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Mustang Dyno - Dyno Tuning

Know What's Up Before You Go

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In 1995, engine shootouts were big around the office, and staffers struggled to build the most power for the least money. One result of those days was a 351 Windsor engine that squeaked out 447 hp at 6,300 with little couth. It had a set of TFS iron heads ported to 278 cfm at 0.550 valve lift and milled 0.040 to get the compression ratio to around 10:1. Then in a fit of cool, they decided to stab a rowdy Comp Cams 305 solid lifter with 260 degrees at 0.050 and 0.590 lift on a 106 centerline. The bottom end was stock, and the motor demanded to be spun to 6,500, but that's what it took to make cheap power back then.

Nearly 10 years later, Four Wheeler Art Director Greg Smith still has this engine, and he runs it at local tracks in his '67 Mustang, which has accumulated a pile of low 12-second timeslips. He's sure there is an 11-second pass in this car, but he's limited to what he can do at the strip. Times have changed, and now we have affordable handheld A/F meters, chassis dynos, and data acquisition at our disposal, making the final tweaks to get this car into the 11s within our reach. We took the it to Westech Performance for a Mustang dyno tuning session to get him going in the right direction.

Mustang Dyno Preparation
Greg has exchanged the original cam for a Comp Cams 248/254 at 0.050 that has a shorter duration and slightly more lift. He kept the original Victor Jr. intake because it was milled and port-matched to fit the TFS heads on the original combination. It also has a Holley 750-cfm double-pumper and MSD Billet distributor that are very similar to the 750 carb and electronic ignition used on the original, so we knew that the power would be similar. Dyno-operator Tom Habrzyk suggested we bring the original dyno sheet to Westech Performance in Mira Loma, California, along with a list of the static timing, total timing, jets in the carb, gear ratios, stall, and tire height so everything can be entered into the computer when we arrived to save valuable time. He also suggested welding an O2 bung near the collector because it sharpens the air/fuel readings on the dyno and allows for a handheld meter to be installed later if needed. Tom also noted that we should inspect the drivetrain for bad U-joints, fluids, and basic tune-up parts, and if the car is track-only, be sure to have good tires that aren't dry-rotted. The rule of thumb here is if you can't pass tech at the racetrack, you shouldn't be on the chassis dyno. Simple.

Mustang Dyno - Carb Operation
The first thing Tom did was perform a quick visual inspection under the hood. It was immediately clear that the air-cleaner lid was almost resting on the air horn, and when we floored the gas pedal, the secondaries were only opening 75 percent. We readjusted the linkage for WOT and set the float levels so a little fuel would slosh out of the bowl sight when the car was gently rocked. We left the air cleaner on for the baseline, so we could see if there was improvement after we changed it.

Mustang Dyno - Baseline
According to the original dyno sheet from the Hot Rod article, the engine made 447 hp at 6,400 and 420 lb-ft at 5,200. The first run on the chassis dyno netted us a maximum 330 hp at 6,200 and 319 lb-ft at 4,600 rpm. Tom told us to expect about a 20 percent loss through the drivetrain, so we calculated that the Windsor was making about 412 hp at the flywheel and 398 lb-ft of torque. We know the smaller cam reduced some of the high-rpm shriek, but we were certain to find some more power during the session.

Mustang Dyno - Air Cleaner Dyno Tuning
We started our dyno tuning with the most obvious problem. The 2-inch air-filter element was causing a restriction between the air-cleaner base and the air horn. We discovered this by marking the position of the wing nut on the carb stud then removing the air-cleaner assembly and reinstalling the lid using the wing nut as a reference. We found that there was only about 11/42 inch of clearance between the two. The solution was to install a drop-base assembly with a K&N 14x3-inch element. We rechecked WOT to make sure the linkage wasn't hitting the base and made a pull. Dyno tuning the air-cleaner change was worth about 7 hp and moved the peak up about 200 rpm. We made another pull without the air cleaner and found no gain so we moved on.

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