TPI's and timing vs LT1
02-17-2009, 07:56 PM
#1
Race Director
Thread Starter
TPI's and timing vs LT1
I was looking at the timing tables from a stock 5.7L TPI speed density car and comparing them to the tables from an LT1. I noticed that the main spark advance table values are very low. For example, WOT at 4000 RPM is something like 20 degrees advance. I can only assume that this is exactly what it says and this is the advance over the base timing which is set in the ECM constants table. For a stock car with a value of 6 for base timing, this would mean a total timing of around 26 at 4000 RPM, 100 MAP.
I made a spreadsheet that calculates the difference between the TPI's timing and the LT1. I found that for almost all values the LT1 is higher than the TPI, sometimes as much as 16 degrees.
So the question... why? What is the major factor in the lower timing on the TPI? Is it different chamber design, compression ratio, intake / cam combination?
The reason I ask is that a friend of mine has a head / cam / headers TPI car that is currently running a MAF computer that he wants to convert to speed density. He wants to do this because eventually he wants to put a HSR intake on it instead of the TPI. Since he has heads / cam / headers already, I would kinda like to have him go ahead and convert that computer before he gets the intake so I can get a feel for tuning it first. If I can get it running really well on the TPI, then I'll know that any issues that come up after installing the HSR are only a result of the HSR and I can address them accordingly. Basically I'm trying to take it one step at a time so that it goes smoothly.
He's running the LT4 Hot Cam, Trick Flow Heads, and Hooker Super Comp headers right now. So what I'm curious about is how would thing thing behave if I put my timing tables into it from my LT4 Hot Cam'd, Ported Head, and Hooker Super Comp LT1? I don't expect it to be perfect, but I'm wondering if this would be a closer place to start than a completely stock program? Is there something inherent to the TPI intake that needs the lower timing, or was it all in the heads / cam and such that has been changed?
Any info anybody can provide would be greatly appreciated.
I made a spreadsheet that calculates the difference between the TPI's timing and the LT1. I found that for almost all values the LT1 is higher than the TPI, sometimes as much as 16 degrees.
So the question... why? What is the major factor in the lower timing on the TPI? Is it different chamber design, compression ratio, intake / cam combination?
The reason I ask is that a friend of mine has a head / cam / headers TPI car that is currently running a MAF computer that he wants to convert to speed density. He wants to do this because eventually he wants to put a HSR intake on it instead of the TPI. Since he has heads / cam / headers already, I would kinda like to have him go ahead and convert that computer before he gets the intake so I can get a feel for tuning it first. If I can get it running really well on the TPI, then I'll know that any issues that come up after installing the HSR are only a result of the HSR and I can address them accordingly. Basically I'm trying to take it one step at a time so that it goes smoothly.
He's running the LT4 Hot Cam, Trick Flow Heads, and Hooker Super Comp headers right now. So what I'm curious about is how would thing thing behave if I put my timing tables into it from my LT4 Hot Cam'd, Ported Head, and Hooker Super Comp LT1? I don't expect it to be perfect, but I'm wondering if this would be a closer place to start than a completely stock program? Is there something inherent to the TPI intake that needs the lower timing, or was it all in the heads / cam and such that has been changed?
Any info anybody can provide would be greatly appreciated.
