[Vettezuki]

Some of you know, but the back story is this. I have a Heads and Cam LSx in my C3 Vette. The "advertised" static compression was 11.1:1. Well, when originally tuning, as I recall 18 degrees TOTAL was all we could get before naughty things started to happen.

Since then I have discovered Torco, which works great to eliminate remnants of knocking on hot days in the summer, etc.

So, say I remember right and timing was set at 18 degrees total. Would bumping that up to X have any possible effect on AFR? For sake of argument let's say I get to around 34 degrees or so.

Yes. I know it's timing, here's why I ask. Increased timing leads to higher combustion pressures, right? (That's where the torque and power is coming from.) Well, I'm imagining the exhaust gases leaving with a higher velocity with more timing, therefore a higher scavenging effect and therefore more air coming into the cylinder and therefore more requirement for fuel.

Am I totally cracked out to even wonder about this? In any event, I imagine with ECU control and O2 sensors, fuel trim would be automatically adjusted, I just don't want to go cranking up timing and come up dangerously lean.

[big2bird]

Your computer should adjust your mixture.

For maximum power, you want to advance your timing in 2* increments until it "pings", then bump back 2*.

Operating with retarded timing increases exhaust temps, read as unburned fuel burning on the exhaust side, as the burn is reaching peak after exhaust.

Ever see headers glowing red hot? That's your exhaust valves warping.

[BRUTAL64]

Originally Posted by big2bird

Your computer should adjust your mixture.

For maximum power, you want to advance your timing in 2* increments until it "pings", then bump back 2*.

Operating with retarded timing increases exhaust temps, read as unburned fuel burning on the exhaust side, as the burn is reaching peak after exhaust.

Ever see headers glowing red hot? That's your exhaust valves warping.

That is all correct.

You've worked on a few engines, haven't you?

[94cobra69ss396]

He won't be able to adjust his timing himself, he'll have to have a tuner do it. Ben, who does your tuning and what do they charge? My tuner Steve at Powertrain Dynamics is located in Huntington Beach and charges $125 an hour. He did both my pump gas and race gas tunes in an hour and he does tunes that are safe and reliable. Just look at the Cobra. I have 70,000 miles on it since he did the first tune. I just recently had him retune it because I added a UPR intake tube and it pick up 38rwhp.

[Vettezuki]

Originally Posted by 94cobra69ss396

He won't be able to adjust his timing himself, he'll have to have a tuner do it. Ben, who does your tuning and what do they charge? My tuner Steve at Powertrain Dynamics is located in Huntington Beach and charges $125 an hour. He did both my pump gas and race gas tunes in an hour and he does tunes that are safe and reliable. Just look at the Cobra. I have 70,000 miles on it since he did the first tune. I just recently had him retune it because I added a UPR intake tube and it pick up 38rwhp.

Andrew Zimmer of Z-Industries. He actually offered a free re-tune because we were having some issues with the A/F equipment at the tuning facility, even though he finally did get it dialed in pretty good. I've always put it off expecting to get headers and whatnot.

The guy I bought the motor from is a very competent amateur tuner (enough to get his twin turbo 402 terrorizing the world with a speed density tune). He has EFI Live and offered to tune if I just buy an additional VIN license. Also, ls1z28 has access to HP Tuners as I recall. So a few options. All the A/F stuff should be fine, but the timing curve is VERY VERY modest. The same exact engine with headers but the older style LS1 intake was making 430 to the wheels. I'm at 390 with stock manifolds, but the much better LS6 intake. I don't think the driveline loss between a C3 to a C5 is all that different (especially since I'm going through a T56 as the trans), so I figure even without headers, some manly timing might kick me up solidly into the low 4s, but especially more low end torque.

[big2bird]

Contact "Oxidizer" at LS1 forum. He is a moderator there, and also known as Richard Waitas , R&D engineer, Magnaflow Inc. He can make that car scream.

[Vettezuki]

Originally Posted by big2bird

Contact "Oxidizer" at LS1 forum. He is a moderator there, and also known as Richard Waitas , R&D engineer, Magnaflow Inc. He can make that car scream.

I think I remember him correctly. He did my dyno when we were at Magnaflow. He said my sheet looked very good. But of course he didn't see all the params like timing etc. If my computer is going to adjust fuel trim with increased timing, I might just try that first. I know headers change the picture since air flow starts to change quite a bit.

[enkeivette]

Not in your case, especially because your computer auto-tunes to a number that you type in.

Your headers might, on the other hand. But then, once again, assuming your fuel system has the capacity your computer will correct.

[TimAT]

ANY engine is just an air pump. Sure, it burns fuel. I can see a difference in spark plugs just by pulling the baffles and running with just the sidepipes.

have you ever done any reading about the "block learn/integrator" in GM's computer system? Good info.

[Vettezuki]

Originally Posted by TimAT

. . . have you ever done any reading about the "block learn/integrator" in GM's computer system? Good info.

Negative ghost rider, the pattern is full. Say, would that be conveniently located online somewhere?