Do you think this GXP is really only 402hp or do you think its the same 430 as the Vette? Is it marketing tactics or what? I knnow back in the day the LT and LS cars dynoed same as a Vette dispite different advertised figures. Why would they tune it down or rework an already developed engine? Makes no sense to me.. the only thing I can think of is to leave room so the following year they have room to bump it up even more...

Now I'll just have to wait to 2010 when the GXP bumps up to 430.. lol

I think it is under rated.

I think we'll need some more details on how the engine was detuned. Given this is an engine that is familiar to gearheads, after market tunes and mods will be plentiful I suspect.

Expect to see tune kits which will bump the hp substantially. Keep in mind they weren't about to put the hp at the same level as the Vette's.

I think we'll need some more details on how the engine was detuned. Given this is an engine that is familiar to gearheads, after market tunes and mods will be plentiful I suspect.

Expect to see tune kits which will bump the hp substantially. Keep in mind they weren't about to put the hp at the same level as the Vette's.

The GTO LS2 was the same as a vette.

It's probably detuned or the SAE rating was taken at a lower rpm to keep the Vettes HP as the king.

I think it was tuned with regular like the L76. And they kept the premium recomended crap too.

Maybe there keeping the horsepower down to help avoid the gas guzzler tax?

It was tuned with premium.

Maybe there keeping the horsepower down to help avoid the gas guzzler tax?

Me hopes so too.

.... Keep in mind they weren't about to put the hp at the same level as the Vette's.

Why not? They have with other vehicles in the past...GTO, CTS-V, the TB SS was within 5 hp (only change was the radiator fan).

I'm a little disappointed, but I'm sure it won't keep me from buying it in a couple of years.

Program guys told us months ago that the exhaust and intake system compared to the vette was very restrictive and to not expect the 430 HP.. I would assume the 402 was the result ;)

Corvette LS3
430 hp @ 5900 rpm
424 lb-ft @ 4600 rpm

GXP
402 hp @ 6000 rpm
402 lb-ft @ 4400 rpm

Both have same 10.7:1 comp ratio but must have at the very least different ecm maps. The 402 is not SAE certified yet, so it may go up or down, but not by 20+.

We know the exhaust manifolds are different. I am curious what is different in the intake tract. In the past, GM has used a more restrictive intake tract for noise control and packaging purposes. The Vettes have always been allowed to be louder.

Chip

Program guys told us months ago that the exhaust and intake system compared to the vette was very restrictive and to not expect the 430 HP.. I would assume the 402 was the result ;)

Agreed. A quick intake/cat back change and that magic 20+hp will be right there in all its glory. Don't sweat the numbers, people, just enjoy the car.

The LS3 will be exactly the same as the Vette. The LS2's are the same in the Vettes, CTS-V's, GTO's, & SS TB's. The LS6's are exactly the same in the CTS-V's & Z06's. The only differences can be found in the air intakes, exhaust(headers back), & the tune. GM also underrates the other vehicles.

I'm speaking from experience since i owned an '04 CTS-V for 3 years. The GXP will be my next vehicle! :D

The LS3 will be exactly the same as the Vette. The LS2's are the same in the Vettes, CTS-V's, GTO's, & SS TB's. The LS6's are exactly the same in the CTS-V's & Z06's. The only differences can be found in the air intakes, exhaust(headers back), & the tune. GM also underrates the other vehicles.

I'm speaking from experience since i owned an '04 CTS-V for 3 years. The GXP will be my next vehicle! :D

I agree with everything with the exception of the underrating comment. Where's the proof in the underrating? Does the new SAE test even allow for underrating? What's the benefit to underrating?

I'm not buying the underrating BS. It would be nice to believe, but it can't be underrated by more than a couple of horsepower on average.

The GTO was rated at 400 hp and so was the C6. So why underrate the G8 GXP? It doesn't add up.

Well, I guess that I also don't agree with your comment that the ONLY differences are found in the air intakes, exhaust, and tune.

There's also the fan differences in the TB SS. And Motor Trend is saying that there are differences in the LS3's water pumps between the Corvette and G8 GXP.

They might have meant they're the only differences that make a difference.

They might have meant they're the only differences that make a difference.

The fan difference in the TB SS does make the 5 hp difference.

And according to an insider, the water pump does contribute to the difference in the GXP's horsepower. It probably does not contribute to the "lost" horsepower as much as the intake and exhaust, but they way I read it, it does contribute....

