I have just bought a 2008 GXP with the LS-4. I need to know what things I could change to the stock tune to improve power with HPT.

Ed

[Please excuse me if this question has been asked before]

 

There's a couple of quick changes that will help out:

GM set the power enrichment (PE) quite rich (12.0:1), it needs to be leaned out to 12.8 - 13.0 to improve high rpm torque.

The PE enrichment rate is slow, needs to be bumped from ~.02 to 1. PE is also delayed before 5000 rpm (well in the older tunes, haven't seen an 08 file yet) so the delay rpm should be dropped to ~2000 rpm.

The timing tables are actually pretty good, not much room to increase WOT spark w/o causing KR, so they're already set pretty close to mean best torque.

Just for basic driveability, you want to ensure that the MAF is properly scaled.

 

set the PE ramp-in rate to 0.8... and the rpm delay to 3000....

the rpm delay only comes into play if the % throttle position is reached anyway...

meaning, if you're not at 80-85% throttle position, but you ARE at 3000 rpm, the PE delay still won't do anything... cuz you have to be at 80-85% throttle position AND at 3000+ rpm for the delay to be taken out...

so, you could lower that % Throttle Position as well... which will make PE kick in sooner, since the delay will be eliminated earlier with less throttle position.

the delay is totally dependent on throttle position - that's what drives everything. if the throttle position isn't met, it doesn't matter what the other stuff is set to anyway.

 

For my LS-4 powered car (a 2008 Buick LaCrosse Super) I replaced the stock air filter with a drop-in K&N for more air flow. I also had the exhaust resonator removed and replaced it with a straight pipe for more sound (without drone). I haven't touched the on-board computer systems (afraid it will affect pollution testing).

 

I see no advantage to ramping PE in slower. i.e. .8 instead of 1 (but really no disadvantage either).

GM sets the PE TPS% enable to 87% at all rpm's which, due to a GM specific calculation is actually 100% WOT. I reduced the TPS enable percentage so that PE is engaged at a lower engine load. In my tune, the higher the RPM the engine is turning, the lower the required TPS% required to engage PE mode.

There's infinite options for setting the TPS enable, I chose 80% up to 2000 rpm and decreased it linearly to 60% at 6000 rpm.

 

aaah, ok...

yeah, either way for the ramp-in, .8 or 1 is better than .2 hehe...

I have the same for my %TPS... except mine goes lower than 60% at the upper rpms...

I based my settings on the info I got from the tune creator at diablosport...

 

I know very little about HPT. I need to know what to turn off and what to leave alone .Do I turn off Active Fuel Management to scan my LTFT and etc?

Ed

 

Yes. I always turn DOD/AFM off when tuning. The airflow characteristics of the engine are completely different between V4 and V8 mode.

You really should spend a few weeks going through the stickies and basic tuning threads on the HPT forum and learning how to use and interpret the data using VCM Scanner. If you don't know what you're doing, or what the effect of a tuning change is, you are risking damage to your engine.

Take it slow and work on only one thing at a time, that way if you don't like the results of a tuning change, it's easy to fix - as long as you documented what you changed (there is built in functionality in HPT for this.

Also, alway retain an unaltered copy of your stock tune so that you always have a fall-back if you muck up.

Get a wideband - fuel trims are only good for tuning part throttle with the engine in closed loop. You can't use fuel trims to tune WOT or when PE is enabled, as the engine is in open loop under those conditions (no fuel trims).

You have the newer E38/E67 ECM, which makes SD tuning a bit more complicated since there is no VE table. Look up the thread Bluecat started on the HPT forum that describes the utility he wrote to help tune SD on these newer ECM's.

Here's a quick run down of some things I did with my tune. Use at your own risk:

On the Engine>Torque Management screen, Set the "Maximum Torque (RPM vs Gear) table so that all cells are maxed.

Same tab, the ETC Limits should be set to 100 for all cells

Same tab, there are two torque management tables - Spark retard vs torque reduction and Torque Loss % vs spark retard. I set all cells to zero.

I find that the Knock sensors are overly protective, I doubled the KR decay rate in the Engine>Spark control>Spark Retard tab, and reset the maximum KR step to 5 from 6

Torque management is also present on the Transmission>Torque management tab. I think you need to retain some torque management during shifts to help protect the transmission. I retained half the torque reduction in the Abuse Mode and Torque Reduction tables.

I suggest you leave the Transmission Score protection enabled.

Under Transmission>Shift Properties tab, consider bumping up the shift pressures a bit, this will give you slightly crisper shifts without adding a shift kit.

Transmission>AutoTCC tab, you may consider increasing the TCC duty cycle, but be warned that this makes the DOD/AFM cycling much more noticeable as "surge" when going from V4 to V8 mode.

 

Thanks for the quick reply. I have tuned my maf with LTFT and set WOT fuel ratio on a dyno for my F-body. Do you think this will work with the LS-4? Are there any '" free " mods that will help with the breathing?

Ed

 

Yeah, it'll work, you just have to pay the dyno guy every time you do a mod that changes the breathing ability of the engine.

Not much for free mods, just pull the "silencer", or air horn out of the air box, it does open up the inlet a bit.