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Old 12-13-2002, 03:48 PM
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Post didn't know where to ask this but HP and TQ relationship?

Okay I konw that the formula for hp is TQ X RPM X 5.(some long decimal)=HP

SO after saying that couldn't you have a low reving engine with alot of Tourque meaning low HP numbers but gear it so the wheels get more RPM in them.. so say if you used a desiel with 2.23 gears or something like that... if the thing was a touque monster wouldn't your rear wheel HP actually be higher than your engine HP and your rear wheel TQ lower than the engine TQ... so then does HP make all the difference or could you have an all TQ engine and still perform..

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Old 12-13-2002, 04:23 PM
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The problem with your scenario is torque is determined by engine rpm not axle rpm, wheel torque/hp is determined by axle ratio and engine torque/hp.

Does that make sense Dave?
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Old 12-13-2002, 06:09 PM
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Umm kinda but the thing is.... when the dyno is put on the rear wheels they wouldn't be able to tell your gearing unless they look at your tach right... so if they just when by rear wheel rpm... could you not increase your hp and decrese your tourque... I mean ricers do the opposite... they have tons of hp because of the rpm factor (can rev higher cuz of less recipicating mass) so they put real low gearing in from the factory so that the car doesn't stall (at least I think this is how it works..) isn't this also how ferraries with very little displacment but that turn over high revolutions end up getting tourque is by having the lower gears???? It does not so much make tourque but use the hp/rpm energy in a different way?

[ December 13, 2002: Message edited by: stonedchihuahua ]</p>
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Old 12-13-2002, 07:06 PM
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Your drive train cannot increase power. It takes power to turn the mass. Period. However, you can utilize the drivetrain so that is does not leach so much. In the case of modern 4 bangers, they use 5sp so that you have steeper low gears to help with the lack of torque. You can take identical 4 bangers except for the trannys, and the stickshift will win every time because the engines don't have the torque to move at low rpms. This also applys to any car or truck. The steeper you make your gears, the easier is is for the engine to overcome it's load. If 5 speeds had not been developed there would be no 4 banger because they would be even slower than they are now. Also, you can indeed go fast with torque. A 71 Buick GSX ran the quarter in the low 13's. This was done with a 455 that had only 390hp, but 510ft/lbs of torque connected to a 3 speed auto. If it did not have the torque, it would have gone nowhere. Hope this doesn't confuse you more and that I answered a few of your inquisions.

[ December 13, 2002: Message edited by: 78novaman ]

[ December 13, 2002: Message edited by: 78novaman ]</p>
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Old 12-13-2002, 07:22 PM
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Read over this and see if it don't answer alot of your questions. Dan

<a href="http://www.vettenet.org/torquehp.html" target="_blank">http://www.vettenet.org/torquehp.html</a>
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Old 12-13-2002, 07:22 PM
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The purpose of the drivetrain is to transfer the engines power to the wheels and plant that power to the pavement. But like what 78novaman said it doesn't make the power but you need to set it up right to deliver the power effectively. If you have an engine that builds it's power at 4,000 rpm's you don't want a drivetrain that will put the engine at 8,000rpm's. Vise-versa if you have an engine that maximizes it's power at 8,000 rpm you'll never see that power if your engine can't rev over 4,000 rpm because of your 2.73 gears and jumbo tall tires. Imagine a crotch rocket style bike that could never rev above 2,500 rpm, it would be a dog cause their engines powerband is at high rpm's. Yet Harley Davidsons are geared to run low rpm's because that's where their powerband is. Hope I made sense.
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Old 12-13-2002, 07:58 PM
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Yeah.. that was what I was trying to mean.. about not having too much hp and utilizing the tourque.. I'm just not good with words...


Me fail engish that unpossible <img src="graemlins/pain.gif" border="0" alt="[pain]" />
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Old 12-13-2002, 08:07 PM
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k that site was good although some of it confusing.. but what i got out of it is hp is basically how long the tq is effective of or how much tq at high rpm.. I have read a similar thing on howstuffworks.com
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Old 12-13-2002, 10:46 PM
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Let me see if I understand your question correctly;
  • You want to know if you design an engine to produce unbelievable amounts of torque at low rpm would this be an advantage over engines that need to rev at a higher rpm to develop their equivalent torque?

This question is best answered by examining how gearing affects torque multiplication. A rear axle of lets say 2:1 would multiply the torque available at the rear tires X2.

Now if we had an axle of 4:1 the torque would be multiplied X4, a significant increase. Lets say this engine developed a peak of 100 pd ft of torque at 2000 rpm. The rear tires would see 400 ft pds being exerted through the lever (the tire, it has a diameter!) to the ground, lets say the lever is 1 ft long (Most 15 inch tires approach this) So exactly 400 ft pds are being exerted at the rear tire at peak load at 2000 rpm. Sounds like a real torquey motor hey? Rpm would also go down by 4 since we are trading rpm for torque.

Lets look at the same motor with the 2:1 gearing, we have 100 ft pds going through X2 equals 200 ft pds at the 1 ft lever. This the basic reason why you cannot increase hp by reducing gearing, it's straight multiplication and low gearing is a direct multiplication of the torque function. Of course rpm would go down by only half.

Designing a motor with a low operating rpm and narrow power range will be hard to gear because of the need to keep the engine turning at peak torque over a narrow range. Essentially you need a lot of gear changes to keep the engine working. Look at semi trucks, this is how they extract work from narrow power range diesels.

Work is time X effort / distance covered, Horsepower represents this work in a rotational fashion by using rpm to denote distance covered. Think of it as an endless fishing reel pulling in the big one. The faster you can reel in and the bigger the fish and the more line you can reel in one second the more work/horsepower you are producing. Fish weight (load) is a direct multiplier just like the gearing calculation. The basic math mistake you are making is rpm or distance covered is a divisor into the time/effort numerator, not multiplied.

Whew. <img src="graemlins/sweat.gif" border="0" alt="[sweat]" />

[ December 14, 2002: Message edited by: 4 Jaw Chuck ]</p>
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Old 12-13-2002, 11:39 PM
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yes that helped me understand but what about 0.5:1 that is one hell of a big pinon i know
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Old 12-14-2002, 09:15 AM
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[quote]Originally posted by stonedchihuahua:
<strong>yes that helped me understand but what about 0.5:1 that is one hell of a big pinon i know</strong><hr></blockquote>

You need to polish your math. That would be a 2:1 ratio.

Chris
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Old 12-14-2002, 03:02 PM
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actually 1:2

cuz 0.5 X 2 =1
and 1 x2 =2
maybe we both need to polish our math
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