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5.0 L Mustang Performance

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Increasing the Performance
of the
5.0 Mustang

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Chassis stiffening


Straight line performance


First Steps

Further reading


This is an introduction to the first steps to take for increasing your 5.0L Mustang’s performance. Although this article is built around the fuel-injected 5.0 liter Mustang most of what’s here applies to other Mustangs and many other cars.

Read all you can before you dive in. If you ask 50 people their opinions on what you should do you’ll get 50 different answers! There’s lots of information on the web and in Mustang magazines. Note that these specialty performance car magazines are not only there to help you enjoy the potential of your car more, but to sell their advertisers' parts. Look at the return on your investment before buying. Lots of parts suppliers are on the Web.

If you’re like most people you’ll want to jump in first with straight-line performance enhancements. If you do then later you’ll discover the weaknesses in the other areas of your car.


This is a balanced approach, not just looking for the best quarter mile times, but a car that can turn and slow down too.

It won’t be necessary to rob a bank to afford these enhancements.

Want a streetable, reliable, legal car.

This isn’t meant to be all-inclusive on how to buy a particular part, or even why you should do this instead of something else. It’s just meant to give you an idea of where to start researching.

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Chassis stiffening


If you want to accelerate hard or corner hard the Fox bodied chassis needs to have the flex taken out. If you have a convertible you should do this now whether you make any other changes to your car or not. When you corner hard and you car’s body flexes the tire contact patches change and your alignment is thrown off.

Tightening up

Subframe connectors. This is the single best thing you can do for you chassis. Get weld-on connectors, not bolt-on.

Strut tower brace. Get a three-point that bolts to the firewall, also.

G Load or K member brace. For bettr turn-in.

These three together make a good basis for future modifications.

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Any improvement you can afford to make is good. Most Fox bodied Mustangs have inadequate brakes. They fade too quickly in performance driving and lock up prematurely.

Cheap braking improvements:

Change your brake fluid. Put in a good quality fluid.

Put on new brake lines. Stainless steel if you want, but just new rubber ones will help.

Replace the front Ford pads with something better.

Replace the front calipers.

Repack the front wheel bearings while you're in there.

Next improvements:

Upgrading the rear drums to discs. This is an expensive undertaking, but worthwhile for performance applications.

Upgrading the front brakes. If you go to the expense of putting discs in the rear think about upgrading the fronts also. About 80% of your braking is done with the fronts.

Install a brake bias valve to allow manual adjusting of the front-to-rear brake bias.

Get a better master cylinder.

Common mistake:

Running racing pads on the street. This is a quick way to ruin your expensive rotors. And racing pads don't stop very well when cold. You could be surprised some winter morning.
Hard pads have to heat up before working their best, but they don't fade with repeated hard braking. Softer pads don't have to warm up much and are best for street conditions. Investigate and find the proper pads for your needs.

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Straight line performance

Your engine makes power by pumping air. In general, the more air you can flow through the more horsepower. At some point you may have to improve the fuel and the ignition systems.

The basic rule is cubic inches equals more HP so if your displacement stays the same as you increase HP with modifications then something has to give. Modifications to increase HP usually moves that horsepower higher up in the RPM’s and you may be robbing torque. This is OK for the drag strip, but not so good for the street or road course. You can fix this by changing you rear gears to bring that power back down to where you want it.


First, work on increasing the flow of your intake and exhaust before getting into the engine. That is, look at the air intake, fuel intake and exhaust before worrying about cams and new cylinder heads. I don’t cover superchargers or nitrous because they can cause too much stress on an engine if not done correctly. There’s a lot of reading you need to do if you’re interested in one of these options.

More is not always better. Increasing one part too much will create a bottleneck elsewhere that can actually bog you down. Think of your engine as a complete system.

Once you go over about 300 HP you need to upgrade your fuel delivery and spark. Also, over 300 HP is where you’ll find other weak links like your tranny, driveshaft and rear-end so this is where it starts getting expensive as the stress levels on your engine increase.

Cheap horsepower gains:

Tune up – good quality plugs, wires, cap, rotor

Clean injectors

Remove air silencer -- it's under the air box in the wheel-well

K&N air filter

Advance timing – experiment to see how high you can advance it and not have pinging.

Synthetic fluids. Not a lot of HP gains, but definitely a good idea for you performance car’s longevity. Change the motor oil, tranny and rear end to synthetics.

Underdrive pulleys. Slows down your accessories, your alternator and A/C, that rob power. Warning: This may slow down your alternator enough to where it discharges at idle.

Next improvements:

Lower (numerically higher) rear gear. 3.55 or 3.73’s are good all around gears.

Exhaust headers.

Tuned cat-back exhaust. Just mufflers don’t make much difference in HP.

H pipe and high flow cats. Your state’s emissions laws determine what you can do.

More improvements:

Intake manifold, Extrude Honed or new, and a bigger throttle body. Stock TB is 60mm. Go to 65 for lightly modified cars. Then new cylinder heads.

Convert the Speed Density air intake to mass air metering. 1989-up ('88 for Calif. Mustangs) came with MAF. This probably only needs to be done for more highly modified cars, especially when increasing the air flow with a better intake, heads or cam. Even then, in many cases, Speed Density can work OK if you have a custom computer chip made for your modifications, but then if you change your car you may need to re-program the chip.

Common mistakes:

Too big of anything. Too big of a throttle body or carburetor, too large diameter of headers, etc.

Ram air using hot under the hood air – cold air is denser therefore better. Draw the air from outside. Warning: Drawing air from under the car is a good way to suck up water, road kill, etc.

