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.

What You Should Be Buying

Our second question to the aftermarket specialists was what parts should'99-'04 owners put on their cars? Like all open-ended questions, theanswers varied, and everyone agreed that to a certain extent it dependson what you want to do with the car. But several key components wererepeatedly mentioned.

Hardly typical of the daily driver norm for late-model edge cars, thisyellow demon from the Kenne Bell shop sports a high-boost screw blower,slicks, and a few extra supporting parts to make well over 600 rwhp. Ittakes an improved short-block for the 4.6 GT engine to live at thesepower levels, plus a prepped fuel system and other supporting parts,which partially explains why such combinations are relatively rare.

The common theme with everyone we talked to was almost everybody wants aMustang that does it all--well mannered on the street, with more power,and better handling and braking. It isn't just about straightline speedanymore.

And we'll say we were pleased to note that what the market is buying andwhat the market should be buying are pretty much the same thing, savefor one point. Everyone goes for more power first, then upgrades thesuspension and brakes. Those items should be tuned up first, then morepower added, but few people do it that way because they're all excitedabout more power.

This is doubly true of supercharging. Do the suspension and brakesfirst, then add the blower. You'll save a ton of wheelspin and possiblya trip backward into something hard and expensive in the process.

Ultimately, we'll repeat our long-standing advice on Mustangmodification. There are two things you need--besides money--to make thebest time of tuning. Most importantly, you need a goal and a plan onreaching it. Interested in drag racing? Then you'll want powerproducers, tons of rear axle gear, and to eliminate as much weight as ispractical (removing the air conditioning is the big one here). The dragguy is also interested in a soft suspension tune, and must budget forslicks and small front wheels and tires. He's a prime candidate for ablower or nitrous, too.

On the other hand, an open-track fan can put up with more weight withoutreal penalty, needs a stiffer suspension, and has durability under toughconditions--namely summer heat--high on his priorities. And theopen-tracker really does need to step up his braking and suspendersbefore adding more power.

As you can see, it depends on what you want your car to excel at whenyou are finished modifying it, so give your ultimate goal some thoughtat the beginning.

The second must-have is opening a dialogue with a tuner or parts vendor. Work with these people on establishing a parts purchase andinstallation plan that suits--or at least comes close to--your budget.Information on what is available, and what works in your region, or evenwhat your tuner is capable of handling, play a great practical part inachieving a fun Mustang with a minimum of false starts and lost money onso-so parts purchases. This is true if, like the vast majority ofowners, all you really want is a nicer, more capable street car thatwill likely never see a racetrack.

OK, what are the near universal recommendations from our tuners? Toppingthe list was an old favorite, rear axle gears. Always the best bang forthe Mustang performance buck, moving to lower ratio gears in the ol'8.8-inch differential is reasonably affordable and gives an immediate,unmistakable increase in acceleration performance.

The devilish detail is which gear to buy. Stock, the New Edge Mustangs,both V-6 and V-8, came with 3.27:1 gears. They really are a goodcompromise between low-speed acceleration performance and freewayflying. By keeping engine rpm relatively low on the freeway, the 3.27gears do a major part in promoting fuel economy.

Performance ratios available for the 8.8-inch differential are 3.55,3.73, the newcomer 3.90, and 4.10. Many 5.0 traditionalists will adviseyou that the 3.55 is the best all-around gear, but that is with 5.0s. The less torquey, smaller displacement 4.6 engines need more help, andso the 3.55 is the Two-Valve's best economy/slight performance ratiogearset. In the wide-open West, where 50-mile commutes are not uncommon,drivers would be happy with 3.55s simply because they're spending somuch time highway cruising and $3.00 for a gallon of gasoline is a realthreat, but there's more performance to be had. If high-speed freewaydriving is not a major consideration, which is typical in the East andMidwest, then 3.73 gears are the default ratio. These will definitelygive a noticeable boost in acceleration more than the 3.27 cogs whilestill not driving you batty on the highway. In fact, if in-town runningaround is really all you do, the 3.73s may actually improve yourmileage--assuming you don't pull a John Force launch from everylight--because the engine doesn't have to work so hard to get the carmoving.

