelling at say 20 mph...there fore as more HP is required at higher speed cruise to over come resistance, the carb is further open and manifold drops,
The curve required on 2 identical engines/cars when determined by dyno or even road testing will be suprisinly different.
This meands the correct us of the dizzy macine is to establish the correct curve for the car..and use the machine to put that curve into the dizzy.
BUT in real life what a dizzy reads on a machine and what is in the car are slightly different....

U have some serious dizzy tools now, invest in an O2 logger, in car vac gauges....and start to tune with a bit od science rather than seat of the pants.

This is the difference of tuning by 'pants and science....Im pretty good at tuning in..vac gauges timing lights, stop watches etc....The camaro carb getting warn so till got a new one a matter od customising spring weights etc.
Overall us went from seat pants tune 12 mpg to 16/17 mpg....and on road test...make note to self have a lot more room around me next time I mput the pedal to the metal.

Next thing to look at is using a chev HEI pickup and 4 pin modules mounted in the bottom of the dizzy.....file off the un needed pionts on the pickup to 2 or 4 cylinder as needed.

[Forumadmin]

I would prefer to test HT on the car as it is affected by compression and spark plugs. OK you could test cap and leads and look for a spark at the plug. I may hook up an oscilliscope which will then find points bounce (but I prefer to use optical points anyway), capacitor problems and perhaps some HT problems. The scope can also help check mixture. Setting that up in the front seat whilst putting the car under load might be a challenge!

The speed wavering is not due in this case to the dizzie bearings. It was a brand new dizzie! I think it is due to the motor control circuitry/bearings in the test kit. Perhaps they need some oil. I may have it completely apart next time. There is quite a lag between turning the potentiometer and the dizzie accelerating. The pot acts more like a throttle than a cruise control.

Ian, all the data is published in links on this thread! But how that should be changed to suit modern petrol and driving conditions is anybody's guess. First you need to understand the theoretical principals, then the empirical criteria followed by a really good rolling road and data logging kit. There are so many variables that you could spend a lifetime of development and do what Jowetts might have done if their experimental department was still functioning.

It would be good to research changes to the VW 1200/1300/1500cc engine distributor over its lifetime, as it went from 1938 to 2003 with very little change to the basic engine.

Hey that might be something for Project B.