Tom Wilson
October 19, 2005
Plenty new enough for daily use, the '99 to '04 Mustangs are the current mainstream of Mustang performance. They need only a few well-picked parts to maximize their real-world street performance.

Horse Sense: What's the next big thing in '99-'04 GT modifications?Short-blocks, we say. Super power is available from the forced-inductionfolks, but it takes a prepped short block to take the pressure. As theselate models age, and depreciation fueled by the hot, new '05 Mustangtakes affect, slipping a kicking short-block and blower to these carswill make perfect sense.

Sometimes it may not seem like it, but we've heard you when it comes tothe Mustangs you're really driving, modifying, and wanting to know moreabout. And you're right, they are not (mainly) the sexy new '05s or inmany cases even the pushrod 5.0s, but rather the familiar '99-'04 GTs.

Why those years? Because they are good years. Nothing against thepushrod 5.0s, we named a magazine after them you may have noticed, butthose cars are on the backside of the curve, old enough to needrestoration, and two generations short of today's quality and refinementstandards when it comes to first line, daily driving cars. And we digthe new '05 Mustangs, but there just aren't that many of them yet. The'96-'98 GTs, with their anemic version of the 4.6 Two-Valve engine, areout there, but they're not your main squeeze, either. Not that they'rebad cars, but they do require the better performance improved cylinderheads that came stock on the later '99 and '04 machines. Which means ifyou're playing with an affordable, widely available Mustang, you'relikely playing with a '99-'04. Good for you.

Now, how do you modify these cars to best effect? That's what we setout to illustrate in this story. To get the latest poop we burned upthe phone lines talking to tuners and parts retailers to get their inputon what people are doing and should be doing to the New Edge cars. Andjust so you know, our main contacts were Brothers' PerformanceWarehouse, Fairway Sport & Performance, GTR High Performance, MaximumMotorsports, Paul's High Performance, plus a host of specialty shops andparts manufacturers.

What People Are Buying

Rear axle gears remain the best return on your '99-'04 performanceinvestment. Most people are happiest with 3.73 gears--if fuel economy isnot a major concern 4.10s do even better yet.

Our first question to the parts houses was what are people actuallybuying for '99-'04 GTs? The short answer is, "all the usual bolt-ons,"but of course, there's more to it than that.

For starters, these cars are almost totally street cars. Track dutyseems a strong point of the lighter, less expensive 5.0s, and the '99sare still young enough to be presentable in daily driver duty. So,people are modifying their cars to drive better on the street, with asmall percentage of folks spending the cash for some track action.

The big dividing line is supercharging. If you have the $3,500 or morefor the blower, great--it's one of the best bangs for the buck. If not,then "the usual bolt-ons" make the most sense.

So, from a plain, old dollars viewpoint, it makes sense that bolt-onspredominate. Easily the most popular of these are intakeimprovers--cold-air kits and throttle bodies--along with freer-flowingexhaust bits--X-pipes and after-cat muffler systems. Lately, intake airplenums have risen to major league 4.6 bolt-on status.

Because many people run cat-less off-road X-pipes, and these cars usefour oxygen sensors, the check engine light burns eternally in many'99-'04 cars. To get around this, MIL eliminators are big sellersbecause they turn off the check engine light. For the same reason, somesort of electronic tuning aid also sells. The Diablo-Sport Predatorseems to lead this list.

An excellent first upgrade is a cold-air kit. This is Roush'sexample--we like how it breathes cooler air from inside the frontfender.

As always, steeper rear axle gears are super popular. The typicalall-around gear set is the 3.73, with the 4.10 for the more aggressivecustomers. Because these cars use electronic speedometers, some sort ofspeedometer recalibration tool is needed after a gear change, so thosealso are easy sells.

Off-road pulleys are just as popular as ever on the '99 and up machines. They're relatively affordable, easy enough to install, and even simpleenough to remove if you want to go back to stock or keep them whenselling the car.

