HP rating for 396???

[crebo]

Hello everyone,
Have a question about the BB 396. Without sounding stupid....Hard for me sometimes. Anyway my car is almost done. 77 putting a 396,427 heads,Holley 800 cfm carb., 700r4 beefed up from Bow Tie overdrives, and 2 1/2in exhaust.

All that for this simple question. I've heard alot of people say that BB engines have more horsepower than claimed. I've been told that mosts of the chevy BB's have roughly 50-75 more horses than documented. If that is true is it due to the low emission years?---or was someone just pulling my chain? I'm happy with what ever the rating 325-375 HP but HEY the more the merrier.

I plan to get in dyno'ed when complete. Just wondering if anyone can straighten me out. Does anyone know whether or not this is in fact true???
Thanks Ashman
Just wanted to say CAC is awsome.

 

[Tom73]

A lot of the high performance big blocks were under rated. Like the L88, rated at 430hp. You could get the tri-power 427 rated at 435hp. But in the real world the L88 had 100-150 more hp. They did not want people buying the L88 for street use. Also, and this is just my opinion, the insurance companies back they had a huge effect on power ratings. Companies tried to hide the high hp cars from the insurance companies.

tom...

 

[crebo]

Thanks Tom,
I heard alot about the hp in the big blocks. I hope I'm looking at alittle more than 375.
Nice looking cars on your page. That is my next vette. I actually wanted a 71 but the cost and the time pushed me up a few years.
Ashman

 

[rwd]

A few of the super bb's- the ones they left the heaters and radios out of the cars with- were underrated. The typical consumer versions more or less followed marketing conventions. The dyno figures I've seen put the stock 390hp 427/454 at around 325rwhp through the stock exhausts. Headers and sidepipes take it back to 390rwhp or so. The torque likely would be similar. The stock '71 and later are lower, primarily due to a revised rating system and lower compression.

It might be worth reviewing the rest of the driveline parts; that's a lot of power compared to what the stock powerplant delivered. FWIW.

 

[crebo]

Thanks RWD,
My rear-end is my next project. I've been told whether I want to or not that theres a good possibilty it will have to be upgraded. I really don't know exactly what I'll have to do. First I'll see how I like the gearing....Then I guess I'll go from there.
Ashman

 

[76L82]

Crebo - Sounds like you got yourself a beast! As you know, there were several 396 BB offerings from Chevy. If I can recall, I believe that two separate 396 packages were offered in the Chevelles and they had quite a difference in horsepower...the 396 they wedged into the Camaro, in the 1968 SS, had 350 HP. My Camaro book also says that they stuffed the 396 in the Z28 package and it had 375 HP. I also believe that the 396 being offered in the 70 Camaro SS was actually a 402 cubic inch engine...the 396 block was actually punched out .032 in. In addition, the 70 396 (402) was a 2 main engine and not the 4 bolt like the earlier 396's.

Irregardless, the 396 was a hell of an engine!! I remember cruising around my part of the world and everytime the 396 Chevelles showed up..you knew who the boss was! Damn, I miss those days!

When you get the engine all done...could you post a picture of the engine compartment? I would sure love to see a 396 in a late 70's Vette...that's the way they should have made them!

 

[Tom73]

The dyno figures I've seen put the stock 390hp 427/454 at around 325rwhp through the stock exhausts. Headers and sidepipes take it back to 390rwhp or so. The torque likely would be similar. The stock '71 and later are lower, primarily due to a revised rating system and lower compression.

Are you talking Rear Wheel HP or are you referencing NET HP. The 390 is Gross HP. A good guess would be that a 390 Gross would end up at about 325 or less NET HP. Then rear wheel HP would be down towards 250 rwHP.

tom...

 

[topless82vette]

wasn't there a 396 that was rated at 425hp ? was a yenko conversion I believe

 

[RalleyRed]

The 1965 396 Corvette was rated at 425HP

 

[crebo]

If the 396 is roughly 325-375hp? What type of hp would 402 have? My block has been bored so I'm looking at eh 402.
I plan to get it dynoed when complete. I'll post the data if anyone is interested.
Another question......is that 325-375 at the rear wheel?
How did they change the way hp was rated?
Thanks everybody for the info.
----Soon I'll have to find out about rear end mods----

 

[Tom Bryant]

.
Another question......is that 325-375 at the rear wheel?
How did they change the way hp was rated?

