QI have a new Chevrolet ZZ4 crate engine. There seems to be some controversy over the correct or optimal carburetor for this engine. Folks have made recommendations ranging from 600 to 770 cfm. Also, I'm using stock ram's-horn, cast-iron exhaust manifolds. Are these OK, or should I install headers? The engine is installed in a shortened '69 Chevy half-ton truck fame with a '51 GMC panel truck on top. The rig is used mostly for towing a small, 16-foot ski boat. Any help will be appreciated. Thanks.
AThroughout the development phase of the ZZ4 engine package, two carburetors were used. For off-road use (performance), we used the PN 4779 Holley 750 double-pumper. This carburetor is perfectly jetted right out of the box for best performance. Second, we used a computer-controlled feedback Rochester Q-jet for an '87 LG-4 305 Camaro. This was the emissions phase of the project. This carburetor ran very well also, with a secondary hanger and metering rod change. The emissions Q-jet is rated at 650 cfm.
As for your application, everyone has been somewhat right! I would recommend a double-pumper somewhere around 650 cfm. For performance and light towing, this carb will give you great throttle response and drivability.
If you don't mind leaving about 25 lb-ft of torque on the table, keep using the ram's-horn manifolds. The cast manifolds will hurt your slow-speed torque below torque peak by upwards of 25 lb-ft. Yes, the cast manifolds are the "install them and forget them" part. Headers would present their own challenges with spark plug wires and sealing over the years. Either will work for your application. It just matters if you need to use all the torque that the ZZ4 has to offer. Good luck with your very neat project.
AWhat size jets do you have in that plate? Best case, your Edelbrock Performer Power Package is kicking out around 325 hp naturally aspirated. To get your C3 Corvette into the middle 11s you must be pushing out 475-plus horsepower on the Jones. That's quite a runner you have on your hands. Are you sure that you want to mess with it?
The Edelbrock Performer aluminum heads are focused on making great torque and all done by the 5,500-rpm range. They have a nice street inlet port that displaces 170 cc's. The heads flow well to 0.500-inch lift on the inlet side flowing 244 cfm. Anything above that amount of lift and the port gets saturated and doesn't flow any more air. Lifting the valve more than 0.500 inch won't really help your performance anymore. The exhaust will give you 175 cfm of flow at 0.500-inch valve opening and 183 cfm at 0.600-inch. Unless you are willing to throw out the baby with the bathwater, I would stick with these heads. Your package is very well thought out and is using all the torque you can produce. If you were to supersize the cylinder heads, you would need a new inlet manifold that wouldn't fit under your hood, a larger-cfm carb, exhaust headers, and so on. Let's look to a cam that will give you about 50 more horses and will work with all your other components.