Quote from MT article...
How will Pontiac do it with a larger, heavier sedan? With precious little modification to the C6's 436-horsepower, 428-pound-foot LS3. There are a different water pump and exhaust manifold, and a slightly modified intake, mostly for packaging. "The Corvette is optimized for airflow," Shipman says. "This car isn't quite as optimized." As in the Corvette, the LS3 trumps the 6.0-liter LS2 with high-flow L92-style cylinder heads, unique camshaft and camshaft timing, a tweaked valvetrain with offset intake rocker arms, high-flow intake and fuel injectors. The extra 12 cubic inches is the result of a bigger bore, with larger-diameter cylinder heads and pistons for high-rpm performance.

http://www.motortrend.com/features/auto_news/2008/112_0806_2009_pontiac_g8_gxp_first_look/

Agreed. A quick intake/cat back change and that magic 20+hp will be right there in all its glory. Don't sweat the numbers, people, just enjoy the car.
exactly......its not like most people can notice 20hp anyways

Well, I guess that I also don't agree with your comment that the ONLY differences are found in the air intakes, exhaust, and tune.

There's also the fan differences in the TB SS. And Motor Trend is saying that there are differences in the LS3's water pumps between the Corvette and G8 GXP.


Well, I probably shouldn't have said "ONLY", but if you want to nitpick about fans and waterpumps, there's helluva lot of difference in all 3 vehicles. I'm not 100% sure but I thought I read the Intake Manifold is different the TB SS.

You've got to look at the applications in which each engine is used. The bottom line, this does NOT take away from the LS1, LS2, LS3, LS6, etc. My point, you are getting the LS3 equipped in the vette: block, heads, cam, crank, etc. Air intakes, exhaust, E-fans, and waterpumps are splitting hairs, IMO.

The heart and soul of the Power Plant is UNCHANGED. Besides, all of us are crazy enough to be part of a car enthusiasts site. In reality, how many of us are really going to leave it stock? Our doors will be opened up to the same modifications the LS3 Vette people will see. We'll just be able to do it with 4 doors, trunk space, and a place to put the kids. :D

The fan would make a difference if they changed them to to be running off the water pump pulley instead of being electric, which I doubt.

And I don't see how changing a water pump for packaging would do anything to horsepower. If it moves the same amount of fluid, which I'd have to assume it does, it'll take just as much power to spin.

The fan would make a difference if they changed them to to be running off the water pump pulley instead of being electric, which I doubt.

And I don't see how changing a water pump for packaging would do anything to horsepower. If it moves the same amount of fluid, which I'd have to assume it does, it'll take just as much power to spin.

The cooling fan being added to the underdrive system would cause a small loss in HP. Additional component causes additional drag on the system.

Right. I was saying I doubt they would do that instead of using an electric fan.

The fan would make a difference if they changed them to to be running off the water pump pulley instead of being electric, which I doubt.


Funny you say that because that is exactly what was done. The fan on the TB SS is motor-driven.

TB SS owners that want to wring out all the performance they can switch back to electric fans.

Well, I probably shouldn't have said "ONLY", but if you want to nitpick about fans and waterpumps, there's helluva lot of difference in all 3 vehicles. I'm not 100% sure but I thought I read the Intake Manifold is different the TB SS.

You've got to look at the applications in which each engine is used. The bottom line, this does NOT take away from the LS1, LS2, LS3, LS6, etc. My point, you are getting the LS3 equipped in the vette: block, heads, cam, crank, etc. Air intakes, exhaust, E-fans, and waterpumps are splitting hairs, IMO.

The heart and soul of the Power Plant is UNCHANGED. Besides, all of us are crazy enough to be part of a car enthusiasts site. In reality, how many of us are really going to leave it stock? Our doors will be opened up to the same modifications the LS3 Vette people will see. We'll just be able to do it with 4 doors, trunk space, and a place to put the kids. :D

Agreed, and I knew that your point was that the internal parts of the engine were unchanged, but like you said, I was nitpicking.

However, the external changes do make a difference. That's why it isn't rated the same as the Corvette. I don't think that we can honestly already say that 402hp is underrated.

The threads in the tuning section are saying the intake and exhaust on the G8 are very restrictive. Just those two things could account for a good amount of HP difference between the GXP and Vette.

Funny you say that because that is exactly what was done. The fan on the TB SS is motor-driven.

TB SS owners that want to wring out all the performance they can switch back to electric fans.

Let me clarify what I meant:

The fan would make a difference if they changed them to to be running off the water pump pulley instead of being electric, which I doubt they will do on the G8.

The fan would make a difference if they changed them to to be running off the water pump pulley instead of being electric, which I doubt.