Using more octane than you need can actually rob power and will at least waste money.

Colder plugs – Maybe for the race track only

Putting a lot of money into fuel flow (fuel pump, injectors) and after-market ignition on a nearly stock engine.

Computer Chips - Putting a chip on a stock or nearly stock engine is a waste of money. You can advance your timing yourself! Once you go into fairly heavy modifications then it's time to think about having a custom chip made to fit your particular engine, especially if you're experiencing drivability problems. Don't bother with an off-the-shelf chip on a stock engine -- put the money into something better.

So how much horsepower do you gain?

Part vendors make unsubstantiated claims. Other improvements move the horsepower way up in the rpm's so the car may actually feel slower around town. And since your engine is a system you may not realize the full potential of a particular upgrade until you do something else. All that said, here's a shot at estimates of horsepower increases for some popular modifications:

Underdrive pulleys -- 5 to 10 hp
Cat-back exhaust -- 10 hp
Headers -- 10 hp
H-pipe -- 5 hp
K&N-type air filter and remove air silencer-- 5 hp
Throttle body -- 5 to 10 hp
Intake manifold -- 15 hp
Don't forget about gears. No HP increase, of course, but the most performance bang-for-the-buck.

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Here’s where "streetable" really comes into play with getting the right compromise between corning ability and a decent street ride. It’s easy to make the car ride so hard you actually lessen your car’s ability to handle on the street as every little imperfection in a corner sends the car skittering off in the wrong direction.

Cheap gains

Performance alignment. Get rid of the factory spec positive camber (causes understeer). Go for minimal toe in. Find a good alignment shop. Try –.5 to -2 deg camber, 1//16th toe-in.

Stiffer bushings at front sway bar, lower control arms and steering rack. These will be noisier than the stock rubber bushings (the newer polygraphite bushings don't squeak). If you have a higher mileage car just replacing these with new rubber ones would be helpful.

Next improvements:

Lowering springs and new struts and shocks. This is a package. Do it all together. You probably shouldn’t lower more than an inch-and-a-half if you use your car on the street. Don’t get springs that are too stiff. Progressive rate springs are best to retain a good ride; linear rate will provide sharper turn in on the track.

Camber plates to fine-tune the alignment on a lowered car.

Aluminum steering rack bushings help control bump-steer, especially on a pre-90 lowered car. These later cars have redesigned tie rods that take care of this problem.

Stronger control arms for better rear end bite when accelerating from a stop or out of a turn.

Tires. If you want lower profile or wider tires get bigger wheels fitted with tires of the same circumference (called "+1" sizing).

Common mistakes

Lowering the car too much. Gets into other problems with your suspension. Puts too much stress on the wrong parts of the chassis; can’t get a good alignment. There’s ways to fix this, but it’s expensive.

Too stiff springs

Cutting the stock springs. OK if you're doing it just for looks, but this doesn't work if you are interested in performance.

Keeping old struts and shocks when putting in new lowering springs. Likewise, putting expensive Konis in with high mileage springs.

Wide sticky tires with an otherwise old, stock suspension. It looks good, but it’s a waste of money performance-wise on a soft suspension.

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First Steps

Let’s assume you have a mostly stock 5.0L Fox bodied Mustang with a few miles on it and you want to enhance the performance, but you’re not quite sure where you will end up. This is a pretty typical starting point. So what do you do first?

First step recommendations:

Tune up. Plugs, wires, cap, rotor as needed. Check timing.

Clean injectors if it hasn’t been done in over 30k miles.

Change to synthetic fluids.

Remove the air silencer and put in a K&N-type air filter.

Get a performance alignment.

Subframe connectors.

New brake lines, fluid and better fade resistant front pads.

If you were to have a shop do all of the above for you it would be about $800.

Second step recommendations:

Finish off the chassis stiffening with a strut tower brace and G Load brace.

For straight line performance:

Exhaust headers and a cat-back tuned exhaust system

Lower gears

For cornering:

Springs, struts and shocks.

You're looking at about $2000 for all of these.

When you get into moderate improvements unless you know what you're doing think about buying a package whether it's a complete disc brake conversion or a suspension package. As I said before your engine, brakes and suspension can be thought of as a complete system. Changes to one part may cause problems elsewhere. If you go with a reputable company that has maybe engineered and at least tested all the components together you may have fewer problems then if you do things piecemeal. The disadvantage is a larger outlay of money at one time.

Do Your Homework!

Have a plan if you go beyond the simple, basic changes. Where do you want to end up? Are you modifying for street use, drag racing, autocross, or open track? How important is a street drivable car? There will always be someone faster than you at the track, but they may not be able to drive their car on the street. If you commute 40 miles on the freeway everyday you may not want the 4.11 gears and the loud exhaust. If air conditioning is a necessity and you sit in stop-and-go traffic a lot then the cam and underdrive pulleys may be a bad idea.

Most modifications have a trade-off. You have to be aware of what they are so you can make an informed decision as to what's worth doing for your needs. There's a reason the Ford engineers built the car with the parts they did. Often it's just a matter of money, but their decisions may also be based on reliability and NVH (noise, vibration, harshness).

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Further reading:

The Corral: Late model Mustangs web site

Muscle Mustangs and Fast Fords magazine

Mustang Monthly magazine

Mustang Works online magazine

Super Ford magazine

5.0 Mustang magazine

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1987 Mustang GT at Thunderhill Park Raceway in Northern California

Page last modified on 10/05/00

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