[dowroa]

Good day all!

Requirements:
- CANNOT touch stock turbo (no P&P)
- HAVE to have a 3rd cat in the system.
- *Has to meet up with a 2.5" catback.
- No boost creep.

Tune:
- ECUtek
- Tuned in 4th

I have been doing research and I have done a search (at work) for a 2.5" TBE (sans back box) for my 05 STi. I am looking for a DP + highflow cat combo that people have had experience with that did not boost creep.

I will be getting the system tuned via ECUtek and a reputable dyno tuner. Any suggestions on a good TBE that will mate up to a stock backbox/muffler (2.5")?

Links and threads of interest are welcomed!!

Thanks for the help, guys (and gals)!

- dow

Ps. Please send me links to the TBE/DP/highflow cats that you suggest! I need a highflow cat, so no catless systems please!

[esemes]

bro, a 2.5" isnt ideal in this case.....

i believe the stock system is 2.5....

imo, get a 3" catted TBE.

ese

[dowroa]

Since I am running the stock turbo, and I will not be changing it, I dont see a reason to go 3". That is also going to require that I get another rear back box - something I am not trying to do.


I can make NO changes to boost and/or physical changes to the turbo, so I believe that I don't need to go 3".

Please send me any links/proof if you believe that a 3" system is the way to go for my parameters.

Thanks!

- dow

[evilSTi7]

maybe im not completely understanding what your saying, but most of the people on this site who are running the stock turbo and have a tbe have a 3in. also, what do you mean by rear back box? and with changing boost, if you go with any exhaust thats flows better, you have gain the possibility of getting boost creep. from what it sounds, in your situation i would not upgrade my exhaust because the things you want to happen are not likely

also, just wondering why you have all of these constraints?

[jgheels2003]

Originally Posted by dowroa

Since I am running the stock turbo, and I will not be changing it, I dont see a reason to go 3". That is also going to require that I get another rear back box - something I am not trying to do.


I can make NO changes to boost and/or physical changes to the turbo, so I believe that I don't need to go 3".

Please send me any links/proof if you believe that a 3" system is the way to go for my parameters.

Thanks!

- dow

If you aren't making any changes to the boost then an Ecutek tune will do little for you and you will waste a lot of money. Leaning out the system with a little smoother curve is the only thing you can get out of what you are looking for and that you can achieve with the stock exhaust system since it is already your desired size. A downpipe is designed to allow more exhaust flow, so you aren't gaining anything from an aftermarket 2.5 inch setup.

[Rdrcr]

I am slightly confused as well?

A Ecutek tune will normally increase your boost pressure. By increasing you boost pressure along with the necessary changes to your maps you get an increase in HP/TQ. I don't see much benefit at all, if you ask a tuner to tune your car, but don't let them increase the boost?

Most STi's that are tuned (Cobb AP, Protune, Ecutek, Street Tuner, Utek) run 3 inch cat backs WITH the stock turbo. Then there are guys like myself that complain profusely about 2.5 inch bottle necks where the downpipe meets the midpipe (you may not find a problem with this?). You have a ton of choices in 3 inch TBE's, I suggest that you look for a 3 inch system.

If your heart is set on a 2.5 inch exhaust, I would just purchase an axel back. The stock midpipe and the factory downpipe is 2.5 inches.

Mike

[dowroa]

Fair enough.

Boost cannot and will not change on this car as this is an STU autoX car. Boost is NOT allowed to be changed under those parameters.

Furthermore, and 'less restrictive' exhaust is going to allow the car to breathe better and thus generate more power with decreased back pressure. Remove the stock DP cat in itself should help reduce spool marginally.

Since I am NOT increasing boost, I don't see how a 3" system would be a given.

Regardless, I was looking for opinions. Reducing EGT and leaning out AFR does allow modest power gains. That is all I am looking for.

- dow

Ps. I am looking for ANY diameter exhaust until it meets up with the back box/muffler flange. I want to retain the stock muffler, but between that and the turbo, I could care less as long as there is a high flow cat within 6" of the stock location.

[jgheels2003]

Originally Posted by dowroa

Fair enough.

Boost cannot and will not change on this car as this is an STU autoX car. Boost is NOT allowed to be changed under those parameters.

Furthermore, and 'less restrictive' exhaust is going to allow the car to breathe better and thus generate more power with decreased back pressure. Remove the stock DP cat in itself should help reduce spool marginally.

Since I am NOT increasing boost, I don't see how a 3" system would be a given.

Regardless, I was looking for opinions. Reducing EGT and leaning out AFR does allow modest power gains. That is all I am looking for.

- dow

Ps. I am looking for ANY diameter exhaust until it meets up with the back box/muffler flange. I want to retain the stock muffler, but between that and the turbo, I could care less as long as there is a high flow cat within 6" of the stock location.

