October 2011 Chevy High Performance Q & A

Scales are for Fish

Kevin McClelland Sep 1, 2011 0 Comment(s)
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We rolled into Fontana for the first pass, set the starting line chip at 4,800 rpm, set the transbrake, and let her rip! As I expected, the car drove to the right with the front end in the air. Coming back after the run, we applied two flats of preload by shorting the top right bar. This was just about enough preload with it still slightly going to the right. After one more flat the car left straight and flat on these full-throttle blasts. It’s my belief that everyone should set their car up to leave at full power. Then, if you’re going to throttle-stop race like in the Super classes, the car will leave correctly. I see enough cars racing Super classes that hit the tires with full power for a few tenths of a second before they come back to about 300 hp. They turn right, go left, or all over the place. If we take the time to work out the suspension in the first place we could win a couple more rounds. If I’d have had a set of scales in the first place I could have set the car with 50-75 pounds on the right rear tire. After I had the car worked out I had the chance to scale the car on my good friend Larry Scarth’s scales. What I found was that every flat of preload on my car was worth 35 pounds on the tires. With the three flats of preload I have 95 pounds of static load on the right rear to compensate for the unloading of that tire on the launch. I’m now in the market for a set of scales. Know of a good deal out there?

Vette Therapy

Q: I am a 27-year-old mechanical engineering student at Old Dominion University. I have been reading this magazine cover to cover since I was 15; what I have learned from years of your PQA is priceless to me! I’m putting together an ’81 Corvette that I bought four years ago when I was working as a pipe fitter. The car ran fine, (67,000 original miles) but the factory 190 hp just wasn’t cutting it for me. I yanked the choked-up 350 out, punched it out 0.040 inch over, and replaced the measly 8.5:1 slugs with some 10:1 hypers. I then turned to the valvetrain; I chose a Lunati Voodoo bumpstick, 0.510-/0.490-inch max lift, with a set of matching 1.5:1 roller rockers and hydro lifters.

The heads are now aluminum 58cc 2.02-/1.60-inch valves with 210cc runners from Procomp with a matching intake. I picked up a Mallory Pro Billet vacuum-advance HEI distributor and MSD 6AL box to handle the ignition duties because the CCC unit and smog system had to go. The exhaust gases are passed through a set of 15/8-inch primary full-tube headers and 4-inch unbaffled side pipes. The rotating assembly is the stock cast stuff; I figure it will hold up fine for what I’m throwing at it.

I have three questions that could help me wrap this Vette up and get her on the road for some much-needed right foot therapy. What carb should I run on this setup? I have a brand-new Edelbrock 650 with vacuum secondaries. Most of my gearhead friends say this will choke the engine, but some say it just needs bigger jets. Will this carb have good driveability and power output?

My next two questions concern the tranny I picked up for the car. The Vette came with a TH350, but I personally found it boring just slapping a Corvette into Drive. I sourced a Muncie M20 wide-ratio four-speed-equipped ’73 Vette that was being parted out. I got everything from the driveshaft to the pedals for a great price. What clutch should I run with the aforementioned engine combo, and what rear gear should I run to get the most out of this tranny and a stock tire size or 255/65 R15? From a little research on the car I believe it has a stock 2.90:1 rear gear. This seems a bit short for the four-speed to me. Any help is greatly appreciated! Great mag! Great column!

Michael W.
Via email

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