Once past these power-producers, '99-'04 customers are turning to thechassis. Short-throw shifters are an A-list item, and then it's on tolowering springs, premium shocks and struts, aftermarket brakes, andperhaps appearance items, such as body kits. Of the latter, Mach 1 chinspoilers are fast movers because they are only $75 and black, sopainting is not an issue--although it is an oversize item for shipping.Hoodscoops from Ford are also super popular, as are the Mach 1 grilledeletes and larger radiators, for some reason.

What People Are Not Buying

For the old 5.0 hands out there, a few heretofore must-have bolt-onsfrom the pushrod days are not on the equivalent 4.6 list. Headers,either short- or long-tube, sell, but not in the land-rush quantitiesthey did for 5.0s. The reasons are simple--the 4.6 engine's massiveexterior dimensions don't leave much room for header creativity, and ifnot sexy looking, the stock cast-iron manifolds are probably no worsethan the crimped tube festivals fitted to 5.0s. Thus, there isn't ahuge power increase to be had by fitting short-tube headers, just a fewponies. Furthermore, the stock manifolds' attaching hardware and gasketsare top-notch, and accessing the manifolds is not anyone's idea of fun.

In short, for what you pay, the installation hassle, and the modestpower improvement gained, 4.6 short-tube headers are a relatively poorreturn on investment. In the end, they do make some power, but they aresomething to consider toward the end of your parts program rather thanthe beginning.

Long-tube headers offer more performance, but the cost is higher, theinstallation is more involved, and then there is the added issue of noemission compliance. That last thought may not be a real concern inyour area, but in many parts of the country, where state inspections aremandatory, it is a complete deal stopper.

While X-pipes are hot, hot, hot with the '99 crowd, H-pipes areyesterday's news with the New Edge cars. Vendors say they still sellwell on 5.0s, but likely the mellow X-pipe sound is a big hit with thelater cars, and not so much with the

H-pipe's throb. Likewise, where the 5.0 market was sold on cheap rumble,the modular market buys sleek, sexy Bassani and MagnaFlow after-catsystems by the trainload.

Intake manifolds have so far not made prime time, which is a no-braineras until recently there have been so few to buy, and the Bullitt or FRPPalternatives are surprisingly big-ticket items.

Aftermarket or even ported stock cylinder heads are not a 4.6 mainstay. Again, with the exception of updating

'96-'98 GTs with the PI heads that come stock on the '99 and later cars,there haven't been any cylinder heads to buy. FRPP has offered itsHigh-Performance Cylinder Head for the '96-'98 cars only, and while it'sa great head, it is a great white on the wallet, too. It's also worthnoting that the Two-Valve PI head seems a fair casting to begin with, sounlike the choked 5.0 units or the lackluster '96-'98 castings, therehas been a reduced need to upgrade these expensive andinvolved-to-install heads anyway.

One surprising note was the lack of sales on mass air meters and fuelinjectors. It seems the market has figured out the stock parts are goodto 350 rwhp, and even with all the bolt-ons, you'll be approxi-mately 45hp short of that, so there's no need until you've stepped up to cams ormore likely a blower.

Camshafts are not really a bolt-on, but have proven popular enough on5.0s (maybe too popular with those looking for just a few extra horses).On 4.6s, the cam change is an involved job--not really difficult, butsomewhat tedious in its length--and similar to short headers, the returnon investment on a bolt-on car has not been exemplary. Again, theypay-off better once all the usual bolt-on parts have been installed. Atthat point, they definitely make more power than, say, short-tubeheaders.

Another change is in electronic tuning. In the beginning, there almostwasn't any, then custom chip burning in conjunction with a dyno testsession was the way to go, and now the small, dedicated electronictuners (the DiabloSport Predator was mentioned continuously) are thecost-effective method.

Another interesting observation was the market for aluminum driveshaftsseems to have peaked and fizzled. They were $159 from FRPP, but whenthe price went to $259, it seems everyone decided they could livewithout one.

Vendors also say they used to sell many coil packs for the '96-'98 GTs.But this dried up as the '99 and later cars don't seem to need them.

Now, before sending those flaming arrows our way, all of the partslisted here do make power, and are being sold for 4.6 engines daily. Butthey are going on the more modified cars, so these are parts to considerafter you've exhausted the easier bolt-ons.