Chevy Car Questions & Answers - Performance Q&A

Kevin McClelland May 1, 2009 0 Comment(s)

A Boy, we can even cause trouble on the Internet! At least people are listening-and remembering some important information. The reason I don't like 1.6 rockers on the ZZ4 camshaft profile is because when GM designed that camshaft, the acceleration rates and the opening and closing velocities were pushed to the max. With the additional acceleration of the 1.6 rockers, the valve actions become unstable. The valve will bounce on the seat on closing at high engine speed. There is also a lot of inherent noise with adding these rockers to the lobe, which was designed for a 1.5 ratio rocker. This camshaft was designed in the early '90s. Today I've seen the same things happen with some of the very high-velocity camshaft profiles. Any time you wish to add 1.6 rockers to a camshaft designed to run with 1.5 rockers, we recommend contacting the camshaft manufacturers for their recommendations. It will save you a ton of headaches and broken valvesprings.

To add slow-speed torque, you're on the right track with tubular headers. The factory tubular exhaust manifolds are quite restrictive. The Hedman Elite series headers are a shorty design. You'd be better served for your torque quest with long-tube, 15/8-inch headers. Hedman offers these headers both coated (PN 68446) and uncoated (PN 68440). Check with Hedman for more information.

Next, you'll need to build a very nice head-pipe system to connect the headers to the catalytic converter. A well-designed collector is the Flowmaster Y-collector, PN 250300, with D-port technology to improve scavenging.

Between the headers and a properly designed head-pipe assembly, you should realize a nice torque gain of 20 lb-ft below peak and at least a 10hp gain upstairs. Enjoy the hard launch!Sources: flowmastermufflers.com, hedman.com

Happy Gap
Q I'm building my first engine for my '72 El Camino. I bought an Edelbrock Performer RPM cam, heads, and intake for it, along with a bunch of other performance goodies. I had the 350 bored 0.030 over and bought a set of Sealed Power hypereutectic pistons, PN H345NCP, for which I bought Hastings chrome-moly rings. I set the gaps like the piston ring instructions said to, a minimum of 0.004 inch per inch of bore, so my total was 0.016 inch of gap. I chose the minimum because I figured that tight gaps would provide better emissions and long-term compression for a street car. But recently I've read that with hypereutectic pistons you need big gaps because of the way they expand. I've never had the instruction sheet for my pistons to know what they called for. Sadly, I have my engine almost all the way back together-I just need to put the intake manifold back on. Do I need to take my engine back apart and change the gaps? If so, what do I set them to? Thanks for any help.
Jered Lobban Kent, WA

A Keith Black/Silvolite was the first to market and sell a high-performance hypereutectic piston. The term hypereutectic is derived from the amount of silicon added to the aluminum alloy. Keith Black hypereutectic pistons are cast with a 16-18 percent silicon content, which dramatically increases the strength and wear resistance. One of the challenges with this amount of silicon is that it also acts as a temperature barrier. This, in conjunction with the piston design, is the reason you must increase the top ring-end gap to the recommended 0.0065 inch per inch of bore size.

As for the pistons you've chosen, Sealed Power has built a hypereutectic piston using optimized metallurgy with 16.5 percent silicon to allow standard ring-end gaps and conventional ring-land locations. The pistons also feature Duroshield antifriction skirt coating, which not only reduces friction but is highly resistant to scuffing. This results in an enhanced ring seal, increased horsepower, and extended piston life. Specifications from Sealed Power state that you can run the standard 0.004-inch ring-end gap for an inch of bore size.

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