rasputin

iTrader: (3)

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.

phantomzer0

iTrader: (17)

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

CamaroSS

iTrader: (2)

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

LS1LT1

iTrader: (16)

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.

BigDaddyBry

iTrader: (15)

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

LSX Performance

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

Buff

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

rasputin

iTrader: (3)

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.

BigDaddyBry

iTrader: (15)

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

rasputin

iTrader: (3)

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.

Honda Nick

iTrader: (1)

where did you get that information?

rayainsw

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 . . .

BigDaddyBry

iTrader: (15)

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

OKcruising

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.

rasputin

iTrader: (3)

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

rasputin

iTrader: (3)

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.

rayainsw

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 . . .

Honda Nick

iTrader: (1)

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.

BigDaddyBry

iTrader: (15)

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.

rayainsw

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...