Tom Wilson
January 1, 2003

Horse Sense: Embarrassing but true, everyone at the first dyno test of Mark Brown's Bullitt was momentarily stumped when we couldn't get the car to rev past idle on the rollers. Stabbing the traction-control defeat button cured everything but the red on our faces.

Mark Brown's Bullitt is a looker as well as a goer, thanks to several small but well-placed details. From the front, a sharp eye can catch a few of those modifications, including GT foglights from Velocity Mustang, a stainless steel running-horse grille emblem from in front of's grille-delete kit, and a Banshee Performance SR71 hood.

Ballistically speaking, hot rodding cartridges with more powder or more efficient bullets is known as wildcatting. It's done by handloaders who start with factory brass, then trim and neck it to accept the powder and bullet they think will work better. The concept is something you might recognize in your own garage, especially if your bullet is spelled with an i and two t's. When it comes to wildcatting that sort of Bullitt, the time-tested staples of supercharging and increased breathing have once again proven themselves.

The wildcatter in this story is Mark Brown. He hadn't pulled the trigger many times on his '01 Bullitt before thoughts of increased cylinder pressure and higher velocities began to take hold. The result of this thinking is a nicely modified daily driver with 369 rear-wheel horsepower and a tasteful collection of appearance and performance baubles. Luckily, we were able to peer over Mark's shoulder while he was wildcatting his Bullitt, and what we learned will be interesting to all late-model hot rodders.

We first came across Mark and his already Vortech-supercharged-and-aftercooled Bullitt as part of a review of Denso Iridium spark plugs. These are not your garden-variety sparklers, but rather sophisticated, new-technology spark plugs designed to flourish in the toughest performance environments. Denso's breakthrough was developing a process for welding tiny bits of Iridium-a tough-but-difficult-to-handle (weld) metal ideal for spark plug electrodes. The costly Iridium is quite heat resistant and is an effective spark plug electrode because it functions in a miniscule 0.4mm-diameter dot on the plug tip. This smaller tip reportedly unshrouds the spark, unlocking otherwise lost horsepower.

Mark's Mustang Bullitt GT is one of the last '01 models built, being Bullitt number 5,368 of approximately 5,500 total. It's Dark Highland Green, but what you can't see underneath in this rear view are the 4.10 Ford Racing Performance Parts rear gears.

We've witnessed several dyno tests where the Denso Iridiums justified their princely $12-per-plug retail price by returning huge power gains. As with any ignition-system improvement, the Iridium plugs really shine when there are ignition problems at hand. Typically this is on a supercharged engine, where increasing rpm and cylinder pressure begin blowing out the spark. The resulting misfiring can begin subtly, enough so that the engine feels OK, and the only indication that something is amiss(ing) is the power is a tad low.

Enter the Denso Iridium spark plug on a white horse. Strapped to the Wes-tech Superflow chassis dyno, Mark's car picked up an amazing 15.5 hp when the Densos were screwed in place of the stock plugs. Admittedly, this is precisely the set of circumstances where these plugs look good-and they really looked good. We'll also repeat our usual plug-testing caveat, that any out-of-the-box-fresh spark plug will give a hair more power over a plug with even a few miles on it, but not 15 hp. Thus, even the curmudgeonly cynical must agree there's at least 12 hp from the Densos. It's the easiest, least expensive 12-15 hp Mark could have found.