No. Engine horsepower before 1970 was flywheel rated with no accessories like alternator or water pump drawing on the engine. This was a gross horsepower rating. In 1971 they went to a net horsepower rating that was closer to the rear wheel horsepower. 396s were available in Chevelles in 1965 in 425hp rating; in 1966 in 325hp, 360hp, and maybe the 350 hp. It's been a while. In 1967 there was the 325, the 350 and maybe the 375 late in production. In 1968 the Chevelles stayed the same and the Nova and Camaro got the same options in SS versions only. There was never a big block or anything other than the 302 in the 1967-1969 Z28s. 1970 Zs used the LT1 only and the L82 at the end. (1974) 1969 396 availabilty was the same as 1968.

In '1970 the 396 was actually a 402 but I'm not sure if the horsepower ratings changed.

 

[Tom73]

Another question......is that 325-375 at the rear wheel?
How did they change the way hp was rated?

Back then the rating was Gross HP. This is taken on an engine dyno at the flywheel. Gross is the engine without any accessories. Open air intake, headers and open exhaust, no alternator or other accessories, no emission controls. Just the max amount of power the engine can make.

In 72 they changed over to NET HP ratings. This is also done on an engine dyno and power is taken at the flywheel. But for net ratings the engine is as it would be in the vehicle, real world power. It has the stock air intake assembly, stock exhaust manifolds running out through stock exhaust system, alternator in place, and all standard emission equipemnt (AIR pump, cat converters, etc).

Then you have Rear Wheel HP. That is a speed shop thing with power readings taken at the rear wheels on a chassie dyno. Chevy has never used RWHP ratings for anything.

tom...

 

[Tom Bryant]

I think you are more correct on how the net rating was achieved than I, Tom. Also on the net rating starting in 1972, I was thinking of the lower ratings in 1971 but those were due to lower compression ratios. Thanks for clearing this up.

Tom

 

[crebo]

I appreciate the way you guys broke that down for me. Now all of it makes alittle sense to me.

 

[Yoda]

A little more information to cloud the waters. Here again memory..

Me thinks: The lower hp 396 and other big blocks had the oval type ported heads and the higher hp head where square ported and where refered to as Mark IV big blocks. The oval ported heads where also refered too as closed combustion heads and the square ported where refered to open combustion heads.

BudD

 

[Gunther]

Hi
Yes, I think they are all underrated.
My 68 Vette has presently a 68 Camaro 396 CI engine installed.
This is a 4 bolt block with L71 type heads and was rated at 375 HP in the Camaro.
Now, exactly this same engine was installed in the 65 Vette and rated at 425 HP.
The reason it was underrated in the Camaro was a weight to HP restriction, which the Vette was excempt from.
So, why should it not still be underrated in the Vette.
The potential HP output of all engines was underrated on purpose for warranty reasons and to make up for the small possible differences between the engines.
The only way to find out is to put it onto a dyno.
Of course, this older engines had flywheel HP, not rear wheel.
All big blocks are great and I don't think that for normal street use, this 2 or 4 bolt main thing makes a difference as you drive with low RPM torque more than with high RPM racing HP.
Gunther

 

[Tom Bryant]

And to cloud it even further rectangular or square port heads are available in either open or closed chamber depending on application.

Tom

 

[crebo]

My plan was to have roughly 300 hp on the ground. Either way I should have more than enough horses for my stinger..
If not it should still be a big difference from stock 350.....
I'm just hoping with all this work being done I can keep it running cool....To add to that I'm in the desert.
Thanks again

 

[76L82]

Crebo - If you were looking for at least 300 HP...you're probably already there. Considering that the 70 Z-28 with the LT-1 had 315 HP, I would have to think that if your 396 came out of a Chevelle or something like that...you're over 300.

This is probably a stupid question but have you already decoded the engine? I may have missed that through this thread.

 

[wagonmaster]

396 H.P.

The '65 396 Corvette did have 425 H.P. with the same rectangular port 427 heads that you have, a 750 Holley and a solid lifter cam. We had one and it was quick! Add headers and good ignition and you should be close!
The '70 Z-28 had 360 H.P. from it's 350, while the '70 LT-1 Corvette had 370 H.P. from the same engine.( Not a factor here, but I felt the need to correct someone's mistake.)Good luck with your car!
Joe