How to make a naturally aspirated 4.6L faster...

[Droptop2001GT]

I wrote this thread on the Yellow Mustang Registry forums last year. I thought the users here would also be able to use it. Be warned, it's long.
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This board often sees the question, "How can I make my 4.6L GT faster WITHOUT going to a supercharger, turbocharger, or nitrous?" So, I offer you this thread as a general idea based on my own personal experience and from tech articles I have read from trusted resources. Feel free to add any thoughts, comments, questions, or observations that you have. When in doubt, use our "SEARCH" feature to try and find a past thread about what you are looking for. Chances are, it has been asked and answered before.

The three major components of speed are: power, weight, and suspension.

Let's start with the most obvious: Power Modifications

Underdrive pullies are a great place to start, and give great bang for the buck performance. Some underdrive pulley sets require a shorter accessory drive belt, some don't. Some pulley sets require you to reuse the factory harmonic balancer, some don't. Be sure to carefully read the instructions before installation. Underdrive pullies utilize a smaller crankshaft pulley, and a larger water pump and alternator pulley, decreasing the RPMs of these two accessories by about 25%. This decreases the amount of parasitic drag generated by your accessory drive belt, and increases power output accordingly.

Another great bang for the buck modification is a rear end gear swap. The rear end gear won't make more horsepower, but a shorter gear (higher number) will definitely give your car the kick in the pants you are looking for by increasing the mechanical advantage in the driveline. The shorter the gear is, the faster the car will accelerate. The only downside to a shorter gear is a lower top speed, which will vary depending on the gear selected.

• If you have a 5 or 6-speed, go for a 3.55 or a 3.73 (more suited for casual drivers with more highway travel), 3.73, 3.90, or 4.10 (good for a daily driver with some drag strip duty), or a 4.30 or even a 4.56 gear ratio (for serious drivers/serious drag strip cars). Another great addition for your manual tranny, that comes relatively cheap, would be a Steeda Tri-Ax or Pro 5.0 short-shifter.
• If you have an Automatic, you are already at a disadvantage speed-wise, so you should consider a slightly shorter gear to make up the difference. Look into a 3.73 or 3.90 (light highway duty/casual driver), 3.90 or 4.10 (street/strip duty) or 4.30/4.56 (serious driver/serious drag strip duty) gear with a good lockup torque converter and a shift kit.

Note: When swapping out the rear end gear, you will need to recalibrate your speedometer. For 1999+ manuals, you will need to purchase a speedometer calibration device such as the "Speedcal" made by Dallas Mustang or Brother's Performance. Or you can use a custom computer chip to reprogram the computer. All the automatic equipped 1999+ mustangs will need a chip burned to fix their speedometers. For pre-1999 manual AND automatic equipped mustangs, the best way to fix your speedo is to install a Speedcal or have a custom chip installed.

One of the other great buys on the 4.6 market is a timing adjuster. Using the timing adjuster, you can manually advance the timing of your vehicle without having to spend the extra cash on a chip. If you advance the timing too far, you may experience pinging, or detonation. If that is the case, you need to run premium grade (93 Octane) gasolines. If you still have pinging problems, you need to back the timing back down accordingly.

A cold air intake can pull a few extra horsepower out, but don't expect to feel the difference from behind the wheel. (Steve Shrader has found that tuning using Pro-M's Remote Optimizer will help churn out a few more ponies from the CAI by fixing the rich air/fuel mixture). More often than not, you are better off going with an intake pipe that does NOT go into the fender well. The resulting 90* bend between the fender well and the MAF causes a turbulent airflow condition which screws up the MAF's Air/Fuel readings. A straight path of airflow before the MAF is ideal, otherwise the result is a rich condition that almost offsets any gains the cold air is providing. A straight intake pipe, with a good filter, and a heat shield (like Steeda's "High Flow GT Intake") is a better buy than the fender well mount cold air intakes.

