How much extra Ignition Advance?

[pilotnbr1]

I have found my 74 tii with a 013 dizzy seems to perform better at the most advanced limits for ignition timing. More power, quicker throttle response, and smoother idle. Right now I would say I am at the limits recommended.

1000 rpm- measured 3 degrees - book range 0 to 4

1500 rpm- measured 15 degrees - book range 10 to 14

2000 rpm- measured 21 degrees - book range 15 to 20

2500 rpm- measured 27 degrees - book range 21 to 26

3000 rpm- measured 30 degrees - book range 28 to 30

I didn't measure beyond 3000 because it was getting late... I am not so much concerned with getting more performance as eliminating a little hesitation and maybe slight bucking at 3000 rpm while cruising. Pretty sure fuel is not the problem- my plugs are beautiful, psi and volume are good! All other rpm ranges while cruising are smooth and no problem while accelerating- its just while holding steady throttle at 3000 rpm. The more advance timing the problem seems to diminish. My question is how far should I go with the advance? What do you guys all run? Right now I am thinking a couple more degrees might not hurt- but where do I start getting into ping range? Not sure what a ping will sound like in this car and really would like to baby it... Thanks for your responses!

[Arky2002]

I remember Ray Korman telling me that they set the distributors at 34 degrees maximum advance and then adjusted for the best idle they could get.

[Harv]

My best guess is that you don't have enough total advance. I would expect somewhere close to 36 deg.

John

[pilotnbr1]

Looking at the manual for a usa 2002tii it is completely advanced at 3500 rpm and 27 to 32 degrees. I have been setting it at 2700 rpm and 25 degrees with the dizzy vacuum line disconnected and capped. I have been tweaking a little off that mark playing with it. I am thinking of just setting it at 3500 and 32 degrees and maybe allowing a couple of degrees extra advance from there. I don't think a couple more degrees advance will hurt anything, do you? It really seems to be making alot more power the more advanced I go. I should also check compression.

[allbim]

The slight bucking can also be caused by a lean mixture.

[Arky2002]

and it will - until you reach the point of preignition detonation.

Then you will be rebuilding an engine.

[pilotnbr1]

I agree with you both. I am doubtful of the lean mixture. Plugs look good and if anything seem to be running rich as I am getting about 15 mpg average city driving. Pic of the plugs below. They are 8 heat range

The slight bucking and hesitation while steady throttle at around 3000 rpm goes away the more advance I go. The Mccarteny book suggests setting timing by a series of driving tests under load adjusting ignition to the point of pinging. I am not racing this car and only want to get rid of this annoying bucking (although who doesn't like more power). His book suggests that for every car there is an ideal ignition timing.

Do these engine give you much warning if they ping? Does anyone have experience with the number of degrees they start to detonate-- very subjective question I know.

[jgerry2002]

I'd check mixture with a wideband.

Motor 100% stock? Modified in any way?

As the linkage / throttle body wears the mixture will lean out. Combine that with different "modern" fuel blends and who knows where the motor is really running.

Is the ball/reference mark 100% steady in a timing light? If not it could be a worn distributor or even a slight ignition miss.

[pilotnbr1]

Thanks for all the replies!

To answer questions-

Stock engine. Lower compression 140 across ( i am thinking this is why it likes more advance) but this test was a while back when I first got the car and it hadn't run in 5 years or received any attention like a valve adjustment... I need to retest but other than this slight bucking it runs great!

Timing mark is rock steady. I have shot the ball in the past but am now using my own mark on the crank pulley. The TDC flywheel mark and my crank pulley mark are spot on. Have an 013 dizzy with fresh plugs, wires, cap,points, and rotor. Black coil hooked up to mark 10 CD system.

Valves adjusted .007 cold.

Linkages have all been taken apart measured and put back together. All sockets were replaced on the throttle linkages. Intermediate shaft is new and cup. Throttle body cleaned. New spring to intermediate shaft and in the tuna can.

Cold start system many new components and verified working correctly (also verified warmup regulator is closing and not leaning mixture when at temp and cold start valve is not leaking).

New fuel pump, filter, some lines, expansion tank, high pressure fuel lines from pump to injectors, and resealed tank. KF pump rebuilt by Fairchild. Injectors torn down and cleaned (not bench tested though). Fuel pressure and volume tested good.

Everything was setup as per the pump guide from the tii registry. I only deviated by setting the idle mixture with a vacuum gauge instead of reading co2. I don't own an exhaust gas analyzer or have an AFR gauge... Idle speed adjustment requires throttle to be cracked significantly to maintain 1000 rpm. With more advance in the ignition I can bring the idle speed way way up. It behaves way too retarded, but it is in normal range at 3 degrees with the vacuum line hooked up to the dizzy.

Only other idea i have for bucking would be driveshaft out of alignment, but that doesn't make sense with it always being at 3000 rpm. Would think the bucking would be at a certain speed rather than rpm.

Sorry this has become so long winded. I am very hesitant to deviate from stock settings and just start advancing the ignition beyond stock. Last thing I want to do is ruin an engine.

[tjones02]

I/we usually set Tii timing to about 32-34 degrees max advance, with no more than 8 at idle. Any higher at idle and we can't adjust the idle mixture smooth enough.

[TobyB]

I would expect somewhere close to 36 deg.

that's my safe word... err, I mean, safe number...

And a small amount of preignition doesn't immediately munch your motor-

our stuff is a lot tougher than a boosted Subie. The problem is that to

catch it, you'll need to be able to read the plugs, and that's hard to do,

since you need to do a 'plug chop' to be safe.

From your description, it sounds like the dizzy's worn to give advance early,

but not enough total.

Just a guess,

t

[pilotnbr1]

Thanks for the info guys- I am going to advance it a couple more degrees for a max of 34 and see how that goes. Will report back

I actually have two distributors one is a 002 that came on the car and it had the 013 in the trunk with a bunch of parts. I set the 002 to stock settings and had the same little bit of bucking/hesitation at 3000 rpm. I chalked it up to the wrong distributor for the car and threw the 013 on. Low and behold I still had my bucking problem at 3000.... Maybe they are both worn and it is time for a rebuild on the 013. The curve I recorded does seem to show a couple extra degrees of too much advance early on.

[jgerry2002]

As the springs age they get soft, and the first symptom is too much advance too early.

You may want to send it for a rebuild. Worth the time to check the advance curve of the 002 as well for comparison purposes.

[ray_]

What's the dwell?

I think it's points-related.

GL,

Ray

[Emyers]

What's the dwell?

I think it's points-related.

GL,

Ray

Conventional ignition is affected by "Dwell time" (or dwell angle). Dwell time refers to the time the points are closed thus recharging the coil. Dwell angle refers to the crankshaft angle of rotation made while the points are still closed.

Earl