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Old 10-19-2008, 11:04 AM
 
Location: Lafayette, Louisiana
14,100 posts, read 28,384,045 times
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Not sure how to word this question so forgive me if I go too long. Engines with overhead valves seem to have a higher torque number than engine horsepower. Engines with overhead cams seem to have a higher horsepower number than torque. Why is it that overhead valve engines seem to have more torque than OHC engines and OHC engines seem to have more horsepower than OHV engines? Personally, give me an inline 6 with OHV. They may not be fast or fuel efficient but they are very long lasting.
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Old 10-19-2008, 02:48 PM
f_m
 
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Can you give an example? I mean, unless I'm missing something, all valves are overhead. The cam can be in a different location, is that what you mean?
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Old 10-19-2008, 05:50 PM
 
Location: Southern Arizona
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Interesting question, Sailordave.

Torque vs Horsepower can vary even in the same engine with different "tunes" and/or applications.

As an example, a Chevy 350 (or 5.7L) V8 engine in a Passenger Car will have higher horsepower while the same engine in a Pick-Up will have higher torque.

Are you comparing Apples with Apples?
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Old 10-19-2008, 06:56 PM
 
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Quote:
Originally Posted by f_m View Post
Can you give an example? I mean, unless I'm missing something, all valves are overhead. The cam can be in a different location, is that what you mean?
he's talking about a modular engine (Ford 4.6) vs a traditional pushrod engine (GM LS_).
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Old 10-19-2008, 07:39 PM
 
Location: Tulsa, OK
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There is a formula for converting torque to HP. (Torque x Engine speed) / 5,252 = Horsepower. The reason most OHC engines produce more HP is that valve geometry allows them to run at a higher RPM. Using this formula an engine that produces 300 FT LB of torque does the following.

OHV engine(300x5000RPM)=1500000/5252=285 HP

OHC engine(300x6000RPM)=1800000/5252=342 HP

for more info HowStuffWorks "How do you convert engine torque to horsepower?"
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Old 10-19-2008, 08:26 PM
 
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OHC design allows for higher rpm versus OHV design. Some OHC's put out lofty horsepower numbers for their size(Civic Si, S2000,etc.), but you'll need to rev it way up to get at that power.
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Old 10-19-2008, 10:40 PM
 
Location: Chicago
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OHV engines tend to have higher displacement compared to OHC engines of comparable horsepower rating, making it easier for them to deliver higher torque; however, OHC engines tend to have higher redlines because of the substantially lower cam profile inherent to an OHC design, making it easier to deliver higher horsepower per unit of displacement.
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Old 10-20-2008, 02:34 PM
 
Location: Eastern Washington
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The main point of OHC is to lighten the valve train and allow higher revs.

There are and have been some high-revving OHV engines, for example the late-'60's Chevy 302, which definitely made a higher HP number than torque number.

If peak horsepower RPM is higher than 5252, due to the definition of horsepower, or at least one simple formula for it of (torqueXRPM)/5252, your horsepower number is higher than your torque number.

Most normally-aspirated (no turbo or super-charge) engines make right around 1 ft-lb of torque per cubic inch of displacement.
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Old 10-26-2008, 04:21 AM
 
13 posts, read 25,166 times
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Quote:
Originally Posted by sailordave View Post
Not sure how to word this question so forgive me if I go too long. Engines with overhead valves seem to have a higher torque number than engine horsepower. Engines with overhead cams seem to have a higher horsepower number than torque. Why is it that overhead valve engines seem to have more torque than OHC engines and OHC engines seem to have more horsepower than OHV engines? Personally, give me an inline 6 with OHV. They may not be fast or fuel efficient but they are very long lasting.
Usually the longer the crankshaft the more torque. Thats why sometimes you will get some of the old inline 6s like the stovebolt motor actually pulling torque close to what some small v8s will pull. The crank in an inline 6 is longer than the crank in a small v8s.thought i'd point out that something that i have noticed. there are other factors that result in torque but thats one i have noticed.
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