GXPJAY

Well, since most people don't surf the LS4 forum I thought I'd post our results so far on the Turbo GXP.

Specs:

Stock LS4 in a 06 Grand Prix GXP

Cartuning prototype/production turbo kit

-Turbonetics T66 Turbo with a .81 exhaust housing
-Alky injection
-42lbs injectors
-FP rewire
-2.5" downpipe (physically limited by the room so for a production kit that you will sell this is the only option)
-electric exhaust cutout before the cat
-Front Mount Intercooler

-Running 94 octane pump gas and regular -40 washer fluid for alky

We wanted to see what the kit was doing HP wise so we went to the dyno. Did some pulls and we noticed a problem that we are looking into right now. The curve as you can see below climbs really nice then at 5400rpm it just takes a dive. We are investigating this as it would be nice to rev all the way to 6000rpm but right now Kevin changed the shift points to around 5400rpm so that we don't loose any power and let me tell you.... This car is a ROCKET!!! If we would have known it was doing this at the track we would of had much better times, can't wait till spring!!! (We did 12.3@117mph with the stock 18" rims and tires a couple months ago)

On the 6th pull at 12PSI we got 467.85whp/449.39ft. lbs @5400rpm Highest HP 04+ Grand Prix

Let me tell you, this is extremely amazing for a bolt on kit on a FWD!



Link to a bigger version: http://i37.photobucket.com/albums/e5...Y/43198a56.jpg

LINK TO VIDEO!!!!!!!
here's a picture:



What do you guys think? And what do you think our problem is at 5400rpm? Maybe Valve Springs? The issue in the middle of the graph the dyno operator said could be torque converter related....?

ninetres

iTrader: (35)

Not sure what exactly an LS4 is.....and how the FWD tranny works/robs power.......but 12 psi on any other LS platform car should yield MUCH higher numbers. MUCH higher.

frcefed98

iTrader: (16)

The LS4 is a smaller 5.3 L (325 in) and is rated at 303hp.

Not bad especially with the bug you guys are trying to chase down. Keep plugging away at it and those numbers will surely rise.

bboyferal

iTrader: (9)

Damn, that thing is dirty.

ls2 bait

iTrader: (11)

thats not bad considering the car prob only made in the 250 range stock. but i would have expected those numbers at about 8-10 psi. but it looks to still be making power when it cuts off.

GXPJAY

Yeah it's a 5.3L V8 with the LS6 heads but LS1 valvesprings with a FWD tranny, Displacement on Demand etc. etc. Calculated drivetrain loss is 20-21% so this is roughly 580hp at the motor.

Stock it dynoed at 250whp so almost double the power for $5400 isn't too bad.

This is on a stock motor and if we could rev to 6k like it should it would be over 500whp for sure. We think it may be a valve spring issue, most likely buy some Patriots and see what happens.

I'm in Canada therefore even if I would have gotten the car washed next door it would still be dirty like that, winter blows!

LSs1Power

iTrader: (5)

It looks like a valve float problem. Change the springs and you should be fine.

hellbents10

iTrader: (10)

It would be cool to see pics of the setup.

Pro Stock John

iTrader: (34)

I'd run something like the Patriot springs to get the car to pull clean to 6000-6500. We all run a lot more spring pressure than we thought we needed in the earlier days of FI.

GXPJAY

I'll be picking up some Patriots this week and will put them in after the holidays.

We were looking at the scans again and the MAF g/s is all over the place, it constantly goes up and down when at WOT. We're using a LT1 MAF in blow through, what is everyone else using? Probably 3 bar MAP SD and no MAF I would imagine? If you are using a MAF which one are you using and does it get clean airflow? I'd like to keep the MAF for drivability, emmisions, fuel mileage etc. it's my daily driver.

hellbents10

iTrader: (10)

SD. or just a 6l truck maf.

Hugger Z

iTrader: (4)

I used LS6 valve springs on my engine with the turbo's. I have had no issues with mine but am only pushing 7psi.

BlackScreaminMachine

iTrader: (17)

Thats bad *** for a DD

Pro Stock John

iTrader: (34)

PM onfire, he seems to know a lot about MAF stuff. Change over the springs, and then you won't have to worry about that as a variable.

GXPJAY

That's what I'll do is the springs first. Just waiting on Larry to reply on a question I asked and then I'll order. Then we'll see if that fixes the problem.

Pro Stock John

iTrader: (34)

I would switch over to an LS1 MAF, the LT1 stuff is a step backwards and I thought that they don't work sample as quickly? I'd run an LS1 one or a GTO one if they are bigger.

dlove

iTrader: (23)

lt1 and ls1 mafs are the same sensor.

GXPJAY

Yeah I think they are the same just LT1 has a metal (or aluminum rather) housing not plastic which always snaps when trying to tighten the T-bolt Clamps.

Here's a engine bay picture of the setup. Mine isn't ceramic coated but the kit will ship ceramic coated and I'll get mine done at some point.



This is where the Alky is

00PewterSS

iTrader: (3)

I worked on the GXP for quite a while and it was not an easy feat to fit the engine in that compartment. I can't believe someone designed a turbo kit that fits in that small area!

That hitch in the middle of the graph could be the tranny. A stock trans isn't going to hold up to that much power for very long.

Nice power, valve springs, your injectors might be at capacity and the intake all could be causing you to lose power up top.

Brian

GreenBlood

iTrader: (6)

cool, the GXPs are nice cars...can't wait to see the results once the problems are fixed...