Nothing on a stock car is top-of-the-line... everything could use improvement. Finding flaws in the car's design is valuable horsepower just waiting to be unleashed. In that respect, the Probe's exhaust system is a virtual goldmine. The conservatively build exhaust system on the Probe is good at muffling the exhaust and keeping the Probe's price tag low, but extremely bad at keeping the exhaust gases flowing smoothly. Ford is also restricted by Environmental Protection Agency guidelines on the overall design of the exhaust system since the Probe is a high production car. The EPA is not concerned with horsepower and torque, but rather the effects of your car's exhaust gases on the world around us. Aftermarket sources for exhaust products don't have any of the restrictions Ford has, giving us a way to give our cars the exhaust systems they need. The downside is we do have local state environment and emission codes that we must adhere to in order to keep our car street legal. Although most companies keep their products within these codes, it's very important that you check all laws in your state before upgrading any part of your car's exhaust. I don't condone anyone altering their vehicles that may infringe on any federal or state environmental codes. If anyone has a question of why these codes exist, take a look at this CNN article.

The main thing to remember is that the hotter the exhaust gases are, the more velocity they have. Oversized exhaust pipes and thin material can cool exhaust gases, slowing down flow and causing more backpressure.

This section is for performance exhaust systems that yield more power, not more sound. I see a lot of people (mostly kids) buying exhaust parts and mufflers based on how 'loud' they are. This is totally absurd and this site will never promote that type of amateurish thinking. It's like buying a steak based on how the cow moos. Personally I'm sick of people upgrading their cars trying to make them louder... they're loud, obnoxious, and I don't even need to see the car to hate it when I hear one go by.

Key
Pros: The benefits of a particular upgrade.
Cons: The down side of a particular upgrade.
Cost: Approximate price range based on numerous quotes and price sheets.
HP Gains: Estimated increase in horsepower you can expect from a particular upgrade. Not necessarily peak horsepower.
Manufacturers: Examples of particular companies that sell a particular upgrade.
Availability: Which Probes the upgrade is for.

Contents
Cat-Back Systems
Catalytic Converters
Downpipes
Exhaust Pipes
Exhaust Wrap
Headers
Hollowed Catalytic Converters/Straight Pipes
Performance Mufflers

Cat-Back Systems

 

Cat-back systems consist of all exhaust parts behind the catalytic converter. Sold as kits, these usually consist of larger, mandrel bent piping, high-flow resonator, and a performance muffler. These kits are usually direct fit, easy to install modifications that significantly increase power, especially at high rpm.

In 1996, the Probe received a minor exhaust change. The new exhaust was designed for OBD-II. If you try to use a '93-'95 cat-back system, you'll come up about 6" short. To get around this, you'll need to have a 6" piece of pipe custom made for the gap. Any muffler shop can do this.

Personal Experience: I installed a Borla turbo-back exhaust system on my '92 GT. The system was completely stainless steel and mandrel bent, with a Borla dual intercooled tipped muffler. Exhaust tone is louder and deeper without being obnoxious and with no interior droning. There was almost no low range torque loss and had considerable mid and high range power improvements with faster turbo spool up.
Pros: Greater decrease in backpressure, more horsepower.
Cons: Increased exhaust sound, possible state emissions codes.
Cost: $150-$700
HP Gain: 10-15hp
Manufacturers: Borla, Bosal, Brullen, GReddy, HKS, PaceSetter
  Availability: All, '96 & '97s may require modifications
 

Catalytic Converters
The catalytic converter is a part of the exhaust system that converts exhaust gases into carbon dioxide and water vapor through chemical reaction. Stock catalytic converters are designed for function with a budget in mind, not performance. A high flow catalytic converter can add a few horsepower while staying within state emission codes and federal EPA laws. This may only appeal to people looking to get every bit of horsepower they can from their cars since it's one of the highest cost per horsepower modifications available.
Personal Experience: Currently looking into.
Pros: Decreased backpressure, some extra horsepower.
Cons: None.
Cost: $100-$250
HP Gain: 2-3hp
Manufacturers: Random Technology
  Availability: All
 

Downpipes

 

The downpipe is the piece of exhaust pipe that connects between the exhaust manifold or turbo and the catalytic converter on 4 cylinder engines. V6s instead have Y-pipes under the engine connecting the two manifold sets to the catalytic converter. This is the most restrictive part of the exhaust system. The downpipe, which is less than 2" in diameter, is press bent and includes numerous 'steps' from welding material that lessen the pipe diameter even more.

