Senior Tech Team
Join Date: Nov 1999
Location: Whittier, California
Simple Chevrolet fact, in 1966, they did offer a 396/425 horse engine for their larger cars, but customers were reluctant to order the 427/425, thinknig that they didn't need the larger displacement engine to do the same work as the 396, so the R&D engineers did a fast one on the 396/425.
They ran one on a dyno, and recorded the rpms at which it made 375 horsepower, and re-certified the engine. Customers didn't question the need for the 427 after this. The rpm levels tested were 396-6800, 427-7250. Both engines were same-same except for the bore sizing.
The 396/425 was only available in 1966 vehicles for about a month, and I haven't ever come across a factory installation of one, documentation or specs on installed units. The factory might have killed the RPO before they actually installed one in a vehicle.
1965 Z16s did have different cams, hydraulic, but were performance equal to the solid lifter engines, just 50 horsepower resiricted by the stock 396/325 exhaust manifolds used to clear the Chevelle frame.
Corvettes used a cast iron 4 into 1 header (carry-over from the 396/425), and a modified version of this header was also used on Impala and Caprice in 1966, Chevelle had even a different one in 1966/1967 for the 396/375.
[This message has been edited by IgnitionMan (edited 04-21-2000).]