Does anyone know how the factory figures horsepower ratings on engines? I was just wondering if the figure it at the crank or at the wheels.
Thank you
Mike

 

It was a standard that measures flywheel horsepower. The standard has changed over the years but all are flywheel based.

 

Thank you, That clears things up for me, I just couldn't figure out how a the 455 had so many different horsepower ratings for the pre. 73 smog engines.

 

Don't forget that in the 60's and early 70's fudging of numbers was common by all manufacturers. Case in point: 1970 Toronado GT rated at 400hp while the 1970 W-30 442 is rated at only 370hp yet it has a much larger cam. Although I believe the Toronado figures the W-30 is clearly skewed. Probably for insurance reasons.

 

OK so 1970 W-30 had 370 hp at the crank, so if it had a automatic trans, I figure the hp at the rear wheels would be 297 hp according to my hp calculator.

 

I guess my point was that the figures for horsepower at the time were inaccurate and skewed for any number of reasons. Although probably correct for some models others were not. Trying to figure out a real number is probably futile.

 

I got, Thank you!

 

I remember a discussion about the published horsepower numbers where one of the Daves (can't remember which one) said his W-31, rated 325 HP from the factory, actually dynoed at 325 HP @ 5400 RPM but it kept increasing from there. I think he said it hit 360 HP @ ~5800 RPM before something happened with the dyno. He also said he regularly ran it well over 6000 RPM.

 

I think it was 1972 when they changed the way they measure the hp. They started putting all the accessories on the engine and I believe manifolds instead of headers for the dyno. There is a thread about all this somewhere on here.

 

Yes, 1972 was when the rating method changed to reflect accessories hooked up and exhaust as well. I believe it also was now measured at the tailshaft of tranny instead of flywheel but not sure on that part. For comparison a 1971 and 1972 Pontiac 400 4 barrel dual exhaust engines are virtually identical specs and both 8.2:1. The 1971 is rated 300 bhp and the 1972 SAE Net HP was rated 250 so this should give you a good idea of the power losses in the way it's measured . Also of interest is in the 72-74 years the Chilton's manual lists single exhaust and dual exhaust differing HP ratings on some 2 barrel and 4 barrel engines. Then of course the 1975 pellet style Catalytic converter on all just killed it besides the further lowering of compression ratios.

 

Thank you guys!

 

you may notice that the published HP figures circa 1970 are CONVEEEEEEENIENTLY
maxed out at 1 HP per 10 lbs of vehicle. 400 HP in 4000 lb Toro; 370 HP in 3700 lb 442. HP readings produced and recorded can be tailored to suit the needs at the time. Select the RPM you read at, vary the timing, intake air temp, engine temp, etc. You tell me the W30 motor should make 370 HP and I can provide that result. Assuming of course that actual capabilities with everything optimized is at least that large.

 

I agree with all comments but another factor might have been available rpm. I have heard of a lot of spun bearings especially oldsmobiles and Pontiacs. I also agree that back then they downplayed the horsepower for insurance purposes. I grew up in the late eightys early nineties and iwas racing and always enjoying these car and my insurance was for liability about 120 a mth and no crashes. remember the technology then was compression and rpm plus a supporting cast behind it and below.