Horsepower ratings exaggerated

stanford · January 1999

Bear in mind that the transmissions in these trucks have more of a parasitic loss than the ones you'll find in cars. That 5.3l number does sound mighty low, though. Rear wheel HP for the 6.8l Ford V10 was recently measured at 170 (against an advertised 275) but that was on a motorhome chassis with HD transmission, rear end, etc.

quadrunner500 · January 1999

Stanford, I saw a magazine test where the Ford Super Duty V10 truck had a number very close to what you just reported for the motorhome chassis.

stanford · January 1999

Which magazine? I'd like to take a look at it. BTW, those equations are obviously 'very' generic and almost certainly not correct -- nowhere in any of them is a correction for rear end ratio, tire size, type of transmission (inc: # of gears), et cetera.

dave40 · January 1999

FOUR WHEELER magazines new DYNO test has Chevys 5.3 even with Fords V-10 in HP. Why does ford make these underpowered engines ?
If you want power get a Vortec 6.0 300hp the most powerful V-8 in the world!

markbuck · January 1999

Dave40 - btw, they only ran the motors up to 4,000 rpm, which is below where either the 5.3 or the 6.8 develop their hp peak.

I think we all should drive the various trucks more and read the idiotic magazines less. You all must know that the winner of these shootouts are the trucks with the most money in the glove boxes.....

quadrunner500 · January 1999

I was afraid you would ask me which magazine. Truth is, I saw it at the library, and I believe dave40 is correct in saying it is Four Wheeler or Four Wheel Magazine. I guess those equations are generic. They have certainly been around for a long time. However, if you do not believe they are correct, there must be some other explanation for why the results you get from them are so accurate. I have used them, and they are always close. Try putting the Truck Trend rear wheel dyno numbers into them, and compare the result with the ET and Speed from the Truck Trend article, and you'll find they are very close for all three trucks. One reason might be that for two given engines with the same horsepower at the crankshaft, usually have different horsepower measured at the rear wheels. That could account for some difference. Axle ratios within 10% of each other, like the 4.10 and 3.73 on the Chevys, have a vastly different feel, but usually make very little difference on ET or MPH in the 1/4 mile, maybe only as much as one tenth of a second. That was about the difference it made when I changed the rear axle on my Camaro from a 2.73 to a 3.23, greatly improved response and pep, but not much difference to the clock on the scoring tower.

stanford · January 1999

Dave40: Who cares about HP (apart from you)? Its torque that counts, both when towing a heavy load and (sigh) when racing your neighbor. A top-of-the-line OTR Cummins engine puts out 600hp at 1500rpm ... and 2000 lb.ft of torque. That's enough HP to carry 80,000lbs at decent speeds. If you're not planning on towing more than 40,000lbs, 300HP is plenty. Your torque is what indicates whether you can get the load moving in a reasonable time.

Aah, why do I bother...

quadrunner500 · January 1999

The Feb. '99 article in Truck Trend dyno-ed the motors to 5000 rpm. The Chevy made its best power, 182.8 peak horsepower at 4750 rpm. Beyond that point, power was declining, to 178 at 5000 rpm.

cdean · January 1999

why don't you just go drive one and quit worrying about what 8 different magazines publishing 8 different things. i have driven all 3, and with all variables in mind, similarly equipped trucks, the old Chevy 350 had the most oomp, with the dodge 5.9 2nd, and Ford 5.4 (pre '99) third. but do we all sit there and look at our engines dyno report. Nooooo. how does it perform in each vehicle is so variable dependent.

Ehh, i've developed the same attitude as you Stanford. i know a few places where there is discussion with substance.

KCRam · January 1999

Horsepower figures are like fuel economy ratings. They're done in a lab, under a specific procedure so that they can be used for comparison. However, engines are assembly-line produced. You can take five random engines from a plant, dyno all 5, and get 5 different sets of numbers.

And stanford is absolutely right about horsepower ratings vs torque figures. Perfect example would be my last two trucks: my current Ram 3500 Cummins, and a 1993 Ford F150 302.

