Thorley Header Project Update
Let's get this straight: your GXP is not a race car: it's cam is small, DOD is intrusive, etc....basically, we have a jewel of a motor being held hostage in a WrongWD chassis. Have you looked at our cam specs and the lift numbers? Likely not. Also, the tune was not changed "before" or "after" header install, plus I had taken timing out of the vehicle (I think it's at 26, if memory serves), as mentioned in my previous post.
TECH Regular
Joined: Oct 2004
Posts: 457
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From: Bay Area, CA
I imagine this is going to make the exhaust sound real good! ****** awesome, good job getting this going guys. 30tq under the curve is awesome since you spend most of the time in the lower RPM's anyways (around traffic, etc). I'm sure with the tune tweaked, a good CAI, and a slightly bigger cam we'll easily see upwards of 300whp. Stainless steel is a good sign, that's what I was waiting to hear. I think I really may just have to order a set when price is finalized.
The numbers are what I expected. Like Buickracer said, he messed with the tune, which could affect the baseline/after numbers. These numbers are also going thru a stock catalytic converter and a:
.
If you were to ditch the stock cat with a high flow cat or straight pipe, I'd bet you would see at least another 5 hp. You also forget that the top end is probably capped by the intake and the stock rockers/springs. Throw a set of HS rockers with patriot springs, and a LS6/LS2/edelbrock intake on it and then you will really wake that thing up!
Sittingmongoose,
I'm sure if you didn't want to weld, you could send the y-pipe to Hogan Performance and they would weld up a high flow pipe for you for a very reasonable price.
.If you were to ditch the stock cat with a high flow cat or straight pipe, I'd bet you would see at least another 5 hp. You also forget that the top end is probably capped by the intake and the stock rockers/springs. Throw a set of HS rockers with patriot springs, and a LS6/LS2/edelbrock intake on it and then you will really wake that thing up!
Sittingmongoose,
I'm sure if you didn't want to weld, you could send the y-pipe to Hogan Performance and they would weld up a high flow pipe for you for a very reasonable price.
They do, but I posted a pic of the v6 u bend cuz thats all i could find. The v8 u bend is still there, just not as kinked looking.
All you guys talking about warranty really wont have a problem if you go to a cool dealer. They wont void your warranty, they will just void certain parts of it that are affected. For instance if you come in for a p0420 code and need your converter replaced, they would tell you to pound sand. However, the headers wouldn't stop them from warrantying a hub&bearing, or a gas cap.
All you guys talking about warranty really wont have a problem if you go to a cool dealer. They wont void your warranty, they will just void certain parts of it that are affected. For instance if you come in for a p0420 code and need your converter replaced, they would tell you to pound sand. However, the headers wouldn't stop them from warrantying a hub&bearing, or a gas cap.
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Verdad Gallardo also you could make the part easy to bolt in and out just go to the local parts store and find some of those two bolt flanges like on the cat/downpipe to the rest of our exhaust location you can weld those anywhere
I've been sitting this one out until some results were available. Thanks to WilliamGT for setting this up and BuickRacer for donating his car for the test mule!
BuickRacer: Does your vehicle still have the stock exhaust system in place?
From the pics that were posted, it looks like these are "shorty" headers, which is pretty much what you'd expect givern the space constraints, I wouldn't expect the gains that a set of LT or Tri-Y headers would provide (you can't tune shortys like the other designs), especially if still dumping into the stock 2.25" exhaust system.
I like the way that Thorley redid the merge collector for the crossover pipe - much better than that abomination of a rear manifold that GM used. I expect this probably accounts for much of the gain at the higher RPM's. What concerns me a bit is that I don't see a flex connector in the downpipe anymore, I'd be worried about cracking things. I suppose this is something you need to include in the installation.
Not sure I understand the comments about DOD being intrusive. DOD isn't active during WOT operation, so it wouldn't have a direct effect on the dyno. Are you just referring to the low lift/low overlap aspects of the stock cam?
BuickRacer: Does your vehicle still have the stock exhaust system in place?
From the pics that were posted, it looks like these are "shorty" headers, which is pretty much what you'd expect givern the space constraints, I wouldn't expect the gains that a set of LT or Tri-Y headers would provide (you can't tune shortys like the other designs), especially if still dumping into the stock 2.25" exhaust system.
I like the way that Thorley redid the merge collector for the crossover pipe - much better than that abomination of a rear manifold that GM used. I expect this probably accounts for much of the gain at the higher RPM's. What concerns me a bit is that I don't see a flex connector in the downpipe anymore, I'd be worried about cracking things. I suppose this is something you need to include in the installation.
Not sure I understand the comments about DOD being intrusive. DOD isn't active during WOT operation, so it wouldn't have a direct effect on the dyno. Are you just referring to the low lift/low overlap aspects of the stock cam?
BuickRacer's car has the stock DP, magnaflow cat-back without resonator and K&N intake.
I do see a flex pipe behind the crossover pipe, ummm maybe I'll turn off my dod once its installed.
I do see a flex pipe behind the crossover pipe, ummm maybe I'll turn off my dod once its installed.
If your not isterested in cutting your stock downpipe. Have a flange welded on and straight pipe the remaining section and flange it at the catback, for a true bolt in application. Do this only for offroad application, lol.
sorry i am just frustrated. i am very glad you did this 
just wanted to see like 30whp lol. I will prolly get them. I am having issues right now with my stage 2 intake so i am just really pissed.
just wanted to see like 30whp lol. I will prolly get them. I am having issues right now with my stage 2 intake so i am just really pissed. 
Thread Starter
Staging Lane
Joined: Jan 2009
Posts: 87
Likes: 0
From: Orange County, CA
I knew going in that we’d probably get 15 or so whP, but I was really impressed with the added TQ, as I am used to high torque motors. I am hopeful I’ll be able to use Thorley’s facility to fine tune things, otherwise I’ll have to use the long stretches of road in the industrial parks in my area where I’ve run the Buicks…on a Sunday…REALLY early…
Tired GXP: yes, I was referring to the small cam and valve overlap; “intrusive” was an inaccurate term to use but I was typing too fast.
The numbers are what I expected. Like Buickracer said, he messed with the tune, which could affect the baseline/after numbers. These numbers are also going thru a stock catalytic converter and a:
.
If you were to ditch the stock cat with a high flow cat or straight pipe, I'd bet you would see at least another 5 hp. You also forget that the top end is probably capped by the intake and the stock rockers/springs. Throw a set of HS rockers with patriot springs, and a LS6/LS2/edelbrock intake on it and then you will really wake that thing up!
Sittingmongoose,
I'm sure if you didn't want to weld, you could send the y-pipe to Hogan Performance and they would weld up a high flow pipe for you for a very reasonable price.
.If you were to ditch the stock cat with a high flow cat or straight pipe, I'd bet you would see at least another 5 hp. You also forget that the top end is probably capped by the intake and the stock rockers/springs. Throw a set of HS rockers with patriot springs, and a LS6/LS2/edelbrock intake on it and then you will really wake that thing up!
Sittingmongoose,
I'm sure if you didn't want to weld, you could send the y-pipe to Hogan Performance and they would weld up a high flow pipe for you for a very reasonable price.
