1. introduction

2. suspension lessons

3. stressing

4. chassis 101

5. Autodynamics

6. jet set

7. sun set

8. Raceware

9. enter the Seven

10. skin deep

11. the DSK concept

12. the list list

13. DSK hits the road

14. postscript

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6. Jet Set

As the Can-Am team was leaving for Mexico City in the spring of 1968, Ray Caldwell lamented that we would probably blow up a couple of expensive engines there again. He explained that the 6000 ft. altitude of the track made it nearly impossible to properly tune the mixtures of the four Weber 48mm DCOE side-draught carburetors that sat crisscrossed atop our Can-Am small blocks. He described the previous year's race as a struggle for all the teams between over rich mixtures that belched sooty exhaust, fouled spark plugs and robbed power and lean fuel mixtures that overheated combustion chambers, caused explosive backfires and burned piston crowns and exhaust valves. No-one had the right carburetor jets or even knew what to try. "The team that gets their jetting closest will probably win this thing," Ray said.

I wondered aloud if jet size was something you could calculate in advance. It seemed to me that if you knew what main fuel jet worked at sea level, you could estimate the right size for 6000 feet of altitude. It made logical sense to postulate a standard barometer day at both places and then adjust the jet size linearly based on the difference in air density at that altitude. When I posed the idea to Del Trott, he pulled out a slide rule and walked me through the calculation. "Let's assume the jet is a tube," he lectured. "The flow through a tube is a function of the diameter to the fourth power over the length. So if we know the jet diameter on a standard day at sea level . . . "

Dell calculated a range of jet diameters and I grabbed the Weber jet box and a set of wire gauges. It turned out there were no main jets small enough. I silver soldered a few standard main jets closed and then had the machinist drill one set for standard conditions at 6000 feet, one for a low barometer and another for a high barometric pressure day. Dick chamfered the edges of the tiny holes such that they were a perfect match for factory drilled jets. The team ran our "standard barometric pressure" jets the first day of practice and never fussed with the engine again. World class racing teams all around us blew up engines left and right. Many driver's and crew chiefs came by our pit to chat about engine tuning, but our team closely guarded the secret jet sizes.

The D-7 ran away from the field that weekend, and but for a bad fuel cell flange that soaked Sam Posey's driving suit in gasoline, we would have won. A leak from the huge side-mounted pontoon tanks poured raw gas onto the 1 1/2 inch aluminum radiator pipes that passed through the cockpit from the front-mounted radiator to the engine mounted behind the driver's seat. Choking on the gasoline fumes, Sam unlatched his seat belts and raised his head up into the air stream to clear his head of the toxic fumes. The explosive vapors threatened Sam's consciousness, but he just stuck his head up into the breeze and tried to win. He could not drive as fast without belts on, because the cornering forces pitched him about in the cockpit. Sam hung in there and finished second behind Mexican driver Moises Salona driving last year's Can-Am Championship McLaren. His crew apparently knew how to jet Webers for high altitude too. It was their home track.

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