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Thread: How do you get Horsepower & Torque #'s to match? Reply to Thread
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  Topic Review (Newest First)
February 10th, 2013 05:49 PM
cliffyk As has been stated ad nauseum in this thread HP = tq * rpm / 5252. Balancing the equation to get HP and torque on the same "side" we get:

tq / HP = 5252 / rpm.

From this it is obvious the when rpm is less that 5252 the factor 5252 / rpm becomes greater than 1.0, and that therefore tq / HP has to be greater than 1.0--I.e. torque must be higher than horsepower.

When rpm is greater than 5252 the factor 5252 / rpm becomes a fraction (less than 1.0) and therefore tq / HP must also be a fraction--I.e. torque has to be lower than horsepower.


Short story, it is impossible for horsepower to be higher than torque at any engine speed below 5252 rpm, just as it is impossible for torque to be higher than horsepower at any engine speed above 5252 rpm.

This also highlights that for any purpose other discussing peak HP and torque only one of HP or torque, and rpm, are all that are needed. If torque at 3500 rpm is 300 lb-ft you do not need to tell me the HP (other than to do the math for me) as it will be 300 * 3500 / 5252 = 200 HP. Nothing can change that.

Similarly if HP at 6000 rpm is 350, then you do need to tell me the torque as it will be 350 * 5252 / 6000 = 306 lb-ft--it has to be...
February 10th, 2013 02:09 PM
Eagle2000GT
Quote:
Originally Posted by GM2Ford View Post
I was just wondering if anyone had a 4.6 2v or 4v that was in that range of power at PEAK rpm, and what they did to get it there.
A third variable now enters the equation? Peak torque and peak horsepower at peak rpm. I'm not sure that's a desirable goal. Just to restate what has been said before: We measure torque and calculate horsepower. The formula is HP = TQ * RPM / 5252.

To achieve this goal, you would have to set the rev limiter to where RPM equals the divisor. The rev limiter would need to be set at 5252. Then you would have to select a set of cams that limited low end torque. You would not want torque to peak too early but at exactly 5252 rpm. My Centrifugal supercharger peaks too early (4800 rpm). So does nitrous, turbochargers and twin-screws with stock cams. Let's plug some numbers into the formula. 450 HP = 450 TQ * 5252 RPM /5252. That is the only way you can maximize all three variable at the same time.

As Cliff has said, there seems to be a misunderstanding of the relationship of horsepower and torque especially by those who say I'd rather have torque over horsepower. Unless we are talking about low rpm motors then that is probably not a desirable outcome either. In the old days, I ran big block torque monsters. But, the hydraulic lifters back then floated out around 5000 rpm. Those motors never reached the crossover point between TQ and HP.

Let's go back to having the goal of Peak TQ = Peak HP and forget about when they reach peak. The only possible way for this to occur in a motor that spins faster than 5252 rpm is to have TQ drop enough to offset the increases in RPM. Again, the numbers: TQ peaked at 450 at 4800 rpm. Max RPM is 6000. 450 HP = 393.9 TQ * 6000 RPM/ 5252. To achieve the goal of HP = TQ then TQ has to drop 56 ft.lbs. between 4800 and 6000 rpm.

A more desirable goal would be flatten the torque curve, to continue having 450 ft.lbs. of torque at 6000 rpm. But that will significantly increase horsepower. Here are the numbers: 514 HP = 450 TQ * 6000 RPM/5252. The only way for TQ to stay higher than HP is to drop TQ as RPM increases. Personally, on any motor that spins faster than 5252 rpm I'll take peak horsepower over peak torque anyday. That simply means you've extended your torque into higher rpm ranges.