Finally, there are 4.10s. Knuckle dragging gears for sure--don't go hereif endless hours of freeway driving figure in your plans. On the otherhand, if brutal three-gear blasts are what you're into, or if you run a28-inch tall slick at the drags, then 4.10s will cure what ails you.

Typically, automatic transmission cars want one more step in gear thanmanuals, and this is where the 3.90 gear ratio comes in. Offered by Pro5.0 (yep, same folks famous for shifters), the 3.90 cog is relativelynew to the Mustang scene, and is proving an excellent gear for automaticNew Edge cars. It's also a good option for manual-transmission ownerswanting everything the 3.73s can offer, and who might really want the4.10s, but are afraid of the high highway rpm and resulting fuel burn.In that case, the 3.90 is just that "little bit more" without having togo all the way.

And if you are from the old 5.0 school, don't sweat the lower 4.6 ratiorecommendations. The 4.6 engine is happier turning higher rpm than the5.0, so more gearing is welcomed.

With the rear gear change comes a need to recalibrate the electronicspeedometer. This is where some sort of electronic tuner comes intoplay, the Diablo-Sport Predator was one we heard plenty about, but theSCT Xcalibrator is popular as well. Not only does the flash-tuner fixthe speedometer, it also cures the check engine light issue brought onby off-road

X-pipes, so MIL eliminators are unnecessary. Furthermore, flash-tunersare reprogrammable so future tuning changes--cam, blower, and so on--canbe accommodated at any time. This saves the delay and cost of havingthe computer re-flashed or a new chip burned every time you make ahardware change.

And let's not forget you can typically get about 10 rwhp even on a stockTwo-Valve with a flash-tuner or chip.

While larger mass air meters have not proven to be a '99-'04 necessity,a larger throttle body is a cost-effective improvement. This pair of 70and 75mm Accufabs are representative of the wide choice available. Theusual bolt-on car will make the expected 300 rwhp with the 70mm unit.

Continuing with the power theme, the next recommendation is to attend tothe engine's intake side. An upgraded throttle body, cold-air kit, orairbox improvement all fall in this category. There are a variety ofimprovements going on here. The stock inlet, for example, is not overlylarge, and has some convoluted rubber hoses, which produce turbulence inthe airflow path. Thus, a smoother tube or pipe helps raise airflowwithout having to grow too large and take up all the underhood realestate on the passenger side of the engine compartment.

We prefer a cold-air kit that places the air filter inside the fender. This avoids breathing hot, underhood air (less dense, less power) andfan wash, which can confuse the mass air meter and lead to maddeningdriveability woes.

The throttle body is a simple call. Aftermarket throttle bodies arelarger and flow more air than the stocker--the large oval unit availablefrom FRPP is appropriately sized, and there are others from Accufab,BBK, and so on, depending on your manifold. Like many other inletimprovements, a larger throttle body by itself is not the magic key toperformance nirvana, but combined with the other breathing mods, ithelps. An important building block, in other words.

Here's another '99-'04 over-achiever; but we wanted to show the Bullittintake manifold. These upgraded factory intakes are all aluminum andbreathe better than the GT's plastic piece, so they are worth power.Pricey for sure, we'd consider one of these intakes once we had finishedwith all the other bolt-ons.

Intake plenums, often called elbows, are recommended. These devices arereasonably priced and do produce a couple of horsepower. Testing hasshown they won't quite match the power gain of a throttle body, but inconjunction with one, they will raise the power curve just a couple ofpoints all across the tach. You'll do best cost-wise when buying thethrottle body and elbow as a package.

At this point, the more drag-racing oriented tuners recommend a shifter,other tuners leave it until later.

Exhaust was the next power recommendation. Luckily, the X-pipe has thetuner's favor, as well as the customer's ear, so it seems the way to go. As for cat or non-cat X-pipes, tuners say it really is up to thecustomer, and in fact, sales are about evenly split on this item. Wehave to say the high-flow cats are our recommendation. We have a strongethical bias when it comes to hobbies and clean air, and from a powerstandpoint, eliminating the cats is only worth a few horsepower anyway.

