
5250 rpm = same hp&torque ?November 12 2012 at 6:03 AM  Highboy69 (Login highboy69) Members 
 Why is it that they seem to always be the same ? Jay's post has 2 engines with completely different builds and cubic inches are the same at 5250 rpm and noticed this on Barrys builds to and im just wondering why it is. Is it the same on all V8s ? What about straight 6s and 4s, Are they the same as V8s or dose the HP&TQ cross at a different RPMs on them ? 

Author  Reply 
Barry R (Login Barry_R) Members  Mathematical requirement  November 12 2012, 6:06 AM 
Since we measure torque and calculate horspower from that measurement  the two MUST cross at 5250 RPM to be legitimate. If you ever see a dyno chart that does not cross at that point you should consider it highly suspect  unless dealing with an engine that power peaks below the 5250 mark.
Barry Rabotnick
Survivalmotorsports.com 

Brent Lykins, B2 Motorsports (Login blykins) Members  Horsepower....  November 12 2012, 6:12 AM 
HP = (Torque * RPM)/5252
The 5252 is a common factor between horsepower and torque....
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B2 Motorsports, LLC


69Cobra428CJ (Login 69Cobra428CJ) Members  HP is a product of tq  November 12 2012, 6:45 AM 
Yes that is because hp is a product of tq. I'm not good with putting it into words and it took me a while to comprehend it but basically without tq you don't have hp.
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e. philpott (Login pooreric) Members  How I awlays looked at it  November 12 2012, 7:14 AM 
torque is a engine ability to move a given weight .... horse power is how fast a engine can move the given weight
example .... a 600 HP , 370 FT lbs torque small block chrevy will out accelerate a BB chrevy 454 with 270 horse power and 480 ft lbs of torque .... but the 480 ft lbs of torque BB 454 will tow a trailer way better than the 600 HP small block ... IMHO anyway 

HALowe (Login Halowe) Members  Accelleration  November 12 2012, 7:26 AM 
Accelleration = force divided by mass. f=f/m
The force is measured at the tire, not at the back of the engine (so it is not the raw torque of the engine). The torque multiplication of the drivetrain (including the diameter of the tires) must be factored to determine force.
At any given RPM, increasing the torque is the same as increasing the power output.
This message has been edited by Halowe on Nov 12, 2012 7:36 AM 


Michael Howard (Login mtburger) Members  Re: How I awlays looked at it  November 12 2012, 7:29 AM 
To add to what has already been said, or to say it a different way, Horsepower is a function of Torque, where function is a mathematical equation that relates an input to an output. Expressed as f(x) and stated as "f of x". 

Rory McNeil (Login RM428) Members  Gotta be some exceptions?  November 12 2012, 8:12 AM 
How about engines that realistically would never see 5200 RPM, like a diesel? Oe even a gas truck engine like say a 361 2 barrel FT?
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Royce (Login RoyceP) Members  Those engines have more torque than horsepower  November 12 2012, 8:21 AM 
The lines never cross if you don't reach 5250.
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DaveMcLain (Login DaveMcLain) Members  No Exceptions Possible  November 12 2012, 8:53 AM 
5252 is where the lines will ALWAYS cross, no exceptions and the reason is simply because of the way horsepower is figured using torque times rpm divided by 5252 which is the constant used to calculate horsepower. Since you're dividing by that number both horsepower and torque have to be the same at 5252rpm that's just the way math works.


Bill Ballinger (Login 65Galaxie394)  If you got even a 2 stoke detroit that high it would be a measure of the torque..  November 12 2012, 9:08 AM 
as it exploded like a 1/2 ton chunk of iron :)If you back into it, the Detroit can make 800 lbs ft of torque at 2000 rpms, but only 210 hp at that rpm, but flat line zero at 5250 if it cant get there, mathematically it could be making 15 hp calculated backwards to a torque value, but I don't even believe that value would turn the engine. 

WerbyFord (Login werbyford) Members  That is a very good explanation!  November 12 2012, 9:22 AM 
For example, I can put out about 1000ftlb with my arm, given a long enough pipe, and easily move a big 4x4 with it. But I wont turn a very good e.t. that way. You'd need a calendar. Horsepower wins, not torque.
The reason folks THINK torque matters is that it reflects horsepoweratlowrpm, which matters quite a bit, usually more than peak horsepower. 

Rory McNeil (Login RM428) Members  The reason I asked;  November 12 2012, 9:55 AM 
I have a 2012 Ford Super Duty brochure in front of me, and they show a dyno graph for the 6.7L Powerstroke diesel. It shows peak torque of 800 ft/lbs at about 1500 RPM, and peak HP of 400 around 3700 RPM. Both lines drop off sharply at about 3000 RPM , and appear to be ready to cross over at about 3600 RPM. The way the graph lines drop off so quickly, it would appear if the engine could get anywhere near 5252 RPM, the numbers would be under 50HP & ft/lbs of torque.
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Rod C (Login MT63AFX) Members  Just a SWAG but today's global engines' power is shown in watts/KWs which can.............  November 12 2012, 10:07 AM 
.............be determined with different measuring devices than the old dino dyno, just a thought, Rod. Mickey Thompson's 63 1/2 #997 S/S HiRise 427 Lgt/Wgt Galaxie,
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Tom P (Login tomposthuma) Members  Re: That is a very good explanation!  November 12 2012, 10:02 AM 
So on the far opposite end of the scale, say a decade old Formula One engine that goes to 20,000 RPM and probably idles at 5250 it probably is only starting it's torque curve at that speed and obviously horsepower hasn't peaked either so where do those cross or is this a repeating scale and that falls at 10,500 (double the 5250)? 

Barry R (Login Barry_R) Members  It'd cross at 5250  November 12 2012, 10:10 AM 
If you could hold it down there
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Survivalmotorsports.com 

Tom P (Login tomposthuma) Members  I'd be curious how it can be calculated  November 12 2012, 10:29 AM 
If a very low RPM or ultra high RPM engine makes no power or torque at 5250 i'm curious how HP can be calculated off that if torque at that speed is nonexistant. 

Jay Brown (Login jaybnve) Members  Pretty simple, Tom...  November 12 2012, 11:14 AM 
Zero torque = Zero horsepower, no matter what the engine speed is. So if the engine won't run at 5252 RPM, it is delivering zero torque and horsepower. If the engine is running though, it is unlikely that it is delivering zero torque. You could stop the flywheel with a feather if that were the case. And if the engine is delivering only 1 lbft of torque at 5252 RPM, then it is also delivering 1 horsepower at that speed. Jay Brown
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e. philpott (Login pooreric) Members  the calander  November 12 2012, 4:27 PM 
so a 7.90 would be 7.9 days on the calander method ??..lol .. 

Nick (Login torinothreeninety) Members  sorry to thread hijack, but  November 12 2012, 11:38 AM 
anyone who can get that much air in a '69 Cobra deserves a mention. I am very very much impressed.
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