OverBudget

OK, now that the new C6 Z06 will have a 427 C.I. (small block) with 500 HP, and there will be a new Shelby Cobra with somewhere between 450 and 500 HP coming out in the next year...

How do these numbers (and ultimately performance) compare to the mid years? I read about how the old cars were rated with gross horsepower which is much less that the newer SAE rating, but I also read about how original muscle cars were under-rated for insurance purposes. I read that a 67 L-88 had something more like 560 HP, but when I read that in a modern book, I wonder if they are saying 560 gross HP, or 560 SAE rated HP, or 560 rear wheel horsepower.

This thread can go two ways: the technical of someone describing the differences between gross, SAE, and rear wheel, and two, speculation on how the under rated HP cars of the 60's would rate to the new breed of muscle cars...

SWCDuke

As a general rule of thumb for vintage engines, net power is about 80 percent of gross. The L-88 rating of 560 was SAE gross for a blueprinted example (including head work) WITH HEADERS AND OPEN EXHAUST. Given the high overlap cam, manifolds would likely cut the SAE gross to no more than 500 and mufflers would further reduce output relative to an engine with a street cam. High overlap racing cams that are designed for headers and open exhaust just DO NOT WORK WELL AT ALL WITH MANIFOLDS AND MUFFLERS!!!

Modern engine SAE gross is probably about 10-15 percent greater than net because they have fewer power robbing accessories, like engine driven fans. The difference in air density correction alone is about 4.5 percent.

RWHP corrected to the same air density as SAE net is generally estimated at about 85-87 percent of SAE net for manual transmissions, less for automatics, and this just represents and average for typical automotive drive trains.

Bottom line is that "as installed" with emission controls, mufflers, etc. the new LS7 probably makes as much, if not more RWHP than a blueprinted L-88 with headers an open exhaust.

An L-88 in "factory configuration" with manifolds and OE exhaust, and OE machined heads won't even be close.

The LS7 SAE corrected RWHP will be in the vicinity of 440. The LS7 with a street and emission control friendly cam (that has broad torque versus poor torque bandwidth for the L-88) can make more power than a L-88 in full racing configuration because of the LS7's much more efficient fluid flow and lower internal friction, eventhough is has a longer stroke. The dry sump and low friction piston skirts are the big story.

Duke

SBR

Chuck Harmon built an L88 clone to factory spec and it dynoed at 483rwhp with open headers. He also said that with further tuning he felt that he could get more out of it. Another forum member dynoed his factory L88 at 471rwhp with slightly lower compression but also had minor ignition problems.

JohnZ

The dyno operator at Tonawanda, during a 1992 NCRS plant tour, indicated that their L-88's regularly dynoed around 440-460hp (with stock iron exhaust manifolds and a muffled dyno exhaust); he also indicated that he had seen them on the dyno during his visit at Chevrolet Engineering (with race gas, headers, and an unmuffled extraction system for the exhaust) at 540-560hp, and said "too bad we don't have that kind of setup in the plant" The L-88 was designed for race use with headers and open exhaust, which was good for another 100hp when properly tuned.

SWCDuke

What did L-72s and L-71s make?

Duke

JohnZ

Dunno - the only questions and data noted in the "Restorer" article were for the L-88.