Ignition timing

[gefopsman]

I have bought a car with a modified Pinto. (2.1 Piper 285, Stage 1 head, Bike Carbs etc) but it has a standard dizzy with the vacuum disconnected. Not good!! It sounds like static timing is too advanced currently as it struggles to turn over which could well be someone trying to compromise on the lack of mid range advance.

I am working on a modifed dizzy for it until I get my head around Megajolt/Megasquirt. I used to mod these many years ago for some Oval racing guys but can't remember the extremes.

From memory I should be looking at a starting point of about 12deg btdc static working up to 32deg btdc at full advance. Does the maximum sound about right.

I can source a modded unit for about £80 but it seems a shame whem I can get fairly close myself, which will do until I go electronic.

Any guidance would be appreciated.

[greenv8s]

Know b*gger all about that engine, but surely with the vac advance disconnected you will have much less advance than normal while cranking? If the static advance has been wound up by more than the normal vac advance (20 deg or so?) so give you the excessive advance you're describing then I would have thought it would be massively over advanced at high revs.

[mongoose]

greenv8s said:

but surely with the vac advance disconnected you will have much less advance than normal while cranking?

would the vac advance have had any effect at cranking speed ?if not then any more mechanical advance than std would only make things worse?

[greenv8s]

mongoose said:

would the vac advance have had any effect at cranking speed ?if not then any more mechanical advance than std would only make things worse?

Don't know. On mine the manifld vacuum drops off sharply as the revs drop, at tickover with a leary cam you probably have less than 0.5 bar depression and at 200 rpm cranking speed you probably have negligeable depression. I imagine there will be some preload in the vac capsule so nothing at all will happen until the depression exceeds some small threshold. So quite possibly there's no vac advance while cranking. By the same logic, you wouldn't expect the mech advance to come in under cranking unless the springs have been left off or broken, hmmm well worth a check.

[mongoose]

I think what i meant to say was that the dizzy being turned to advance,to compensate for lack of vac advance,would make the starting worse if you see what i mean.Got my mechanical and static mixed up there i think!

[Rubi]

gefopsman said:

I have bought a car with a modified Pinto. (2.1 Piper 285, Stage 1 head, Bike Carbs etc) but it has a standard dizzy with the vacuum disconnected. Not good!! It sounds like static timing is too advanced currently as it struggles to turn over which could well be someone trying to compromise on the lack of mid range advance. I am working on a modifed dizzy for it until I get my head around Megajolt/Megasquirt. I used to mod these many years ago for some Oval racing guys but can't remember the extremes. From memory I should be looking at a starting point of about 12deg btdc static working up to 32deg btdc at full advance. Does the maximum sound about right. I can source a modded unit for about £80 but it seems a shame whem I can get fairly close myself, which will do until I go electronic. Any guidance would be appreciated.

The figures you quote for timing seem about right - maybe a little more max advance? We used to use 34 deg max advance on our racing Pinto (10.5:1 compression and 100 octane fuel)- which also had its vacuum disconnected. You want it all in by 3000 rpm. If it is for street use I'd hook up the vacuum again - it'll give far better part throttle response and fuel economy. For racing it is a waste of time. Incidentally the best "std." dizzy advance curve was the one from the 1.6 Emax engine post 1988ish (if I remember correctly), it's the one with the 2 litre crank (77mm stroke) and very small diameter pistons. I think that with this dizzy and 34 deg max we used to be at about 10 degrees static - certainly starting was never a problem hot or cold.

[tr7v8]

12 deg static I'd say would be too much, I'd expect a figure around 6-8 dependant
on CR. All ou I reckon 34-36 would probably be where I was aiming for.
If you can run vacum advance you'll see better economy by a long chalk.

Jim

[gefopsman]

mongoose said:

would the vac advance have had any effect at cranking speed ?if not then any more mechanical advance than std would only make things worse?

Vacumm has no effect at cranking due to lack of depression. Nor does Mechanical as speed of rotaion is not sufficient.

greenv8s said:

By the same logic, you wouldn't expect the mech advance to come in under cranking unless the springs have been left off or broken, hmmm well worth a check.

I used to set the springs to start mechanical advance around 1500rpm one lighter spring and one stronger one to control a progressive advance. I seem to remember that we aimed maximum advance to come in by 3500rpm.I just can't remember whether it was 32 or 36 degrees.

I could reattach the advance tube, it would just nessesitate removing the manifold and drilling to fit take offs for the tube. I am not sure what effect the 4 bike carbs will have on Manifold depression but guess that it will be reduced sufficiently to make the combined vacuum/mechanical standard advance less than perfect. Not that they ever were.

As it is a Caterham variant, brick in a wind tunnel, economy will never to too good anyway.

It would be interesting to see the advance maps created for anyone with programmable ignition on this engine.

I guess any advances on modifying this engine are now quite old as most people tend to go for newer lighter untis or later engines with significantly better potential. I would follow the example but don't want to spend too much time or money on this as it is just a stop gap to keep me in weekend fun.