And I don't see how changing a water pump for packaging would do anything to horsepower. If it moves the same amount of fluid, which I'd have to assume it does, it'll take just as much power to spin.

Since cooling/heat rejection is directly dependent on 1) flow and 2) radiator cooling efficiency, if the flow isn't as high as in a Corvette, the engine could theoretically run hotter with a lower-flowing water pump. If this was determined to be a potential problem, the cal might be adjusted to not allow as much spark advance or to not run as lean to prevent the extra heat.

But more likely, the flow through the intake and the exhaust is culprit of the lower horsepower figure. The Corvette very likely has a lot lower backpressure (which is determined by the vehicle platform). The G8's exhaust is almost certainly more restrictive to make the car quieter, and thus more "driveable"

I agree.

Are you counter pointing or elaborating on what I said? When they say "changed for packaging), I take it to mean shape only. Not function (ie flow capacity/rate).

Well, shape could affect flow rate, depending if they had to add a notch in it for clearance or something....

I'm saying that I could see how a cahnged water pump could affect performance, but I think the water pump difference is negligible in light of a different intake and exhaust

The Corvette has always had the least intake/exhaust restriction of any of GM's V8s and this should be no different. Just look at the Vette's injection intake versus the GXP - Vette goes straight forward and GXP immediately turns 90 degrees. Probably the same with exhaust routing and tubing diameters - the Vette gets the best from GM.
Surprised? Why?

Alright kids, It's called longer exhaust plumbing. The more length you add the restrictive it becomes.402-405 is correct.

Alright kids, It's called longer exhaust plumbing. The more length you add the more restrictive it becomes.402-405 is correct.

Alright kids, It's called longer exhaust plumbing. The more length you add the more restrictive it becomes.402-405 is correct.

Alright boy...the length of the exhaust has minimal effects. Size, bends, mufflers, cats, header design....that's where the hp is lost....not by a difference of 12" of increased length.

TROLL.

Agreed. The differences in length are minimal to the overall design of the system. It may actually be a smaller diameter tubing as well. It will be interesting to see. The bottom line is that with a good intake, headers, and exhuast setup you'll be right back there after a tune.

The Corvette has always had the least intake/exhaust restriction of any of GM's V8s and this should be no different. Just look at the Vette's injection intake versus the GXP - Vette goes straight forward and GXP immediately turns 90 degrees. Probably the same with exhaust routing and tubing diameters - the Vette gets the best from GM.
Surprised? Why?

The Corvette is the one program that caters more towards the powertrain than to the platform. The reason every other vehicle line has larger, more restrictive mufflers, and more curves and bends and lntricate airboxes is to keep engine and exhaust noise down. It's interesting to see how much less of a priority having a quiet cabin is in the Corvette :-) Too bad more programs aren't set up that way

Some of you old timers may remember the L69 5.0L H.O. motor that came out in '83. It was 190hp in the Z28 and 180 hp in the Monte Carlos SS. Camaro got the electric fans, Monte got the engine driven fan. Later when the 305 TPI motors came out, Camaro got 215hp and the Firebird got 205hp because of the restrictive intake due to the Firebird's lower hood.

GM's been doing this stuff for years.

Ford did it to in the Mustang but that was a manual vs. 5 speed thing.

Some of you old timers may remember the L69 5.0L H.O. motor that came out in '83. It was 190hp in the Z28 and 180 hp in the Monte Carlos SS. Camaro got the electric fans, Monte got the engine driven fan. Later when the 305 TPI motors came out, Camaro got 215hp and the Firebird got 205hp because of the restrictive intake due to the Firebird's lower hood.

GM's been doing this stuff for years.

Ford did it to in the Mustang but that was a manual vs. 5 speed thing.

Yes, I remember the L69. It was a mid-year introduction. Three of my friends bought (or had purchased for them). One guy quit playing ball so he could work to save and buy the car. He actually still has the car and has kept it in pretty good shape. Two were 5 speed 83 1/2 models, the other 84 auto.

Sorry for the reminiscing.

Chip

The vette has always been 20-35 hp less at the wheels than on the advertised window sticker or in mags. The only cars that are close in power figures at both the wheels and the crank are turbo\supercharged cars and the old HEMI's from the late 60's and 70's. FYI: FACT: The current SRT8's are not real HEMIS either I've taken many apart and there's nothing hemispherical in them anyplace. The main reason the GXp is really around 408 bhp\crank hp instead of the 430 in the vette is due to extra exhaust length and weight\restriction. The mags and Pontiac say 402 but a friend on the inside says 408hp is more realistic, not really anything to write home about.