295 stock to 270 Supercharged?!? Is my Predator tune wrong??

[Gustav]

Just had my '06 Avalanche dyno'd and it came back with 270HP at the wheels. It's 295 stock so WTF?

Yes, I do have 35" tires on 20" rims. But I don't believe that the tires will defeat a Vortech supercharger with JBA headers and performance exhaust. Various forum types have suggested that the problem is likely due to the Diablo tune.

How do I fix this??

(It does perform well in terms of pick up and passing power but what's up with the HP??)

[jsk06c6]

Believe thats 295 flywheel not the rear. Figure 30% drivetrain loss and you would have had 206 HP at the wheels on stock wheels, you probably added another 10% loss believe it or not with that big rubber. So that would have put you down around 177HP....

Conservative I would figure your mods would give you 150+ HP, take away 40% drivetrain/wheel loss and guess what, your at your 270HP!!!

[Gustav]

Wow, I didn't know the drive train loss was so much. I was calculating HP increase (per vendor estimates which appear to be a tad optimistic) from mods based on 295 and wound up with 400+ (not counting tire losses) Needless to say I was disappointed with the dyno results. Thanks for the input.

[jsk06c6]

Yea, the trucks are notorious for drivetrain loses, they're geared for torque which really kills your HP. No different than if I were to add 4.10 rear gears, my HP numbers would nose dive. But their just numbers, I'd be faster, and i bet you truck screams.

[mikel]

Was this a Predator that came with the Vortech kit?
If so, those tunes while being set up a bit safe (rich) should make good power.
Did you monitor for KR?
Did you have good gas in the tank?

[Gustav]

Yes, the Predator came with the blower kit - it has Vortech tune right in the menu. No idea what KR is so I doubt it was monitored. It was full of 92 octane for the dyno. While we're at it here, what about dumping in some octane booster? Just recently, I didn't have access to high octane gas so I used regular and reinstalled the stock tune. Immediately got a service engine light and Onstar diagnostics said it was a fuel issue. Was that a legitimate trouble code or did the computer just think it was getting too much air with the blower on a stock tune. Flipped it back to the Vortech tune (same gas) and the light was gone. (It was actually 75% 92 octane and 25% 89 octane since I topped it up with regular). I had flipped to the stock tune because I was afraid I'd start getting engine knock. So..., should I leave it in Vortech tune mode with no service engine light or go back to stock and have an engine light? I drove it a bit with the diluted gas with no ill effects but have a long trip coming up and want to have the right tune for the gas.

[Gustav]

OK - I got this off the Performance Truck site and it would appear that the tires really are the problem. (Diablo is blameless once again!) Still would like to know which tune is safe though as per the previous post. - Thanx.


"YOU BET YOUR DAMN ASS THEY DO!

I knew large tires lowered output a little bit on the dyno, but check this out.

foggy had his trucK on the dyno, his truck has 35" mud tires, very aggressive tread.

Can you guess how much HP was lost with these tires?

How's 100hp sound? That's right, power jumped 100hp when we put the stockers back on.

Just an FYI,"

allen
__________________
Performance Programming and Installation
Nelson Performance

[mikel]

Yeah, tires are killers.
As for the tune, you need to ALWAYS have the Vortech tune installed.
Running the truck without the tune is asking for trouble.
Also, you MUST run the highest octane fuel you can find, you really no longer have the option of running low octane with the blower on the truck.

Thanks

[jsk06c6]

Told ya gustav, not trying the lead ya astray.

[Gustav]

Told ya gustav, not trying the lead ya astray.

Truly, you are wise.

I believed you! - I mean you've never lied to me before!

[sickREDsierra]

not to be a buzzkiller, but 270 rwhp seems very low for a 5.3 supercharged. i make around 310rwhp n/a with my 4.8....

those tires must really be killin it. and FYI, drivetrain loss is around 13-15% on our trucks, not 40%.
if that were the case, i would be over 430+ at the flywheel, which we both know is false. cam + headers + cai + tune= not 430+

i think stock 5.3 with stock tires will be around 245-255 rwhp, being that your is an 06, having e-fans.... should have been rated at 315 flywheel.... supercharged should be way over that, maybe 350ish at the wheel.