Preface:

Engine:

348 (LS6 Block)
- Diamond forged pistons, Eagle rods, stock crank
- Clevite bearings throughout
- ARP bolts and head studs
- Stock Heads with comp 918 springs (springs soon to be changed)
- Lingenfelter GT-9 cam (208/230 .547/.579 121LSA)
- Stock LS1 intake, stock throttle body, 2 bar speed density tune
- Single T70 (p-trim wheel) front mount turbo kit (TTI style)
- Log style manifolds, all ceramic coated inside and out
- FMIC, Snow Performance water/meth injection
- Some loud BOV

Drivetrain:

- 6 speed, Spec stage 4i clutch.
- Moser 12 bolt with Eaton Posi, 33 spline axles 3.73 gears, TA girdle


I picked up this car recently and made a few changes since I purchased it. Previous numbers were 550/605 @ 10psi - with straight denatured alcohol in the snow kit coming on at 7psi and full spray at 15psi on the controller (controller was set, tuner didn't adjust). Through Hooker catback, filter on the turbo on both instances. 88* outside, 52% humidity.


Went back to the dyno a couple days ago, tuner offered to check the tune after some changes were made (same tuner, same dyno, he tuned the car previously/built it and offered to check it over). Since I bought the car I used 70/30 meth/water on the snow kit, installed a 3" cutout in the I-pipe. Car previously saw 10psi on the dyno, this time it was seeing 14psi with no other changes. Meth kit coming on at 4psi, full mist by 10psi.




I'm pretty happy with the torque, but scratchin my head about the hp. Thoughts on why its falling off at 5200? So far suggestions are weak valvesprings/valvefloat, blowing out spark, or tuning issue. I figured I'd post up and get more ideas before I go spend $300 toward new valvesprings. I know these aren't the greatest, and will change them eventually, but for now, just gathering ideas. Thoughts?

 

Your just running out of turbo, at the top end,.valve springs power dips then generally recovers agian.

 

Did you happen to measure exhaust back pressure pre turbine wheel? Boost leaks?

 

No but I may look into that.

I think the turbo is sufficient for the combination.

 

Well, last week I had another local tuner take a look at the car. He ended up doing a total retune of the car. I went back to the original shops dyno, and it ended up showing a gain of about 50rwhp, and about 10 more rwtq. Final numbers were 595/626 on the original shops dyno, and 600/620 on the new tuners dyno (SAE correction factor on both dynos and both of them dynojet) It seems the lil t70-ptrim turbo is about maxed out, and the wastegate is pretty junky - it's some eBay jobber that was on the car when I got it and doesn't hold 15psi - boost is dropping off to 13.5psi at peak hp even with a manual controller on it. All in all I'm very pleased with the car, and I'm real happy to have hit 600rwhp. Can't wait to hit the track later this month and get some seat time!

 

you are out of turbo, especially on the exhaust side. P-trim = small.

 

Yeah, figured as such. Think I'll probably upgrade to a TC78 and a new WG next year, but for now, I'm really happy with it and how streetable it is.