Here are their respective engine ratings:

Cummins: 180 hp/420 lb-ft
302: 185 hp/270 lb-ft

Believe me, the Cummins is a hell of a lot stronger, despite having 5 fewer horsepower, and both trucks can hit and hold 95mph. If both engines were in the same truck, the Cummins would outrun the 302 with a load (bed or trailer).

quadrunner500 · January 1999

The rear wheel torque and horsepower of the Ram/Cummins has been understated grossly, the exception to the field, producing numbers at the rear wheels exceeding the published figures for the crankshaft.

cdean · January 1999

i guess we're just going to have to disagree, quadrunner. the only games I ever see anyone playing with horsepower and torque numbers is when they don't mention the RPMs. I can pretty much guarantee you that the 5.3 puts out 270 hp at the crank-- if it didn't, the FCC (or whoever is in charge of that crap) would be ALL OVER GM for false advertising. hey, if i'm wrong, it's because GM is getting sued..

did they just make up that number out of the blue and hope no would ever actually try it? you're talking about the biggest US carmaker, that's not going to happen.

Not being demeaning, but I think those equations are a bunch of hooey. In the engineering world, you can solve just about anything with dimensional analysis. the world of physics follows it. And first look at your equations show no coherency really. not disregarding, they may be upper level math derivations, which would be impressive, but I'm really skeptical of total lack of gear ratio, tire size, and for dear goodness WHERE THE HELL IS TORQUE??!! you're saying that a '99 v6 with 200hp could run the same as '92 chevy 350 dodge 361 with 200 hp. Nope, sorry, I don't buy it.

stanford · January 1999

quadrunner: You're correct. However, the HP needed to tow a load at well-above legal speeds is very low. As kcram pointed out, a 180hp engine can quite happily move 20000# combined weight at highway speeds up and down all but the fiercest hills. The new 240hp diesels can probably pull the same load through the hills without slowing down. Debating the merits of 200hp vs 300hp, especially in 10000# combined weight vehicles, is fairly useless. Engines with either rating can keep you moving as fast as you'd like... assuming they have the torque (engine or gearing) to get you there in the first place.

quadrunner500 · January 1999

Stanford, well said.
Cdean, I need to quote you from your post because I am replying to a specific point about "I'm really skeptical of total lack of gear ratio, tire size, and for dear goodness WHERE THE HELL IS
TORQUE??!!"
The answer is that torque is already represented by the horsepower term of the equation for calculating ET and MPH. So is gear ratio and tire size. How? Because horsepower itself is nothing more than a calculation with terms for torque and rpm. Same for gear ratio, it gets reduced to the term RPM. Horsepower is equal to torque at the rear wheel times rpm at the rear wheel. The actual equation is:
HP = Torque*RPM/5252. The number 5252 is a units constant. When you work at the rear wheel like the chassis dynomometer does, it measures two things, torque and rpm. The result gets plugged into that equation, so horsepower is a calculated result. The key point is that without both torque and rpm together, no horsepower is measured or produced. Why does this matter? Because you have stated it's your opinion that the equations I posted earlier for ET and MPH (not my equations BTW) don't work because they don't consider gear ratio, tire size and torque. What I'm saying is that those factors are indeed included already when you enter the number for horsepower into the equation. If it's still hooey to you, you can keep that opinion if you want, but already, there is proof to me the equations have merit because they support the numbers that Truck Trend produced. One last question. In the same post you asked, "you're saying that a '99 v6 with 200hp could run the same as '92 chevy 350 dodge 361 with 200 hp. Nope, sorry, I don't buy it."
I said no such thing, and for you to infer that I did is a misunderstanding on your part. You may not be buying it, but I wasn't offering that opinion for sale either.

stanford · January 1999

It does neglect the differences in torque curves between engines with the same peak HP, but it works fine for most real world engines (+- 25% or so) in 3000-6000 lb situations. Diesels tend to be much stronger for the same HP ratings, but rev lower and so don't get the same benefits of gearing, et cetera.

