: LT1 B/D PCM tune vs LT1 F/Y Tune



N0DIH
02-16-07, 10:30 AM
Something I have noticed, all the B/D cars have a 20 degree offset on the timing table, and the F/Y cars don't.

I think I found out why.

The Timing tables can go from 0 to 110 degrees. But there are some places in the timing table that GM goes negative in the B/D tune at a couple places in the timing table. The F/Y tune does not go negative.

Simple!

bigbluebrougham
02-20-07, 04:08 PM
Any particular reason?? I am so new at all this, just wondering why they did that...

BBB

N0DIH
02-20-07, 08:06 PM
Just what I said, they can push the timing below 0 degrees. The stock B/D has negative timing, the stock F/Y doesn't, so they don't need to.

bigbluebrougham
02-21-07, 06:51 PM
I guess what I meant is why would a car go below zero in timing, moreover, is it good?? Must be since my car still runs good! I just don;t have the slightest clue what a timing table is. My old pickup I know you have initial and total timing, that I understand. Is this the same?

BBB

N0DIH
02-21-07, 11:07 PM
They have it set to do it in odd conditions like super low vacuum and low rpm. Like engine start. If you get very high at that condition you can get starting pinging.

My 454 sees 0 degrees timing factory at high load conditions. Even negative timing. There is initial timing in the PCM tune, but it is the closed throttle timing now, and the timing maps handle it all now. There isn't "advance" like in a distributor anymore...

bigbluebrougham
02-24-07, 05:01 PM
Now I get it!! :worship:

Thanks for the clarification!

BBB

P.S. As soon as my laptop is done in the shop, (friend is fixing it for free, for some reason he is slow on fixing it, can't complain, free fix!). I will let you know on the tuning part.