Since there are only a few direct fit replacement downpipes, the best thing to do is go to a muffler shop and have one custom made. The main point to remember is to have the pipe mandrel bent. To keep the gases hot and engine compartment cool, ceramic coating is highly recommended. Most aftermarket headers include the downpipe.

Personal Experience: The exhaust system for my '92 GT included everything from the turbo to the muffler. The downpipe was much wider then stock and made a big difference in turbo spool up. When I purchased the Hotshot headers for my '89 LX, the headers included a mandrel bent downpipe.
Pros: Greater decrease in backpressure, more horsepower.
Cons: Possible drop in low end torque.
Cost: $100-$300
HP Gain: 5hp
Manufacturers: Bosal
  Availability: 1st Generation
 

Exhaust Pipes
When upgrading your exhaust system, it's important to remember that the hotter the exhaust gases are, the more velocity they will have when flowing through and out of your exhaust system. When it comes to the exhaust pipes, unlike what most people think, bigger necessarily isn't better. On a stock Probe, 3" exhaust pipes will reduce the backpressure over, but will allow the exhaust gases to cool, slowing overall flow. For up to 150hp, 2-1/4" pipes would be sufficient. For engines from 150hp to about 250hp, 2-1/2", and for engines from 250hp-300hp, 2-3/4"should be fine. If you're not too worried about low end torque, you can add a 1/4",  but any bigger could drastically reduce low end torque.

The stock exhaust pipes on the Probes are press bent. Although cheaper, this method will cause increased backpressure in the exhaust system. Any pipes you get should be mandrel bent to keep exhaust gases flowing smoothly.

Personal Experience: All exhaust pipes on my '92 GT have been upgraded. My '89 LX's exhaust pipes will be replaced with custom made pipes.
Pros: Greater decrease in backpressure, more horsepower.
Cons: Possible drop in low end torque.
Cost: $100-$500
HP Gain: 5hp
Manufacturers: Borla, GReddy, HKS, PaceSetter
  Availability: All, '96 & '97s may require modifications
 

Exhuast Wrap
Exhaust wrap can be used to cover and insulate exhaust pipes and headers. This will keep the engine compartment cooler and the exhaust gases hotter. The hotter the exhaust gases are, the more velocity they have when flowing through the pipes.

Wraps are not as good as ceramic coating since they only trap the heat around the pipes, which increases the temperature inside. This can stress the pipes. A good ceramic coating applied to the inside and outside of a pipe will increase the gases only without stressing the pipes.

Personal Experience: Would rather ceramic coat the exhaust.
Pros: Cooler engine compartment, hotter exhaust.
Cons: Traps hot air against exhaust.
Cost: $20-$50 per 50ft.
HP Gain: 1-2hp
Manufacturers: Design Engineering, Thermo Tec
  Availability: All
 

Headers
Exhaust headers offer the best improvement along the exhaust system. When the exhaust valves open and release the burned fuel/air mixture from the cylinder, the exhaust gases are usually called a pulse. This pulse goes through the manifold, into a collector where it meets the pulses from the other cylinders. The collector simply forces all the pulses into one pipe where they travel through the exhaust system and out the muffler. Headers can improve this flow in three ways:
  1. The pipes are mandrel bent to allow smoother, unobstructed travel of the pulses, reducing backpressure.
  2. Each of the header's pipes have a calculated length to allow one pulse at a time to enter the collector, instead of all being forced together. As each pulse enters the collector, it creates a vacuum behind it which effectively pulls the next pulse smoothly along behind it. This allows for smoother exhaust flow decreasing backpressure.
  3. Most headers today are ceramic coated. This keeps the exhaust gases hot, allowing the gases to flow faster, as well as keeping the engine compartment cooler, keeping intake temperatures at a minimum. If you have a set of headers that aren't ceramic coated, it's highly recommended that you have them coated.
Personal Experience: I bought Hotshot headers for my LX. Although I haven't tested them out yet (engine's still being rebuilt), the weight difference alone is worth a note... the stock manifold with downpipe weights a hefty 26 lbs. The HotShot headers, on the other hand, with the included downpipe weights only 9 lbs... a drop of 17 lbs.

