Pontiac G8 2008-2010 - G8 GT underrated???

I received a G8 promotion card in the mail, and it says that the G8 is 364hp @ 5300rpm. Of course that is old news, but the rpm seems extremely low for an LSX motor. My guess is this motor has more horsepower than that if measured at a higher rpm like 6000 where the horsepower should peak.

using the simple formula: HP=TQ*RPM/5252

We learn that for the G8 to make 361 hp @ 5300 rpm, torque has to be at 357.73 lb-ft. Its not dropping much from its peak at 4400RPM. Lets say that the torque number drops to 350lb-ft at 5600 RPM, then the new HP would be 373HP. This is not an LT1 after all, so we know that the torque should not drop till around 6000, so lets do it @ 6000 RPM. With 350lb-ft at 6000RPM, we have 399.84 HP. Perhaps torque will not stay that flat, maybe it will drop to 330lb-ft, then we have 376HP. Even with 300lb-ft at 6000RPM, the G8 is making 342HP.

You can play with the formula and the numbers all day long, but the bottom line is this motor is probably underrated because of the low peak RPM for HP, and the fact that GM small blocks have the uncanny ability to keep torque high in the RPM's, which essentially means more horsepower.

Damn, I hope that this is true. More horses are better than none!1

I could see this being true. GM likes to lie about output and make a car seem less powerful.

I think it's also common knowledge that they're rating it with the lowest octane fuel available to the masses and it's likely tuned accordingly...put in some premium gas and/or maybe a good dyno tune once the software becomes fully available and this thing could really wake up as well. :nod:

I could see this being true. GM likes to lie about output and make a car seem less powerful.

In certain instances I can see that being true, but not for a flagship sedan, that would be counterproductive.

Remember that the G8 runs on 87 not 91 like say the old LS2 so 361 should be pretty close.

hopefully the G8 will have a sensor in it that detects if you put preminum fuel in it, thus changing the fuel tables to give you more power. That would be nice to have rather than having the PCM reflash to accomodate premimum fuel

the whole point of my post was to say that torque probably does not drop off that fast, and torque is a function of horsepower, and the way you make more horsepower is keeping more torque higher in the rpm range. so if the torque does not fall off that fast like all the other GM V8's with their awesome flowing heads, this thing is definitely underrated.

I still think in this day and age it would be absolutely retarded to under-rate your car.

I still think in this day and age it would be absolutely retarded to under-rate your car.

well guess what, the Nissan GT-R is HIGHLY underrated. Its somewhere around 550hp, give or take a little. it dynoed 470 all wheel horsepower or something.

In the edmunds review they were wondering why it was as fast as the charger....my answer is above.

the Nissan GT-R is HIGHLY underrated. Its somewhere around 550hp, give or take a little. it dynoed 470 all wheel horsepower or something.


where did you get that information?

well guess what, the Nissan GT-R is HIGHLY underrated. Its somewhere around 550hp, give or take a little. it dynoed 470 all wheel horsepower or something.

In the edmunds review they were wondering why it was as fast as the charger....my answer is above.


My answer is:

I believe that part of the answer here is the gearing.
The Edmunds test refers to the 2.92:1 final drive ratio.
Not considered very ‘aggressive’, normally.
In this particular case, paired with the 6L80’s first gear ratio of 4.03:1, it actually is fairly aggressive.

[[ For reference, the 2006 – 2008 Corvettes with versions of the motor and this automatic trans. have standard final drive ratios of 2.56:1. And now, for 2008, an optional ‘performance’ axle ratio – of 2.73:1. ]]

The Charger R/T’s first gear ratio is 3.58:1 and the final drive ratio is 2.82:1.

