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1991 Pontiac Firebird Formula - Build A 12-Second TPI Pontiac Firebird

It Has No Clever Name, But It Sure Is Slow.Enjoy The Victories And Defeats As We Show You How To

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14.12 At 92.43 With A 1.98 60-FootThe best way to improve your e.t. is to concentrate on getting the 60-foot time down. This means getting the car out of the hole in less than 2 seconds. A fast street car will see 60-foot times around 1.60 and each 0.10 you can take off this time should result in a quicker e.t. provided you have enough motor to pull all the way through the lights. Our first mod therefore was a 3,000-rpm Holeshot converter from B&M. Its job is to move the rpm of the launch up into the part of the powerband where the most torque is made. Also, the more torque the engine makes, the higher the converter will stall. The Holeshot stalled to about 2,600 and immediately shaved 0.015 second off of the 60-foot and about 0.10 off the e.t. The hidden glee factor here is that on the street you can lift off the gas at about 25 mph and when you stab the throttle the car downshifts and flashes to about 3,000 then absolutely obliterates the tires in a sideways smokefest. You'd better be paying attention.

Nitrous: 12.95 At 100.94If you were at the track to test a torque converter and you also had a full bottle of nitrous oxide, what would you do? Yeah, we thought so. We cracked the bottle and squirted the car to a best-ever 12.95. Heh heh.

Gears: 1.88 60-Foot TimeWe'd heard that TPI engines don't like the steeper gear ratio, and we proved it when we switched to a new Auburn differential and a set of 3.73:1 cogs from Rockland Gear. We ran another series of frustrating 14-teens that was seriously irksome even though we shaved another 0.10 off the 60-foot time. The gears will multiply torque by the same percentage as the increase in ratio, right? So with 14 percent more ratio (stock is 3.23) you get 14 percent more grunt. This thing is fun off the line but about half-track it's time to flip through the CD tracks.

Back To Work: Intake ModsWe had installed the intake runners on the first test but never tested them with the matching plenum and base. Back in the shop we added the other two components. We found these two mods kicked ass in unexpected ways at the track, but meanwhile we noticed that the plenum requires that you modify the gasket heavily to get it to fit while the base uses the stock stuff. Doing the math? We need to port the entire deal all at once to get the most out of these parts.

Rocket Pack: 12.71 At 105.01 With A 1.79 60-Foot TimeRemember when we ran the nitrous at the track the first time? Well, we found another 0.20 with the nitrous and the intake mods combined. We were wondering if the hugeness of the ported plenum was helping to get the good stuff into the runners or to act in the way aftermarket plenums increase torque with increased area. Either way, this thing is brutal in the first 60 for a heavy car with only 245 naturally aspirated horsepower. We even got hoots from guys in the stands at the Wednesday-night drags. This car launches hard on the bottle. We recommend it.

So How is it Done?Get the converter first, you will like it a lot. Street fun, hard launches, all good. Wait on the gears until you decide what kind of speed you want. If you are building a bigger engine with good heads and a cam, 4.10s will likely show you a better e.t., but if you are spraying, be careful. We chose the 3.73s because a 150 shot of nitrous usually gives you about 1,000 rpm in the traps. We caught ourselves in the 6,500-rpm range a couple of times because the engine revved so fast on the squeeze. Get your engine/nitrous combo right then do the math (RPM = MPH x Gear Ratio x 336 / Tire Diameter) to see what you will be spinning in the traps. The exhaust stuff is obvious, just do it. The intake mods are necessary if you are building a 355 or 383 or in our case using lots of nitrous so you can probably do this last, when it becomes the horsepower cork. Want more? Tell us at CarCraft@primedia.com.

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