Where do car makers get their hp ratings for their production cars. We all know it is not from the wheels. Do they all rate the same way ? where do they get the numbers

 

They are all supposed to rate the same way base on SAE standards.

Some manufacturers (including nissan) choose to rate their cars LOWER, but they cannot rate HIGHER.

The actual horsepower is measured at the flywheel, before it goes through the transmission/driveshaft/wheels/etc.

 

So The Gtr Is Rated At The Flywheel?

 

by SAE standards it should be. Though you gotta remember the GT-R is hand built, everything is built custom for the engine after wards as well. They advertise 480hp but some have been tested as over 520hp. (that info I got from Top Gear).

 

factory hp numbers take into consideration drivetrain loss like mike mentioned. usually 15% for manuals and 20% for autos. so if you take dyno #s and multiply for loss -that should be about your crank hp.

top gear and other sources get confused with the gt-r. its rated 480hp at the crank but has been dynoing higher than a normal car would. they assume its because nissan underrated the hp. however, nissan has repeatedly stated that the gt-r only sees about 10% loss because of its special drivetrain.

 

If only someone measured the hp at the flywheel...

Of course that would require specialized equipment, but I'm sure porsche/GM/etc have already done it...