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Old 02-14-2011, 07:55 AM
 
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Also what usually is the difference?
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Old 02-14-2011, 08:34 AM
 
Location: un peu près de Chicago
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Default When did HP change from gross to net?

≈ 1971, 1972

Munch on this for awhile ☛ Understanding Gross vs. Net Horsepower Ratings
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Old 02-14-2011, 09:18 AM
 
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In the most simple terms, gross horsepower is what a bare engine (no accessories) running optimal timing through headers is capable of. Net ratings are what the engine produces when all accessories are present and the proper exhaust system is hooked up.

Gross ratings really became nothing more than market speak and are a very unreliable means to quote a vehicles power. Net ratings are truer, but not dead on. The current stanard was refined a few years ago to end number rounding and the practice of some manufacturers to test the engine in a non-showroom way.
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Old 02-14-2011, 10:31 AM
 
Location: Earth
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1972 was the first year for net hp ratings, although I don't know if any engines rated gross were done with headers. Maybe open manifolds.
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Old 02-14-2011, 12:04 PM
 
Location: Victoria TX
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The gross horse power used be listed in the literature as "bhp" for Brake Horse Power.
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Old 02-14-2011, 03:29 PM
 
Location: South Jersey
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and the rating now are SAE hp.. So generally.. Say, a 300 hp engine now would be equal to about 375-385 60's horsepower. A new 550 hp GT500 would be about 675 60's hp. Pretty damn impressive out of a 330 cubic inch engine.,
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Old 02-14-2011, 05:46 PM
 
Location: Earth
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What year did they go to SAE hp?
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Old 02-14-2011, 06:31 PM
 
Location: South Jersey
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Quote:
Originally Posted by Deez Nuttz View Post
What year did they go to SAE hp?
after 2005..

While the late sixties were a golden age of horsepower compared to the late seventies or early eighties, the differences weren't quite as vast as they appear at first blush. A '67 Impala with the 396, rated 325 gross horsepower (242 kW), probably had something like 220 net horsepower (164 kW) in pure stock form -- decent, but no muscle car.

The net rating system was used until 2005, when the SAE issued standard J2723, eliminating a number of loopholes in the existing methodology and requiring an independent observer present when the ratings are measured. Under these new "SAE-certified output" guidelines, some engines ended up with lower ratings (Toyota's 1MZ-FE engine, the 3.0L V-6 in the previous-generation Camry, dropped from 210 to 190 hp (157 to 142 kW) under the new system), while a few actually rose (Cadillac's supercharged Northstar went from 440 to 469 hp (328 to 350 kW). The engines were not actually altered in any way -- the testing methodology had just changed. The new rating method is voluntary, but most, if not all, manufacturers now use it for their U.S.-market cars.



http://ateupwithmotor.com/automotive...orsepower.html
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Old 02-14-2011, 08:40 PM
 
Location: Earth
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A 325 hp 396 that really only puts out 220 hp net? LOL I doubt it's that low. But hey....
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Old 02-15-2011, 09:29 PM
 
Location: Wellsville, Glurt County
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Quote:
Originally Posted by Deez Nuttz View Post
A 325 hp 396 that really only puts out 220 hp net? LOL I doubt it's that low. But hey....
It could be - in 1971 Chrysler published both gross and net HP figures for all of their engines across the board. The most common 440 V8 in their full-size cars was rated 335 gross and 220 net. That's pretty extreme, though... usually it's more like 10-20% lower. There's no reliable conversion because of huge variations in gross testing and reporting methods - however usually if you look at the 1971 (gross) and 1972 (net) ratings - those are basically the same exact motors in most cases so you can "kind of" go back and figure a rough conversion for earlier models by each manufacturer.
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