rear wheel HP ??????

Buckhunter125@h said:

how much HP do you lose from flywheel #'s to the rear wheel #"s ????? ...................... 68 FB 302 4 speed

Also how to the factory #'s compare to todays #'s ............... for example if an engine was factory rated at 300 hp in the sixties and seventies , I assume that was at the flywheel ??????

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You lose approximately 17% through the drivetrain at the wheels, but dynos will differ.

Ratings back in those days were way overrated IMO. 300hp back then was probably more like 200 by todays standards. And yes they rated everything at the flywheel.

Fast63 said:

You lose approximately 17% through the drivetrain at the wheels, but dynos will differ.

Ratings back in those days were way overrated IMO. 300hp back then was probably more like 200 by todays standards. And yes they rated everything at the flywheel.

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The general rule is 15% through manuals and 20 through autos, but those #'s vary from transmission to transmission (a C6 usually sucks more out than a C4, etc). Plus, it isn't all just a percentage... there's a basic amount that it takes simply to turn the transmission, and then after that as you make more power you start losing a little more because more heat/friction.

Basically the only way to tell for sure is to get a rear wheel dyno and a separate engine dyno.

And what Fast63 says about HP ratings is true. The old 69 351w's that were rated at 290 hp definitely do NOT put the same power to the ground as a 290 hp 2007 BMW etc. Old A colde '225 hp' 289s have been known to put less than 150 to the wheels stock.

Another illustration with the 4.6L-3v motors on the 2005-2009 Mustangs. 300 hp rated by the factory works out to about 265 rwhp manual and say 245 rwhp with the automatic in real life dyno pulls. Some engines make more and some less that is about what I see reported on a bone stock motor.

shatter said:

Another illustration with the 4.6L-3v motors on the 2005-2009 Mustangs. 300 hp rated by the factory works out to about 265 rwhp manual and say 245 rwhp with the automatic in real life dyno pulls. Some engines make more and some less that is about what I see reported on a bone stock motor.

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I was pretty sure (I posted on the 05 Mustang Tech forum for the first year it was out) that they were dynoing in the 27x rwhp range (ie, they were a bit underrated). Been a while, but 265 (and especially 245) seem low.

That said, it was primarily because they were a bit underrated if anything. Kinda like the 03 Cobras, which put down 365 rwhp stock regularly (rated at 390, most actulaly made 420 or so).

The 99-04s put down somewhere in the 230s, I believe.

im losing about 250