So I got this car a while ago and didnt think it had the power it should have. I took it to the dyno yesterday to see if we can figure out whats going on.

2004 GTO
SLP 402
Unknown cam (idles stocklike)
AFR 225cc 72cc big bore heads
SLP LT's into catted mids with LM1 catback
K&N Intake
3200 stall

The car made 318 RWHP @ 5500 and 325 RWTQ @ 4700. I know the tune needs to be adjusted as the dyno's wideband was hooked up post cats and had ann afr reading of about 11.5 through the whole run and had almost no timing. This was done on a Dynojet with great conditions. 74 degrees, 28.94mm hg, and 8% humidity.

 

Yikes, that could be more than just a tune out of wack. Let us know what you find.

 

you should be around 460-480 rwhp range. for a na build your 72cc will hurt compression. having a unknown cam won't help. sounds like nothing is working well together. keep everyone informed.good luck.

 

what pistons are you running are they - dish? do you know this?

your far far off.

hope you figure all out, but you will need to know more about your engine...

baezi

 

@318 something is way off for a 402

who tuned it?

 

Compression test, leakdown test and tune - in that order.

You're making close to stock 346 numbers.

 

Sounds like a stocker to me. Sure you got the 402?

I'd be pullin the pan.......

 

Ditto that except for his peaks.

To the original poster: FAR too little information and detail about the set-up to determine the origin of the problem(s).

Do the compression/leak down, then find out what displacement and accompanying parts you have.

 

Take a look at my sig and WKMCD's sig to see what kind or hp/tq a 402 or 403 ci motor that is running well should make. I'm very curious to see the outcome on this because before my 402 was built in house at LGM, I almost bought an SLP 402.

To echo whats already been said, need more info.

SUBSCRIBED !!!!!

 

I bought this car like this. I know it has at least a 4" bore due to the heads. I dont know what pistons are in it or anything like that. Its got 185 across the board for compression. Again I dont know who tuned it. Can you drop the oil pan on a gto enough to see the crank?

 

The oil pan is easy to pull on a goat......

Should say 6.0 on the front of the block too. Passenger side IIRC.

FWIW, those numbers are low for a 6.0 with headers.

 

I say contact the person you bought it from and ask if they have any paperwork on the motor. If they bought it as is then have them contact or give you the contact info on this car. I would hope whoever installed this motor knows the details. Good luck.

 

You don't have a 402. Or somebody got really cute and turned off 2 cylinders. As suggested, you need to drop the pan and confirm it's really a 402. I'd also call SLP and see if they put any stamping on the block anywhere to identify it was one of theirs.

FWIW, this isn't the first issue I've seen with the elcheapo 402's they were selling. I removed one about 2 years ago that was total junk, but it made ok power.

Moving this to internal tech so you can get more answers.

 

It could possibly be 9-1 comp,stock Cam and cloged cats. That will make the same power.

 

SLP said they didn't mark it in any way when I called. Is it possible to put the AFR 225 big bore heads on a 346? Or did the previous owner get really creative and make stock heads look like some AFR's

 

The block should have 6.0 on it from the factory. If its a true 402 then I bet it was being built for boost. I mean 72 cc heads stock like Idle for the cam maybe a stealth set up? But even if it has 6.0 stamp I would drop the pan and take a pic there are a number of guru's on here that can spot a phoney. Or pull the head to see what kinda piston is in there. If I know slp that motor may have eagal everything in the bottom.

 

Throw a blower on there to see if it makes the right power since it appears to be built for boost lol.

Honestly, I agree with what has been posted above, pull the pan and/or search for the 6.0 stamp on the block.

 

Do any of gurus know what number should be stamped in front of the pass side head to identify if its a 6.0 or a 5.7 block. I cant get any view to where the 6.0 stamp is supposed to be. I am going to have to try and pull the pan and see whats in there.

 

Its right here below the drivers side head.

 

heads off...