March 2011 Chevy High Performance Q&A - Performance Q&A

Under Pressure Round II

Kevin McClelland Feb 11, 2011 0 Comment(s)
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A: The Edelbrock Torker manifolds did turn the carb at an angle to help fuel distribution, but also to help equalize the runner lengths. This helped the distribution of fuel and also the air feeding into each cylinder. As for jetting your blown baby, you have two big mixing rotors directly below the carburetors. These rotors are going to mix the air and fuel and steer the mixture. There isn’t anything you’re going to do with the jetting of your two four-barrels above the blower that will make much difference in the intake manifold. When you do get down to jetting your engine, you’ll want to stay to the safe rich side of the fuel curve. A 12:1 AFR is a safe fuel mixture for your supercharged engine at wide-open throttle. As for part-throttle cruise conditions, you can shoot for 14.7:1, but with the volume of the blower and all the distance from the carbs to the cylinders, you may need to run it slightly on the rich side for good driveability. If you have an issue with distribution, this will cover up most of them. The last thing you want a boosted engine to do is go lean. A quick lean period at full throttle could spell disaster for your engine.

Your best investment would be a wideband air/fuel ratio meter for your car. They have really come down in price and will give you instant feedback on the fuel mixture going into your engine. We’ve now used about four of the AEM Digital Wideband Air/Fuel UEGO Gauge kits PN 30-4100 in our own race cars, and several of our friends’ cars. This completely takes the guesswork out of dialing in the fuel mixture of either a carbureted or EFI system. We prefer the digital gauge, because at a glance you can see the air/fuel going down the track. They utilize a very quick-responding Bosch wideband oxygen sensor for optimum accuracy and reliability. Another really nice feature is that the sensor has a 0-5V output to be used with data loggers, so that can interface with your race car data logger or laptop EFI tuning software.

A Little Spin?

Q: I just finished building a ’69 Chevelle and have a 598 big-block backed by a Tremec TKO II five-speed with a Ford 9-inch rearend and 3.73:1 gears. I have ladder bars, Hotchkis 11/2-inch drop springs, QA1 double adjustable shocks, and I’m running a P295/65R15 Mickey Thompson drag radial.

I had it dyno’d, and it generated 631 hp at 5,600 and 647 lb-ft at 4,500 to the wheels. I’m having a little trouble hooking up coming out of the hole and was wondering if I took the ladder bars out and installed a sway bar, would that help or do you have any other suggestions for this situation? This is a full body car with factory front suspension.
Via email

A: A little trouble hooking up? You’re trying to control 647 lb-ft of torque with a TKO II five-speed with a 2.87 first and an M/T drag radial! That gear ratio, coupled up with your 3.73:1 rear screw, gives you a total First gear ratio of 10.70:1. That’s a lot of power for a stick-shifted A-body, and it must be an absolute blast to drive. Have you ever tried to take off in Second? The 1.89 gear drops your launch multiplication down to 7.05:1. Yes, that’s very high, but 650 lb-ft of torque is a lot to hit on a small street tire.


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