How to calculate engine torque
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,710
Likes: 285
How to calculate engine torque
I had my '96 LT4 dynoed yesterday (see thread in tech section) but I have a question. The Rear wheel torque was 310.84 the rwhp was 303.28. I was told to divide the rwhp by .85 to find the flywheel horsepower (356.8). Do I do the same thing with the torque number of 310.84? The spec on the LT4 states it makes 340 foot lbs at 4500 rpms.
Thanks,
Bob
Thanks,
Bob
Last edited by Trebor; Oct 16, 2009 at 09:33 AM.
Safety Car
Joined: Sep 2002
Posts: 4,971
Likes: 9
From: The reason time exists is so everything doesn't happen at once
Generally the rear wheel hp is 80 - 85% of the flywheel. The only sure way to know is to pull the engine and run it on an engine dyno. Remember, on a dyno torque is measured, horsepower is calculated. Don't really think this is necessary; rwhp (and torque) is what you're putting to the ground not the flywheel numbers.
Saw your videos - sounds great. Are you running the stock exhaust?
Oh, BTW, the divisor is .85 not 8.5.
Saw your videos - sounds great. Are you running the stock exhaust?
Oh, BTW, the divisor is .85 not 8.5.
Last edited by jrzvette; Oct 15, 2009 at 07:57 PM.
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,710
Likes: 285
Generally the rear wheel hp is 80 - 85% of the flywheel. The only sure way to know is to pull the engine and run it on an engine dyno. Remember, on a dyno torque is measured, horsepower is calculated. Don't really think this is necessary; rwhp (and torque) is what you're putting to the ground not the flywheel numbers.
Saw your videos - sounds great. Are you running the stock exhaust?
Oh, BTW, the divisor is .85 not 8.5.
Saw your videos - sounds great. Are you running the stock exhaust?
Oh, BTW, the divisor is .85 not 8.5.
trebor
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
It is divide by 0.85.
I had my '96 LT4 dynoed yesterday (see thread in tech section) but I have a question. The Rear wheel torque was 310.84 the rwhp was 303.28. I was told to divide the rwhp by 8.5 to find the flywheel horsepower (356.8). Do I do the same thing with the torque number of 310.84? The spec on the LT4 states it makes 340 foot lbs at 4500 rpms.
Thanks,
Bob
Thanks,
Bob
Melting Slicks
Joined: Oct 2006
Posts: 2,238
Likes: 10
From: College Station TX
Generally the rear wheel hp is 80 - 85% of the flywheel. The only sure way to know is to pull the engine and run it on an engine dyno. Remember, on a dyno torque is measured, horsepower is calculated. Don't really think this is necessary; rwhp (and torque) is what you're putting to the ground not the flywheel numbers.
Saw your videos - sounds great. Are you running the stock exhaust?
Oh, BTW, the divisor is .85 not 8.5.
Saw your videos - sounds great. Are you running the stock exhaust?
Oh, BTW, the divisor is .85 not 8.5.
http://www.mazdas247.com/forum/showt...hp?t=123629978
For a Dynojet, I think 15-18% losses is too high, that would put his torque between 364 and 378, which is too high for a stock LT4 (and his dynoed very close to a lot of other LT4's on Dynojets). Using a 10% loss, it comes to 344 ft/lbs, which is right with the factory rating.
If these were Mustang dyno (or other eddy current dyno), I think the 15% would be much more applicable.
Safety Car
Joined: Sep 2002
Posts: 4,971
Likes: 9
From: The reason time exists is so everything doesn't happen at once
He ran on a Dynojet, which actually measures power and calculates the torque. An eddy current dyno, like a Mustang dyno, measure the torque and calculates the power.
http://www.mazdas247.com/forum/showt...hp?t=123629978
For a Dynojet, I think 15-18% losses is too high, that would put his torque between 364 and 378, which is too high for a stock LT4 (and his dynoed very close to a lot of other LT4's on Dynojets). Using a 10% loss, it comes to 344 ft/lbs, which is right with the factory rating.
If these were Mustang dyno (or other eddy current dyno), I think the 15% would be much more applicable.
http://www.mazdas247.com/forum/showt...hp?t=123629978
For a Dynojet, I think 15-18% losses is too high, that would put his torque between 364 and 378, which is too high for a stock LT4 (and his dynoed very close to a lot of other LT4's on Dynojets). Using a 10% loss, it comes to 344 ft/lbs, which is right with the factory rating.
If these were Mustang dyno (or other eddy current dyno), I think the 15% would be much more applicable.
Tq = HP x 5252/RPM
Two paragraphs later it states
HP = Tq x 5252/RPM
both statements can't be correct. From the first formula (Tq = HP x 5252/rpm) it follows that HP = Tq x RPM/5252.
Melting Slicks
Joined: Oct 2006
Posts: 2,238
Likes: 10
From: College Station TX
http://www.revsearch.com/dynamometer...orsepower.html
But either way, not all dynos work the same way.
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Safety Car
Joined: Sep 2002
Posts: 4,971
Likes: 9
From: The reason time exists is so everything doesn't happen at once
The first formula is correct, and your formula is correct.
http://www.revsearch.com/dynamometer...orsepower.html
But either way, not all dynos work the same way.
http://www.revsearch.com/dynamometer...orsepower.html
But either way, not all dynos work the same way.
