The Sad State of Motorsports - Performance Q & A

Kevin McClelland Jul 1, 2009 0 Comment(s)

Throwing in the towel on this engine isn't the right thing to do. All you may need is a jet change. From your description of the running conditions and the fact that it loads up the plugs in a cruise mode, it sounds quite rich. The Edelbrock carburetor should give you very good performance on that engine with acceptable fuel economy. Either someone has modified this carb or you have a problem with float level or power valve operation. You stated that you're running an Edelbrock 600-cfm competition carburetor. Edelbrock offers the Performer and Thunder series. The AVS Thunder is the series of high-performance calibrated models; however, it doesn't include a 600-cfm size, only 650- or 800-cfm. Contact the Edelbrock tech line with the specific number off the carb for calibration information. They can give you the specific jet size and power-valve rod and spring information to match your carb. This should give you a baseline to calibrate from. These carburetors, when properly tuned, will give you trouble-free performance and good fuel economy.

Light My Fire
Q: I have a '97 Chevy 4x4 extended cab truck with a Vortec 350. The engine is all stock except for Edelbrock shorty headers and after-cat exhaust from Flowmaster. It also has a Powerdyne supercharger kit that makes about 6 psi of boost. My problem is that at WOT, near 5,000 rpm, the engine develops a miss. Is there a simple fix for this? The truck still has its stock in-tank fuel pump and the inline pump from the supercharger kit, and the spark ignition is stock. Hope you can help.
Dana Oulundsen
Via email

A: Cylinder pressure is a wonderful thing. It boosts the power by forcing the piston down the cylinder with authority! As cylinder pressure rises, it takes more and more spark energy to bridge the gap of the spark plug. The stock ignition is borderline for engines with mild bolt-on upgrades, but when you up the cylinder pressure with 6 psi of boost, it's tough to light your fire. This is probably where you're going to find your problem.

First of all, check for adequate fuel delivery. If the engine is going lean at high engine speeds, it won't last long before you'll find piston remains on the spark plugs. What you'll need to do is install a temporary high-pressure fuel pressure gauge. The CPI fuel injection on your L-31 fuel injection should have 58 psi of pressure, and at WOT at peak rpm, the pressure should fall more than 2 or 3 psi. The CPI system uses a vacuum-biased regulator, which will lower the fuel pressure to approximately 52 psi at idle. Now, you should have installed a new fuel filter when you installed the blower. The factory fuel filters on the GM trucks are way too small and plug up all the time. This kills the fuel pump in the tank. If you still find that you're losing pressure, check the in-tank pump and its filter sock. Work through the fuel system until you have steady fuel pressure during full-power tests.

After you have verified your fuel pressure, check your air/fuel ratio. With aftermarket supercharger systems, you must increase the fuel flow with either calibration changes or other enrichment. The only safe way to know that you have sufficient fuel is to install a wideband O2 sensor. Innovate Motorsports has very affordable O2 sensor kits that are much cheaper than a new engine. Innovate's DB Gauge Kit comes complete with the O2 sensor, harness, and dash gauge. This will take the guesswork out of your tuning.


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