If all you are doing is getting a higher flowing cat and staying 2.5 inch you are losing neglible amounts of exhaust restriction. Save your money and keep it stock. There is very little restriction at stock boost levels.

[Rdrcr]

Originally Posted by jgheels2003

If all you are doing is getting a higher flowing cat and staying 2.5 inch you are losing neglible amounts of exhaust restriction. Save your money and keep it stock. There is very little restriction at stock boost levels.

I agree.

I am still not 100% sure on exactly what you are looking for. From what I understand, you want a downpipe, cat., and midpipe that connects to the factory muffler. I would recommend the Turbo XS stealth back. It is much larger than 2.5 inches, but I have not heard any complaints about this product. However, I don't think the cat is mounted within six inches of the factory location?

http://www.jscspeed.com/part_pictures/txs_sbe_wrx.jpg

http://www.jscspeed.com/wrx/exhaust/..._turboback.htm - about half way down the page. $689.00

Hope this helps?

Mike

[mx_9]

Damn, everyone confuses noobs like me. Here's what I found on another suby site in their exhaust faq:

Which exhaust diameter is best? Exhausts have 3 diameters:

1. 2.5": Good for 300-350 HP
2. 3.0": Good for 500-600 HP
3. 3.5": Good for 600HP +

There is no irrefutable evidence that one diameter is better than the other. Purchasing a larger exhaust than needed for your level of modification has no advantages or disadvantages. Naturally aspired vehicles, as they respond better to backpressure, should always choose an exhaust catered towards their specific needs.


I can see how tapering down within a given TBE may affect things depending on the location of the taper but for what Dow's looking to do for power the 2.5" should suffice.

[Tortfeasor STi]

Turbos make power by turning wasted exhaust energy into power to turn a turbine forcing air into the engine. The more efficient your exhaust is at routing out the exhaust gass the less power the engine uses pumping the gas out which leaves more power to turn the turbine which makes more power. Essentially the larger the presure change in the exhaust from before the turbo to after it the quicker the turbo spools and the faster it reaches peak efficiency. Simply quoting tubing size does not tell the whole story of exhaust gas flow. A well designed and engineered 2.5" will out flow a poorly designed 3". So dont worry about the size of the DP as long as it mates to the factory exhaust system and is designed well.

Since you are building this car to fit into a racing series I would suggest you buy the most agresive down pipe that fits the rules of your racign series. As a side note the stock down pipe has two catalytic converters in it one just after the turbo and one further down stream. There is no 3rd catalytic converter. WRXs have a third that the STi does not and it is located pre turbo in the up pipe. So even the stock set up does not have a 3rd cat. When buying a catted down pipe it is important to note that they usually eliminate the first cat that is located close to the turbo in favor of a high flow unit located at the back of the DP.

If I was buying a down pipe right now I would buy the Cobb down pipe as it is well designed and uses a metalic substrate catlytic converter which flows better and is not as fragile as the standard ceramic substrate used in most facoty and high flow cats. But this was not designed to fit into a racing series so might not fit your requirements. I would contact the manufacturers of the DPs people suggest and see if they conform to the rules of your racing body. If they are interested in your business they will get back to you.

Lastly, there are many ways to make power through custom tuning your computer. Between boost maps, fuel maps and ignition timing you have many places to find power. Just because you cant increase the boost does not mean you cant make more power in the CPU. Consult your rules and find ways to make power within the letter of them.

Sorry for the length of this response.

[esemes]

i found that APS makes a 2.5" TBE system......

[silver arrow]

Stromung DP mates to the stock 3rd cat and requires no modification to the stock turbo. http://www.scoobytuner.com/products/?productID=593 but it is 3". I think stromung makes a 2.5" though I couldn't find it. These are inexpensive too.

[dowroa]

Thanks for the feedback gentlemen.

I am going with either a TurboXS Stealth back which will mate up to my 2.5 Axle back, or a Cobb... which I am not 100% sure about right now as I dont know if I am going to need the stock resonator + muffla for.

Still doing some slight research, and sorry the inital topic was poorly worded... that's what I get for trying to post at work when I am doing like 10 things at once.

- dow

[silver arrow]

Originally Posted by dowroa

Thanks for the feedback gentlemen.

I am going with either a TurboXS Stealth back which will mate up to my 2.5 Axle back, or a Cobb... which I am not 100% sure about right now as I dont know if I am going to need the stock resonator + muffla for.

Still doing some slight research, and sorry the inital topic was poorly worded... that's what I get for trying to post at work when I am doing like 10 things at once.

- dow

Why no the Stromung? They are inexpensive and if you are using the stock CB you will notice no diffence than with the other 2.