Checked the normal stuff. Timing at 6 deg at idle, reset minimum idle air rate, fuel pressure at 43.5 psi. Engine not running hot, exhaust not plugged, runs on all 8.

Damn thing pings around 3000 rpm. Can't get more than about 1/3 throttle. Won't risk it.

Engine is a fresh vortec 383 TPI, 218/224 comp cam, AS&M LTR and shorty SLP's. 24# SVO injectors, usual bolt ons. Runs great while not under load. Yes it has a tuned prom until I can get my 0411 put in there..040" quench, 10.7:1 compression.

Possible leads...idles ok, but somewhat unstable at times. Could have better throttle response. No SES. All vac hoses are new. Recent t56 conversion.

Anyone have any ideas before I contact the tuner asking for a prom with a little less aggressive timing curve?

This car has fought me every step of the way on this swap...literally, everything is new. I'm considering pulling base timing to 4 deg btdc to confirm timing, though it would probably run like a$$.

 

what kind of gas you running (non ethonol / 10% , octane)

 

93 octane. Even used gas from different stations to rule out bad fuel.

 

well then that was my first thought

 

10.7:1 on an iron head? thats a little high for my tast, not that its never been done before, what the dynamic compression at?

 

Don't remember off the top of my head but I did clean up the chambers a lot so compression.is probably lower than that. If I remember correctly, don't L31 heads require a lot less timing for max power?

 

What did you set the SA tables at? and yes they normally need less timing the the stock heads.

 

Why not just twist the dizzy to 6 degrees retarded from where it is now?

 

I didn't tune it. Actually, the prom I'm using in the old 165 is just an interim chip until I have the time to finish my 0411... I already asked the tuner about the timing issue.

Still doesn't explain my idle instability issue and off idle response. Fuel pressure is good, system is new and holds pressure for quite awhile after shut down.

 

It would ping at 6 deg btdc. I'm pulling base timing in an effort to shift the ignition advance at 3000 back enough to not ping.

 

It has everything to do with the tune, thats were you need to start.

 

10.7 to 1 on iron with 218 deg cam is why its pinging. Try going a step or 2 colder on the spark plugs and work the tune more. Your not going to beable to run alot of timing under load and lower rpms, so pull some out and see where that gets you.

 

I already contacted the tuner. I'm not sure if the Vortec heads were factored into the equation when the first chip was burnt but it appears as if it has a timing curve for stock heads. Gonna pull some timing out of the programming and fiddle with it from there and see where that goes.

 

Keep the timing low for now, alot lower than stock heads...especially if it uses a ARAP based bin. It may only want 25-28 deg in most cells and 30 at WOT but at that compression and small cam, it may only take 26-28. Hard to say.

Need to get air fuel about spot on before you can really start adjusting timing.

 

I really need a dynotune but can't justify it with the 0411 paid for waiting in the garage...just don't have the time right now.

 

Just curious.
Have you done a compression test? It would be interesting to know your cranking pressure.
Do you have the Comp Cams part number?