# Question on torque



## Nissan00 (Nov 13, 2003)

Ok if a car say an old civic makes 89 @ 4500 RPM (which it does I think)

Would it make the civic go faster if the torque was at lower RPM?? Say 2500-3000 RPM? 


Thanks if you can help!


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## Harris (Nov 11, 2002)

The faster the torque is made, the faster the car can move.


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## Nissan00 (Nov 13, 2003)

so at lower RPMS huh? cool man thanks!


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## Harris (Nov 11, 2002)

Yes, but if you go too low on the rpms, you start burning rubber like you do an effigy of a politician you REALLY hate.


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## Nissan00 (Nov 13, 2003)

like how low RPMS? like 2500? 2800?


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## sr20dem0n (Mar 19, 2003)

Nissan00 said:


> Ok if a car say an old civic makes 89 @ 4500 RPM (which it does I think)
> 
> Would it make the civic go faster if the torque was at lower RPM?? Say 2500-3000 RPM?
> 
> ...



The 89 is the peak torque, you're asking if it would go faster if the peak torque was at 2500 INSTEAD of at 4500, so the torque at 4500 was lower? Overall the car would be slower since it would be making less torque up high where it matters more, but it would be nicer for driving around town since it would have more power at low rpm.


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## Nissan00 (Nov 13, 2003)

so it's better if it peaks up high, next to the HP


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## sr20dem0n (Mar 19, 2003)

I don't really think you understand, HP is simply a function of torque. When you measure a motor's hp and tq, all the machine does is measure the tq, then it plugs it into the equation

(hp @ x rpm) = (tq @ x rpm) * (x rpm/5252)

So the higher up in the rpm band that you make the torque, the more hp it will give you. This is because the faster the engine spins the more often that torque is being applied. If you have your peak tq at a lower rpm, you will have more hp at that low rpm, but if the same torque was being applied at a higher rpm the difference in hp would be much greater. For a difference in 5tq at 5252rpm you get 5hp, for a difference of 5tq at 2500rpm you only get a difference of 2.4hp.


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## Harris (Nov 11, 2002)

He needs to go here:

http://www.howstuffworks.com


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## himilefrontier (Jan 21, 2003)

Remember that horsepower is a function of torque as predicted by the formula: HP=(torque x RPM)
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5252

This is why HP and torque will ALWAYS be the same at 5252 RPM-no matter what kind of engine it is! 

Further, torque as measured at any one RPM point, is meaningless as far as predicting acceleration. Rather, it is the area under the torque curve that matters.More average torque will yield a better acceleration curve than just a high peak number. This is illustrated well by the comparison between the 1969 Camaro Z-28 and 1969 Ford Mustang Boss 302. Both engines had the same displacement, and both had the same bore and stroke (4" x 3"), 11:1 compression ratio,780 CFM Holley Carburetor, and peak horsepower(290 rated). However, in stock trim, the Z-28 was a better accelerating car due to a smoother power curve than the big valve (2.08? vs 2.02)Cleveland headed Boss 302. The Boss was built as a high RPM engine, but could not utilize the air flow available. The Chevy however, could rev high as well, but it's heads were better suited to the overall combination of parts and thus was the more driveable of the two(Although it still is lacking in the lower RPM range). This also illustrates why bigger is not always better when it comes to head ports and valves. A larger head will flow better at higher RPM's and air demand, but at lower speeds, it will lack runner velocity and the air will stall in the ports causing a myriad of problems contributing to a lack of power. Remember that in the case of high performance engines, it is the overall combination of parts that is important, and using the wrong pieces, no matter how expensive or trick, can and does result in a loss of power and driveability.

There are other factors to consider also, and I will touch on them briefly as I do not have room to write an engineering paper here!(Plus, I am a pizza delivery driver and not an engineer!) The bore/stroke relationship is important as is the Rod lenght / stroke ratio. The shorter the stroke, the higher an engine will rev.The longer the stroke, the lower the engine will rev, but the more mecahnical advantage(and thus, torque) it will produce. A longer rod is preferred to a shorter one since it increases the dwell time at TDC and makes for more complete combustion.It also slows the piston speed and adds more leverage, making for an engine that can rev higher and make more torque. There are things like: resonance tuning for the intake and exhaust manifolds, combustion chamber efficiency, and piston crown design which can also affect things, but I won't go there. I hope this gives you an idea as to what affects these things and what affect that the numbers have on acceleration.


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## Dan-zig (Apr 19, 2003)

welcome to Physics 2A.....maybe diff for other people


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## Galimba1 (Aug 16, 2002)

Where does the 5252 factor come from?

1HP = 5252 ft-lb-rev/sec?

I forget, is revolutions dimensionless?


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