Jizz, here is a guy with an 04 GTO. Look at his mods and look at his RWHP. he is close but he has spent $11,000 so far and he is getting a break on install cuz he works at a dealer. I dont know how the slp heads/cam differ from the Z06. anyway just FYI.

SLP Heads & Cam Package-2595
SLP double roller timing chain -179
SLP-assembly kit-199
SLP Power-Flo Exhaust-699
Taylor 10.4 wires-59
HP Tuners Tune-450
SLP 160 T-stat-20
CS MAF Tube-179
MPD Airbox-299
ASP pulley-250
NGK plugs-15
SLP MAF-169
MTI TB-359
SW LT headers-1300
Diff technics 3.91 gears-600
Nitto Drags-280
Mistakes:
JBA shorties-659
Ed wright tune-450
Installation-2500
RT Cat Pipes-599

Grand total-$11,860

Keep in mind. I work at a dealership and I got a break on installation as well as a huges break in prices on all the SLP stuff. I just can’t post that info. I had a pretty modded vehicle before this so I sold all the performance parts and was able to re-coupe $5000.00 bucks from that. That coupled with the price breaks it's not as bad as it seems. I haven't installed or dyno'd the with the LT's either. I would assume there is another 20-25hp to be gained. I would guess I'd end up in the 430whp range. Pretty good especially since most people told the the SLP package was crap and that I shouldn't expect more than 360-370whp.

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2004 GTO-Torrid Red M6
292.4rwhp & 306.6rwtq stock
411.0rwhp & 376.8rwtq modded
12.73 @113.22mph