Overall T-bird Mods

Air Filter

For the start, invest in a K&N panel or conical filter for about $30 to $60. These things help out by allowing better airflow to the engine, and it's a one-time buy. K&N sells a reusable air filter element that just requires periodic cleaning and re-oiling. Whether or not the K&N is better than a clean paper filter is debatable. However, if you clean it more often than you would replace a paper filter, on average it will present less of an obstruction. The instructions give some insane cleaning interval (like 50,000 miles or so), but I clean mine at least every other oil change.

VERDICT - Use it, but clean it regularly

Air Intake Silencer (EFI engines only)

The air intake silencer is located next to the air filter housing, on the opposite side of the sheetmetal (inside the fender). It's a big plastic doohickey with more than a passing resemblance to a Jarvik artificial heart. It's sole purpose in life is to quiet down the air as it's sucked into the engine. The silencer presents a bit of an obstruction to air flow, so removing it will put you one step closer to a better intake path.

VERDICT - Yank that puppy. Why should you only hear the exhaust?

Change (or remove) the factory thermostat

This is based on the fact that cooler air is denser, so the less you heat the air coming into the engine, the more air/fuel mixture you can pack into each cylinder. An old shade-tree mechanic fix, but it's got several strikes against it. First, you never want to remove the thermostat completely. The cooling system has been designed with the thermostat restriction in mind, and removing it will actually _hurt_ cooling. Second, cylinder wall wear increases as operating temperatures are lowered. The stock Mustang thermostat is set for 196° Fahrenheit. Dropping to 180° will increase wear somewhat, and dropping to 160° or 140° will increase wear dramatically.

On EFI cars, cooler thermostats are rumoured to increase performance because the engine will run richer at temperatures below 180° Fahrenheit. True, the EEC-IV will richen the mixture, but staying in "warm up" mode entails more than just a richer mixture. The EEC-IV will be more conservative with the timing curves, and will never get into "closed loop" operation (where it uses the oxygen sensors to fine-tune the mixture). The result will likely be poorer drivability and _decreased_performance. Also, catalytic converters can be damaged over time by an engine that's continually running rich.

VERDICT - Don't remove the thermostat entirely, and don't use a thermostat below 180° Fahrenheit on an EFI car.

Underdrive Pulleys

The idea here is to reduce the parasitic loads on the engine, freeing up more power to go to the rear wheels. Underdriving the accessories will reduce the loads, but not as much as the manufacturer's ads would have you believe. The accessory loading isn't linear, so reducing an accessory's RPMs by a third won't reduce the needed power by a third. In addition, if the alternator is underdriven, it may not provide enough power to keep all the electrical loads happy at lower RPMs (especially if you have a mega-watt stereo), and underdriving the power steering pump may result in increased steering effort when idling through the parking lot.

There is another reason to underdrive accessories. The accessories were designed to operate at a particular RPM for most of their lives, and can fail or cause problems if run at higher RPMs for long periods of time. This becomes a problem for cars that run on the track. Installing underdrive pulleys in these situations can put the accessories back at their normal operating speeds and increase their useful life.

VERDICT - You may pick up a couple of horsepower, but be careful or you may end up with a dead battery. If you run on the track, your power steering pump will thank you.

Mufflers

As far as sound goes, as someone suggested the cheapest way is cut the mufflers off to just to see how it sounds. If you not going to like it, you can always put the stock ones back on or replace them with higher flow after-market models.

Eliminating bottlenecks anywhere in the intake or exhaust systems is almost always a help. However, the mufflers are part of a larger system and can only do so much by themselves. The factory headers, catalysts, and pipes put a limit on how much can be gained by replacing the mufflers.

Better would be to add dynomax, or probably 2-chamber Flowmasters if you want big sound. Best would be a cat back, but the gas tank in all the birds up to - '92 is a screwy configuration and would probably be best off changing it (the jog in the exhaust isn't as big) before going with whole exhaust upgrade. I would also say removing the mufflers also added about the same horsepower (an honest 5hp at the rear wheels).

VERDICT - Good as part of an overall exhaust system improvement, otherwise buy them for the sound, not the performance gain.

Shift Kit and a cooler

Add a shift kit. It makes the shifts firmer, so as a quicker shift, and also saves the transmission by making possitive shifts without the ford overlaping of clutch packs during the initial shifts.
It runs in between $25 to $125 depending on which you get. Trans-Go makes probably the best out there for these trannies, and it comes with a video to walk you through it. The chip will do the same if not less than the B&M Shift+ (electronic shift improver) for the shifts for $40.

I HIGHLY recommended a transmission cooler, especially when you are running a shift kit. These trasnnies are known for trouble, and between the shift kit and cooler, you can manage to keep your tranny alive for nearly 100,000 miles with no troubles.

VERDICT - Very good idea. Your tranny will thank you and you will love that racing touch.

Swap the gears

Some say to save the money and grab some steeper gears. Most Birds probably have 3.08s which are very high. 3.73s would make your car feel lighter and much more powerful without increasing hp at all. Your 1/4 mile times would significantly drop as would your 0-60. But without extra hp your 1/4 mile ets would stay the same. Higher ratio gears will increase acceleration but decrease top speed and fuel economy.

VERDICT - You will get some impressive pickup but your fuel economy can suffer-especially on the highway.

Crank up the fuel pressure (EFI engines only)

Increasing the fuel pressure on an otherwise stock engine (by by going to an aftermarket regulator) is a bad idea. Within limits, the EEC-IV will compensate for the excess fuel by reducing the injector duty cycle. Beyond this, it will give up and resort to "limp home" mode, in which your engine will run like dog meat. Modified engines sometimes require additional fuel pressure to keep up with the higher airflow, but on a stock engine you're wasting your time.

VERDICT - Don't do it.

Install aftermarket headers

VERDICT - Makes sense, but don't expect huge gains, and do clean them up first.

Higher stall Torque Converter

Now, if your lookin for a little more than that, Precision Industries at www.converter.com make an awesome converter for these cars. You can drop more than a full second off your quarter mile times, made the car easier to maneuver in traffic (due to acceleration), and because it is still a lock-up converter, your highway MPG is still high, and your around town milage is up.

VERDICT - That's if you have some extra money and want more performance.

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