Cigarman

I was reading an old Popular Mechanics mag article comparing a '66 and an '88 and the hp was considered to be roughly equivalent:

'88 350 @245 hp (SAE net) at 4000 rpm and 345 ft-lb at 3200 rpm
'66 327 @ 350 hp (SAE gross) at 5800 rpm and 360 ft-lb at 3600 rpm
--'66 calculated at roughly 270 SAE net hp

How is the hp converted from one to the other. What is the meaning of Gross v Net hp (I know that SAE refers to Society of Automotive Engineers Standards) What is the equivalent hp of a 245 C-4 in SAE gross?

Thanks in advance for the education.

Oh, by the way, the '66 stayed "wheel to wheel" with the '88 in everything but the slalom--all stock except with Goodyear Eagle tires for the run.

scorp508

Gross HP is a naked engine mounted on a stand with no accessories. Net is with the entire accessory system installed and turning as it would in the car.

Cigarman

Thanks, Do you know what the conversion may be? I grew up with the old muscle cars and the obsession with horsepower. I'm curious how the C-4 measures up in the old way of measuring power.

scorp508

I honestly don't know. :nonod:

Juliet

The change occurred in corvettes between the 1971 and 1972 model years. The only year where BOTH Net and Gross was listed was the 1971 model year. In 1971 the base engine was 350/270 Gross and also listed as 350/210 Net. The L-46 was 350/330 or 350/275 and the LS-5 was 454/365 or 454/325 I don't have LT-1 specs. By comparison in 1970 the base engine was 350/300 Gross, the L-46 350/350 and the LS-5 454/390. The reductions in Gross was due to the emissions crap they started with in the early 70s. ~Juliet


[Modified by Juliet, 4:43 PM 12/2/2001]

65Z01

That's a tough one because the current rating depends on accessories, exhust configuration and I'm not sure about intake setup on the old Gross rating system.

You might get some idea by comparing 1971 to 1972 Corvette HP ratings as they went to Net in 1972. Consider that the 350 cid AT dropped from 270hp to 200hp, though "EC" was added in 1972 and possibly some internal changes. That's a drop of about 25%. You also can get some idea by considering how much HP is gained from a free-flowing exhuat and some paraistic pulley eliminators or underdrive pulleys on the L98 & LT1 engines.

Lets say a 20% underdrive nets 10hp gain, then would a 100% underdrive (no parasitics) net 50hp?? I've gained about 20-25hp from a rewoked exhaust so would no exhaust past the collectors be worth say 30hp?? If these are close, my bone stock 240 HP net might be 320 HP gross?? This 25% difference would be consistent with the 1971 to 1972 HP ratings change for the 350 CID motor.

jcazin

bout 20% seems to be the rule of thumb; depends on systems the car has, and recent improvement in things, such as belt drive and compressor technology, have made a difference, also. Exact conversion is unique to every car.

silver & red CE

There is no such thing as SAE gross HP. SAE (Society of Automotive Engineers) never recognized gross, because it was a scam. If you look, Chevy claimed the 65 Fuelie motor had 375 gross HP, and the 70 LT-1 had 370 gross HP. But everyone says the LT-1 is the most powerful small block...until the LT1 came out in 1992. Mark McPhail of GM says they pulled out a 1970 LT-1 and tested it. The 1970 LT-1 made an SAE net measurement of 295HP. Then GM tweaked the LT1 until it had net SAE 300HP so they could honestly say the LT1 was the most powerful SBC ever to come from the factory.

Eric

GRX

Great topic!