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Tractor Pulling Discussion Forum

HP for Cubic inch

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bobb

01-14-2005 16:01:49




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I was wondering how much HP can be expected out of 522 cubes 4 7/8 by 7. I heard you can say 1 hp for every 3.5 cubes. Just wondering what some of you guys thought.




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roadgear

01-14-2005 18:25:16




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 Re: HP for Cubic inch in reply to bobb, 01-14-2005 16:01:49  
how much hp you have has to do with just more than cubic inches. you may have 522 cubes but if you put a crappy low compresion head on top of it it obviously wont have as much as a professionally flow benched head.



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ejr

01-14-2005 16:18:29




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 Re: HP for Cubic inch in reply to bobb, 01-14-2005 16:01:49  
I think it depends allot on RPM high RPM probably.



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PULLER

01-14-2005 17:15:21




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 Re: HP for Cubic inch in reply to ejr, 01-14-2005 16:18:29  
Wrong ,RPM does not make hp, RPM will hold hp longer ,but does not make hp.I have done this many times. put the tractor on a dino and check for yourself



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buickanddeere

01-14-2005 18:00:40




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 Re: HP for Cubic inch in reply to PULLER, 01-14-2005 17:15:21  
If volumetric efficiency is maintained or drops at a slower rate than the rpms are increased. The engine will make more HP. Windage and friction losses will use some of that extra HP up. Peak torque and volumetric efficiency occurs at the rpm where the engine can fill it's cylinders the fullest for peak cylinder pressure on the power stroke. Peak HP occurs at a higher rpm where the cylinders are not filled as full and cylinder pressure is not as high. It's the point where the engine flows the highest cfm of airflow through it. Torque is just turning force. HP which is work per hour is how far that force moves something in an hour. 100lb ft at 5000rpm makes more power than 125 lb ft at 3750 rpm.

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Cody

01-14-2005 19:31:40




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 Re: HP for Cubic inch in reply to buickanddeere, 01-14-2005 18:00:40  
RPM= More HP and less torque

Cubic inches= More torque and less HP.

You can take a higher rpm engine, run less gear and run with big cube low rpm engines with more gear providing your cam is ground for your rpm range and your head can flow enough CFM. A 300cid engine @ 4000rpm will require as much air as a 600cid engien @ 2000 rpm., The CFM of your head will be the limiting factor on how much HP your engine makes, anything that you can do to remove any restrictions on the air flow will increase your HP at any rpm. Hope this helps.

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C

01-15-2005 06:56:01




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 Re: HP for Cubic inch in reply to Cody, 01-14-2005 19:31:40  
torque and hp are equal at 5252 rpm.



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buickanddeere

01-15-2005 09:44:28




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 Re: HP for Cubic inch in reply to C, 01-15-2005 06:56:01  
There is much discussion on the numbers. HP = torque x rpm /5252. Where the confusion starts is where two tractors pulling at the same ground speed. The clutch input will have, say 400ft lbs torque before the rear wheels break traction and spin. One tractor engine has 100HP peak and 375 ft lbs peak. The other tractor engine has 60HP peak and 425 ft lb peak. This is were a 60HP tractor walks all over a 100HP tractor and the confusion starts. Now if the 100HP tractor could find a little lower gear it could use the extra HP/rpms available without exceeding it max available 375 lb ft torque. The 100HP tractor will pull as much as the 60 HP tractor and do it much faster.

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Shane Falco

01-18-2005 12:18:51




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 Re: HP for Cubic inch in reply to buickanddeere, 01-15-2005 09:44:28  
RPMs vs. Cubes? Heck, do it the easy way and have the best of both worlds. First, build it as big as possibly can (if you don't, you'll just end up building bigger in a few years anyway). Next, find the biggest carb you possibly can, and then flow your head and manifold as best as possible.
The more cubes you can spin faster, the more horsepower--period!



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buickanddeere

01-18-2005 13:33:27




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 Re: HP for Cubic inch in reply to Shane Falco, 01-18-2005 12:18:51  
Increasing displacement by 25% will not increase airflow,torque or HP by 25%. Increasing displacement by 50% will not increase airflow,torque or HP by double the gains of of the 25% displacement increase. If no suporting work is done on the induction system the HP per cubic inch drops on the bigger engine.Overall HP and torque will be up some. The point of dimishing returns happens pretty fast. Increasing the displacement with no other changes. Will tend to lower the peak torque and HP down in rpms. "RPM's vs cubes " is a saying that doesn't fully explain the relationship between rpm,torque and HP or even what they are.

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