Forums - CorvetteForum.guru

Re: Weird timing issue

Subject: Re: Weird timing issue
by bam on 2013/5/27 23:40:36

Quote:

djxib wrote:
I've seen that too. The only things I'm aware of that would cause the actual timing to change for a given RPM are the 'closed TPS advance' (that you'll see if you lift off the throttle between shifts) or spark retard due to knock.

I meant to do some research on this a while back but too many projects..

I have noticed however that at WOT the timing is exactly as described at 100KPa unless I get knock (1992).

Assuming your closed TPS advance table maps to your main spark table, 14 degrees at idle sounds very low for your cam, you could try different degrees of advance to get the best vacuum at idle. I run about 30 degrees on mine.

Good luck!

1. Are you saying you have tried to adjust timing in the main spark advance table and it does nothing except at WOT?
2. I will try adjusting the "closed TPS advance" table and see if that does anything. Although I think that must be to use the engine to brake the car when the throttle is closed completely by momentarily bumping the timing up. I notice that is the only time the timing goes down, and that is when I want it to stay the same.
3.It is very hard for me to believe that these LT engines need 30 degrees of advance at idle, that says a very inefficient engine at idle. I know the cam does make a difference but that much?? I can see it at 6000rpm when the dwell of the piston at TDC is split seconds. But at idle why wouldn't you want the timing much closer to TDC. I know when I built a 406 small block with a CC cam it liked 12-14 advance at idle, it would simply not run with stock advance of 8. When I set it I remember it would hardly run with timing over 20 at idle, are LT engines really that much different?

MAP