ignition advance

[Coops]

after being on the rolling road yesterday,
i was wondering if my ignition is doing what it should be,
what sort of advance timing should i be seeing at what rpms?
and if mines out how do you change it on a unilite dizzy.

[mgbv8]

The first thing to find out is what the advance curve should be for your engine.
And also to find out what the advance at idle should be.

Then its easy enough to stick the strobe on and run the engine through the various rpm points to see if the dissy is doing what it should be doing on the mech advance.

[r2d2hp]

See Below.

[ian.stewart]

Tony, does your Squirt control your timing, if it does, have you locked the dissy shaft,

[r2d2hp]

Hi Tony,

You adjust by inserting a 3/32 in allen key into the vacuum advance where the pipe attaches. When first on the rolling road mine was found to be way out.

[Coops]

hi guys,
Ian, no my ignition is dizzy controlled at the mo,
Cheers for that Reg,
Perry will the ignition curve be the same for a stock 3.9 to one with a different cam and heads?

[Coops]

tried looking for my 3.9 manual today and can't find it,
anyone know what ignition advance v rpm i should be looking at?

[dnb]

This is more-or-less what I use on the TVR. It works OK, but I have a different engine spec and the timing curve was derived with a slipping clutch at the top end. So yours should accept a little more.

RPM Timing
1000 15
2000 18
3000 21
4000 23
5000 24
6000 25

[Coops]

so what do i have to do hold the car at said revs read what the timing is at, then disconet vac adjust through the vac unit via the vac pipe intake reconct and try again?
and anyone know what size allen key is needed?

[CastleMGBV8]

Tony,

The accepted advance for a 3.9 engine is 10 deg. at 1000RPM and total advance of 34deg all in by 3400RPM this with vacuum disconnected.

you need too acertain the amount of available centrifugal advance on your distributor, for example most of the lucas dizzys have 11 deg distributor advance equating to 22deg crankshaft advance.

If you have the spec sheet for your dizzy and can find the amount of total advance available and then if setting the initial advance at 1000RPM does not give sufficient total advance then you can increase the initial advance usually up to 14deg. if necessary. You may have to change the springs if it doesn't give total advance by 3400RPM.

It is very important to get an accurate TDC and mark your pulley.

Kevin.

[Coops]

acording to the paperwork it says,

most unilite distributors with p/n ending in 01 have 24deg (crank deg) of mechanical advance between 3k and 3.2k

does that mean i should set the timing to 10 degrees?

[RoverP6B]

If the distributor has 24 degrees of advance built in, then what ever amount of initial advance you set will add to that total.

In other words, if you set 10 degrees initial at 600 rpm say, then the total advance will be 34 degrees.

Ron.

[CastleMGBV8]

Tony,


If you have 24deg. of total centrifugal i would suggest it would be ok to run 10 deg of initial at 1000RPM as the centrifugal advance doesn't start to approx 1000RPM.

I would also suggest that when at the track you disconnect the vacuum advance to avoid the possibility of over advancing when you come off the throttle at the end of the run at high RPM and high vacuum from a closed throttle.

From you dyno figures it would appear that you cant be far out but possibly next time your at the track would be a good time to experiment with different settings and you will be able to acces the results.

If your there at the same time as Perry he has a very good timing light that will measure the advance right through the RPM range.

Kevin.

[Coops]

sounds like he has one like my snap-on timing light

[bones]

hi Tony, the allen key should be a 3/32", i will have to keep an eye on this post as im still trying to do the timing on mine rich