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Does tire size and gear ratio affect the dyno??

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Old 04-21-2003, 10:50 PM   #1
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Does tire size and gear ratio affect the dyno??

My buddy has an LS1 Trans Am, that dynoed at 380 HP at the rear wheels. (Heavy engine mods, T56 tranny, 3.42 gear). He just got the Holley LS1 intake manifold and a ported throttle body put on. He also got a 4.10 rear installed and I believe a little bit taller of a tire. It dynoed again at nearly the same as before, actually a tad bit less. I would of thought for sure the intake would have helped tremendously, considering he has a different cam and heads than stock. So my question is, can the tire size and rear end ratio have an effect on the dyno results? If so, how? Thanks in advance.
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Old 04-21-2003, 10:55 PM   #2
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Dyno results are always corrected to sea level. To make a proper dyno run, specs need to be imputed into the dyno. They want to know tire size and gearing so that the dyno can compensate for each setup.

Changing from 3.42 to 4.10 gears will increase the amount of torque multiplication. Dyno results are base on torque then hp is calculated from the results. Putting in the lower gear then increasing the tire size will still give the same amount of torque but the mph should be higher because of the taller tire.

Not all dynos are the same. Getting a dyno run at one shop then getting another the next day at another dyno can give different results.
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Old 04-22-2003, 12:14 AM   #3
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I am about to dyno my Yukon... 4:56 gears and 38.5" tires... We will see..

When I had my Camaro on the dyno, they never asked tire diameter or gear ratios.. ??

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Old 04-22-2003, 08:18 AM   #4
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NO, tire size and gear ratio have no effect on Dyno results. You are measuring Horsepower & Torque. There is a SAE correction factor.
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