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Old 05-07-2004, 00:35   #1 (permalink)
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Torque vs Horsepower

G'Day,

Run thru some different cam profiles on desktop dyno. I know its a very open question, ref the whole RPM range, but just asking in general terms.

Would you prefer an extra 30ft/lbs of torque or 30HP?

Cheers
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Old 05-07-2004, 02:50   #2 (permalink)
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Re: Torque vs Horsepower

Well they're not 1:1 in equivalence (ft/lbs to HP), but in general I would say the intended application will answer that.

Street car/Drag car: torque
Race car ie circuit etc: HP

It takes torque to get a weight moving, so where acceleration is important, shoot for an improvement in torque.

In terms of graphical representation, the overall performance potential of a motor comes from the total area under both the TQ and HP curves when you combine them. Dyno2000 doesn't do that, but mathematically you can use calculus formulae to derive it if your up with that side of things. But you can get a rough idea just by comparing two engines - which of the two has the biggest area under the curves by eye, though it's not a very quantitative way of doing it.

So what I'm saying is two motors with identical peak HP, and identical peak torque at the same revs can perform very differently. In graphical terms, the motor with more total area under the curves will perform better. That's because it will have more HP and TQ available throughout the rev range.
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Old 05-07-2004, 02:50   #3 (permalink)
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Re: Torque vs Horsepower

Quote:
Originally Posted by TruBlu351
G'Day,

Run thru some different cam profiles on desktop dyno. I know its a very open question, ref the whole RPM range, but just asking in general terms.

Would you prefer an extra 30ft/lbs of torque or 30HP?

Cheers
Whole rev range on a street car? Torque, any day of the week thanks!
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Old 05-07-2004, 02:57   #4 (permalink)
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Re: Torque vs Horsepower

torque, give me the torque
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Old 05-07-2004, 10:20   #5 (permalink)
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Re: Torque vs Horsepower

Quote:
Originally Posted by TruBlu351
G'Day,

Run thru some different cam profiles on desktop dyno. I know its a very open question, ref the whole RPM range, but just asking in general terms.

Would you prefer an extra 30ft/lbs of torque or 30HP?

Cheers
The answer is that it depends on what RPM each occurs. Also, if a camshaft "steals" torque from one RPM area to move it to another area, it may be a "bad thing" depending on the RPM ranges involved.

The corrected answer should be that you want to build the broadest, flatest possible torque for the engine and its intended usage. If it is a street engine, you want basically 1800-5500. Don't give up 15-25 foot pounds at 2000 to move them to 4000+ for example. If a camshaft takes a few from the bottom end RPM range and adds a bunch more to the 3600-4200 area in a "hot" street car, that is probably a good thing. As you can see, it is all rather subjective and very dependent on both usage and "when" everything is happening. (when = RPM)

If the car never or very rarely sees the drag strip, focus on making the best possible torque up to about 3800 RPM. This means dual plane intake, small port heads/extractors even a 2bbl carburetor is something very worthwhile considering. Peak RPM on a cam like this would definitely be nosing over by 5000 RPM. A small (500-600) 4bbl or a spreadbore with vacuum secondaries.

If the car is more likely to see some time at the track, a mid-RPM range power band, some more converter and rear gear is going to see a peak torque around 4200-4600 RPM being the sweet spot for a camshaft profile that also makes very broad torque from about 2500-5000 RPM.

A bit "more of everything" will push it out to about a 3800-6500 RPM engine. These are absolutely great for a lightweight stick car that sees limited street duty and plays a good bit of time as a strip thrasher.

A "big cam" where an engine makes power between 4000+ and up to maximum redline is going to be mostly non-streetable and a good bit of a PITA on cruise nights, but will be considered a very "nasty" animal by everyone encountering it. Nearly every single part on an engine like this needs special attention. You can easily build one using mostly stock parts, but by the time someone is looking into this range of activity, aftermarket hot-up parts tend to fill the list of what's going into it.

You may want to take a quick look at the "camshaft selection" section of this:

Crower Cams

...PDF file. It really makes good sense to consider these "intended usage" values and carefully note their recommended RPM ranges. Basically, you'll find that a particular camshaft simply moves the RPM range where the engine makes power. A camshaft is really the "brains" of the engine and the cylinder heads are its "heart." As Cleveland owners, we've already got a lot of heart in just the factory pieces. Find a camshaft that puts you as solidly into the RPM range where you intend to use the vehicle. Focus on making the broadest and "overall" highest amount of torque. Don't let the curve slip down in the front end for a bit more peak somewhere else, rather, find one that "comes up quickly" and "stays up a long time." This is a proven strategy for any man!

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Old 05-07-2004, 13:32   #6 (permalink)
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Re: Torque vs Horsepower

Whats the old saying: Hp is what you talk about:torque is what you feel......
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Old 05-07-2004, 18:18   #7 (permalink)
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Re: Torque vs Horsepower

i thought it was also horsepower sells engines, torque wins races ? :)
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Old 05-08-2004, 02:25   #8 (permalink)
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Re: Torque vs Horsepower

Torque's Cheap, lets Race!

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Old 05-08-2004, 07:07   #9 (permalink)
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Re: Torque vs Horsepower

Good to go then - put some torque on your fork.

Cheesy quote of the year.

The camshaft I was referring to has a gut load more torque across the whole rev range, compared to the one with higher "peak" figures. It holds about 50-60fl/lbs ahead just until peak rpm. The other power curves were clearly coming in much later, were a lot steeper - and only just peaked higher.

So I'll be sticking with the flat broad one.

Thanks for the calculus hot tips there stroke! Calculus brings back some phobias that I've locked in the closet! I'll stick to printing out the torque curves and cutting them out with some pre-school scissors and holding them up to the window!

Thanks guys for all your info.
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Old 08-18-2004, 18:09   #10 (permalink)
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Re: Torque vs Horsepower

torque ya say
hows 400hp@5000rpm /500lbft@2000->3750 acording to DD2K with a small cam under .500 lift
ford 400 oh ya
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