Greg Clears The Air On The 1965 Chevelle SS396 Z16 And The 396 Engine

Greg Zyla
Q: Greg, I’d like to know more about the 1965 Chevelle Z16 you wrote about in that special “Cars We Remember” section in the Gainesville Sun. Can you tell us more from your viewpoint and why Chevrolet put it out the same year as the Corvette 396, but with the Corvette horsepower at 425? Thanks, Paul S., Ocala, FL.
A: Paul, I’m happy to oblige on those Z16s and the 396 engines. As I mentioned in that special section, the Chevelle debuted in 1964 as the new midsize Chevrolet joining its lineup including Corvette, Corvair, Chevy II and full size Biscayne, Belair and Impala.
The new ’64 Chevelles were available in base 300, 300 Deluxe, Malibu and Malibu Super Sport trim. An L74 code 327 with 300 horsepower was the biggest Chevelle engine available in ‘64, but you could also order an SS with the inline-6 cylinder engine, too. Thus, not all early Chevelle SS models were V8s.
To continue, things were starting to get serious at Chevrolet following the popularity of the 1964 GTO over at Pontiac. While Jim Wangers and John DeLorean were making the GTO the talk of the town in 1964 and 1965, Chevy responded by moving the needle by offering an L79 code 350-horse 327 SS in the ’65 Chevelle line, which was quite the performer but not capable of outrunning a Tri-Power 389 GTO.
And this is where the Z16 comes into play. If you want the insider info I highly recommend taking a look at a great website called Here you will find a five page document from Corporate Chevrolet explaining the “when, what, where and why” of the special Z16 SS396. It’s really a must view and here’s the link to the internal memo:
To those who take the time to look at this memo, it is clear that Chevrolet was full-speed-ahead concerning the muscle car as GTO continued booming. Thus, the 1965 Z16 SS396 was to be the mother ship of the Chevelle performance initiative that to this day is worthy of explanation.
Chevrolet built 200 Z16 coupes in early ‘65, and one convertible. The ragtop was purchased by a Chevrolet employee, but it disappeared after the original owner sold it.
Following the five-page June of 1965 internal memo about the 200 already built Z16s, dealers and public relations firms knew what to expect from this powerful Z16 Chevelle, and the reason it was created. That reason? Total performance excitement and to better introduce the new 396 big-block engine.
Consequently, all Z16s came with the very first consumer available big block 396 engine, which were a direct evolution of the “for racing only” 1963 Mark II big-block canted valve “Mystery Engine” 427s that won the pole for the Daytona 500. This first 396/375 has been many times misunderstood since two 396 engines debuted in 1965: one the Z16 375 horse engine and the second, the 425 horse 396 in the Corvette.
And here’s where the misinformation hopefully clears up.
The engine code for the 396/375 in the ’65 Chevelle SS Z16 is code L37, which differs from the code L78 396/425 engine from the Corvette. The Z16 code L37 came with a hydraulic cam and lifters and a compression ratio of 10.25 to 1. The code L78 1965 Corvette meanwhile was rated at 425 horsepower and came with a more aggressive solid lifter cam and an 11 to 1 compression ratio. Both, however, did have the better breathing larger valve rectangular port heads instead smaller valve oval port heads that came with the 325 horse 396 that debuted in 1966 engine code L35.
The confusion continues when enthusiasts finally realize that the L78, 425 horse Corvette engine is the exact same L78 396/375 engine available in all those Chevelles, Camaros, El Caminos and Novas that cruised the boulevards. I know this engine well, as I had one in my ’68 Camaro SS/RS 396/375. But Corvette already had a 375 horse engine available in 1965 with the 327 small block with fuel injection, so they needed more ponies to advertise from the 396.
And here’s how Chevy accomplished this big horsepower “difference:” The 375 horse L78 and that first Corvette 425 horse L78 came about simply by reading the horsepower output at different RPMs on the dyno sheet. The 375 horses arrived at around 5,400 RPM while the 425 horse Corvette number came at over 6,000 RPM. Thus, these engines are identical.
In summary, those first big-block SS396 Chevelle Z16s are today very valuable as less than 70 are accounted for. And yes, there were two different 396 engines in 1965; the L37, hydraulic cam 375 horse engine in the Z16 and the L78 425 horse solid lifter engine in the Corvette. Then in 1966, the L78 was rated at 375 horses and stayed that way right on through the end of the decade regardless of whatever Chevrolet it powered.
That about sums it up and thanks for your Letter Paul.
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