There is one bothersome exception to this, and that is if you arebuilding an open-track car. The extended periods of full-throttleoperation on a road course can seriously heat catalytic converters ofany type, and in that case, not having cats can save a fire. The rightway to do it, of course, would be to have cats on the street and swap toan off-road X-pipe (or a dedicated track-only exhaust system withstraight-through mufflers and no tailpipes) for track days.

For street cars that occasionally go to the dragstrip for a couple offun runs, don't sweat overheating the cats. They'll be fine. And, infact, the same is likely true at the road course if you are notabsolutely flat to the floor, but rather out to enjoy your car withouttraffic, police, and road hazards.

After-cat choices are as wide-open as always, but the Bassani andMagnaflow systems that are so popular seem to be doing a fine job. Thereality, of course, is that on a street car where some semblance ofdecorum is required, there will be a small top-end power loss due tomufflers anyway, and just as likely a low-range torque gain compared torunning short, open pipes. But, with the realistic bolt-on powerexpectation just over 300 rwhp, losses due to mufflers are notoutlandish anyway. Bottom line: today's popular quality systems arelikely giving all the power a street-licensed car can.

Stock '99-'04 GT exhaust manifolds are cast iron, which isn't the lastword in weight reduction. But, they are free, essentially leak-free, anddurable. They also fit the tight engine compartment well.

Underdrive pulleys are next. Again, the market has stabilized on saneunderdrive percentages, so there is little chance you'll fall prey tothe "race-only" mentality when it comes to pulleys. The alternatorstill needs to produce juice at low rpm, and the water pump still needsto turn at stoplights, and after years of over-slowing 5.0 engineaccessories, the industry has found a good balance with the street 4.6market.

One option the 4.6 pulley buyer will face is the type of pulley to useon the harmonic balancer. Because the 4.6 engine integrates the crankpulley with the harmonic damper into a single piece, you either replacethe entire balancer/pulley unit, or fit a piggy-back pulley over theexisting pulley. Our tuners recommended the one-piece damper/pulleyreplacement method as the installation is the same (you have to pull theharmonic damper in either case), and the replacement style keeps theharmonic balancer in the stock location on the crank snout. The slip-onpulley moves the balancer forward on the crank, which doesn't seembeneficial to the crankshaft, and can foul the transmission oil-coolerlines on automatic GTs. Popular brands in the pulley arena are ASP andSteeda, as well as pulley perennial March.

Headers for '99-'04 GTs make a handful of horsepower because there isn'tmuch room to get creative in their design. They make more sense onceyou've exhausted other bolt-on possibilities.

Another major pulley consideration is if you plan on supercharging your4.6 at a later date. All supercharger kits--roots, screw, andcentrifugal--are designed to work with stock crankshaft and accessorypulleys. So, if you buy underdrive pulleys now, then a supercharger ayear from now, you'll find yourself needing to reinstall your stockpulleys. And you did keep your stock parts, didn't you?

Advice from the vendors and tuners was to simply stick with stockpulleys if you plan to supercharge at some date. Inevitably, it savestime and money.

While on the subject of supercharging, there doesn't seem to be theblower envy among 4.6 owners as there is among 5.0 and Mustang Cobraowners. For a fun daily driver, you can have a good time without asupercharger--on the other hand, a blower makes great street power anddefinitely has sex appeal. It's also a fair chunk of change, and in theend, a question each owner must decide on for himself.

Where the blower question is appropriate for bolt-on buyers is onceagain, will there ever be a blower on this car? If yes, then what kindof supercharger? It's important because there is little sense indressing the engine with a bunch of bolt-ons that either must be removedor are supplied with the blower kit. That, and optimizing thesupercharger combination calls for slightly different components than anaturally aspirated one will.

Don't Forget Maintenance

Premium shocks are fast movers on late-model GTs--both Konis andBilsteins seem the most popular. Your best buy is to get springs andshocks in a package.

Although still fairly new, many of the GTs we're talking about havereached the age where major maintenance items are due for renewal. Thisincludes things such as brake pads and clutches.

It's interesting that something like a stock clutch hangs in therepretty well behind bolt-on power modifications, but when it comes timeto replace it, aftermarket clutches are all anyone buys. Either peoplebelieve aftermarket parts are better than factory parts, or preparationfor more power production is taking place.

