ps374

According to my Corvette black book the 65 396 had 425 HP. The following year the 427 was first rated at 450 HP and then Chevrolet changed those numbers to 425HP. As far as I can remember no 396 ever had more than 375 HP. Was Chevrolet just playing number games with the public or were those horsepower ratings real?

5thvet

Yes, the 396 in the 65 did indeed have the 425 HP version. You may be thinking of the 375 HP in the Chevelle SS.

Don

Nowhere Man

Take a look at the RPM reading on the ratings

BrentF

Can't speak to the 396 of 1965, but the L72 427 in 1966 was rated at 425 hp @ 5,600 rpm, and 450 hp @ 6,400 rpm. The change in stated HP ratings occurred in the third week of October 1965 according to Noland Adams.

Apparently this switch was motivated by the insurance premiums that high hp cars were commanding at the time and the drag on sales that might have meant for GM and its dealers. Presumably 425 was a threshold above which higher insurance premiums kicked in.

My L72 car was built on October 8, 1965 and currently sports a 425 hp air cleaner decal. I am toying with the idea of switching it over to 450 hp.

RestoMike

Brent......it's only a decal. Wha'ta ya wait'n for....change it.

toddalin

Probably the cheapest, easiest, instant 25 hp gain out there.

Ironcross

the 450 HP engines use the suffix,..'IP' and only a few months into production

BrentF

Here's my engine stamp:



I have the decal on hand. Ordered it this spring from Corvette Central. Wasn't sure what the convention was in C2 land concerning the use of this 450 hp decal?

About $9.95 to be precise. Think the car will go an faster after the decal goes on?

toddalin

Doesn't matter. It will feel about 25 hp faster when you open the hood.

427435

How many of you remember the joke that Duntov made about why the 396/425 hp engine was changed to a 427/425 hp. Basically a reporter was wondering why the hp rating hadn't changed.

Zora told the reporter that it was for a weight reduction as 31 cu. in. of cast iron was a lot of weight.

BrentF

Okay, I added the 25hp this morning. Didn't even get my hands dirty either

kenba

I beleave most 425 HP engines had the IP mine did & it was a midproduction car
KEN

63Corvette

The 396/425 Corvette motor was EXACTLY the same motor as the 396/375 Chevelle motor (rectangular port, four bolt main, forged piston etc). They made exactly the same horsepower (whatever that was), and thus the NHRA "factored" all 396/375hp Chevelles, Novas, Camaros etc at 425hp to drag race. (remember that the "later" 396 engines of all persuasions 325, 350, and 375hp were actually 402CID)

SBR

The Corvette version of the L78 did receive freer flowing exhaust manifolds that would not fit on the Chevelles and Camaros. I am sure it added some power but not 50hp.

ps374

I guess this get even more confusing when you look at the Chevelle LS6 in the 72 Corvette.In the Chevelle it rated at 450 HP but in the Corvette its rated at 425HP ? Is it the same engine in the Corvette as in the Chevelle? Why did the folks at Chevrolet play such number games with the buyer.

62Jeff

They played number games with the insurance companies.

JohnZ

Because ALL manufacturers played "horsepower games" with buyers in the 60's; it was a Sales & Marketing thing, not an Engineering thing in those days.

62Jeff

1970 was the peak of HP in Chevrolet engines.

The LS6 in the 1970 Chevelle was detuned by the time 1971 arrived, thus the 425 HP rating.

There was no LS6 in 1972 for Corvette.

By comparison, the LS5 was rated at 390 horse in the 1970 corvette, but 365 horse in 1971. Then the rating dropped to 270 in 1972 due to the change in Gross versus Net HP ratings.

SBR

Actually, the 71 LS6 vette motor and the 70 LS6 chevelle motor are not the same motor. The chevelle motor had 11 to 1 compression and used closed chamber iron heads. In 71 GM lowered their compression ratio to 9 to 1 for unleaded fuel. Since they did not want to spend the money on developing a new piston, they installed the aluminum open chamber heads which were used on late 69 L88s and ZL1 Corvettes. The larger combustion chamber lowered the compression to 9 to 1. I have been told that the vette motor actually puts out as much or more power than the chevelle motor. When you account for the freer flowing exhaust manifolds plus the better heads, this seems very likely. This explains why the LS6 option was so costly back in 71.

Joe Sprintbros

The 65 was 425 hp. Seems to me the piston for the '65 (only) 396 had slightly different dome giving 12.25:1 compression, instead of the 11:1 for the subsequent year 396's. I may be incorrect, experts chime in!