Disclaimer: The above discussion wasn't meant to compare a big block torque monster to a high reving 4 cylinder. It was meant for a discussion of HP and TQ on a single motor. Comparing 450 TQ on one motor to 450 HP on a different motor is a completely different discussion. In that case I would probably prefer TQ over HP.
February 10th, 2013 11:54 AM
cliffyk I think I am beginning to understand the question, the concern is that those asking do not want to have an engine built around maximising the peak HP at the expense of usable power at other than peak HP--coupled with a misunderstanding of the relationship of HP and torque, that at any given rpm they are so immutably joined that any discussion of one is a de facto conversation of the other.

It is a variation of something I have been telling people for years, peak HP and torque numbers are quite interesting however they are only a very small part of the story--Show me the curves? I would quite gladly lose 15% of peak HP if that loss in peak power could be translated to 15% more mid-range torque.

I think what is being asked is "How do I maximise the torque across the whole powerband?". HP can be left out of such a discussion as it will be whatever torque * rpm / 5252 says it is. This is much less of and issue with a V8 than with a 6- or 4-banger where torque starts out pretty anemic until the revs get up...
February 10th, 2013 11:45 AM
cliffyk
Quote:
Originally Posted by Froush View Post
Well i was only able to take mine to 5500 rpm. But id say mine is pretty damn equal. Torque doesnt fall below 500 over the entire curve. Once i find my problem hp will most likely continue to rise quite a bit higher than torque. Mods in garage or build thread

Very nice numbers! Gotta love positive displacement blowers...
February 10th, 2013 11:36 AM
Froush Well then spray it. Spray will yield way more torque than hp. You could also spray on top of boost. I just like the idea of power on tap rather than having to fill up a bottle for power. I may get bored eventually and spray on top of the kb but for now, 580/570 is plenty enough power. Its a blast to drive. Im sure just a centri at 9-12 psi will hold off your power needs for a while. You will feel the torque. No need for a dyno graph that shows torque higher than hp. Whats the point?
February 10th, 2013 11:03 AM
cobra241
Re: How do you get Horsepower & Torque #'s to match?

https://www.moddedmustangs.com/forums...e-than-hp.html
February 10th, 2013 10:59 AM
cobra241
Re: How do you get Horsepower & Torque #'s to match?

I think I'd actually like a little more torque then then horsepower. Let me find my question
February 10th, 2013 10:55 AM
Froush Well i was only able to take mine to 5500 rpm. But id say mine is pretty damn equal. Torque doesnt fall below 500 over the entire curve. Once i find my problem hp will most likely continue to rise quite a bit higher than torque. Mods in garage or build thread

February 10th, 2013 10:20 AM
cliffyk
Quote:
Originally Posted by cobra241 View Post
I actually asked same question few months ago
I still remain curious as to why? What is it about having torque and HP peak at the same rpm (5252) that is felt to be desirable?

----------------------------------------------
- The rpm, if HP and torque are equal, will always be 5252 rpm because of the formula's simple maths and fixed constant.
February 10th, 2013 12:08 AM
cobra241
Re: How do you get Horsepower & Torque #'s to match?

I actually asked same question few months ago
February 10th, 2013 12:02 AM
Eagle2000GT I don't know how anyone could plan equal peak torque and horsepower. My motor reaches peak torque around 4800 rpm and peak horsepower around 5900 rpm. Below 5252 torque is higher than horsepower. Above 5252 horsepower is higher. Horsepower will continue increasing until torque drops off faster than rpm is increasing.
February 9th, 2013 08:00 PM
GM2Ford
Quote:
Originally Posted by cliffyk View Post
I mean absolutely no offense, however you need to learn much more about the relationship of torque, rpm, horsepower and gear ratios before asking questions like "I'd like to have 450rwhp AND 450rwtq...". Once you learn more you will realise that that is a nonsensical question.

And who said anything about "it being a Camaro or Chevy"?
Okay. That's cool. Thanks for not being an asshole about it like many people on forums. I was just wondering if anyone had a 4.6 2v or 4v that was in that range of power at PEAK rpm, and what they did to get it there.

