Difference in 300 HP and 340 + engines

[Steve D.]

In the 63 service manual, the only difference in the descriptions of the 300 HP engine and the 340 HP is "special camshaft and solid lifters". My questions are:

1. What was the "special" cam ? Does it have a part number, or is there an

aftermarket equivalent ? The 300 and 340 heads are the same?

2. I have never seen torque curves for these engines, are they available?

Are they pretty similar below 4500-5000 RPM, i.e. street use, not racing?

3. The engine in my 63 convertible is not correct '63 , but from checking Black Book casting numbers ( I haven't developed a library yet), it appears that the block is '64 vintage and the heads are '67 300-350 HP. I realize that there are infinite combinations, but if I just change the cam and lifters to get a little more push, is it necessary to change (upgrade) anything else? The carburator is a Holley 4150(?) .

[Bill Clupper]

Re: Difference in 300 HP and 340 + engines

Steve, there are a number of differences in the engines, I will list some of them and I'm sure others will add more. The block and Heads were the same castings, almost everything else was different to some extent, including the Pistons, (10.5 vs 11.25 comp ratio, forged vs cast, Front damper and timing cover, crank (tuftrided), bearings (Moraine 400 hi-perf) and the cam, which was the "097" cam used in hi-perf Corvettes from '57. Oil Pan was different, 6quart vs 5. I'm travelling the the NCRS Fla meet, so I don't have all my references available, but you should have some idea from this. The 300 hp engine has great low end torque, the 340 decidedly less.

[Duke W.]

Re: Difference in 300 HP and 340 + engines

Despite the seemingly modest 13 percent difference in power these engines have totally different characteristics. The 300 HP has a smooth 500 RPM idle and gobs of off-idle torque. The Special High Performance (340) has a lumpy 1000 RPM idle and is torque shy, but screams beyond 4000 to the 6500 rev limit at WOT. An automatic transmission is not suitable with this engine, and it was only available with a manual. The 300 had a (gross) torque rating of 360 lb-ft at 3200, 344 at 4000 for the SHP. If you call Chevrolet customer service and give them a '63 VIN they will send you the "restoration package" which includes the AMA specs with torque and power curves for all engines.

The 340 was a FI long block with a carburetor instead of FI. Bill covered most of the major differences. It used the same carb as the 300/manual trans, but with an aluminum manifold rather than cast iron and an open element air cleaner. The cam is obsolete by today's standards, and I always recommend the LT-1 cam for solid lifter rebuilds. An exact repro is available from Federal Mogul Performance parts. Unless you want to deal with valve adjustments or want a solid lifter cam for originality, you're probably better off with the 327/350HP hydraulic cam (also available from FMPP).

This cam will make more top end power at some loss in low end compared to the 300 HP cam. How this cam would function is somewhat related to your drivetrain.
It will work okay with a WR trans and 3.36 axle.

Duke

[Joe Pennington]

Re: Difference in 300 HP and 340 + engines

I believe that in '63 the Carter AFB was used on both the 300/340 engines. A Holly 4150 was used starting in '64 on the 360HP. At least thats what the service manuals say. The 300HP heads had 1.94/1.50 valves with the SHP heads having 2.02/1.6 valves.(I think)

[Bill Clupper]

Re: Difference in 300 HP and 340 + engines

'63 valve sizes were 1.94/1.50 for both 300 and 340hp engines. The 2.01/1.62 valves wee not introduced until '64 with the 365/375 hp engines

[Joe Pennington]

Re: Difference in 300 HP and 340 + engines

Thanks for the clarification on the valve size. I wasn't sure when the change was made, so I didn't want to make a statement of fact.