The PONTIAC TEMPEST
Hood clearance was tight. We thought it would be cool (pun intended) to take fresh air from the cowl and duct it into the carb. We did a little metal work and cut a four-inch K&N air cleaner apart. The air cleaner was inset into the cowl. Next we fabricated a plenum box to fit on top of the carb (left photo below).
All things in order, we drove the car to the Dyno Shop in Ft. Myers Fla and put it up on the drum.
The bottom curve (shown in green on the dyno chart above) was the result. An erratic pull that peaked in the neighborhood of a wimpy 400 horsepower at the rear wheels. Next we disconnected the two four-inch ducts and let the motor breathe through the plenum box alone. The power smoothed out a little but the machine still only showed about 415 rear wheel horsepower, so we scrapped the ducted cold air system entirely. It was just too small! We headed back to the garage to fabricate a new NASCAR-style cowl induction with the air cleaner around the carb (center photo below). It took air through an opening in the cowl that measured 40 square inches. Not quite enough, so we added the two 4-inch ducts onto the sides (below right) so all the air was coming in cold from the cowl. Now it was breathing easier.
The output moved up to 440 rear wheel horsepower, and the curve began to smooth out. This is very important for a street-driven machine that will operate over a wide power band. Torque showed about 485 ft. pounds at 2000 RPMs and climbed to 515 ft. pounds at 4000 RPMs. (RPMs are half the MPH on the bottom axis of this particular dyno chart) Now we were getting some place. Timing was set at 36 degrees total (24 in the HEI and 12 at the crank). Before we left the Dyno Shop we tried 34 degrees and 38 degrees. Both settings reduced the power slightly; 36 degrees was apparently the right number. The oxygen sensor showed about 13.5 to 1 so we were still a little lean. We took the car home and made some adjustments.
Back in our own garage we had several things to attend to. First out came the plugs. A careful inspection confirmed that things were a little lean. The jetting went up one number: to 75 on the primaries and 85 on the secondaries. The electrodes were facing every which way (plug photo below) so we indexed the plugs and opened the gaps up to .055". We double-checked the fuel pressure of the carb. Shop electric bypass pump and bumped it up from 6.5 to 7 psi @ 1500 RPMs. A couple of weeks earlier we had switched from single dampened valve springs to double springs. We went back over the valve settings and found a couple of them a little loose. This car runs a Comp Cams 284 solid lifter cam with 236 deg of duration @ .050" The cam has .570" of lift with 1.72 rockers. The power begins to fall off at 5000 RPMs. We had selected this cam figuring the car would be running at high altitude in the desert of the Southwest. Now, at sea level in Florida we can handle a little more cam.
For now we have retarded the cam 4-degrees and tightened the valve lash down from .022 to .018. Back on the dyno we had picked up about 20 HP and 20 Ft Pounds of torque from those changes. The bottom end of the curve was identical with the changes all coming in from 3,500 to 6,500 RPMs. This is about where we wanted to be. We also went up one jet size and brought the fuel air ratio down to 13.
Now we were looking at 460 HP and 535 Ft Pounds of torque. All this at the rear wheels and through the mufflers!
Is that be enough? It's never enough! The goal is 500 HP to the rear wheels
In 2008 with a change to a bigger cam (a solid roller, the old Comp 288ARwith .625 lift and 246@50 duration) and a different manifold with some jetting changes and some work on the air box, and a quarter point more compression from a .020 cut on the heads.
We then saw 508 HP and 595 ft pounds of torque to the rear wheels. Now we're talking! And right where we want to be.
HOW DYNO TESTING WORKS: Back your car onto the top of two large drums that protrude from the surface. The operator secures your vehicle with straps and chocks to hold it in place atop the drums. The operator will swing a monitor out where you can see RPM, speed and exhaust O2 sensor reading. You start out in first or low range and work your way up through the gears easily. When you get to fourth or high gear you bring the RPMs up to 2,000 (or wherever you want to start from) and then mash the gas down to the floor. Hold it until 6,500 (or whereever you want to stop) let off the gas and shift into neutral. DONT TOUCH THE BRAKES! The machine will slow the tires down and compute your output, correcting for temperature, humidity, and altitude. The machine saves the results of each "pull" and can print results out in graph form later. Make one change at a time to see how it effects your output. We were able to make about six or seven pulls in an hour and a half with minor adjustments between each pull. Dyno time costs about $50 an hour and is a very worthwhile investment. There is a Dynoshop link in the links section of this Website.
We Never Give Up & WE NEVER LIFT!
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© 2005 Wolf Wengler, a.k.a. The Wheelman