Also, there are plenty of chevy/camaro haters out there. So in no means was I directing that toward you, but you know... you get those people that are like... ew, its a chevy, F that, blah blah blah blah blah ya know? So I just said that to weed out the people saying that.
February 9th, 2013 07:51 PM
cliffyk
Quote:
Originally Posted by GM2Ford View Post
I know 450rw won't get me there... but eventually so I can do this

burnouts at 70 mph on slicks - YouTube

Please, leave the comments about it being a Camaro or Chevy out of this Thread. Thanks, I'm a fan of all cars.
I mean absolutely no offense, however you need to learn much more about the relationship of torque, rpm, horsepower and gear ratios before asking questions like "I'd like to have 450rwhp AND 450rwtq...". Once you learn more you will realise that that is a nonsensical question.

And who said anything about "it being a Camaro or Chevy"?
February 9th, 2013 05:20 PM
cliffyk
Quote:
Originally Posted by GM2Ford View Post
So my goals for my car are around 450rwhp...

BUT!

I'd like to have 450rwhp AND 450rwtq, if not very close to matching numbers.

Is there any way I can do this?
Why?

As others have implied, there is only one rpm where it is possible that peak torque and peak HP can be equal, 5252 rpm. Why is this so important?

------------------------------------------------------
James Watt guesstimated many years ago that a "good dray [draft] horse" could do 33,000 lb-ft of work per minute. I.e. move 33,000 lbs one foot in one minute--or 330 lbs 100 feet in one minute. When referring to rotational power transmission the distance traveled is always the circumference of the circled traveled; which is the diameter of the circle * pi (a constant = 3.14)--or the radius of the circle * 2 * pi.

Well as it turns out 33,000 / (2 * pi) = 33,000 / 6.28 = 5252. That is why lb-ft * rpm / 5252 = HP.
February 9th, 2013 03:07 PM
DJNASTYNATE
Quote:
Originally Posted by boduke0220 View Post
PD blower or nitrous. a centri wont do it. or a bigger cube motor.
When I put mine on the dyno with a centri, it was showing more TQ than HP. It was only a difference of 5-7 but it was still more. Also it wasn't at 450 either, but hoping to find out soon if it will stay around the same margin.
February 9th, 2013 01:43 PM
y2k02
Quote:
Originally Posted by limited View Post
also tq and hp are the same at 5252 rpm on all cars
While this is true it doesnt mean that is where it sees peak tq.

Quote:
Originally Posted by boduke0220 View Post
a centri wont do it.
Small pulley and a wastegate and it can.
February 9th, 2013 12:49 PM
boduke0220 PD blower or nitrous. a centri wont do it. or a bigger cube motor.
February 9th, 2013 12:49 PM
WickedSnake00
Quote:
Originally Posted by DeathBringer View Post
You want more torque than HP anyways.
Then you must love diesels.


There really is no simple answer. It involves a variety of factors, one of which is the bore/stroke ratio. The 4.6 is relatively square (they are roughly the same) which favors a balanced hp/tq rating. A longer stroke compared to bore will favor more torque, like in diesel engines and the old stump pulling big blocks, like the olds 455. There is also optimization that can be done with the intake manifold/runners, head CC design, and especially cam profiles to favor hp or torque, which is basically to say low end torque or high end torque.
February 9th, 2013 12:48 PM
blownstang A positive displacement blower will give you HP and tq numbers that are close, but you also have to choose the right cam that will give you a nice tq power band. For example there is a blue bullitt on this forum that makes 517/456 with bolt ons, Vortech S trim at 11psi and MHS Stage 1 cams. The cams provide a very nice wide tq band. From 3500-6300rpm the torque is above 400rwtq and doesn't drop off. Getting the numbers closer together would be difficult. The amount of tq the car makes also depends on how much timing is in the tune throughout the rpms.

My numbers are close, but as I add more power the hp will increase more than the tq. Longtubes helped out my torque numbers.
February 9th, 2013 12:28 PM
limited I am close. a pd blower will give you close results. also tq and hp are the same at 5252 rpm on all cars
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