388 stroker timing problem

When i set the timing to what it wants, it seems to idel fine, but if you listen to each side of the exhaust you can hear inconsistency. But it aint that bad, when i hooked up the compression gauge and turned it over i got 120lbs, which is weird for a stroker i thought, i am goin to do that vacume test and see what that does for it or if i am close. the spark plugs burn all the same color lite lite brown. The only time it backfires is when i let off the gas after having it at 1/2 half throttel at least, like if i launch and get up to 50 and let off it backfires a low thump unless i have the timing at 12 degrees then it pops a few times loud. With the edelbrock 750 on it, the screw are 1 1/2 turns out and on the holley 600 i have them about 1 turn out, even if they are off just a half turn, it shouldnt cause it so much. I havent hooked up a tach yet, i been being stingy on spending money of such parts right now, but i would say its running 800 to 1000 is where it seems to like it.


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Are multiple cylinders 120psi? 120 psi sound really low for a 383, vortec heads and a cam with mild duration and tight lobe seperation angle. I would expect it to be 160-180psi or maybe even higher. Do you know what the compression ratio is? It sounds like maybe your camshaft is set too retarded.



Well the idle misture screw 1-1 and 1/2 turn out would indicate the ifr is probably big enough. I would first look into why your compression seems low. I think you need a tach and a vacuum guage to properly first set the ignition timing and then idle mixture and idle speed. You might need a little more timing and a little richer idle mixure setting.

i talked to a professional performance engine specialist and he asked if i had a exhaust leak, and which there is a slight one and he said thats why it back fires when deaccelrating and that i needed to either recurve the distributor and total timing again or get a new one with adjustable curve and time it to 34 degrees. That would take care of the hesitation and backfire, does he sound right?

This is what RSIII was saying to you several posts ago and yes, it sounds OK.

Backfiring when letting off of a revving engine would have been good to know- much different thing than backfiring otherwise! Maybe you said earlier and I missed it...

As for the "low" compression readings- as long as they're consistent, I wouldn't worry too much. Could be just the gage. Of course, it could be the cam timing as well- in which case you will be chasing your tail until that's resolved.

Good luck!

I think an exhaust leak could cause backfiring on deacceleration, but I think it would depend on how close the leak is to the header and cylinder head. That might explain why you notice backfiring from one cyl bank. Where is the leak located? I still think you should get to the bottom of why your compression seems low, whether it's an inaccurate gauge, late valve timing or what have you. Late valve timing could cause poor low speed performance and a backfire.

the exhaust leak was in between cylinder 3 and 5 the gasket backing somehow pulled and chiped off, i have never seen this before, but i am putting on a new gasket and hope for the best, the other side is fine so i dont know what happened, and i have posted on this site and on another site about leting off the gas petal and it backfiring, but oh well i will install that and see how it does, on the other hand, i think the gauge must be messed up cause anytime i have used it its always been around the same number. but could also be that the timing was set at 23 degrees where it was running the best so maybe when i recurve and total time it, maybe it will be higher.

The gage isn't used w/the engine running, so I don't see the readings changing with an ignition timing change. It could change w/a cam timing change, however. This was mentioned earlier, I believe.

In any event, it sounds like you have a plan of attack.

Make sure you don`t have any plug wires crossed, this is easy to do and is easily over looked. Next, yes a exhaust leak will cause a backfire as it`s pulling in fresh air from the pulses from the exhaust system. 120 PSI compression is dirt low, far too low with a mild cam in a 383, If it reads this low I would think the valves are out of adjustment by quite a lot. How were the valves adjusted? The vac advance should be connected to a manifold full time vacuum source with the base timing set at 12 degrees BTDC with the vac line disconnected and plugged. After setting it at 12 degrees, connect it to a full time manifold source and you should have 24 degrees timing at idle.