I really need some help here!!!
I have a 2004 GTO with a LS1

I have a stock bottom end other than ARP bolts, Fast 92/92 4" CAI
Stock 07 5.3 Tahoe 243 heads with dual lunati .670 springs and a 231/231 .605/.605 lift cam Texas Speed 7.40 pushrods
Blue demon 42# injectors and OBX long tube headers
Fuel pressure at idle 63# at WOT it drops to 58#
Problem I have is this combo is only putting 340 RWHP
I know this is exceptionally low.
Any ideas! I know the cam is installed dot to dot.
My tuner said it was off a tooth.

 

Why do you think thats exceptionally low? Sounds about right to me...

 

I did another gto with stock 241 heads .650 springs a fast 90/90 same CAI
And exhaust with a hot cam 2 and it made 400RWHP
So with that thought process this should be right there or better
Right?

The initial tune was changed several times due to being told we need this that and the other but as it went further down the line of other parts needed the RWHP actually dropped. The first tune made 389 but said fuel pump was bad then next was it needs injectors so put them in then MAF then it went SD now it's at 340RWHP.

Thanks in advance for any and all responses

 

I guess what I'm looking for is has anyone had a similar combo
And if you did what power did you make.

 

At wide open it could be loosing spark in 1 cylinder.

 

I don't think power is that far off. I would not expect a regular gas 5.3 to make the same power as a premium fuel 5.7L LS1, with a truck rear end and big heavier tires & wheels as a GTO with a smaller rear end and smaller, lighter tires & wheels. The GTO is not stellar, but the truck is not that far off from what I have seen.

 

I think hes saying the heads are from an 07 5.3
So stock 799s
It should be closer to 410-415 wheel in a 5.7 through a fairly light drivetrain
If it kept dropping after tuning changes thats where i would look first.

 

I thought the same as Ed. Very hard to see what the OP is tring to get across.

 

The heads are from a 07 Tahoe w/a 5.3 they are 243 castings and other than the springs they are untouched

 

What kind of dyno?

What's the A/F and spark?

Is it down a cylinder?

Does it have CATS? If so it is possible one or both are collapsing.

Too many unanswered questions. Too many variables. Need to find someone with a good diagnostic mind. Fuel pump, injectors won't make you low on power, unless an injector is working, or the fuel pump is so weak the A/F is so lean it noses over. Even if the pressure is somewhat low, and the injectors are at 100%, won't cause loss of power as long as you can achieve the correct A/F ratio.

 

I guess I'll be tearing this thing apart after only 1500 miles I haven't even got to beat on it yet

 

Why not troubleshoot the problem before tearing it apart.

 

It seems to me everyone thinks its mechanical

 

6 speed or converter? [Didn't see it in your FP.]
Sounds like your "tuner" is throwing your money at whatever he thinks is "next".......

 

Sorry A4 with a vigilante 3600 one piece aluminum shaft the high end BMR axles stage whatever. Built transmission. This isn't a race car by any means but it should be able to put better numbers down. I was talking to someone earlier that suggested many possibilities and we talked about maybe changing the cam.

 

Unless the cam has some serious damage its not the reason for the low hp. A stock cam should make more power than that.
Before you start throwing money on new parts and taking stuff apart, id find the problem

 

Make sure your not losing spark on one of the cylinders. I had a weak coil give me fits for a month before i figured it out. Could also be in the tune. How does it run on the street? Don't always go by dyno #'s. Are you sure your pushrods are the right length?

 

It runs good street driving just low seat of the pants power. I will check coos I suppose

 

Stalled auto with an IRS. Unless the converter was locked on the dyno, I think you are fine.

A vigilante 3600 is probably as loose as a yank 4000 based on my experience with them. I bet you are losing 30rwhp or more through the converter alone.

 

Yes was locked on the dyno. The problem is we started the tune and had 389 then after all the parts needed it dropped to 340