[supersport#69]

I’m sure I could search this somewhere but taking a shortcut.

So I had a 1968 Camaro about 13 years ago with m21 and 396 engine. When I had the engine rebuilt I requested the specs similar to L78, which was 375 option for that 396 that year or in 69.

Since GM based gto horse rating on hp per lb, did the do the same for other brands like Chevelle and Camaro?

Also, although I haven’t mashed on my current 68 400 HO option just shifting gear to gear it sure feels like more power/torque than my Camaro did. The Camaro had oval ported heads with air gap intake, msd, rv level hydraulic cam, headers, about 9.50 compression pistons and 3.73 gears in rear. (Not a race engine but a few upgrades to gain the l78 equivalent I wanted)

The gto is stock everything with 3.55 out back and wider pipes.

To me why this gto feels more powerful even being heavier, and stock 360 hp. Opinions?

[ponyakr]

Longer stroke producing more low end torque, maybe ?

[supersport#69]

I know there’s tons of variables here but it surprises me how an unopened stock motor feels like it more powerful than that 396 .30 over and “upgraded”

[b-man]

The Chevy 396 actually has a slightly longer stroke (3.76") than a Pontiac 400 (3.75").

The Pontiac head has smaller high-velocity intake ports than a comparable big-block Chevy, which is likely the reason for the better low-end and mid-range power.

The Pontiac cast iron Quadrajet intake used was pretty much a copy of the earlier aluminum 421 Super Duty 4-barrel runner design. This cast iron Quadrajet intake which was used on Ram Air and High Output 350, 400 and 455 engines as well as run of the mill street grocery-getter 4-barrel engines runs as well as or better than many supposedly superior aftermarket intakes.

Pontiac engineering simply had the right recipe for strong street performance engines.

[ponyakr]

" The Chevy 396 actually has a slightly longer stroke (3.76") than a Pontiac 400 (3.75")..."


I never knew that til now. Never bothered lookin it up. I drove a few SS 396 Chevelles, but never built a BBC of any kind. I just assumed that since the 454 had a bigger bore & shorter stroke than a Pontiac 455, that the same was true for the 396 vs the Pontiac 400.

https://www.google.com/search?rlz=1C...30.tiqBuQuRuts

Maybe the big solid lifter cam used in the 375hp 396 produced less low end torque, which made the Pontiac 400 feel stronger in the low rpm range. Or, maybe not. I certainly don't know.

[supercar]

With all due respect, the way that 396 was built was nowhere near an L78 396/375 engine. The L78 375horse engines had square port cylinder heads, 11:1 compression, and a pretty aggressive solid lifter camshaft. You can not compare that to a 396 with oval port heads and an rv cam. I have run a bunch of big block chevys over the years and I agree that a good running high horse Pontiac is more enjoyable to drive. I currently have an LS5 454 with a hydraulic roller in a 70SS454 Monte Carlo that does a good job.

[supercar]

As B man said, Pontiac engineers had it right for street driving. Low end torque and mid range second to none. In a drag race the Chevy really starts breathing on the big end due to their staggered valve setup. However, a lot of races are won before the rat motor gets into top end mode. I had a really strong 69 GTO with a 350 horse 400. I let my Camaro buddy drive it one day going to the parts store and he couldnt get over how smooth and powerful that car was. It would outrun his hot rod Camaro with the air on!

[gtokid1968]

Pontiac rule Chevys drool!
No misplacement for displacement!

[supersport#69]

oh I know I didnt have the right parts. The only thing maybe in common was it was a 396 engine and according to shop is was around 375 hp. With a Muncie close ratio and 3.73 seems it would have been the other way around.
I have no way of telling for sure since I wasn’t provided a dyno sheet. Just simply saying my 375 (if right) sure didn’t feel like this unopened stock 400 ho.

