FireDemonSiC

Trying to decide on an optimum setting for my distributor base timing.

Engine is a 334 stroker. Cam is a hydraulic roller .536/.570 lift 110LSA. Duration is 222/230 @ .050. Ported/siamesed TPI intake.

Here is the whole idea. I know that distributor base timing has a direct effect on cranking performance and more timing stresses the starter more and can even lead to kickbacks. However, I want enough base timing that in the event I experience an ECM controlled advance failure, I could still limp the car home off the distributor timing alone (Before anyone comments on the odds of this happening, I had it happen before on a stock-ish LB9. I had to drive several miles home with the advance curve locked at 8* BTDC. Slow drive, but I made it).

The last time I went to set my base timing, I had it at 13* at it was still barely able to idle smoothly enough to even get a reading. I tried 10* and the engine surged so badly I wasn't even able to set it.

Once running, the engine idles happy at 28* of advance but the big question is, just how much distributor base is too much?

Also note the way the ECM handles the timing during cranking. The lowest cell it can read is 400rpm at 100kPa (Atmospheric pressure or WOT). When cranking, until the engine is above 400rpm, it will be cranking off of the base distributor timing.

mikeyt

It's funny what you said about timing stressing a starter. I've got a 92 rs 305 that I just put a GM stroker cam in and the tune calls for 10* advanced and I do notice a draw on the starter that is different than before. Do you recommend changing to a starter from a 93-95 Camaro? I understand they're a gear reduction that bolts right up and has a lot moer torque.

FireDemonSiC

I should note an important fact that I omitted from the OP.

I am running a 3.73:1 gear reduction mini starter.

AlkyIROC

The best base timing is dependent on the camshaft grind. With your 222/230 @ 0.050" duration, a recommended base timing should be 14-16*. Once set, you don't play with the base timing. To change your total timing, mechanical advance etc do not change the base timing. With a computer controller distributor, where the computer wants the timing during idle is up to the ECM. Timing is set with the EST wire disconnected. If you need more or less total timing with a computer controlled distributor, it needs to be changed in the ECM programming.

The trouble with timing marks is that they're never 100% perfect. Back when I ran a 383, my total timing was something like 44* which is way to high. That was with a large cap HEI so changing things was easy. I decided to use a degree wheel and piston stop and discovered that the timing mark was out 8* so my 44* was actually 36* which made more sense. An adjustable timing pointer or timing tape on the balancer can bring the timing marks back to where they should be but you need to find out how accurate the timing mark is first.

When using a piston stop in the spark plug hole, you need to remove both rockers from that cylinder or the valves will hit the piston stop. bar the engine over so that the piston isn't at TDC and install the piston stop into #1 cylinder. Use a coat hanger as a pointer for the degree wheel. Bar the engine over until the piston hits the stop and record the position on the degree wheel. Bar the engine over in the other direction until the piston hits the stop again and record the position on the degree wheel. Divide the distance between the 2 marked positions in half. Remove the piston stop and bar the engine over until the half way mark is lined up with the coat hanger. The engine is now exactly at TDC.

Now look at the timing pointer on the balancer. How close is it to TDC? Chances are it's not.

FireDemonSiC

This is precisely why I built and tuned my own motor.

AlkyIROC

That's a big camshaft for a 350, That's an even bigger camshaft for a 334. I doubt it will idle very well below 1000 rpm.

FireDemonSiC

I have it idling good at 900rpm. My completely molested MPFI setup is making power well north of 5500rpm. I have to put it on the dyno but I regularly shift it at 6k.

RBob

iTrader: (1)

Wanted to comment on this (LHM), the ICM has advance built into it. With the EST/BYPASS open, or the ECM is in LHM, at 1600 - 1800 RPM the ICM should kick in another 10 - 12* of advance. You can check this with a timing light, if it doesn't add any advance the ICM is bad.

RBob.

FireDemonSiC

Totally forgot about the advance built into the ICM. As long as I can have a base timing that will at least allow the engine to idle I'm not too worried.