Factory HP ratings -BS or what happened?

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zkx14

zkx14

Duster De-ruster
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From its beginning (I think) the 225 slant was rated at 145hp. In 1972 it dropped to 110 hp and by '75 it's down to 95 hp. Are these number real or what where did the power go? (other engine sizes had big drops same years, but just looking at the 225 here)

I saw the recent dyno results on Power Nation slant build. They test the tired old engine at 70hp - OK, whatever. The reworked one with a four barrel and 8 degrees advance still only gives 130? How did a factory 1bbl ever give 145hp?
 
depends on how it was rated,,,,with or without assesories ....which rating changed some where in the early 70s....

power nation dyno probably can give you any number you want
 
145 HP was flywheel HP with NO accessories, etc. The 70 and 130 HP was wheel HP. You can figure out the percent loss in the drivetrain and extrapolate what the estimated flywheel HP of the modified engine is. The numbers come out to about 204 HP at the flywheel.
Keep in mind that numbers can vary significantly between dynos.
-Matt
 
Prior to 1971-72 (?) horsepower ratings were sort of a free-for-all. If I was running an engine for power ratings, I wouldn't have to run any engine accessories and could run a tuned header if I wanted. Air filter, smog equipment; nope could ditch that too. I could also tune the engine for peak power while the engine was running. This means I could retard the dizzy to start, then advance it to optimum at higher rpm. Not only that, I could jet the carburetor for maximum power.

The SAE standard that had to be adopted in 71 or 72 cut a lot of that non-sense out. Engines were required to run with accessories the model car came equipped with. They also had to run a full exhaust system. Remember that by 1975 just about everything was trying to exhale through a catalyst. The result was plummeting horsepower and confused people wondering where it went. The short answer is some of it went to smog abatement the rest went to method of measurement change.
 
Thanks guys for pointing out some of the variables.
I think what 2 Darts said about the adoption of the SAE standard is the big thing I was missing.
Keith
 
X2 with all above. Really the numbers were being manipulated to pacify Insurance companies more than anything.There were Many fatalities with the muscle cars, and theft was rampant. Insurance companies needed to be convinced that Horsepower was being reduced, which in turn supposedly reduced claims.
 
I also believe that the engines that the hp and torque were based off of were probably as close to dimensionally perfect as possible. Thus the "blue printing" of engines. Lot of variables tie into mass production.
 
The factory HP ratings are dead BALLS accurate for how THEY measured it. You measure it the same way and you will get very close or the same results.
 
The drop in compression wasn't the only thing. They also went from measuring gross HP to net HP. That made a bigger difference than the compression change.
 
were they already diluting gas back then ?
that sure would account for some of it
 
IMO, gas has been cut for a long time. I remember pumping gas when I was a kid in the 70s that some of the gas smelled like it had diesel fuel in it then. When I mentioned it to friends, they agreed. Who knows, really?
 
If the 225 was refactored from 145hp down to 110hp, I wonder what the little 170s 101hp would be factored down to?!

Honestly, if my little 170 didn't put down close to 70hp at the wheels I'd be stunned. That little bugger feels way to peppy to be that little hp!
 
trapster said:
Didn't they also drop the compression ratio's in 72 on the slants ?
Click to expand...

They might have changed the advertised CR, but the factory specified dimensions that affect CR never changed. I have seen slant CR's listed any where from 8.2 to 8.4, but have never actually measured a slant that had more then 8-1 from the factory. Most were in the range of 7.8- 7.9
 
Here's some data from Allpar. Most of it is '68, but near the end is a chart of CR and HP for various years. Rated compression remained at 8.4 through most years. The RPM they rated at changed.

http://www.allpar.com/mopar/V6/slant-six-specs.html

I guess it's like most statistics. They can be manipulated. You can usually get the number you want by changing other variables.
So what I'm getting is that the engines of the 70s were nearly the same as the earlier ones. Just that they have been bogged down some by emissions, and they were measuring with a different yardstick...
 
To me, the SAE numbers were the closest to being correct at the rear wheel.
The Gross method was manipulated by the manufacture for advertising or taking advantage of race rules.

Also, when SAE number started being used, it also help with the insurance rates some.
 
mikedevore said:
To me, the SAE numbers were the closest to being correct at the rear wheel.
The Gross method was manipulated by the manufacture for advertising or taking advantage of race rules.

Also, when SAE number started being used, it also help with the insurance rates some.
Click to expand...

I don't know.....that would mean an LS6 Chevy would have 460 HP at the rear wheels. Somehow I doubt that.
 
mikedevore said:
To me, the SAE numbers were the closest to being correct at the rear wheel.
The Gross method was manipulated by the manufacture for advertising or taking advantage of race rules.

Also, when SAE number started being used, it also help with the insurance rates some.
Click to expand...

No, they were never intended to represent rear wheel HP. Just flywheel HP with all normal accessories, full exhaust and factory tune.
 
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