The only problems I can see with the HotShot headers has to do with installation. First of all, one of the bolt holes were off centered, which I had to use a Dremil to fix. Not very impressive. Also, with the air conditioning compressor in the way, removing the stock manifold may be a bit difficult.

Pros: Increased horsepower.
Cons: Possible drop in low end torque, possible state emissions codes.
Cost: $150-$600
HP Gain: 10-15hp
Manufacturers: Bosal, Brospeed, Hotshot, PaceSetter
  Availability: 1st gen 4-cyl non-turbo, all 2nd gen
 

Hollowed Catalytic Converters/Straight Pipes
The catalytic converter is a part of the exhaust system that converts exhaust gases into carbon dioxide and water vapor through chemical reaction. Replacing the it with a straight pipe or removing the inner material from the device will decrease the backpressure in the exhaust system and add a few extra horsepower. Although a seemingly easy way to boost horsepower, doing so may put you at risk of state emission code violations. In New York, for instance, there's a $1500 fine for removing or hollowing the catalytic converter. I don't know which states, if not all of them, have laws pertaining to catalytic converters. Check local laws where you live before attempting this. Your car will not pass state inspections where emission tests are required.

Replacing the cat with a straight pipe is the best method. It provides a better exhaust flow and frees you up of the extra weight of the cat... they usually weigh 15-20 lbs! All you would need is a 2-1/4" pipe about 18" long, which you could get from a local muffler shop for a small price. The only drawback of this method is that the missing catalytic converter is very apparent.

Hollowing the cat is the cheapest method... and sneakiest. All you would need to do is remove the cat, and break out the brittle inner material. This can be done with a long screwdriver or tool. The best part of this method is that the shell is still on. You can't tell the catalytic converter isn't functioning unless you take an emissions test. A good method for states like Texas that only look to see if the cat is there.

Personal Experience: Right after I got home from getting my LX inspected, I hollowed out the cat using a drill with a long drill bit, and a screwdriver. There are 3 sections of asbestos type material locked into place by flat metal rings. I drilled straight through the cat from one end to the other then used the screwdriver to break the rest out. The metal rings could then be worked out with the screwdriver or pliers. Barely noticeable power increase, but the deeper exhaust sounds tell me there's less backpressure.

When I got the GT I swapped the LX's cat for the GT's. It had a very little bit more noticeable power then when it was on the LX. I'm currently looking into a high flow catalytic converter to make everything legal.

Pros: Decreased backpressure, extra horsepower.
Cons: Legality, possible state emissions codes.
Cost: $0-$25
HP Gain: 5hp
Manufacturers: None
  Availability: All
 

Performance Mufflers
The muffler, obviously, muffles the sound of the exhaust gases coming from the engine. The stock muffler on the Probe is badly designed for consistent exhaust flow, since its number one priority is to tone down the sound, while staying inexpensive. Performance mufflers use better sound absorbing materials along with a better flow design to lessen backpressure in the exhaust system, while keeping the noise level at a tolerable rate. There are a wide variety of performance mufflers on the market, ranging anywhere from a decent one from Midas, to a top-of-the-line one from Borla... the only barrier being cost.

When purchasing a muffler, remember that there is a fine line between a deep performance exhaust tone, and an annoying, obnoxious exhaust racket.

Personal Experience: The exhaust system I installed on my '92 GT included a Borla muffler. This muffler is perfect, since it had dual intercooled tips rather then one large tip, which I strongly prefer. These tips are perfectly sized since they are big enough for smooth exhaust flow, but not so big that they don't look like they 'could' be stock.

I installed my GT's stock muffler on my '89 LX for an improved flow, but with a stock look.

Pros: Decreased backpressure, some extra horsepower.
Cons: Increased exhaust sound, possible state vehicle codes.
Cost: $100-$700
HP Gain: 3-5hp
Manufacturers: Borla, Brullen, Dynomax, GReddy, HKS, PaceSetter, Remus
  Availability: All
 

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