QUOTE=supercar;5971925]With all due respect, the way that 396 was built was nowhere near an L78 396/375 engine. The L78 375horse engines had square port cylinder heads, 11:1 compression, and a pretty aggressive solid lifter camshaft. You can not compare that to a 396 with oval port heads and an rv cam. I have run a bunch of big block chevys over the years and I agree that a good running high horse Pontiac is more enjoyable to drive. I currently have an LS5 454 with a hydraulic roller in a 70SS454 Monte Carlo that does a good job.[/QUOTE]

[300deluxe]

My 68 Lemans H/O is a little 350 with 320 hp. MY buddy has 69 Chevelle with a 396 325 hp engine. My car feels more powerful, but also my car is lighter, and my trans is manual and he has a turbo 400.

[supersport#69]

I figured chevelle and gto/lemans would be the same as Chevelle or less actually with full frames.

I didn’t think of the weight of man/auto trans. I assume significantly more for the big 400 auto.

[dataway]

Can't be a big weight difference between auto and manual ... I can lift a TH400 and put on my bench. And can't be much of a difference between a clutch/flywheel and a converter/flex plate.

I would maybe guess that a four speed manual actually weighs more than the auto.

[north]

As installed a Muncie M20 weighs 21 pounds less than the standard M13 floor shift 3 speed. A TH400 adds 38 pounds over the 3 speed weight so 59 pounds is the spread between a Muncie and a TH400. By as installed I mean I’m taking into account the weigh difference for bell housing, flywheel etc so the weights I mention are the actual change in car weight.

[A Schab]

The first L78 in 1965 was rated at 450 hp then lowered to 425hp.

[dataway]

That's surprising ... is the case on the 4 spd. aluminum or cast iron?

Also ... I forgot all the fluid in an Auto .... converter isn't bad empty, but they probably hold about eight pounds of fluid.

[north]

Muncie 4speed has an aluminum case and tail so is lighter than the Saginaw 3 or 4 speed (not used on the GTO) and much lighter than the Ford toploader M13 that was standard fare on the GTO.

[dataway]

That explains it, didn't realize the 4-spds were alloy cases.

[geeteeohguy]

Originally Posted by north

As installed a Muncie M20 weighs 21 pounds less than the standard M13 floor shift 3 speed. A TH400 adds 38 pounds over the 3 speed weight so 59 pounds is the spread between a Muncie and a TH400. By as installed I mean I’m taking into account the weigh difference for bell housing, flywheel etc so the weights I mention are the actual change in car weight.

That's without the torque converter. With converter, a TH400 is about 100 pounds more than a Muncie 4 speed. At least I think so... As to the original post, Pontiacs produce more low end torque than Chevrolet, which on the street, wins races. Way back in the day, a colleague of mine replaced the 400 in his '67 Firebird with a 396 Chevy. We raced it against my '67 GTO convertible, base engine, with 170,000 miles and a burnt exhaust valve. Possibly the worst beating I ever gave anyone. We're talking bus lengths. I much prefer the small block Chevrolet engines on the street. The big blocks never impressed me.

[dataway]

I'd believe the 40 pounds ... no way 100 pounds. I can lift a TH400 with converter (no fluid) and put it on my work bench. I'm stout, but not that stout.

Bear in mind the very robust flywheel and clutch on a manual, has to be about the same weight as a converter.

Not to mention the giant over sized heads on the owners of manual gearboxes

[geeteeohguy]

Originally Posted by dataway

I'd believe the 40 pounds ... no way 100 pounds. I can lift a TH400 with converter (no fluid) and put it on my work bench. I'm stout, but not that stout.

Bear in mind the very robust flywheel and clutch on a manual, has to be about the same weight as a converter.

Not to mention the giant over sized heads on the owners of manual gearboxes

Well put! I actually checked into it, and the consensus is that a dry TH400 without converter weighs 134 pounds. A Muncie 4 speed alone and dry weighs 76 pounds. So, about a 60 pound difference between the two, as bare units.