[[ This means the G8 GT ‘launches’ with around 10% greater mechanical advantage. Assuming that the tire diameters are approx. 7% different ( the Charger’s tires, in the Edmunds test are 225/60x18s vs 245/40x19s on the G8 GT w/Sport Pkg - means the Charger has roughly 7% higher RPM ) and assuming similar initial Torque Converter behavior in the 2 automatic transmissions. ]]

AND ( I think particularly relevant here ) Pontiac chose a final drive ratio that allows the G8 GT to hit the Quarter Mile lights at the very top of Third Gear.
Third gear @ redline ( 6,000 RPM ) is 104 MPH.
And the Quarter Mile Terminal Velocity in each test I have seen so far is between 102.8 and 104.1 MPH.
So: The motor is at peak HP and no 3 – 4 shift is required before the end of the Quarter.
The Charger ( non-SRT8 ) in tests I have see is geared for 118 MPG in Third gear – and clears the Quarter running at roughly 97 to 101.

Just my 0.02 gallons worth . . .
- Ray
Pleased to see these acceleration times . . .

well guess what, the Nissan GT-R is HIGHLY underrated. Its somewhere around 550hp, give or take a little. it dynoed 470 all wheel horsepower or something.

In the edmunds review they were wondering why it was as fast as the charger....my answer is above.

I'd link to see a link to that info, otherwise, it's BS.

And it's no wonder that the edmund's reviewers aren't engineers or physicists but merely journalists.

they think something must be underrated if it's too quick for them to comprehend.

You gear something correctly, and it's going to maximize the acceleration.

My answer is:

I believe that part of the answer here is the gearing.
The Edmunds test refers to the 2.92:1 final drive ratio.
Not considered very ‘aggressive’, normally.
In this particular case, paired with the 6L80’s first gear ratio of 4.03:1, it actually is fairly aggressive.

[[ For reference, the 2006 – 2008 Corvettes with versions of the motor and this automatic trans. have standard final drive ratios of 2.56:1. And now, for 2008, an optional ‘performance’ axle ratio – of 2.73:1. ]]

The Charger R/T’s first gear ratio is 3.58:1 and the final drive ratio is 2.82:1.

[[ This means the G8 GT ‘launches’ with around 10% greater mechanical advantage. Assuming that the tire diameters are approx. 7% different ( the Charger’s tires, in the Edmunds test are 225/60x18s vs 245/40x19s on the G8 GT w/Sport Pkg - means the Charger has roughly 7% higher RPM ) and assuming similar initial Torque Converter behavior in the 2 automatic transmissions. ]]

AND ( I think particularly relevant here ) Pontiac chose a final drive ratio that allows the G8 GT to hit the Quarter Mile lights at the very top of Third Gear.
Third gear @ redline ( 6,000 RPM ) is 104 MPH.
And the Quarter Mile Terminal Velocity in each test I have seen so far is between 102.8 and 104.1 MPH.
So: The motor is at peak HP and no 3 – 4 shift is required before the end of the Quarter.
The Charger ( non-SRT8 ) in tests I have see is geared for 118 MPG in Third gear – and clears the Quarter running at roughly 97 to 101.

Just my 0.02 gallons worth . . .
- Ray
Pleased to see these acceleration times . . .

this is a very good post, thanks for the info.

if you want to take it even further, you can measure the total torque multiplied by the gearing in first gear for the two respective cars.

4.03*2.92*385=4530 (G8)
3.58*2.82*420=4240 (SRT8)

4240/4530= 93.6%

interesting stuff, looks like first gear should be a blast in the G8! a gear swap to around 3.42 would be really fun :)

to hondanick and bigdaddy, here are the two links:

http://www.nagtroc.com/forums/index.php?showtopic=21447 (rollers)
http://www.nagtroc.com/forums/R35-Dyno-t20782.html (hubs)

the one on the rollers made 458awhp and the one on the hubs measured 475awhp.

with 20% drive-train loss 458/.80=572.5 crank hp
with 25% drive-train loss 458/.75=610.67 crank hp

rwd manuals usually have 14-16% drive-train loss, rwd auto's have roughly 20% drive train loss, *but* awd manual cars have somewhere around 20-25% drive-train loss.

for it to be rated at 480HP at the crank, it needs to be 383awhp @ 20% drive-train loss, or 360awhp @ 25% drive-train loss.

this is a very good post, thanks for the info.

if you want to take it even further, you can measure the total torque multiplied by the gearing in first gear for the two respective cars.

