Dan Simons
January 1, 2004

In the November '03 issue, we introduced you to the initial installation of a 5.4 SOHC engine into a '99 Mustang GT ("Size Matters," p. 49). If by chance you missed that article or you have short-term memory problems, here's how it turned out. Torque. Lots and lots of torque. Huge amounts of grin-inducing, shove-you-in-the-back, no-waiting-for-the-rpm-to-build torque. Any questions? Rear-wheel torque increased by more than 90 lb-ft at low rpm compared to the stock 4.6. We couldn't even measure the actual peak with the 5.4 because it was below the 2,500-2,600 rpm that the stock torque converter would flash to when we matted the pedal.

At that point, the torque curve was already on the way down. We also ended up 22 rwhp over the 4.6 baseline (peak to peak). But by 5,600 rpm, the 5.4 output had fallen below the 4.6 as the runners in the stock Mustang intake manifold are simply too long to let the big motor breathe well at high rpm. In this next round of testing, a short-runner Reichard Racing intake will solve any airflow restriction problems we might have, at least from the intake manifold standpoint. At the time of the initial test, the only modifications to the car were a drop-in K&N air filter and Flowmaster three-chamber mufflers with stock tailpipes.

This round of changes will focus on gaining some easy power by freeing up the inlet and exhaust sides of the motor, adding a set of underdrive pulleys, and then, of course, installing the current big daddy of bolt-ons, the Reichard intake. Worthy of mention is that this round of testing was done with the torque converter locked, so not only were we able to get data at a much lower rpm, but we also took away the effects of torque converter slippage to gain a true picture of the torque curve. The shape of the curve should now be the same as you would have with a stick-shift setup, although the numbers are still lower as the auto transmission is less efficient.

What fun is it having something different if nobody knows it? We purchased custom-designed stickers from Sticker Dude Designs to let the casual observer know this isn't your average 4.6 GT.

Changing the procedure necessi-tated a new baseline, which showed that locking the torque converter was worth some power all by itself. Below 3,000 rpm, the unlocked converter showed a significant advantage in torque output, which it should as the converter is slipping and giving additional torque multiplication. But above 3,000 rpm, the slippage was simply resulting in a loss of power transmission efficiency, and we were better off with it locked. With the new baseline established, we got down to the business of gaining horsepower, and what better business is there?

As before, all testing was done at HiTech Motorsport in Ramsey, Minnesota, where Brian Ebert took care of the wrench spinning and tuning. Special thanks go out to Brian, Jim Reichard for arranging testing of his (at the time) one-and-only round-throttle-body version intake, George Klass for getting us the Accufab throttle body for testing, and Dan Wolfson at DB Performance for setting us up with the MAC H-pipe. Check out the pictures, captions, and dyno results to see how we ended up this time around.

Photo Gallery

View Photo Gallery

For the most part, everything we bolted on did just what it should, i.e. the pulleys gave nice steady gains, the exhaust really uncorked the top end of the tach, and the other inlet mods showed some good gains as well. At first glance, someone might wonder why we didn't see huge gains from the intake swap, but the simple answer is that we don't have the combination to really utilize it yet. The test showed that the intake wasn't the main restriction to power production at this point. The biggest culprits appear to be the stock cams.

With only 6 inches or so of runner length in the Reichard manifold, it would appear that we should be able to pull all the rpm we dare on this motor, and yet power peaked way down around 4,900 rpm. The problem is not enough cam to work with the intake. To put it into perspective, look at it this way. The stock cam in a 5.0 H.O. motor has 210 degrees of intake duration (at 0.050 lift) to feed air to 302 ci. On our 5.4, we are trying to feed 330 ci with only 201 degrees of intake duration. The intake valve isn't held open long enough to allow the cylinders to fill at high rpm.

This motor is absolutely begging for different cams, and hopefully we'll have a chance to let Brian at HiTech spec out some custom grinds for us soon. At that point, we'll revisit the Reichard intake and let it rock and roll with a setup that can take much better advantage of the airflow potential. For now, though, even without big peak gains, track times would still improve con-siderably with the intake as we were up as much as 33 hp at 5,800 rpm. Our dyno pulls didn't quite go to 6,000 rpm, but extrapolating the curves out that far puts the Reichard intake up by 38 lb-ft and more than 43 hp. So, running through the gears in the 4,500-6,000 rpm range would show some nice increases in average power and torque. When we get more cam and possibly ported heads under this intake, that upper rpm range should really begin to sparkle.