Performance Q&A Tech Section

Our Resident tech guru, Big Mac, tells all.

Kevin McClelland Apr 1, 2009 0 Comment(s)

Now for the electrical wiring side of things. With your 305 and the TH700-R4, we'd recommend using the stock 350 van harness and computer. You will need to swap out the chip in the ECM for a '90 van calibration with a 305 engine. Also, swap out the TBI injectors for the 305 injectors. If you leave the 350 injectors in the pod, it will run too rich.

For your TPI-injected 350, things get a little touchier. Use the harness and controller from the Trans Am. Since the '88 engine controls use a mass airflow sensor, things are a little more forgiving. With this you'll need a custom chip to change the engine displacement. You'll also need to match the injectors to the calibration. Give Tom Woodside at GMCOPO a call. He can spec out the proper injectors and help you with the calibration changes.

Using up the components you have to make two nice street rod projects isn't that tough. Just a few gaskets-and hours turning wrenches-will get you there. Enjoy your cruising.

Short Course
I'm trying to figure out what stall to go with. I built an '86 Monte Carlo with a small-block 350 that is bored 0.040 over, with Scat 6-inch H-beam rods, Keith Black 0.150 dome pistons, Dart 200cc heads with 62cc chambers, a Speedway solid cam with 0.531/0.533-inch max lift ground on 106 centers that is good for 3,000 to 7,000 rpm, and a Victor intake with a 750 Holley. The trans is a TH400 with a Hughes transbrake. The rearend is a Winters Grand National with a 5.43:1 gear for eighth-mile racing. I used to have a TH700-R4, but I smoked it. I might try a 4.56:1 gear if the 5.43:1 gear is too steep. I thought I should go with a 3,500 stall. The car weighs about 3,400 pounds. I still want to make the car streetable. Could you help me out? Thanks.
Trevor MacNeill
Via email

A When setting a car up for eighth-mile drag race competition, you may think that you can gear the car for top rpm in high gear at the eighth-mile mark, just like racing the quarter-mile. This would work out just perfect if our cars were geared to the race track. By gearing the car for top speed at the eighth-mile, you run into the problem of having too much gear multiplication on the starting line for the tire to hold traction. Going over the engine specs and the vehicle weight you listed, you should be in the low 11s or high 10s based on how well the car works on the starting line. This will put you at about 122 mph in the quarter and around 95 mph at the eighth.

Now we have to cast some assumptions. You're probably running a 28x10-inch slick on the rear of the car unless you have done chassis work in the rear. With a 28-inch-tall tire, your 5.43:1 gears are going to put you through the light in the quarter at 122 mph and approximately 8,000 rpm. I think you're going to be out of power by 7,000-7,200 rpm based on your package. Also, if you multiply the 5.43:1 gear by the First gear ratio of your TH400 of 2.48:1, you come up with a starting line ratio of 13.46! Your 10-inch tire isn't going to be too happy with that.

Now let's go back to your eighth-mile package. The 5.43:1 gears will put you right at 6,500 rpm in the eighth at 95 mph. This is perfect gearing if you can keep the tires under the car. This is where a two-speed Powerglide really has an advantage. With its 1.76:1 First gear and your 5.43:1 rear gear, you have a starting line ratio of 9.34:1. This is just about perfect for a consistent bracket car.


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