Then again, I think we've beaten this particular horse half to death. Agree to disagree?

stanford · January 1999

One question: How were these measured? Did the dyno measurements correct for tire size and rear-end ratio? If they did, then the numbers wouldn't work as well in the formulae. If they did not (as I believe), the numbers would fit well (and they did) but they wouldn't be directly comparable (as it seems they are not). In other words, if the Chevy had a 3.42 rear end and the Dodge had a 3.73, the total rear wheel HP would vary differently.

cdean · January 1999

thanks for the explanation, quadrunner. I didn't do a whole lot of thinking about it, but you've cleared a lot of my questions and skepticism. One big thing was that I thought the HP in the equations was engine horsepower. If it is rear wheel power, then I can see how tire size, gear ratio and such are hidden within. that's what i meant about "if it is indeed a derivation."

I made up the little example about the 200 hp engines, meaning two different same HP engines with different torque. I thought your equation was saying you put in HP (200 in my example) and you would get an ET or whatever, and I was trying to say how different torque motors with same HP would run very differently. all goes back to misunderstanding which HP goes into equations.

I'm on the same page now. still a skeptic though. And yes, I think the horse is dead.

ladyblue · January 1999

My condolences to the horse. May he rest in peace. {*_*}

quadrunner500 · January 1999

By popular demand, I'm taking the revolver out of the holster, and shooting the horse dead after this reply.
Cdean, you have it! I'm a skeptic too. That's why I get into this.
Stanford, you asked several questions, all good. The chassis dynomometer does not care what gear, or axle, or tire you are using. The horsepower will measure the same no matter what gear, or axle, or tire you are using. But torque, on the other hand will be much greater in first gear than in overdrive. But opposing this, rear wheel rpm will be much lower in first than in overdrive. The net result is that torque goes down by as much as rear wheel rpm goes up when you up-shift through the gears. The horsepower stays constant through the driveline, but the amount of torque gets multiplied with each gear ratio. The chassis dynomometer can measure your maximum horsepower and torque just as easily in overdrive as in first gear. The torque the dynomometer measures will be greater in 1st gear than in overdrive. But even though torque is measured at the rear wheel, it is expressed back to the crankshaft. Thus for example on the V10 Triton, the actual rear wheel torque measured on the dyno, in whatever gear the transmission was in, the number measured was divided by the overall ratio of the transmission and driveline to arrive at the published specification, expressed at the crankshaft, which was 280 ft/lbs at 3000 rpm.

KCRam · January 1999

(dialing glue factory)
"We got another one for ya"

ladyblue · January 1999

LMAO, kcram!!!

Hey quadrunner, what was that, the eulogy?

Oh, Wilbur!

stanford · January 1999

Doh! That's a good point. They'd just have to make an index pass (ie: measure speed of drum @ 3000rpm engine) to convert the numbers back (since they were quoted as flywheel RPM, not drum RPM).

etuffly2 · January 1999

NEW CHEVY 6.6 DIRECT INJECTION - AN AMAZING 600 FT-LBS OF TORQUE!!! THIS SHOULD END ALL DISCUSSION ON THIS SUBJECT.

dave40 · January 1999

RIGHT ON !

dodgeram · January 1999

Where you here about 6.6l engine having that much torque.

etuffly2 · January 1999

I GOT IT STRAIGHT FROM GM. HAVE RELATIVES WORKING THERE. THIS TRUCK'S GOING TO BE AWSOME!!!

etuffly2 · January 1999

AWESOME!!! SORRY ABOUT THAT.

jrice · February 1999

If you haven't driven the truck, or seen anything concrete, how can you believe this. Why don't you settle down until you actually know what this engine will produce.

fleetmaster1 · April 1999

i was just wondering how a c/c pickup could handle so much torgue. i have 30,000 gvw trucks that don't have that much torgue.

Horsepower ratings exaggerated

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