Seems to me,"all things being equal," we still need to know what these "things" are: cams, ratios, etc. A high HP car with a high rpm motor and short gears will beat a high torque car with lesser HP and the same drivetrain.Conversly, give the cars tall gears and the high torque car should be faster. "Fast" and "quick" are often confused as well. A short geared car may be quick as heck off the line and up to topspeed, but that top speed may well be less than a tall geared car which is slower accelerating but reaches a greater top speed, i.e., it's faster. The determination of who wins depends on where the finish line is in relation to the performance of the cars. 60 ft, 1/8 mile, 1/4 mile, 1 mile, flying mile.......
I guess the best way to know is to head out to County Line road on Saturday night and put 'em to the test.....(Just kidding- I would NEVER do THAT! )

John

 

http://s12.invisionfree.com/Nationwi...ex.php?act=idx

 

The torque number is irrelevant in this theoretical scenario. The HP is the meaningful number here. RPM is not relavant because if RPM mattered, the HP would be different. Torque x RPM = Power....The question posed here LIMITED the POWER so rev's in THIS SCENARIO are not relevant. You rev the engine to increase HP....BUT you limited the HP in the first place so you need not concern yourself with RPM given the scenario. The car does not know or care what the RPM is, it only knows it has either 300 HP or 400 HP maximum to "work" with. Power is a measure of ability to do "work". More work/unit of time is more power.

-Mark.

 

Since we are taking about drag racing here, the cam selection for a drag car is usually leans toward a cam that will give you max HP not max TQ. YOu don't see them selecting cams like XE256 which, out of a 383 and depending on parts, you might make 500TQ and 350HP. THey would much rather have it the other way around. Most drag race cams Comp Cams sells are going to get you more HP than TQ.

Without getting scientific torque gets you off the line and horsepower gets you the win light at the end of the track, so the answer to the question is the 400HP and 300TQ motor would win in a 1/4 mile race

 

Which is ALWAYS 5252 rpm. So, I don't think this is correct.

 

This topic makes my head hurt every time it comes up. Although I think stingr69 has the right idea.
All Corvette small blocks in 1970 were advertised to have 380ftlbs torque. Which do you think is fastest? The 300hp base car or the 370hp LT-1? The point is not just how much torque but also where in the rpm band the peak torque is made.

 

I think optimal gearing would be all the difference. Gear your vehicle to best use your power wherever its at.

Have you ever seen a V8 motorcycle at the dragstrip. Have you ever seen a 500 horse turbo busa at the track. They run about the same times but the busa probably used 4 gears and the V8 bike uses 1 gear. If you swap engines between those two bike then i bet both of them would be much slower. The busa motor would have trouble at those low rpm and no torgue trying to push that bike and the v8 motor would spend too much time in the high rpms. Proper gearing is just as important as the power

And i don't think you would want to shift a 5252 all the time i think you would want to shift when you stop making power or just before that. Unless you r car is like mine making 180HP and 270torque then i focus shifting based on torgue curve

 

[Richard Dawson]
" NUMBER ONE ANSWER ON THE BOARD, DARLIN' !!!!! "
[/Richard Dawson]

 

Isn't this fun???


Or you can go my way...build a BIG motor for Tq...and then spin the BEEJEEZUS out of it!!

Best of both worlds!


"He who has the most "explosions" (rpm) between the start and finish lines will likely win!"

The whole discussion is over math formulas. I can tell you that an engine that makes lots of TQ and then runs out of breath early is a slug. Think diesel....or many of the cars folks build when they read all the Hot Rod magazines. You can either gear it like crazy and build it to operate in a very narrow rpm band like a real race car, or build it to make as much TQ as possible over the broadest rpm range. Shoot for peak TQ and HP to be at least 1500-2000 rpm apart. THAT engine will make plenty of off the line power as well as pull like a freighttrain up top.

The other option is to utilize a "variable stall speed" setup....otherwise known as a clutch. You can launch at any rpm you want to keep it in the power band.

JIM

 

If you only run 1 rpm your fine. Otherwise you need the whole curve, so the car does care. more tq down low means more hp...you gotta get that tank off the line and unless you're launching at 5k on the street you need the whole power band. That's why when they do the engine build-offs they use avg hp numbers because that's the engine tha t generates the most power, and they do an avg across a typical rpm range where you run the motor.

 

'cuz Jim knows a little 'bout what he's talking

 

Power to Weight Ratio is the GENERAL driver of performance.

True if the 400 HP occurred ONLY over a VERY narrow rpm (say 6950 to 7000, and ther engine had only 20 ft-lb over the rest of the rev range) and the other engine had 400 ft-lb of torque over a wide rpm range (say 600 to 3950 rpm - the point where 400 ft-lb torque produces just under 300 HP), the lower HP car would be faster. This ONLY assumes that both engines have 4 to 6 speeds forward; if you had an infinitely variable transmission with enough ratio range, the 400 HP engine would still be faster!

If the torque curves were normal or typical and the gearing allowed both engines power bands to be used the High HP would ALWAYS be quicker.

 

Given equal, real world cars (we'll say it's a chrome bumper 350 auto with a 1800 converter, 3.55 rear and tires that hook with either engine) the torque motor wins. This is because the torque power band is in a more usable RPM range than the horsepower power band. By the time the horsepower car has the power advantage the torque car has a 1/4 th 1/2 second lead courtesy of its 100Lb.ft. advantage in the first 100 to 125 feet of the race.

