'A straight-bodied, two-door sedan from 1967 for $2,000 that runs and drives? Sold. Our fantasy was to build a car and drive it solidly into the 10s because even factory cars are running 11s, and Car Craft hasn't had a really fast car since former Editor Matt King's Super Nova went deep into the 11s with a correction factor. We need to be faster.
With insurance cash in hand, we set out to buy the lightest, coolest car we could find. We apprehended a six-cylinder '67 Rambler American that we cobbled together in the May '06 issue and got running with gear from a V-8 Gremlin for a total of $3,500. It smoked its way down to San Diego for the Car Craft Anti Tour then lost oil pressure. We didn't care because we already had a plan.
Why 10s and not 9s? A quick glance at the NHRA rule book told us that 9s required a valid competition license and lots of expensive, SFI-approved goodies like a flexplate shield, a rollcage, and an unfashionable driving suit. We also found that if the car is full bodied and running anywhere between 10.00 and 10.99, you can get away with a rollbar instead of a 'cage. A 'cage requires a side bar on both the driver and the passenger sides of the car and a forward hoop that crosses between the roof line and the top of the front windshield. To us, the look of a 'cage draws the line between a street car and a race car. The 'cage is more complicated and expensive, and the rollbar is easier to hide and requires only one side bar that can be removable. According to the rules, a car with a rollbar cannot exceed 135 mph. So to give ourselves a little wiggle room, we settled on 130 mph as a top speed in the quarter-mile that should put us right around 10.50.
Gears, Mph, And Tire Height
After you've figured out how fast you want to go, you need to find the weight of the car and determine how much horsepower you'll need to accomplish your goal. The formula to estimate amount of horsepower for a terminal mph in the quarter-mile is: hp = (mph / 234)3 x weight. As an example, if your car weighs 3,000 pounds, you'll need about 500 hp to run 130 mph, and if your car weighs 4,000 pounds, you'll need about 685. This is simply a power-to-weight calculation, and experience has shown us it is a little conservative, much depends on the engines torque potential. There are a lot more factors involved in goin' fast, but this is a good place to start, and it shows why weighing less is better.
The next thing you need to do is find out where your engine will make peak horsepower and pick a rear gear that will put the engine at about 200 rpm above that number going through the traps in High gear. Here is the math: gear ratio = (rpm x tire diameter) / (mph x 336). This is closely tied to the size of the tire you are going to run, so before picking a rear gear ratio, find the largest tires that will fit under the rear. You should also note that an automatic transmission in High gear will exhibit about 5 percent slippage, so you will need to add that to equation.
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