July 2011 Chevy High Performance Q&A

Kevin McClelland Jun 6, 2011 0 Comment(s)
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Finally, a nice 2,400-stall converter would work just fine with this camshaft and your 700-R4 trans to get into the meat of the torque curve. As for a carb, I recommend going with a Holley 650 double-pumper carb. (The list number for this carb will be a 1-4777.) You may be able to pick one up at a swap meet or from one of your friends. They have been around forever and with a quick rebuild, they will give you many more years of service. Good luck with your Mustang-hunting Apache.

Sources: compcams.com, holley.com, summitracing.com

It’s a Drain

Q: I have a ’68 small-block in my ’55 Chevy. I am using a recently rebuilt Q-jet from around 1973. I am using a stock fuel pump and have changed it, but I am still getting the same results. What happens is when the car sits for several days the gas drains back to the tank. I disconnected the fuel line, and it doesn’t drain from the carb. I am using a stock fuel tank. Any idea why the gas drains back? It requires extra cranking each time. Thanks for any help.

Jim Baker
Dover, OH

A: Fuel drain back from the Rochester Q-jet has been a problem just about from their first introduction. The fuel isn’t draining back through the fuel pump; it’s draining through the carburetor. There are “Well Plugs” that are in the bottom of the main wells and secondary feed wells on the bottom of the main body of the carb. These plugs are made from lead on the primary main wells, and aluminum on the secondary side. These plugs are driven into the main body at the factory and over time they become slightly loose and leak very small amounts of fuel past them. Usually they don’t leak enough fuel to affect the performance of the engine. However, after the vehicle sits for several days the fuel will slowly drain down into the intake manifold and evaporate. Between natural evaporation out the main bowl vents and the slow leak, there is no fuel for the engine to start on until the fuel pump can fill the float bowl.

You can remedy this problem by rebuilding your carburetor and lightly peening the well plugs back into place with a small ball-peen hammer. You will then want to seal them with a coating of either epoxy or JB Weld. This will help seal up and keep the plugs in place. If you’re not comfortable doing this yourself you can ship your Q-jet out to Jet Performance in SoCal and have them do a performance rebuild. They correct this drain back problem with their standard performance rebuild.

Source: jetchip.com

Too Cool For School!

Q: I’d like to run a quad exhaust on my Chevelle. I found an Australian site that goes by cross-sectional area. If my calculations are correct, does that mean for a 21/4-inch single pipe after muffler I would want dual 13/4-inch pipe on each side of the car? Any information would be much appreciated. I just don’t want to plug the engine up.

Phoenix, AZ

A: You’re spot-on by using the cross-sectional area to calculate the area needed to evacuate one larger pipe with two smaller pipes. The formula to find the area of a tube is pi r2 (the radius—half the diameter—of the inside of the tubing, squared and then multiplied by 3.1416). This will provide you with the cross-sectional area in square inches (in2).


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