A bigger throttle body will allow more air into the engine and will somewhat improve the throttle response. More air = more power. A 70mm throttle body is a nice step up for stock or lightly modified 4.6 engines. A 75mm throttle body is a good step up for cars with a good number of bolt-ons. If you decide to go up to the 75mm TB you should get the car dyno-tuned immediately. Flowing more air means you need to flow more fuel to avoid going lean in the critical Air/Fuel ratio. The addition of an upper intake plenum, a throttle body, and a high flow intake with proper tuning can show nice results.

An aftermarket upper intake plenum is a good upgrade for your Mustang. C&L, Accufab, Trick Flow, and other companies now feature upper intake plenums that do an excellent job of outflowing the factory model. These plenums will allow for better airflow from the throttle body into the intake manifold, and net you a few more horsepower, with better throttle response. If you are ever planning on changing your intake manifold (detailed later in this post), don't spend the money on the plenum. It won't bolt up to the aftermarket intake manifolds.

A lot of Mustang owner's first modifications come in the form of exhaust.

• The easiest to change is the mid pipe (exhaust piping between the exhaust manifolds and the mufflers). Changing out your factory H-pipe for an aftermarket H or X pipe is just a matter of loosening and tightening a few bolts and is usually good for a fair amount of horsepower. It's been said that X pipes make a little more top-end power, and H pipes make more low-end torque. But really, the only noticeable difference between the H and the X pipe is the sound. The H pipe makes your more traditional muscle car sound: low and rumbling. The X pipe has a more high-pitched sound under heavy acceleration. The only other decision to be made is whether or not you want catalytic converters. Some states require you to have catalytic converters to pass inspection, some don't. You should check with a local vehicle inspection center to see if your car needs cats to pass inspection or not before you make your purchase. For what it's worth, midpipes without catalytic converters are considerably louder than their catalytic counterparts. If you want a quieter ride, get the cats. For an idea of what the different exhaust combinations sound like, you should check out www.mustangexhaust.com to see what combo better suits your taste.
  
• If you are really wanting to make more power, and are considering changing out the factory exhaust manifolds, long tube headers are an absolute must. Shorty headers are just NOT a compromise in this case. For the money you will spend, shorty headers just don't make the power when compared to the long tube headers. If you want to do it once, and do it right, get long tube headers, with a matching short mid pipe (factory length midpipes will NOT bolt up), Ford OEM exhaust manifold gaskets, and Stage8 locking header bolts to keep the headers from backing out and causing an exhaust leak.
  
• Mufflers. Ah, mufflers. What mustang owner doesn't really enjoy the sound of a good Flowmaster 40 series 2 chamber muffler? But, as nice as they sound, chambered mufflers don't make as much power as straight through mufflers. You honestly won't notice a big jump in power (up or down) based solely on what muffler you choose though. So the only real deciding factor in what muffler to choose is based on your taste in sound. Once again, I cannot recommend browsing through the sound clips at www.mustangexhaust.com enough before you make any exhaust purchases.

An aluminum driveshaft won't make more horsepower per se. You won't make more flywheel horsepower, but you will make more horsepower at the rear wheels due to having less rotational mass in the driveline, thus leading to greater driveline efficiency and less "lost" power.

There are a plenty of options out there when it comes to computer chips. Many companies make generic upgrade chips, custom burned chips, or computer tuners. A generic chip isn't really going to do you any good unless your car is basically stock and you don't plan on doing much else to it. A custom chip is good for cars with several modifications, but should be tuned on a dyno for best results. Any new performance modifications might require you to dyno tune again to get the most from the chip. By adding a chip you can alter the air/fuel ratio, the timing curve, recalibrate your speedo for a gear swap, raise your rev limiter, eliminate any top speed governor you may have, firm up shifts in an automatic, and more. Most chips will require you to run only 93 octane fuel because of the advanced timing. One of the more popular things going right now is the handheld computer tuner. The SuperChips Tuner (SCT) seems to be the best on the market right now as most Diablo Predator buyers are having a hard time getting customer support from Diablo. The SCT is capable of altering all the above parameters, and reflashing them onto your stock computer. The SCT retains the stock tune in case you want/need to revert back for some reason.