No matter, the point is, budget a little something for all thosewindshield wiper blades, filters, brake pads, clutch jobs, and so on.You don't want to max the credit card on exciting go-fast parts only tofind you need a set of tires, brakes, and a clutch all at the same time.

Ford Racing offers the red Bullitt brake calipers in its catalog. Theyhave become a popular upgrade because the price is reasonable, the redpaint and pony graphics dress-up the exterior, and they provide a bitmore clamping power. They can be combined with any number of largerbrake rotors, too.

As examples, a throttle body, plenum, and 4.10 gears are great on anaturally aspirated Mustang, but if you later fit a Kenne BellTwin-Screw blower, you'll find the kit comes with its own throttle body,eliminates the elbow, and makes so much torque that 3.73 gears arefaster than 4.10 cogs, and you might even be happier with 3.55s, orhappiest playing the cheapskate and staying with the free 3.27s. On theother hand, go with a centrifugal such as a Paxton or Vortech, and thebig throttle body and elbow will support extra power, and those 4.10gears will still pull the Mustang out of the hole until the blower boostbecomes meaningful around 3,750 rpm.

At this point, the average owner has reached the practical end to hisengine modifications. The fuel and ignition systems are quite good fromFord and don't need any help at the bolt-on (non-blower) level. Thatmeans the stock fuel pump and stock 80mm mass air meter ought to see youthrough the bolt-on stage. Of course, if you go past bolt-ons, you'llneed to step up the fuel system, and possibly the ignition system if youreally turn up the boost. But at 300 rwhp, the stock gear is OK.

Excellent braking is becoming a hallmark of late-model performance carsof all types. When more than just a good pad or simple caliper upgradeis desired, Baer Braking systems offer mild-to-wild brake improvementsthat achieve the superior feel and impressive fade resistance of trulyhigh- performance braking.

Attention should then turn to the chassis if it hasn't already. Wheelsand tires are a subject unto themselves, so we'll pass by them here,other than to say good tires are a critical performance part. Allforces pass through the tires, so they need to be as grippy andpredictable as possible. For street use, an ultra-high-performance tireis the ticket--track duty calls for specialized tires, such as DOT roadrace tires, or drag radials. While a big tire budget isn't necessarilygoing to change your life on the street, where so much driving isnowhere near the limit, specialized tires make all the difference at thetrack. Put another way, if track time is your plan, a dedicated set ofwheels and tires should be you first purchase, whether its drag, roadracing, or slaloms.

Brake options for the '99-'04 cars are varied. A powerful andcost-effective solution is to fit more performance- oriented brake pads,especially the fronts, and keep your pads at no less than 1/3 thickness. A step up to the Cobra 13-inch braking system or equivalent fromspecialists such as Baer or Stoptech is also a quick mover at tuningshops. Because they come painted a snazzy red with the running horselogo, the FRPP Special Edition Bullitt calipers are very popular. Theycan be mixed with aftermarket slotted rotors to come up with a dressybrake for relatively few dollars.

Another popular upgrade for '99-'04 Mustangs is lowering springs. Asimple 1-inch lowering improves handling and looks. You'll need toupgrade the shocks and struts with the higher rate lowering springs, orthe car will ride like a baby buggy.

Suspension tuning comes in two basic forms. By far the most popular iswhat we'll call the upgrade approach, where lowering springs, a fewurethane bushings, and other replacement parts are fitted. Perhaps theultimate expression of this strategy is the Eibach Pro System Plus kits.Given the workably rigid SN-95 chassis, these parts provide a definitefirming of the suspension and a notable improvement in street handling. They also work well on the road or slalom course until you really starthammering. Then, they prove skittish as the limits of the stocksuspension geometry are reached.

The second approach is to essentially replace the suspension with partsfrom Griggs Racing, Maximum Motorsport, Steeda, and others. These areexpensive, no-excuse solutions, but offer truly impressive results.

There you have it, late-model Two-Valve tuning in a nutshell. Thesecars are ideal as warmed-up daily drivers--we hope you've learned a fewtricks to improving yours. And remember--have a plan and talk with yourparts supplier.