I call this the paradox of drag racing. You see it in Pro Stock all the time. The cars are so evenly matched that 90% of the races are won or lost in the first 100'. A .02 second advantage at the 60' mark is invisible yet at the top end it is something like 6'. From 60' to the finish line the two cars may run the same et but the car that had the early advantage will appear to pull ahead of the other car. This is because .02 second at 30 MPH is a lot smaller distance than .02 second at 200 MPH.

To get back to our Corvettes, the horsepower car simply runs out of race track before he can catch the torque car. Now, if you give the horsepower car 4.11 gears and a 3000 converter it's a dead heat. But then we're not comparing just torque and horsepower but also gears and converters.

I'll take the torque car any day.

BigBlockk

Later.....

 

But he said "all other things being equal", so both engines can spin. However, for the reasons BigBlockk stated, I'd have to vote for the TQ guy in this case...

 

hi, i'd like to take advantage of some you more expert then me beeing in this debate to ask: my engine shows at the dino 573 hp at 6.200 rpm and 552 FT of torque at 4.400 rpm? where actually is (in rpms) the point where my engine 'pulls' the most with the minimum effort in terms of power spending, i mean what is the rpm for the best compromise between pulling strong and power expenditure (also for rialiability of engine/trans). gear ratio is 3.73, manual trans a rebuilt stock T-10, the car is a C3 weighting around 3.000lbs, on street tires.
i dont know if i could explain properly my meaning, thanks....

 

To all you math PHD's, I'd like to know the answer of the above question myself....what would be the optimum RPM for both HP and TQ?

 

no always true glen242, what if your using a 9000 rpm cam shaft??

 

The rpm at which the torque peaks is where the engine is most efficient (not counting internal drag/friction). That is peak volumetric efficiency and it occurs at the torque peak. If you’re talking about the most efficient running regime that includes all the variables of the car then that is going to require a whole bunch of empirical testing. Most car engines make way more power than is needed to maintain a constant speed so they aren't as efficient at lower power settings. This is the kind of thing that car companies spend millions on in testing.

 

WAYYYY too many Hot Rod magazine articles have tainted folks minds!

A HP and TQ engine are not mutually exclusive. What some folks call a TQ engine...I call a slug! It's just a big 'ole dumptruck motor that can't make power past peak TQ for very long.

A "HP" engine as is being described here is just an engine that doesn't "fall off" like a brick after peak TQ and peak HP. IF it continues to make good TQ after peak and not fall off quickly, it will "make" a bunch of HP by virtue of making lots of TQ at higher RPM. This doesn't mean it won't make lots of TQ at low speeds, it just means it's a well designed combination.

The first version of my 540 was a decent setup. It made 676 ft lbs at 4600 rpm and 732 HP at 6200 rpm. I am using large heads that "should" have helped the top end better, even though I know they would give up some lower end TQ. There are many 700 ft lb combos out there, but hey...the tires are already smoking...don't need any more! You'll also notice there was a 1600 rpm spread between peak TQ and Peak HP. Problem was that it fell like a rock after peak HP and was down to 591 HP by 7000 rpm. This made the car very peaky to drive under full power. It was like an "on/off" switch as it came on the powerband and then fell off. Still ran well....but I had a new idea....

Next version used identical shortblock. Only changes were to port the heads, change intake and the cam. This time it made 668 ft lbs ( I think..going from memory here)@ 5300 rpm and 825 HP at 7400 rpm. Even at that speed it was literally only dropping 3-5 ft lbs per 100 rpm, which means a couple of things. For one, my cam was too big for the rpm range I wanted. Made great power, but I had overcompensated with the cam not thinking the heads would be as good as they are. #2....the heads are REAL good..they never stop breathing! #3...I needed better parts in it if I wanted to rev it to the 7800-8000 rpm range it was going to like. It would likely have made 840+ HP if I had kept beating on it reving it higher..but I had already seen the trend.

You will also notice there is at least a 2100 rpm spread between peak TQ and HP......I can tell you it's a LOT more fun to drive. It never stops pulling! So I gave up about 50 ft lbs at under 5000 rpm...big deal..it still makes over 600+ ft lbs. down there. I moved Peak TQ to 5300 rpm and make essentially the same TQ number..just at a higher rpm (more HP!). That's OK and right on target.....it makes car much easier to control. The real cool part is that it is up over 215 HP at 7000 rpm. THAT is power you can feel......like having a nitrous bottle that is never empty!

I've since moved back downward to a cam in the middle and have hit the perfect spot.. It makes killer power, goes faster at the track (141 mph trap speeds) and has great manners.

Now I know these numbers are extreme..but the concept is the same. Make good power and then HANG onto it as long as possible. MY last version of my 427 was the same way. It made peak TQ at 4300 rpm and peak HP at 5850 (1550 rpm spread), but the best part was that at 7000 rpm it was only down 6 hp from peak! I could have used a larger cam, but that one had killer manners, held 14" of vacuum and would lug to 1000 rpm in high gear with 3.36's...then pull to 7000 rpm if you wanted to. Again...THAT's a FUN engine!! Again, a case of excellent heads, oval port (ported Merlins) with a basic shortblock and a BIG carburetor.

Whatever you do, get GOOD heads and intake, don't starve it with too weenie of a cam and carb and let it breathe!


JIM

 

How someone percieves a TQ engine and HP engine may be different. It's just as easy to say a good TQ engine will produce a good torque through all of its rpm range including low rpms and not fall flat after peak tq. A HP engine could then be described as an engine that is a slug until the rpms are much higher.
I think the common thing whether its called a TQ or HP engine, is to make good torque across a very broad rpm range.