I was just wondering what the differences are between SAE net horsepower and gross horsepower ratings. My uncle, who owns a 1967 impala SS 427 which I think is rated at 385? He gives me a hard time about how weak horsepower ratings were common in the 80's and 90's. To some extent he's right but his is rated in Gross while today's are rated in SAE net. I was wondering about how much power my 89 iroc would have if it was gross rated. I know it is nowhere near the '67 but hell the new fbodies are probably right up there. Factory it came with 230hp and 300ft/lbs. If anyone can figure it out let me know.

------------------
1989 Iroc-Z. 305TPI 5spd, G92 (230hp/300ft/lbs). 91-92Z28 groundeffects. Corvette Admiral Blue Metallic paint. Thermomaster chip, 160*stat & fan switch, Bosch +4 plugs, MAF screens removed, custom ram air, Flowmaster cat back, K&N, adj. fuel pres. reg.
72,000 miles. SWEET!!

 

net hp is with all the accessories, gross was without accessories..

230 would be roughly 265 i believe

 

It wasn't just without accessories, the manufacturers would time the ignition and jet the carb for maximum performance before making gross horsepower measurements. The net measurement is taken with accessories and with the engine tuned as it is when delivered to the customer.

------------------
1984 Camaro Z28 Astral Silver w/ 2 1/2" cowl induction hood
Engine: Decked 385 cid 4 bolt w/ oil cooler, 9.6:1 compression, ARP fasteners, 600 cfm Performer carburetor, Torker II intake, Performer RPM Heads, XE268H cam, Magnum roller tip rockers, MSD6AL ignition, Blaster2 coil, recurved HEI distributor
Exhaust: Terminator headers, Custom 3" TIG welded stainless exhaust, Twister muffler
Transmission: 4L60 w/ Corvette servo, .500 boost valve, TransGo 7-CS clutch springs, 700 PKH pump rings, 700-2 reprogramming kit, Borg-Warner High-Energy frictions & bands, 2400 RPM lockup torque converter
Drivetrain: 2.73:1 limited-slip Dana 44 w/ disc brakes
Tires: Front P225/50VR15 Rear P265/50VR15 Eagles

Because you can always sleep in your car, but you can't drive your house.

[This message has been edited by Apeiron (edited January 22, 2001).]

 

Is there some sort of equation you use to interchange the two numbers?

------------------
--Steve S--
1984 Trans Am 305 LG4, 5 speed Auto
RPO codes point to Recaro version
Daily Driver, Flowmaster 80 Series

 

I heard that net hp is about 25% less than gross. Therefore 400 HP Gross rating would be roughly 300 net.

BUT, this is more accurate for small block V8s. In the 60s, while they did use the Gross system, most of the manufacturers underrated the Big Blocks for various reasons, like insurance.

A great example is the L88 427. It was rated 435 HP, but closer to 500 something. Same with the 426 Hemi. So your uncle's engine may be rated 385 Gross, but you may find that it is closer to 385 Net.

There were a lot of "number games" played during the 60s.

 

Change "gross" to "net" in this sentance.


------------------
West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

Sorry, my bad.