Plasticman

November 06 issue of Vette magazine has an article on "The Optispark Option" in which the author makes the statement (comparing the C4 LT1 engine with the 1970 LT-1 engine):

"At the time, the 300hp (net) LT1 was the most potent small-block Chevrolet had ever produced, besting its legendary namesake. (Although rated at 370 gross horsepower, the original LT's true output is beleived to have been in the 270-290hp range.)"

Comments?

Plasticman

StickShiftCorvette

Based on GM numbers for the '71's which were rated with BOTH Net and Gross ratings, the '70 LT-1 would have 315 Net HP. (The '71 LT-1 was rated 330 gross, 275 net).

Many believe that the '70 LT-1 was somewhat underated, so it could be maybe 20 net HP higher.

SWCDuke

The '70 rating was SAE gross. GM did not test SAE net until '71 so only an approximation of SAE net can be made for earlier engines. As a rule of thumb, 80 percent is used, which would yield a little under 300, but in reality the difference between gross and net may be less on a small block in a Corvette because they have a very efficient exhaust system. The vehicle's exhaust system is a BIG determining factor in net versus gross

With some mild head work an otherwise OE '70 LT-1 would likely make well over 300 net.

Recent chassis dyno tests of a '65 L-76 with massaged heads and LT-1 cam indicated about 325 net with the fan clutch "locked", which was probably consuming at least 10 HP. With the LT-1 manifold and a 780 carb this engine would be essentially indentical to a LT-1 except for stroke and would probably make close to 350 net if sufficient cooling flow was available to keep the fan clutch from tightening.

Stroking the engine to 3.48" will not materially increase peak power, but peak power will be achieved at a lower RPM corresponding to the same mean piston speed as the 327.

So with only some head work a '70 LT-1 should make close to 350 net HP, which would be about 300 at the rear wheels.

Duke