Vette SledQ I own a '77 L48 Corvette. I love the car, but wanted it to run a little better without replacing the engine. I ran a straight 2-inch dual exhaust, put in a new cam with 214/224 duration at 0.050 inch tappet lift, 0.442/0.465 inch max lift, an Edelbrock dual-plane manifold, and an Edelbrock 600-cfm carb. A friend offered me a deal on a set of 202 heads, and I think this is where I went wrong. The heads are 76cc chambers with some port work. The car sounds great, but doesn't run as good as it sounds. Has crap for low-end torque, and only seems to pull well above 4 grand. The car only shows 22,000 miles, and I believe it because when I pulled the heads, you could still see the crosshatch in the cylinders. This is why I don't really want to mess with the pistons. It will run on any kind of bad gas, and no matter how high I run up the timing I can't make it knock. I know I need more compression. If I went to a set of 194 heads, with maybe 58cc, do you think that would do the trick? I can probably get these with or without port work. Thanks for your time.Bill Esper
A Those L48-powered Vettes should never have been sold. They produced a whopping 180 hp! How sick is that when the Corvette is supposed to be your company's flagship sports car? The L82 cars with their 210 hp barely gave you a thrill. You are going in the right direction stepping up the performance. Like you said, I think you stacked the deck against yourself.
The L48 engines came from the factory with 8:0:1 compression. They have dished pistons, 1.94/1.50-inch valves, and 76cc chambers from the factory. Who knows what type of port work your friend had done to your heads? Also, when you installed the heads you probably used aftermarket head gaskets that were thicker than the stock '77 gaskets, taking more compression away from your build. Combine this with stepping up the camshaft duration and it kicked you right in the shorts! If you go to a set of 58cc heads using factory-style head gaskets, it will boost your compression ratio up to 9.6:1. This will make a huge difference in the output of your engine. Now, taking this a step further, we wouldn't go with a set of iron 305 heads. We would either pick up a set of rebuilt or new L98 aluminum heads. These are the same heads used on the 350 H.O. ZZ4 crate engine. Between the smaller 58cc chambers and 1.94/1.50-inch valves, you will see the benefit of the 165cc inlet port. This will build great torque and support the horsepower potential of the rest of your combination. You can get these heads new from GM under PN 12556463. If you shop around, you should be able to pick them up for a very reasonable price. You will need to change over to center-bolt valve covers (stops leaks) and to rail-type rocker arms. The valvesprings on these heads will work perfect with your camshaft and the heads will require no machine work to match your max lift. Also, pick up a set of head gaskets, PN 10105117. These gaskets are 0.026-inch compressed thickness. This will reduce the quench clearance to give you better mixture motion in the combustion space.
Shop around for the best price from GM Performance Parts dealers around the country for the parts listed above. With your camshaft and manifold and these heads you should be close to the 300hp range. This will be a major step up from the 180 hp that your Vette came with. Enjoy.
Rocker ActQ I have a '98 Chevy 350 I am building an engine for and need to know if I can change the rocker arms from a 1.5- to a 1.6:1, since it has computer-controlled timing. Any advice would be appreciated.Kevin Hults