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Why do some dyno operators use SAE and some use STD numbers on the dyno,and what is the percentage difference?I know STD read higher
 

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SAE and STD horsepower numbers are both set by the society of automotive engineers, and both are corrected to slightly different temperature and barometric pressures. SAE is calculated at 77 degrees and about 29.2 inches of mercury, STD is calculated at 60 degrees and almost 30 inches of mercury. the correction factor differs 17 degrees and .7 inches barometric, the hp readings are approx. 4% higher for the STD reading due to cooler more dense air factored over the SAE measurement. barometric pressure is largest factor, not temp. in our real riding world, you can run pretty close to normal on a hot day, but let the barometric pressure drop or climb in elevation, both result in less dense air, and you will lose hp. for our tens, the hp diff. is generally 6-7 hp lower SAE vrs. STD #.
 
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