October 2011 Chevy High Performance Q & A

Scales are for Fish

Kevin McClelland Sep 1, 2011 0 Comment(s)
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A: We’ve driven some crazy things in our days, but this one is going to be a handful. We assume you’re upgrading the chassis to handle the power and speed that this little Mouse is going to produce. Going over your specs, you need to focus on the street aspects of your build and let the power fall where it may. You could easily produce close to 600 hp with the above components without trying hard.

As for angle- versus straight-plug cylinder heads, we’d go with the angle plugs. In the late ’60s, Chevrolet found that by angling the spark plugs toward the exhaust side of the chamber, they would get better combustion efficiency and power. Since you’re having custom headers made, the header fabricator can build clearance around the spark plugs. Where angle plugs can give you fits is on street headers that have been built around straight-plug heads. It’s usually tough to get the plugs in and out, and you burn off plug wires with regularity.

Back to the street theme, we would stick with a 13/4-inch primary tube diameter around 32 inches long. This, matched with a nice 3-inch collector, will allow you to build a street-friendly exhaust system. Blown engines will produce a very aggressive exhaust note at WOT. Controlling that roar can be a challenge!

When you build your engine you’ll need to work out the compression with all your engine components. The cylinder head combustion chambers are just one of the factors. We ran some quick numbers and with a flat-top piston with two valve reliefs displacing 6.0cc, a 0.041-inch-thick head gasket taking 9.1, 1.5cc ring land volume, and the piston at zero deck you have 9.3:1 compression. This, with 8 pounds of boost, can cause issues for street driving on pump gas. You may need to look toward a mild dish piston to bring the squeeze into the 8.5-9 range.

Finally, the stall speed of your torque converter will depend on the camshaft you plan on running. Since you’re not trying to set any national records, go with a mild blower camshaft. Keep the intake duration in the low 220 range, the exhaust with 10-12 degrees more, and at least 112 separation angle. You don’t want to lose too much boost on overlap. This will give you a mildly aggressive idle that will not drive your EFI crazy. With this type of camshaft specs, you can keep the converter on the tighter side around 2,800 rpm. This will allow your engine to get right into the torque curve and the boost will take over from there.

When you get this beast together, make sure you take a picture and send it in. We know it’s a Ford, but it will have a killer Chevy underhood. Be careful and make sure that you hold on tight when you hit the loud pedal!

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