For Mustang owners that already have most of the basic bolt-ons, but are still looking to make more power, you should look into swapping in a set of aftermarket camshafts. Start by looking at places like Comp Cams, Crower Cams, Crane cams, and ModMax. From what I have read, SHM makes the best NA cams.

There are finally more options for Mustang owners when it comes to intake manifolds. There is the Ford Bullitt intake manifold, Reichard Racing's intake manifold, Foxlake Power Products P-51 intake manifold, and the X2C Motorsports intake manifold. The biggest positive aspect is the reliability of the metal intakes over the stock plastic one, but that really isn't too important when you aren't using a power adder. The biggest negative is that these things are expensive. You can expect to pay at least $1600 for the Bullitt intake manifold conversion kit, $1489 for the Reichard, $1299 for the Foxlake manifold, and $1800 for the X2C model. The Reichard and X2C intakes aren't a viable option for 99.9% of the naturally aspirated crowd. Their intakes compromise lots of low-end torque in exchange for top-end horsepower - horsepower that most NA cars won't be able to make because the intakes are more suited to compliment high-revving and high horsepower racing motors instead of streetable daily driven Mustangs. The Foxlake P-51 and the Bullitt intakes are much more reasonable options for the naturally aspirated crowd. They both make good power increases all the way across the band, and are even better performers should you install a power adder later. All of these intakes are designed to bolt onto the 99+ PI heads on the SOHC 4.6, except for the X2C intake. The X2C is currently only offered to fit the DOHC 4.6/DOHC 5.4. After making a phone call to X2C, I found out that they will soon start development on an intake for the SOHC 4.6 engine. Just don't expect the price to be much better, if at all.

One option for the 1996-1998 GT owners is a PI cylinder head swap. Ford introduced the PI heads on the 1999 GT and they produced about 30 more horsepower than the heads used on the previous model. The PI cylinder heads are not cheap, but will make a nice power gain on your pre-PI GT. Just be sure to get a 1999+ stock intake manifold as the shape of the intake ports changed from the non-PI heads to the PI heads. This would be an excellent time to do a Bullitt/Foxlake intake swap should you have the cash to spare.

Ford is also working on a 3V cylinder head for the 05 Mustang GT, another future possibility to make better power numbers from our current modular motors.

When you have done everything else and still want more power without going to forced induction or nitrous, you can have your cylinder heads ported & polished. Depending on the amount of porting done, this can greatly increase the power your 4.6L engine makes due to the greatly increased airflow. The best way to make more horsepower is to feed more air into the engine. Porting and polishing the heads are the second best way to make power other than your typical power adders: nitrous, turbochargers, and superchargers. Your fuel system will definitely need to be looked at again to ensure it is providing your engine sufficient amounts of fuel to compliment the newfound airflow. This is expensive, but is definitely worth the money if your budget allows it.

If you really want to steer clear of forced induction, but still yearn to make some higher horsepower numbers, get forged internals and bump up the compression in the process. This is not cheap by any means, but can really up the power curve on the dyno sheet. 1999+ 2V motors come with a factory compression of about 9.6:1. Get a Cobra's billet steel crank, forged rods, and 10.5:1 or 11:1 compression forged pistons. Let the fun begin. (this is also good because it allows for great nitrous applications later if you decide to go that route). Once again, you will likely need to upgrade your fuel system to handle the extra air coming in.

Many companies offer a stroker kit to expand your 281 cubic inch engine to a higher total displacement. It's the same as the Cobra crankshaft mentioned above, except the stroker crankshaft will be larger and give you more displacement in the engine than a forged one of stock size.

