Topic: 71 vs 72 ratings
in Forum: C3 Engines
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Can anyone shed some light on the power ratings. I knwo that 71 were reduced in C/R as compared to the 70. I believe that the only difference between 71 and 72 was that the power rating was taken at the rear wheels (net) and in reality the 71 and 72 were indentical. Any facts would be appreciated.
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Toledo, OH - USA
Joined: 9/4/2002
Posts: 147
Vette(s): 1976 Stingray, L48 auto Buckskin/Buckskin Leather originally. Numbers matching.
You hit it right on the nose, before 72, the engines were tested sitting on a stand, no accessories, air cleaners or mufflers. To the best of my knowledge, they are pretty much as they were in 71. LS5 in 71 rated 365hp gross, LS5 in 72 rated at 270hp net, showing a 25% reduction. I had always thought the loss was about 30%, then I just read an article that said it was 20%, but when I sat down and figured out the LS5's, it worked out to 25%.
71 LT1@330hp, 72 LT1@255hp = about 22% loss
71 LT1@330hp, 72 LT1@255hp = about 22% loss
'76 L48 Auto
Project
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Former Member
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DOWNINGTOWN, PA - USA
Joined: 11/24/2001
Posts: 962
Vette(s): 1969 Monza Red Black Conv / Black Vinal hardtop
454/480 Tremec 5 Speed 308 Posi.Black Leather Interior, PS, PW, Air cond., tilt/tele,AM/FM Cass.-5 Pack CD, Hurst Shifter, side pipes
2004 Yellow convertible with black top and black interior
I was always under the impression that gross HP was the engine on a stand with no accessories, net HP was the engine on a stand with all the accessories and rear wheel is ( as it indicates ) rear wheel HP. A supposed loss of 15 to 20 % from gross to net and another 15 to 20 % from net to rear wheel.
My 427 is rated 390 gross but the dyno shows 248 rear wheel which is a loss of 142 which is about 36% of gross. Doing the math, that is -78 ( 20 % ) from gross and -62 ( 20 % ) from net, give or take a few. That would all depend on your accessory load and the transmission, clutch or torque converter loss etc.
Hopefully I will get a better feel for this if I ever get my engine back and can assemble it and get it to a dyno for tuning before it goes into the car.
|UPDATED|5/13/2003 10:53:25 AM|/UPDATED|
My 427 is rated 390 gross but the dyno shows 248 rear wheel which is a loss of 142 which is about 36% of gross. Doing the math, that is -78 ( 20 % ) from gross and -62 ( 20 % ) from net, give or take a few. That would all depend on your accessory load and the transmission, clutch or torque converter loss etc.
Hopefully I will get a better feel for this if I ever get my engine back and can assemble it and get it to a dyno for tuning before it goes into the car.
|UPDATED|5/13/2003 10:53:25 AM|/UPDATED|
Not sure if this helps, but I referred to it quite a bit before getting my '79
http://www.cccvette.com/fast-corvettes.htm
http://www.cccvette.com/fast-corvettes.htm
EdelBrock Performer w/ 750 doub pumper,port/polished heads, triple cut valves w/4th cut down the throat of the exhaust valves, 286 Comp Magnum cam, 1.6 roller rockers, ball-peen pushrods w/guides, screw in rocker studs w/girdles, Comp double-roller chain, , hi-rise valves covers w/ spacer (needed for the girdles), Flowtech by Holley long-tube ceramic coated headers into Stage II pipes (no cats), chrome wire looms for the MSD 8.5 mm wires, MSD 50,000v coil kit w/advance springs, cap, rotor, module, steel-braided radiator,heater,vacuum hoses, Infinity Kappa 4x6 plates (dash), Sony Xplode 6 3/4" (rear), chrome T-stat housing, A-arm shields, B&M Hammerhead shifter
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in Forum: C3 Engines
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