I have a 1991 Z28. The mods I have are bored 30 over, ported heads, cam, 1.6 roller rockers, mini ram intake, a 58 mm throttle body, and a custom burned computer. I'm not sure what my timing is set at now, but for some reason i think its at 4* BTDC. Should I advance the timing more? Whats a good base to start at? Or what is the best way to find where to set the timing at? Also how much power can can you gain from timing? About the intake backfire, i have checked all of the vacuum lines and they are all fire. I just happens occasionally when i floor it. Any idea what might be causing this backfire?

 

can some one help me out??

 

We just built and engine for my son's 91 RS. Won't go into all the engine stuff but it's a little different. Anyway we also had a backfire up through the throttle body with the timing set at stock settings (or near stock). We ended up advancing the timing a lot. It's out in front of the timing plate now by a half inch or so and it stopped backfiring. Ours is a TBI set up so it "breathes fire" when it popped. Oh yeah, we could have installed the cam gear up to 4 degrees advanced or retarded but choseto set it in the "stock" keyway.

Don't know if that will help you or not but it's something to try.

 

Hey Z's r Best, did ur pop go away and the backfire disappear? i am having the same issue, we went through everything to figure it out but it only occurs when you go full throttle quickly, it hesitates and pops through the throttle body and flames occasionally accompany the pop. we have the timing set at 0. everything else is dead on in the car, w e had it hooked up to a scanner to test everything else, but no answers.

 

i to am having the same problem???? help??

 

I cant be sure, but typically you are supposed to centerline your camshaft if you swap a new one in.
Even though a cam may be approximately centerlined by the dowel with stock timing gears and lineup marks, deviation from stock number one intake valve centerline angle needs to be adjusted with the cam sprocket to ensure desired operation and ease of tuning. Also centerlining the cam ensures your cam lobes are properly timed to piston position.

Other changes in the cam profile can also result in higher base timing being necessary. Some inexpensive dyno programs can estimate the general effect of different cam timings.

Without accounting for a large change in intake centerline and duration increase (a result of lift increase) you could end up with an intake valve slightly open while firing while the advance is properly set compared to piston position.

Can someone back me up here? Or explain in more detail?

This isnt neccesarily your whole problem, but it could be part of it.

 

God I hate intake backfires. I had this happen after I installed my ASM runners. The short version of it is, the runners were warped -even after I had sent them back- and I continually overlooked it looking for something else to be the culprit. I had a massive vac leak on the runner and had to advance the timing to some crazy number just to keep the car running. Fixed the leak and the car just purrs.

Eric

 

I think that you are too retarded. Start the engine up and get it up to proper operating temperature. Shut the engine off, remove the EST wire on the distributor. Start the engine up again and set the timing to 6 degrees or a bit higher. Do it right with a timing light. You have to do this with the EST wire disconnected. Otherwise the computer is going to undo every move you make.

 

TPI intakes will Pop when you hit the throttle if the fuel mixture is too lean. Commonly referred to as "Lean Pop".

Check your fuel pressure at the Fuel Rail with the vacuum line disconnected from the Fuel Pressure Regulator. It should be set somewhere between 44 to 50 psi.

 

I know this is a old thread but I want to hit on what mnorton said, this can be your problem.

I had to put a new pump in a 2002 blazer because it's pump was way too weak and back firing in the intake. the guy bought one from the internet that claims it will work but was labled for a different truck. ( trying to save a few $) so he ultimately ended up buying a proper pump.

the lesson here is don't jerry rig to save a buck. it often ends up costing you 2x as much in the end.
and yes, a weak fuel pump can cause them to back fire.
the blazer vortec needs at min 58 psi to even start. the pump he bought would only produce 45psi. once started it would run around 55 but didn't have the *** to pump up the psi when you give it some gas.
that's why everyone working on it was so stumped. they were going to give the truck away they were so fed up. over a $250 pump.

 

I also wanted to add the pressure should jump almost instantly up to full psi when you turn the key on. not gradually climb. that's another tell tale sign the pump is weak.