1965 396 hp ratings !

[Steve Antonucci]

Hello all !

Over on the Yenko.net forum, there is a debate over factory hp ratings for the
1965 396 ( L/78 ) engine as related to the Corvette and all other models. The
Corvette showed 425hp and the others showed 375hp. I believe we discussed
this here before as well. According to my research, the Corvette 396 only
used different exhaust manifolds and ignition type. I am not sure if the cam
was the same or not. In 1966, the 427 came into play and it used the same cam
as the '65 396-425hp, yet hp ratings stayed at 425hp. See the dilemma?

Here is what one person added to the debate:

"GM also had a marketing dilemma. The L78 was originally listed as making 425 hp
at 6400 rpm in 1965. Then the L72 came along and that made 425hp at 5600 rpm.
So the L78 was dynoed and became a 375hp motor at 5600 rpm. This arrangement
gave Chevy two distinct levels of hp they could offer the public."

The Yenko.net topic ( link ) is listed below if you are interested.

Can any members here comment on this?

Thanks,
Steve

http://www.yenko.net/ubbthreads/showflat.php/Cat/0/Number/242137/page/0/fpart/1/vc/1/nt/2

[Clem Z.]

Re: 1965 396 hp ratings !

the 396 used in a 65 chevelle Z-16 used a hydraulic cam in place of the solid lifter in the corvette. the very first 66 427 corvettes were rated at 450 HP and later they were rated at 425 HP

[Steve Antonucci]

Re: 1965 396 hp ratings !

I remember that ( now ) Clem. But how did a 396 rate at 425hp in '65 and get
downgraded to 375hp in '66? What exactly were the hp gains using the Corvette
exhaust manifolds and the different ignition? I can't see that totaling 50hp.

Steve

[Wayne M.]

Speaking of other forums, ...

....for you people that lurk elsewhere, anything recent on the Jim Mattison GM (Chev, Corvette) records search/compilation, or is that rumour dead as a doornail ?

[Steve Antonucci]

Re: Speaking of other forums, ...

I hear that was no more...... Wish it weren't so.

[John H.]

Re: 1965 396 hp ratings !

Steve -

Marketing was more involved in advertised horsepower ratings than Engineering.

[Clem Z.]

i am sure the exhaust manifolds made some

difference but how much is a good guess. they just took the HP reading at a different RPM but my guess is that these engines were close to the same in max HP

[Jack H.]

Can't find it now...

But, I had a copy of a Chevy engineering white paper delivering an address to SAE on the 396 engine. Among other things, it detailed nicely how the same basic block was offered in different states of tune for for its different applications (pass car performance, pass car endurance, truck and marine) and that laid to rest how there WERE different 396 engines made from the same basic block....

[Steve Antonucci]

Re: Can't find it now...

Jack!

I'd love to see that.....

Steve

[Mike McKown]

Re: Can't find it now...

'65 Corvette 396/425

'66-'69 Chevelle 396/375

'67-'69 Camaro 396/375

'68-'69 Nova 396/375

All the same as far as any impact on horsepower except maybe the exhaust. The same engine used in '70 with I think a '030 overbore and made it a 402. Same power rating.

I think the '65 Pass car used the same engine after 409 balance out but I wouldn't swear to it.

Just marketing.
Wasn't there a 10 lbs/horsepower rule (Corvette excluded) GM abided by? The other two of the BIG 3 operated the same way.

[Joe L.]

Re: 1965 396 hp ratings !

Steve-----

The 1965 Corvette L-78 and the 1966-69 L-78 used for Chevelles and Camaros were, basically, the same engine. All internal parts were exactly the same or, essentially, the same. Ignition and carburetion was different but, essentially, the same (e.g. obviously the Corvette and Chevelle/Camaro applications would use a different distributor since, with just a few very minor exceptions, only Corvette used a tach drive distributor). Intake manifolds were different but, essentially, the same.

The real differences between the applications was, as has already been mentioned by others, the exhaust manifolds AND the RPM that the engines were rated at. The latter was the biggest factor in the horsepower rating difference.

By the way, the 1965 L-78 used in passenger cars was exactly the same as the L-78 used in Corvette EXCEPT for the distributor. The exhaust manifolds were the same and the engines were rated at the same RPM.

[Dick S.]

Re: i am sure the exhaust manifolds made some

I thought the heads on the 65 Corvette 396 were unique to it. Rectangular ports, large intake valve but small exhaust valve, same size as oval port exhaust valves. I know that they can be identified externally by a triangle cast in the end of the head. I thought the Chevelle heads were oval port. Also wasn't the Chevelle a hydraulic cam? The 65 Corvette is a solid cam.

[Eric J.]

Re: 1965 396 hp ratings !

Steve, The 1965 "Chevrolet Interim Shop Manual" rates both the 'Corvette' and 'Chevrolet' 396 as a 425HP. See attached Eric 3,182

[Eric J.]

Specs from Interim Manual 1 *NM*

[Eric J.]

Specs from Interim Manual 2 *NM*