You could just do an entire engine swap if you are tired of basic, intermediate, and major bolt-ons and still need more power. If you have not yet done so, now would be the perfect time do forged internals (stroker kit if you so desire), with higher compression pistons, camswap, headswap, or porting and polishing, etc while the entire engine assembly is out of the car.

• Ford offers an entire 302 cubic inch modular stroker motor.
• You could pull out your 2V motor in favor of a 4V motor (IE 99-01 Cobra, or Mach 1 engine).
• Some 96-98 owners have taken out their pre-PI engines for new PI engines. Some even go straight for the Bullitt engine for their swap.
• 5.4 swaps are possible. From there, all of the above applies. But this would be a VERY meticulous process and would require a good bit of time, money, effort, and skill to do right.

Other than adding power, there are other ways to make your car faster, especially at the drag strip.

One such way to make your car faster without actually adding power is to upgrade the suspension. Most aftermarket suspension products are lighter in weight and stronger than the factory equipment, and will make your mustang handle better, ride better, or launch better (depending on what you get). Here are most of the more popular Mustang suspension companies:

• Steeda
• Mustang Racing Technologies
• D&D Motorsports (my personal choice)
• X2C Motorsports
• Kenny Brown
• Maximum Motorsports
• Wolfe Racecraft
• Competition Engineering
• Sean Hyland Motorsports
• UPR Products

Or, in order to raise your Mustang's power to weight ratio, you could reduce the weight of the car instead of adding power to it. You can get a rear seat delete, lightweight racing seats (the front leather seats in a mustang weigh around a combined 100 pounds), a fiberglass hood, lightweight wheels, an aluminum driveshaft (as said above), and many other lightweight replacement parts. I'm sure that Steve Shrader has something to add to this section

"Miscellaneous" factors

At the drag strip, experience will help immensely. You can't expect to click off a 13.9 second pass in the quarter mile with a 2.00 second 60' time the first time you take your new GT to the track. You have to learn the car. Also, at the track, if you want to win, you need to learn the lights. A very quick reaction time can make up for a having a slightly slower car. Just keep practicing. You'll only get better.

Tires. Tires are often overlooked and not thought of when it comes to making your car faster. But a better tire is very important, especially when accelerating hard from a dead stop. You want a tire that will provide you with good grip and traction so you can drive a little harder and not worry about breaking the tires loose. A lot of races are won and lost on the very start, and the tires you choose could be the difference. Make sure your tires are up to the task. 375 horsepower doesn't mean very much if you can't put it to the ground.

And the last point I'll cover here: Safety. Please don't forget about safety when making your car faster. Upgrading your brakes, suspension, and bracing your chassis to maintain structural integrity should be a priority as well while trying to make your mustang faster. You want your safety to be paramount at all times. What good is a fast car that doesn't keep you safe? You could wind up with a totalled mustang, or far worse.

Happy tuning
Ryan D.
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[jason2004gt]

DAMN! Now that's alot of reading, but very useful!

[Novadvr187]

Thats gotta be the post I had ever seen! thanks bro! You might know the answer to this question then.. I have an 03 mustang gt. I plan on replacing the catted x-pipe and flowmaster muffler inserts i have now with BBK Long tube headers, shorty o/r h-pipe, and the flowmaster 40series cat-back exhaust. my last dyno was 242rwhp, what do u think it will be now? I'd like to put some pullies on it but I have a high watt sterio in the back seat during show season which i think will kill the battery with the alternator pully..

PS. I am also about to buy a set of 3.73, and try to save some money for some cams... <--good idea??

[AmericanMetal]

I'd like to put some pullies on it but I have a high watt sterio in the back seat during show season which i think will kill the battery with the alternator pully..

I would be reluctant to put pullies on with more than the stock stereo. Gears - yes, yes, yes. Totally worth it!

[AmericanMetal]

Thanks for all the info, Ryan! I've been thinking about an alum. driveshaft for awhile but you've just added an intake manifold to my shopping list.

[stangmanx]

Thanks man this is very usefull info.