63 engine specifications

[Bill #36445]

Would anyone be able to tell me the differences between the 250hp, 300hp, and 340hp 327's available in '63? I'm looking at purchasing a '63 with a 250hp engine and I would like to know what could be done internally to make this engine more powerful while still remaining faithful to a stock '63 engine option. I don't want to make this into a rumbling street machine but would like to get more life out of the engine. Were there any differences between the major components (block, heads, manifolds) that resulted in the higher horsepower or were the differences related to things like the cam, carburetor, pistons, etc? I would also like to know if the base motor used 2-bolt main bearing caps or 4-bolt caps; what did the other hp variants use? Your help would be greatly appreciated.

Thanks,

Bill #36445

[Len Rayca]

Re: 63 engine specifications

Bill: All the engines used the same casting number for the blocks. The heads for the 250HP engine were different than the optional engines, #3795896 vs
33782461 for the optional engines, In addition the carburetors were different for the 250 HP and the others as well as the manifolds and the cam. In addition the ID# stamped on the pad of the block would identify what the engine was built as originally at the factory. Hope this helps you with your thinking. Len

[Joe L.]

Re: 63 engine specifications

Bill-----

There were lots of differences between the 1963 small block variants. However, the blocks were all the same. All were of 2 bolt main configuration as were all 327 cid small blocks ever produced by GM.

The 327 250 cylinder heads were unique to that engine for 1963 Corvettes. These were GM casting #3795896. These are "small valve" heads which use 1.72" intake and 1.50" exhaust. All other 1963 Corvette engines used the GM #3782461X. These heads use the larger 1.94" intake valve size, although the exhaust valve size is the same as your heads. Due to a slightly different combustion chanber design, the 461X heads have a slightly larger chamber volume, too. Externally, the heads look identical except for the casting mark on the ends of the heads. Your heads will have a rectangle with a triangular peak; the "461x" heads have the "double hump" so-called "fuelie" heads.

Your camshaft is the same as the 300 hp engine, but different than the 340 and 360 hp. Yours is a medium performance hydraulic lifter; the others are SHP mechanical lifter.

Your intake manifold is also different than all of the other engines. It is a cast iron unit of GM #3783244 and it's designed for use with a Carter WCFB carburetor. The cast iron unit used on the 300 hp engine is similar to yours in configuration, but it's designed for the Carter AFB carb. Basically, the carburetor and exhaust were the only difference between the 250 hp and 300 hp engines. The 300 hp engines (except with Powerglide) used 2-1/2" outlet manifolds and exhaust while 250 hp used 2" outlet manifolds and exhaust.

The 340 hp used a high rise aluminum intake manifold with the same carburetor as the 300 hp. The 360 hp was, of course, fuel injected and did not use a conventional manifold. 340 and 360 both used 2-1/2" outlet exhaust manifolds and exhaust pipes.

Internally, the pistons were also different. Your engine uses flat top, conventional cast pistons with 4 valve reliefs. This is the same as the 300 hp and produces a compression ratio of about 10.5:1. 340 and 360 used forged, domed pistons in order to achieve higher compression of about 11.25:1.

Your crankshaft is, basically, the same as the other engines except that the 250 hp usually lacks the crankshaft snout bolt used for most SHP engines. However, it's a forged steel unit as all Corvette 283 and 327 cranks were.

The harmonic balancer used on your engine is also smaller and lighter than those used on the SHP engines due to the difference in maximum RPM range of the engines.

The connecting rods used for 250 and 300 hp engine are basically the same as those used for the 340 and 360 hp engines. Both are forged steel. However, there are some slight differences with respect to the rods.

If you wish to keep your engine externally stock, the best improvement that you could make would be to use the L-79 or other aftermarket camshaft. The L-79 camshaft used in conjunction with your existing engine will deliver a lot of the performance benefits that the SHP engines deliver. It will be an easy and inexpensive upgrade, too. However, the L-79 cam produces it best power at an RPM range that your core engine was not designed for. So, you would need to watch the revs.

You can also go with an aftermarket retrofit hydraulic roller camshaft like those available from Speed-Pro, Crane, Comp Cams and others. A mild grind of no more than 270 degree advertised duration will give great power and torque within the RPM range that your engine was designed to work within. That's the way that I'd go.

[Duke W.]

Re: 63 engine specifications

There's not much you can do with the 250 HP engine because of the small port heads. In order to soup it up it would need better heads.

The 300 HP engine can be "upgraded" to near 350 HP spec with the installation of the L-79 cam.

Duke

[Joe L.]

Re: 63 engine specifications

Duke and Bill-----

Certainly, if the heads were upgraded a LOT of increased power potential would be possible. There's no doubt about that, at all. If external configuration of the head was not an issue, modern aluminum heads could be used. A set of AFR or Edelbrock heads would do wonders. Even '461' or '462' heads could be used and very little external difference in the heads over the originals would be apparent, but performance potential would be much greater.

However, assuming that the owner wants to maintain all external stock engine components, I still think that considerable performance improvment could be realized by a camshaft change. Due to the breathing limitations of these heads, the L-79 '151' cam might not be the best choice, though.

I think that a camshaft like the Speed-Pro retrofit hydraulic roller #CS-1061R would, by itself, go a long way to improving the performance and within the RPM limits of the stock engine.