Exhaust Frequently Asked Questions

Exhaust Modifications

If you are building your own system, or have questions about replacing your exhaust parts, check here first... We also have some examples of what other users have done to spark your creative interest. If you have a custom exhaust Email me so we can show everyone what you created.

Q: How can I make a "turbo back" exhaust (Straight from the turbo to muffler)

A: It's not that hard if you put your mind to it.. It's a lot easier to go with 2.5" piping and you will still achieve a much greater performance over stock. 3" of course would be ideal. If you can make the downpipe using mandrel bends an exhaust shop can take care of the rest. Some people have made their own downpipe. The best bang for the buck formula is: Have your cat gutted. Go to an exhaust shop and have the 2nd cat replaced with a straight pipe. Finally have a catback exhaust made with a high flow straight through muffler and 2.5" piping. This setup yielded 13 sec 1/4 mile time on my All Trac and easy on the ears.

Q: How do I make a downpipe with the strange shape of the turbo elbow?

A: Here's a picture of the exhaust side of the turbo, ST165 and ST185 respectively. You can see that it's quite an odd shape. If you take your turbo gasket to a CNC machine shop, they can make a steel weldable flange for you for around $50. From that point on you just need mandrel bent piping. You will also need flanges for your o2 sensor and the bottom to bolt to your current exhaust. Below you can see what a finished downpipe looks like. You see the flange at the rear. It's using 2.5" mandrel piping and the smaller flange at the bottom to bolt to the stock exhaust system. The piping you see at the top to the left of the main pipe is a piece of pipe that has been welded to cover the rest of the opening of the flange. This also allows the wastegate gases to join more smoothly with the turbo exit gases.

Q: How do I make the rest of the downpipe?

A: Once you have the flange created, you will need some piping. It is preferred that you get mandrel bend piping that is capable of high heat. Stainless steel is the best here. You will also need flanges for your o2 sensor and the bottom to bolt to your current exhaust. Below you can see what a finished downpipe looks like. You see the flange at the rear. It's using 3" mandrel piping all the way. The piping you see at the top to the left of the main pipe is a piece that has been welded to cover the rest of the opening of the flange. This also allows the wastegate gases to join more smoothly with the turbo exit gases.

ST185dp1.jpg (393856 bytes)ST185dp2.jpg (431047 bytes)ST185dp4.jpg (350849 bytes)

Alltrac.net will be providing 3" downpipes to members in the near future. We also can provide you the flange to make your own for $35.

Q: I have an ST165, Can I buy an commercial ST185 cat back system and have it fit?

A: YES, well sort of. 2 things support this answer. First the HKS system fits both ST185 and ST165. Second in the original Toyota parts database the pictures of ST185 and ST165 exhaust are identical. So they are essentially the same. You *may* have to make a minor modification depending on the manufacturer. Basically ST165 is an old car, and a manufacturer would not bother to test out their product on an older model. We actually did confirm this with a member, who stated simply that the hangars need to be relocated, and the piping will sit slightly lower than an ST185. I have also myself bolted the ST185 Blitz exhaust system on my ST165. It fit, but the flanges that connect the 2 pieces had to be grinded down some. The hangers all bolted right up. Also the rear tow hook over the exhaust rubs against the tip. I will have to have that bent up or cut off.

Q: I have heard of people gutting out their catalytic converter, what is that?

A: This is the process of removing the internal parts of your catalytic converter. Not an easy task, but well worth it. Major gains are to bad had with this mod. Remove your cat, soak it with brake cleaner and let it sit over night. The next day punch out the insides with something and try not to breathe any dust. Once all cleared smooth out the inside and replace. You will notice boost come in alot faster. The only drawback is a slightly higher exhaust sound and possibly failing an emissions check.

Q: If I have no cat, how can i pass smog?

A: That all depends on you car. If it is running in top shape, you can still pass emissions. Luck for AWD cars is that they don't have to go on the dyno rollers. They are tested at idle and another RPM. Otherwise, you will have to have a high flow cat installed in your system somewhere down the exhaust path.

Q: How much would I expect to pay for a 3" exhaust?

A: A member just had his done. It was 3" catback exhaust with a Apex N1 muffler. The N1 Muffler goes for $249 retail. He paid $350 total for the muffler, piping, and labor. $100 is typical labor charge for welding any exhaust on your car. That sounds like a good price, but there are drawbacks. While they used 3" piping, the bends are not mandrel. So where the exhaust bends it's more like 2.75" or so. Also they welded it on in one piece to cut cost. What that means is that the exhaust cannot be taken off. It must be cut off. The stock exhaust system is in 2 pieces so that you may unbolt it if necessary.

The same job using mandrel bends and putting a proper flange in the middle of the system to make it unbolt would cost around $500-600 depending on the muffler. A bolt on 3" system also costs in the neighbor hood of $600.

Q: It doesn't look like 3" exhaust will fit over the rear axle, will it??

A: Yes it will, but it is very tight, you might end up having to make a small dent in the pipe, or grind some area off the bottom of the car, as highest bend will rub on the bottom of the frame if it's not perfect. Another option is to go under the axle. A couple of people have done this and reported no problems other than less ground clearance. As long as yours is not slammed to the ground, then this option is the easiest.

Q: What is catback?

A: When we refer to exhaust systems on this website. We use the term catback. What that means is from the catalytic converter, back. There are 2 cats in our system. The first cat is the big giant one directly under the turbo. There is a second smaller one that exists about under the front seats. 2nd cat back refers to an exhaust system that bolts to the end of the 2nd cat and goes back. A primary catback system would go from the end of the 1st cat which ends around where the oil pan starts. Then off to the muffler in the rear.

Here are the components of the exhaust system in the order that they appear:

  • Turbo

  • Turbo Elbow (contains o2 sensor)

  • Primary Catalytic Converter

  • Midpipe/B Pip (contains flexible pipe and 2nd cat)

  • Catback Exhaust (contains 2 mufflers and is in 2 pieces)

Q: All this sounds great, but is making downpipes and exhausts legal?

A: First there is emissions, as mentioned before you should have some sort of catalytic converter. Even still a smog check can still be failed by visual check if they feel it is not legal. Second there is the noise factor. Gutting your cats and running straight into a single muffler will be loud. Legally any sound under 95db (California) is legal. A good way to keep the noise down is to use a resonator before the muffler, while u might get as much peak power, it could mean the difference between getting that ticket or not. Even if your exhaust is under 95db they can write you up if they feel like it. Finally common sense, a large tipped stainless steel big shiny muffler looks cool, but is attractive for the law enforcement. So if you are concerned about it get a subtle muffler that looks stock, and keep the piping 2.5", use a resonator and a cat. The money you will pay for a ticket will most certainly have went better towards another upgrade for your car. Good Luck.

Q: How much power can I gain from a downpipe or gutted cat.

A: While all downpipe and car variations do not allow us to give you accurate numbers, we have come up with our own estimations. Based on several different examples, here is how much horsepower can be achieved at the motor (not wheels). As you can see the major improvement comes from going to a full downpipe. The difference to go from a 2.5" downpipe to a 3" downpipe is not as big of a jump in power. In any instance your peak boost will be raised automatically.

Gutted Cat - 10 HP (dyno proven)

3" Cat Pipe - 12 HP

2.5 Dpipe - 20 HP

3" Dpipe - 25 HP