4.03*2.92*385=4530 (G8)
3.58*2.82*420=4240 (SRT8)

4240/4530= 93.6%

interesting stuff, looks like first gear should be a blast in the G8! a gear swap to around 3.42 would be really fun :)

I thought about that as well.
My problem was: I do not know the exact TC behavior
of either trans. under these conditions...
But I do know that first gear in my Corvette is ( um )
really fun.
- Ray
Looking for a 4DR Corvette - for less than $40K . . .

to hondanick and bigdaddy, here are the two links:

http://www.nagtroc.com/forums/index.php?showtopic=21447 (rollers)
http://www.nagtroc.com/forums/R35-Dyno-t20782.html (hubs)

the one on the rollers made 458awhp and the one on the hubs measured 475awhp.

with 20% drive-train loss 458/.80=572.5 crank hp
with 25% drive-train loss 458/.75=610.67 crank hp



I'm not saying that the GTR isn't underrated, but I have a hard time believing that it's underrated by 80hp. If it's underrated by 20-30 hp like the LS3 then I might buy that, but I'm from Missouri, and I'm going to need more than a dynopull on a 'Dastek' (never heard of it before) dyno with 96 octane. I'll wait for the Dynojet numbers (or maybe a mustang or dyno-dynamics) before making judgements.

to hondanick and bigdaddy, here are the two links:

http://www.nagtroc.com/forums/index.php?showtopic=21447 (rollers)
http://www.nagtroc.com/forums/R35-Dyno-t20782.html (hubs)

the one on the rollers made 458awhp and the one on the hubs measured 475awhp.

with 20% drive-train loss 458/.80=572.5 crank hp
with 25% drive-train loss 458/.75=610.67 crank hp

rwd manuals usually have 14-16% drive-train loss, rwd auto's have roughly 20% drive train loss, *but* awd manual cars have somewhere around 20-25% drive-train loss.

for it to be rated at 480HP at the crank, it needs to be 383awhp @ 20% drive-train loss, or 360awhp @ 25% drive-train loss.

Great info, I almost stand corrected.:) I'm glad you didn't take me almost calling BS personally, it's just because I haven't seen any info and people tend to create info out of thin air and will post it as fact.

A few potential problems:
1. the fuel used (102 octane)
2. your math/calculation used to guesstimate crank hp
3. Nissan's drivetrain loss estimate of 15%

I believe when calculating from whp to crank, you multiply by 1.x (x=% drivetrain loss), or you could multiply the whp # by x, then add it to that number (1.x is the same and is easier to perform). Someone will correct me if I'm wrong.

At 15% drivetrain loss, 458whp becomes 526.7. And the dyno that spit out 457.7 calculated (using its own numbers) to a crank hp of 520.5. So that would be a 40hp increase vs. Nissan's stated #s. How much of this is attributed to the higher octane fuel... we don't know. All we could both do is guess.

Even the forum from which the info came seems to have little/no consensus as to the accuracy of the numbers.

I look forward to seeing more dynos of this car as undoubtedly once it hits the streets in numbers in America, we'll have a more accurate assessment.

But, I still stand by my statement. In a nutshell: in this day and age, I see no motivation/logic for a manufacturer to underrate power figures.

Great info
.....

But, I still stand by my statement. In a nutshell: in this day and age, I see no motivation/logic for a manufacturer to underrate power figures.

