GMCtrk

iTrader: (27)

I never lost any lowend with multiple sets of headers. Sounds like BS to me

07NBSChevy

I average around 19-20mpg. So no loss at all. 2k rpm at 65 and 2500rpm at 80.

black00chev

iTrader: (2)

I kind of know what you mean. When I did my headers and exhaust it almost felt not quite as snappy off the bottom. But at the same time, I can also light the tires up a lot easier now than ever before.

Fast355

Sounds like your GMS/CYL reading has increased and retarded your timing or you are hitting the torque limit value and the PCM is retarding the timing. My Express van did both when I put headers on it. Fixed the tune and had more torque than ever.

Stock 5.3 probably runs about .56 to .60 gms/cyl. With headers and exhaust mayve .64 to .72 gms/cyl. Substantially retards the timing at all RPMs.

smokeshow

iTrader: (16)

An increase in actual cylinder air mass would increase torque, despite there being less timing. The timing decreases because the knock limit is reached at a lower ignition timing value at higher g/cyl. For higher air mass, timing must always decrease.

The scavenging effect from long tube headers is efficient enough not only to deplete the cylinder of exhaust gases, but also to draw fresh air and fuel out of the cylinder when the intake and exhaust valves are both open. This is air mass that would ordinarily be contributing to torque production, but is instead wasted as it is expelled as exhaust. There is no parameter to manage this effect directly in the tune, so it must be implicitly addressed in the VE table that generates the cylinder air mass estimate and in the timing table. Firstly, since the header changes the effective volumetric efficiency of the cylinder in question, the VE value in the tune must be adjusted to correct the injected fuel mass while in SD mode. This will maintain the target fuel mixture and therefore keep the efficiency model accurate. The timing table is where you make changes implicitly for rpm and load-dependent efficiency effects that cannot be modeled in the VE table. Since actual g/cyl is lower than PCM predicted g/cyl due to the scavenging effect, you may actually increase timing at higher cylinder air mass. In fact you should because otherwise torque will be left on the table.

George C....

loss of lowend would be in the tune, yes you may be tuned by blackbear but that doesnt mean the tune isnt soft

Infernohoe

Fast355 and smokeshow, Guys.... I don't even.... What?
Ok, Fast. I get what your saying more or less. Grams of what exactly per cylinder?

Smoke. I am fully with you up until "so it must be implicitly addressed...ect"

I am still new to this whole tuning deal, Dumb it down a bit for me guys.

Infernohoe

This is how reading yalls posts made me feel

smokeshow

iTrader: (16)

Grams of air per cylinder, according to the efficiency numbers that you enter in the VE table and the equation that the PCM uses to calculate the air mass.

You adjust the efficiency number in VE to account for the extra air that moves through the cylinder, regardless whether it stays in the cylinder or ends up flowing out of the cylinder during valve overlap. Fuel must be in proportion to air. But that efficiency value is false if you think about it...it's an overestimate because of the air/fuel mix that left without being burned. But the tune can't account for that; there is no way to tell it how much fuel and air leaves the cylinder without being burned. And since there is less air in the cylinder than the PCM thinks, you can and need to increase the timing to account for that. These effects are minimal with stock camshafts, but it becomes very important when you have a camshaft suited to high-rpm power.

Markystang

Those were some tasty looking birds in that video!