Horse Power

[Guest Mr. Solutions]

Hi

Can somebody please explain the difference between old horsepower and new horsepower calculations to me, and relate this to my vehicle.

Thanks

[YellowLark]

The changes were in effect for 1972 American-sold cars.

Basically, what changed was including parasitic devices like water pumps and alternators that would be in a production car, as opposed to a test engine on a stand.

Several years ago, I read the specs for 1971 and 1972 for many popular engines, and the reduction in advertised horsepower was 22-25 percent.

So, my 1966 engine with 260 hp would be sold in 1972 with 195 hp.

[NTX5467]

The Society of Automotive Engineers (SAE), I believe, has stated procedures for how these tests were run. In the "gross horsepower" days, it was a bare engine with probably only a water pump, "shop" exhaust hooked to the production exhaust manifolds, AND a carb air inlet temperature regulated to something like 60 degree F. In some cases, these figures were inflated for marketing purposes. There were some engine brands that put out more of their "rated" horsepower than others. Those were very competitive times so everyone had to be in pretty much the "benchmark" ballgame for how much power a certain size motor would produce.

When the "Net" ratings were phased in, the engines were supposed to be pretty much just like they would be installed in the car, plus the applicable vehicle's exhaust system. That would include the alternator and other typical belt driven items too. One main difference was that carb air inlet temperature was now 100 degrees F. (as that was what temp the carburetor calibrations were not designed around with the "hot air" air cleaners).

Just like happened when the compression ratios dropped for unleaded fuel, some engines dropped more than did others. For a few years, many manufacturers put "gross/net" power figures in their sales brochures. Seeking out one of them with ratings for an engine similar to yours might be the only reliable way to project what your vehicle's engine might produce on the "net" side of things.

Hope this helps,

NTX5467