The one reason I think this is possible ( and the BMW 335i w/twin turbos is quite well documented as being underrated ) is insurance rates.
Much as in the late 1960s \ early 1970s.
- Ray
Still believing gearing + quicker shifts in the G8's six speed automatic may be enough to 'splain the difference...

the 335I is definitely underrated, as it puts out 300rwhp much like an LS1 F-body, but its actually near 350hp, like the LS1 Vette. So good point Rayain! The Lexus ISF is another one that I suspect is a bit underrated, like its brother the IS350 which is documented to be underrated.

Hondanick and BigDaddy;

Good call on reading more on those threads and finding the octane numbers, I just read them and ran with the numbers. Still if the car is not tuned for the better octane, it might not react significantly enough to make it have the power levels I was saying it had. It definitely has an effect, but without a boost controller or a tune, I bet its not doing much.

As for my math, I have used that equation of the years and other websites like supraforums have too. Its pretty damn close to being right, the hard part is guessing the drive-train loss. Here are some examples of the math being accurate.

300rwhp LS1 Fbody - 300rwhp/.85= 352 crankhp
340rwhp LS2 GTO - 340rwhp/.85 = 400 crank hp

as you can see, its pretty damn close, and with 15% drive train loss from an M6 (100-15%=85), you cant deny thats pretty much nails it. You can take it with a grain of salt, but I will keep using it :)

As far as the drive-train loss with the GTR, it should be really high. Manual RWD cars the f-body's are around 14-16%. Auto RWD's are usually around 18-20%, hence the reason LS1 auto's dyno lower than M6's.

The real kicker is AWD; it has super parasitic drag because of all the moving parts. Even worse is that the GTR has two drive shafts and all of these crazy ass differentials which I wont get into, but I am guessing its much more than 20%. Other people on the other forums have said that M6 AWD cars lose as much as 25%, but I have no proof to back this up.

Either way, the car is underrated fo sho. Why do they do it? To beat other cars like the Z06 or the 911 Turbo and have supposedly less hp, and also to keep insurance, prices, emissions, and safety people off their backs. No one would be impressed if a GTR beat a 911 Turbo with 100 more hp ;), that would not make for a fun article.

LOL, I was hoping someone would mention "insurance rates" as the reason to underrate the power of these cars.

I wish I could post the info, but major insurance companies are not relying on manufacturer estimates for power like they did 40 years ago in setting their rates.

This is coming from an actuary with a MAJOR insurance company. It's a friend of mine's wife and I won't "out" a friend, so don't ask.

Because I can't post the info, take it with a grain of salt until someone can collaborate or verify what I stated.

Still if the car is not tuned for the better octane, it might not react significantly enough to make it have the power levels I was saying it had. It definitely has an effect, but without a boost controller or a tune, I bet its not doing much.

Again, we can only guess. What if the ECU/ECU/PCM/etc is tuned for knock retard and is set to retard timing at higher rpms? With higher octane fuel, there won't be any... see where I'm going?

I'm only guessing b/c we don't know.

As for my math, I have used that equation of the years and other websites like supraforums have too. Its pretty damn close to being right, the hard part is guessing the drive-train loss. Here are some examples of the math being accurate.

300rwhp LS1 Fbody - 300rwhp/.85= 352 crankhp
340rwhp LS2 GTO - 340rwhp/.85 = 400 crank hp

as you can see, its pretty damn close, and with 15% drive train loss from an M6 (100-15%=85), you cant deny thats pretty much nails it. You can take it with a grain of salt, but I will keep using it :)

I beg to differ ONLY b/c we read of "factory freaks" all the time on this forum. Read the dyno results of people wondering where their hp/tq is. I'm sure it will balance out then.

As far as the drive-train loss with the GTR, it should be really high. Manual RWD cars the f-body's are around 14-16%. Auto RWD's are usually around 18-20%, hence the reason LS1 auto's dyno lower than M6's.

