Gross vs. Net horspower–how big is the difference?
Question:
——-snip—— – Hide quoted text — Show quoted text ->BTW, the ‘71 LS-6 was originally planned to be available >in the ‘71 Chevelle, El Camino, and Sprint, but was pulled >from the option list before production began. > ____ _____ _____ _ > / / | | (Dan Carr) – –==== ,—’ `–. > / /__ |____/ |____/ (Research Systems) – –==== `–O—O-’ > / | | (Boulder, Colorado) E_l___C_a_m_i_n_o > 1972 CHEVY EL CAMINO SS-454 (LS-5,at,ps,pdb,ac,cowl,tach,posi,buckets,etc.) > 1968 CHEVY EL CAMINO SS-396 (L-34,at,ps,pdb,tach,posi,buckets,etc.) Hot Rod. > 1971 GMC SPRINT SP-454 (LS-5,at,ps,pdb,cowl,tach,posi,buckets,etc.) Project. > 1968 BUICK GS-COLORADO (350-4,at,ps,pb,ac) Next project. > 1971 BUICK GS-350 (350-4,at,ps,pdb,ac,posi,buckets,etc.) Daily driver. > 1971 BUICK SKYLARK CUSTOM (350-4,at,ps,pb,ac,buckets) Parts car.
All the literature i’ve read seems to point out that the LS6 was available for chevelles in ‘71.. Just a little note
Response:
Hi, I’m currently looking to buy a big block Corvette. I read that Chevrolet switched from gross to net horsepower ratings some time in 1971. The most powerful Corvette made was a 1969 427 which made 435 horsepower (gross). By today’s horsepower measuring standards, about how much net horsepower would this 427 engine make? Is there a conversion formula that can give an estimate? Thanks a lot, Alan
Response:
>I’m currently looking to buy a big block Corvette. I read that Chevrolet >switched from gross to net horsepower ratings some time in 1971. >The most powerful Corvette made was a 1969 427 which made 435 horsepower >(gross). >By today’s horsepower measuring standards, about how much net horsepower >would this 427 engine make? >Is there a conversion formula that can give an estimate?
Alan, Gross HP ratings were last used by GM in the 1971 model year. The government mandated the switch from gross to net ratings. I have one data point for GROSS vs NET comparison. The 1971 GMC Sprint sales brochure shows both ratings for several engines. The two 454s listed (the LS-5 and LS-6) were rated as : HP TORQUE GROSS NET GROSS NET LS-5 454 365 285 465 390 LS-6 454 425 325 475 390 As I have said before on the net, auto makers have frequently inflated and deflated the horsepower ratings of various engines due to marketing, government, and insurance concerns. Only a dyno test can tell for sure ! I would guess that if the ‘69 Corvette 427 was rated at 435 gross HP, it would equate to about 345 net HP. Gross ratings were usually determined from engine tests where the engine had no accessories (fan belts, etc.), and sometimes had no exhaust manifolds. Net ratings are supposedly for engines as installed in a vehicle with all equipment attached. However, both gross and net ratings are measured at the FLYWHEEL, not the rear wheels. So, put a new 310 net HP (or whatever) Z28-SS on a dyno and it would probably pull about 280 HP at the rear wheels. Another thing to consider is that while these old high-horsepower motors ran well straight from the factory, they were often not in the optimal state of tune. An hour or so of fine tuning the carb and distributor could ofter increase the power substantially. BTW, the ‘71 LS-6 was originally planned to be available in the ‘71 Chevelle, El Camino, and Sprint, but was pulled from the option list before production began. ____ _____ _____ _ / / | | (Dan Carr) – –==== ,—’ `–. / /__ |____/ |____/ (Research Systems) – –==== `–O—O-’ / | | (Boulder, Colorado) E_l___C_a_m_i_n_o 1972 CHEVY EL CAMINO SS-454 (LS-5,at,ps,pdb,ac,cowl,tach,posi,buckets,etc.) 1968 CHEVY EL CAMINO SS-396 (L-34,at,ps,pdb,tach,posi,buckets,etc.) Hot Rod. 1971 GMC SPRINT SP-454 (LS-5,at,ps,pdb,cowl,tach,posi,buckets,etc.) Project. 1968 BUICK GS-COLORADO (350-4,at,ps,pb,ac) Next project. 1971 BUICK GS-350 (350-4,at,ps,pdb,ac,posi,buckets,etc.) Daily driver. 1971 BUICK SKYLARK CUSTOM (350-4,at,ps,pb,ac,buckets) Parts car.
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