Greedy for speed, we’ve pushed the stock 302 and drivetrain in Ron Burgundy, our ’87 Fox Mustang, to their limits using the Hellion Street Heat turbo system peaking at about 11.5 pounds of boost. The baseline run for the car was 9.78 at 74 mph in the eighth mile. That translates to 15.22 at 93 mph, slightly slower than nearly every vanilla V8 Mustang and Camaro ran in the quarter-mile back in the day. After we added the turbo (Jan. ’12, “Cheap Car = Big Fun”), we took Ron to the dyno at Westech and made 441 hp and 555 lb-ft at the rear wheels. The endless dyno runs to tune the car combined with weapons-grade desert heat melted the stock transmission.
The new 4R70W overdrive transmission came from Performance Automatic (Sept. ’12, “Return of Ron Burgundy”) and while “testing” the associated transbrake, shop manager Grant Petersen managed to ventilate the head gaskets about an hour later, on the street behind the shop. Summit Racing took pity and zip-lined a fresh pair of Cometic MLS replacements.
After more fiddling, we made it to Irwindale Raceway in Irwindale, California, for some track time. Our driver was pumped out of his skull with greenhorn jitters and went right to the rev limiter before letting go of the transbrake button. The car hit 7.87 at 91 mph, or 12.25 in the quarter. The off-and-on traction and the donuts we did for the cover shoot ended the life of the factory limited slip.
So here we are. We’ve managed to pickle the trans and the diff, but we also took two seconds off the car’s e.t. That’s pretty good for a single power-adder. The next step is to fix the broken rearend outlined in the story here, then work the suspension a little to get rid of the wheelspin off the line.
Let’s Play With the Math
Gear Ratio = (RPM x Tire Diameter) / (MPH x 336)
Using this equation, we can determine, roughly, what gear would be needed to put the car near horsepower peak in the quarter-mile based on quarter-mile mph. Let’s say that Ron is feeling good and has the power-to-weight ratio to get into the traps at 130 mph. Using this formula: Gear Ratio = (6,000x28)/(130x336), we know that to get the engine to 6,000 in the traps, we will need a 3.70:1 gear ratio (the actual result is 3.84, but a 3.70 gear is the closest ratio). Now you can play with power to weight—RWHP = (mph/234)3 x weight—and discover that the more power you are making at the wheel, the less gear ratio you need to hit your desired mph in the quarter-mile. The formula is RPM = MPH x Gear Ratio x 336 / Tire Diameter, and it can be used to determine the engine rpm at cruise. Don’t forget to multiply 0.70 for the 4R70W overdrive transmission.
|Moser Axle - 31-spline
|Moser Axle installation kit
|Moser Axle Differential cover
|Royal Purple 75W90 Max Gear synthetic
Autolite, Allied Signal Inc.; Autolite.com
Flaming River; 440/826-4488; FlamingRiver.com
Ford Racing Performance Parts; 800/367-3788; FordRacingParts.com
Hellion Power Systems; 505/873-4670; HellionPowerSystems.com
Lincoln Welders; 216-481-8100; LincolnElectric.com
Maximum Motorsports; 888-378-8830; MaximumMotorsports.com
Mickey Thompson Performance Tires; 951/817-0101; MickeyThompson.com
Moser Axle; 260/726-6689; MoserEngineering.com
Performance Automatic; 240/439-4650; PerformanceAutomatic.com
Precision Industries; Converter.com
Royal Purple; 888/382-6300;RoyalPurple.com
Summit Racing Equipment; 800/230-3030; SummitRacing.com
Tokico Performance Shocks; 800/548-2594; TokicoPerformanceShocks.com
Trick Flow Specialties; 330/630-1555; TrickFlow.com
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