e-man

OK heres the deal a while ago I had a problem, my scanner was showing knock at WOT. I thought the knock sensor was bad but before I changed it I was thinking, with the three chips I have (stock,hypertech,fastchip). I was getting the most knock with the fastchip,I know the fastchip leans the car out more and the stock and hypertech are on the rich side. So put the stock chip back in and switched the stock runners to ported SLP's and the knock counts rose higher than before. So now I think its safe to say Im running lean in WOT. I tried raising the fuel pressure up didnt help the fuel pump is only a couple months old and is a high flow 255lph! Im going to check to and see if the pressure drops in WOT. If the pump is ok think the injectors could be cloged or bad? What else should I check?

------------------
89 350 TPI,comp cam,edelbrock intake base,SLP headers,highflo cats,flomaster cat back,accel 300+ ign,ported plenum and runners,ported maf,auto w/shiftkit,cold air induction,AFPR,Ed wright chip,3.23 posie best ET 14.011@98.72mph without cam/New best 13.926@98.27mph

Grim Reaper

First, you MAF will be compensating for any addiontional (and it really isn't that much with just runners).

Hate to say this, but you are encountering a common problem with TPI motors. First, TPI seems more notorious for knock counts than other setups. But, it also is a function of the heads and the age of the motor. Just a little oil leaking past the seals is enough to trigger big time knock...and we all know how great Chevy's Valve Seals are.

The bottom line is that the stock heads on these engines promote "swirl and tumble" so you don't need as much spark advance as you do with older "large combustion chamber" heads. Forget the magazine articles with 36*-38* spark advance @ WOT. On a basically stock L98, if you "capped" the Knock Retard, you would be hearing BIG TIME "ping".

The best thing I have found is to control the amount of retard the eprom pulls out when it detects knock. It is NOT a false knock, even though you don't hear it. It is the ecm doing its job and pulling out spark advance BEFORE you hear it.

I have done a lot of experimenting with the knock sensor within the eprom and when I basically "neutered" it, I found I would start to encounter "audible" knock around 32*.

If you talked to Grumpy (Bruce Plecan) who has done a lot of tuning on these motors within the eprom, he'll tell you that these heads don't like a lot of advance and are designed to develop max power with a lot less advance. The true measure of performance is the e.t. and mph at the track.

Bruce will also tell yo that if you can get the same level performance with a lower spark advance...go with the lower spark advance...its easier on the motor.

e-man

Glenn I read your post in the prom board,for the time being untill I order all the prom burning equipment think this will work? I'll put the fastchip back in (better part throttle programing I think?)and lower the base timing till I get about 29* total advance.Also I changed the valve seals when I did the cam a couple of months ago.

[This message has been edited by e-man (edited July 10, 2001).]

e-man

OK with the base timing adjusted to 0* the scanner shows total advance at 32* and the knocking is down but not out it is pulling 2-6deg instead of the 10-16deg before this is with the hypertech chip didnt switch to the fastchip yet.The throttle responce is not as good as before.If I drop the timing any more Ill be ATDC? What to do now??