HP Who's right

[Stocklook]

Ok, here it is, a few trucks on here claim 220 hp on dyno's but GM claim's 270 hp

on the 4.8 and 285 on the 5.3

 

Please explain how they can say one thing and when we dyno it's diff

[rascal]

guessing ones measured at the rear wheels and one measuring at the flywheel. still that sounds like lot of difference. /shrug

[DMAX Daddy]

As Rascal wrote, GM, and every major manufacturer claim Flywheel HP since its higher.

 

When folks Dyno, its Rear Wheel HP.

 

For my 2004 5.3L, 295 was published by Chevy and the most common Dyno Rear Wheel HP I have seen is 250ish.

[02denali]

from what i know the manufacture claims are all flywheel hp. thewn take away about 20% parasitic loss and that should be close. and there are different type dyno's that will yield different numbers.

[vhato]

guessing ones measured at the rear wheels and one measuring at the flywheel. still that sounds like lot of difference. /shrug

 

<{POST_SNAPBACK}>

 

 

 

 

That is correct. GM advertises SAE corrected flywheel HP numbers. For reference in 1999 when GM released the NBS I bought a Z-71 w/5.3. For 1999-Pre July 2000 the 5.3 generated 270 HP and the 4.8 only put out 245 HP. On a chassis dyno the AutoTrac 4WD and 4L60-E tranny were only allowing 191 HP to be put to the ground.

 

So a later model 4.8 with 285 HP laying down over 220 HP in 2WD and the converter locked sounds about right.

[Stocklook]

I know, Chevy says 4.8 270 @ 5200 / Tq 285 @ 4000 this is an 03, If this is correct and the dyno's are right we can take at lest 50-60 hp off what they claim.

no wonder we have to put so much money in or trucks

 

Not sure about the 04's can't find mine right now.

 

This a very Competitive and aggressive Truck market you would think they would have correct numbers

[02denali]

if gm claims 285 hp at the flywheel it will yield 228ish on the dyno. 240 will let go of 192ish.

 

285X20% loss=228

[Stocklook]

My Bubble is BUSTED,

 

Its a shame we have to Buy the truck and then dump more $$$$$$ just to keep up.

[Nick99Chevy]

My Bubble is BUSTED, 

 

Its a shame we have to Buy the truck and then dump more $$$$$$ just to keep up.

 

<{POST_SNAPBACK}>

 

 

Why, every manufacturer does it, always have.

[ManyCamaroz]

I have a '99 OBS Yukon w/ the 5.7 in it. What is the standard HP rating for that?

I'm wanting to think about 265 HP.

 

My previous Yukon was '92 w/ 5.7 and I think it was rated at 200 HP. Do these numbers sound correct?

 

Personally I could not tell a 65 HP increase between the '92 and the '99.

 

I had buddy that traded in his '99 5.7 for the new 5.3, He said he didn't care what they claimed, that the 5.7 was more potent in pulling and off the line.

[vhato]

I have a '99 OBS Yukon w/ the 5.7 in it. What is the standard HP rating for that?

I'm wanting to think about 265 HP.

 

My previous Yukon was '92 w/ 5.7 and I think it was rated at 200 HP. Do these numbers sound correct?

 

Personally I could not tell a 65 HP increase between the '92 and the '99.

 

I had buddy that traded in his '99 5.7 for the new 5.3, He said he didn't care what they claimed, that the 5.7 was more potent in pulling and off the line.

 

<{POST_SNAPBACK}>

 

 

 

Well,

Depending on the temperature and which butt cheek has an itch will determine if GM says the Vortec 350 had 250 HP or 255 HP. You were correct about the 92. 200 HP.

IMO, I am glad to see the ole 350 go to the way side and replaced by the 325 and the 346 we have now.

[Kgry]

I think the main reason the hp is limited to the wheels is because of the factory computer tuning. It's extremely mild and preventitive. That's why a lot of guys get a custom tune, you can change everything and get close to that fwhp rating from the factory.

[GMC_DUDE]

Just to confuse things more, the situation used to be worse many years ago. Up until about 1971, manufacturers used to rate engines in what is called "gross horsepower", which was just the bare engine, no intake, no exhaust, no water pump, no fan, etc. This of course resulted in the highest possible numbers -- great for advertising. Then around 1971 or so two things happened. First, emission controls ended the HP race, and second, insurance companies started basing premiums on engine HP, so now suddenly lower is better. The manufacturers then switched to "net horsepower", which is still measured at the crank, but includes the stock air cleaner, exhaust system, water and power steering pumps, fan, etc., and is about 10 - 20% lower than the gross numbers, something to keep in mind when comparing with the 1960's muscle cars. That "four-speed dual quad positraction 409" that was rated 425 gross HP back in 1963 probably made only about 380 net HP using today's measuring methods.

 

As for drivetrain losses, these vary widely, but can be substantial. Two cases in point. On one "Horsepower TV" episode they dynoed 454 CID engine and got 405 HP. After installing it in a car (Oldsmobile I think?) with a Turbo 400 automatic, they got 320 HP at the rear wheels. Also, the other day on a different show (I think it was NOPI Tunervision) they dynoed a HEMI-CUDA, which of course had the 426 CID hemi rated at 425 gross HP. The results were 314 RWHP, same as my truck . Hope this info helps some. Any mistakes, errors, or omissions, please let me know.

 

Peace and Cool-ness,

 

GMC_DUDE

[02denali]

405X20%=320