The real kicker is AWD; it has super parasitic drag because of all the moving parts. Even worse is that the GTR has two drive shafts and all of these crazy ass differentials which I wont get into, but I am guessing its much more than 20%. Other people on the other forums have said that M6 AWD cars lose as much as 25%, but I have no proof to back this up.
I would agree with the parasitic loss, but Nissan has stated otherwise. But, we really won't know the real data until someone takes one of these cars off the assembly line in the US, runs a dyno at the crank, then runs one at the wheels, unfortunately. :)

Either way, the car is underrated fo sho. Why do they do it? To beat other cars like the Z06 or the 911 Turbo and have supposedly less hp, and also to keep insurance, prices, emissions, and safety people off their backs. No one would be impressed if a GTR beat a 911 Turbo with 100 more hp ;), that would not make for a fun article.

Sorry buddy, I don't agree with this. :(

Insurance (insurance industry), emissions (government), and safety (government) people all report to someone other than the manufacturer of the vehicle. Emissions and safety won't differ if the vehicle is 480 or 550hp.

LOL, I was hoping someone would mention "insurance rates" as the reason to underrate the power of these cars.

I wish I could post the info, but major insurance companies are not relying on manufacturer estimates for power like they did 40 years ago in setting their rates.

This is coming from an actuary with a MAJOR insurance company. It's a friend of mine's wife and I won't "out" a friend, so don't ask.

Because I can't post the info, take it with a grain of salt until someone can collaborate or verify what I stated.

this is turning into a GTR thread, what happened to our beloved G8??? Well I guess it makes for a more interesting day :)

interesting story, but I bet power has more than we think to do with insurance rates! my camaro is killing my wallet and its only "285hp."

Again, we can only guess. What if the ECU/ECU/PCM/etc is tuned for knock retard and is set to retard timing at higher rpms? With higher octane fuel, there won't be any... see where I'm going?

I'm only guessing b/c we don't know.



I beg to differ ONLY b/c we read of "factory freaks" all the time on this forum. Read the dyno results of people wondering where their hp/tq is. I'm sure it will balance out then.


I would agree with the parasitic loss, but Nissan has stated otherwise. But, we really won't know the real data until someone takes one of these cars off the assembly line in the US, runs a dyno at the crank, then runs one at the wheels, unfortunately. :)


its pretty common that LS1's dyno 300rwhp, well pretty damn common. if I was to make a post anywhere on this site, cz28.com, or a corvette forum, the overwhelming answer would be that LS1's make 300rwhp.

the only reason I used that example is to show how my formula works. if you dont like it, I dont care and I am not gonna go bouncing around the internet to prove it. But its a shorthand way of finding crank hp for sure without too much statistical discrepancy.

the bottom line is that AWD cars lose a phuq ton of power from powering all four wheels. stock evo 8's and sti's put down something small like 220-240awhp and they are said to have near 300crank hp. its pretty common knowledge, and there is no way of getting around it. a gearbox and a tranny is what it is, and having more gears and all that crap sux power.

Sorry buddy, I don't agree with this. :(

Insurance (insurance industry), emissions (government), and safety (government) people all report to someone other than the manufacturer of the vehicle. Emissions and safety won't differ if the vehicle is 480 or 550hp.

then why do they do it? reason I ask is because of all the examples out there with high performance cars.

:engarde:

Rasputin, your formula is correct... it is simple math and little algebra...


Follow me for sec,
if we have an engine with a known 300hp at the crank, and we placed it in a car with a known 20% driveline loss, we all can agree it would chasis dyno 240whp (20% of 300 is 60,,, so 300-60 is 240)


So Lets reverse the process and take our car to the chasis dyno and
and we get 240whp if we used Bigdaddybry's formula we might
think the engine had 288hp at the crank.... huh what? (20% of 240 is 48
or 1.20 x 240 = 288)


We are not gaining the 20% hp from whp to bhp we are losing it from bhp to whp...

So we need to divide the whp by 100% minus the driveline loss to solve for crank hp.

