69 350/350

[Jim M.]

I was wondering what the difference is between a 350/300 and a 350/350, or maybe I should say, what gives the 350 HP model the extra horse power?

[Joe L.]

Re: 69 350/350

I was wondering what the difference is between a 350/300 and a 350/350, or maybe I should say, what gives the 350 HP model the extra horse power?

1) Larger valve heads (2.02/1.60 for L-46 versus 1.94/1.50 for 300 hp);

2) Different camshaft;

3) different distributor advance characteristics;

4) slightly revised carburetor calibration (both used Q-Jets, though)

Also included but not directly affecting horsepower output:

1) forged steel crank (versus nodular cast iron for 300 hp)

2) special connecting rods (both are forged steel but L-46 received shot-peening and magnaflux inspection);

3) larger harmonic balancer (both were 8" but the L-46 was thicker)

[Jim M.]

Re: 69 350/350

Thanks Joe. I was looking for that information in the books I have but couldn't find anything on what parts on the engine were different that would make up the extra horsepower.

[Kenny C.]

Re: 69 350/350

The compression ratio was also bumped up from 10.25 to 11.00 not certain if this was due to a piston change or as a result of decreased combustion chamber size of the heads. Either way the added compression is a major factor in the power increase.
Kenny

[Duke W.]

Re: 69 350/350

L-46 used forged, domed pistons (2.4 cc net dome, versus about a net 5 cc net "dish" due to the valve relief notches on the 300 HP cast, flattop pistons), and the head chamber volume was 1-2 cc larger due to the relief machined for the 2.02" inlet valve.

The LT-1 long block is essentially the same with the exception of the camshaft, and the LT-1 had a higher flowing aluminum inlet manifold and Holley carburetor. The L-46 cast iron inlet manifold was the same as used on the base 300 HP engine, and other than minor calibration differences, the same Quadrajet.

Back in that era a buddy had a '70 L-46, and it ran about even with my 340 HP SWC.

Duke