Here it is 240/(100%-20%)= crank hp or 240/.80= 300hp which is what we know we have.

Sorry to have a long explanation, but I think it is simple to follow.

One thing to consider is that GM uses SAE J1343 to rate the power in most all of their vehicles. http://media.gm.com/us/powertrain/en/product_services/2008/08car.htm The purpose was for all auto makers to use the same scale when rating power. When you put the engine on an engine dyno it should give you the SAE horsepower number.

Is the G8 GT underrated? If GM is true to SAE, No.

If our L76 makes an SAE 361 hp, and our drivetrain has a loss of 15%, should give us about 306 hp at the rear wheels.

I think it's also common knowledge that they're rating it with the lowest octane fuel available to the masses and it's likely tuned accordingly...put in some premium gas and/or maybe a good dyno tune once the software becomes fully available and this thing could really wake up as well. :nod:

Tuners here in Aus have been getting some impressive power out of these cars for a while now I've seen VE's run in the 12's with nothing more then a tune and exhaust.. Since my Wife is American there's a good chance I may move to colorado in the future and the GXP is already on my shopping list, along with a nice 69 camaro..

Sure it is going to be underrated...but it is not going to be 50 HP underrated like the LS1...nor will it weigh what a light 4th gen FBody weighed.

W

rumors of GT-R engine making 600 hp at the flywheel are greatly exaggerated: http://www.autoblog.com/2008/03/13/nissan-gt-r-meets-the-dyno-997-porsche-turbo-and-e92-bmw-m3/

Mustang dyno says: 406 hp to the wheels

http://www.blogsmithmedia.com/www.autoblog.com/media/2008/03/gtrv997tharman.500_450.jpg

rumors of GT-R engine making 600 hp at the flywheel are greatly exaggerated: http://www.autoblog.com/2008/03/13/nissan-gt-r-meets-the-dyno-997-porsche-turbo-and-e92-bmw-m3/

Mustang dyno says: 406 hp to the wheels

http://www.blogsmithmedia.com/www.autoblog.com/media/2008/03/gtrv997tharman.500_450.jpg

mustang dyno's suck a lot more power relative to a regular dynojet. how much? its up in the air, either way, the GTR is underrated.

Does this help? http://www.g8board.com/forums/showthread.php?t=1282

Does this help? http://www.g8board.com/forums/showthread.php?t=1282

um yes, thank you, and thank you to the guys who had the audacity to go out and dyno it!!!

327/.8= 408hp
327/.85= 385

I WIN!

Lol. He had 31 miles on it when he dynoed it. That's pretty funny. I can't wait until we hear more about the specifics on the GXP model.

um yes, thank you, and thank you to the guys who had the audacity to go out and dyno it!!!

327/.8= 408hp
327/.85= 385

I WIN!

yea, i saw that on the g8 board. If it already making north of 400hp, I hate to see what it will do will a tune. Damn!!!!!!!!!!!!!!!!!!!!!!!!!!!!

they said the dyno is either plus or minus 10rwhp compared to other dynos which makes sense. Not only that, but the car needs to be broken in. It probably has another 10 left in it, and this was the auto :). 330rwhp, sounds great to me. Intake and exhaust with a tune, a conservative 350rwhp daily driver, hell yeah!

I wish I could post the info, but major insurance companies are not relying on manufacturer estimates for power like they did 40 years ago in setting their rates.

So where do they get their info from? I know a thing or two about insurance companies, underwriting & actuary - these guys are not auto enthusiasts. They don't the difference between an LT1, LS1, L76, LS7, etc. Now, as far as physical damage costs - those are different, meaning the cost to repair the car after an accident, how well the car does in an accident, etc. Those are statistical based.

Lol. He had 31 miles on it when he dynoed it. That's pretty funny. I can't wait until we hear more about the specifics on the GXP model.
And it will most likely pick up a few more HP as the engine breaks in.