3 ½” Custom exhaust & CEL

[Onyx]

Good morning all.

I’m planning to install a custom 3 ½” exhaust (turbo-back) on my 6MPS. Does anyone know if it would give a CEL reading? If so, how can it be corrected?

Thanks!

[Doug_MPS6]

Most advice I've had is that 3" catback to tailpipes is overkill. I'd say that 3.5" would be more-so.

[Scaredycrow]

How about giving us some background? Other mods on the car? Why your chosing a custom exhaust over the tried and tested off the shelf products?

Power goals?

I hope you like drone

[rogwick]

I agree, I have a 3" on mine (welcome to see pics and description of it) Not sure if its over-kill or anything, I left it in the trusted hands of my usual mechanic who does significant work on all types of vehicles including turbocharged vehicles, V8's etc. Although I have a 3" I also have a catalytic converter, 2 resonators and split into two mufflers. This all adds to back pressure so by design, my 3" is probably acceptable. Unless you're planning on getting a bigger turbo and possibly custom manifolds etc I would suggest that a 3 ½ is too big. Welcome to shop around on the forum as there are a few threads detailing effective exhausts on the MPS6. Again, welcome to view mine in fair detail on my thread.

[rogwick]

Stainless Steel = Drone, just for info.

[240MPS]

3" & 3 1/2" will be a over kill un less you have some serious work to the motor and a big turbo, I knew someone who put a 3 1/2' system on his MPS3 3 years ago and only had it for 3 fuel fill ups and got rid of it he lost power and the fuel economy got worse plus the drone....

[rogwick]

3" & 3 1/2" will be a over kill un less you have some serious work to the motor and a big turbo, I knew someone who put a 3 1/2' system on his MPS3 3 years ago and only had it for 3 fuel fill ups and got rid of it he lost power and the fuel economy got worse plus the drone....

What have you got on yours Rino? Yeah you're right drone will most likely be really bad on a 3.5". Just to throw it out there, typical exhaust size for a 4cyl ~2.0L turbo is around 3" as with WRX, Silvia, EVO etc. Yeah? Although they have bigger turbo's but the MPS is typically running higher boost than most

[240MPS]

What have you got on yours Rino? Yeah you're right drone will most likely be really bad on a 3.5". Just to throw it out there, typical exhaust size for a 4cyl ~2.0L turbo is around 3" as with WRX, Silvia, EVO etc. Yeah? Although they have bigger turbo's but the MPS is typically running higher boost than most

I'm just running a 2 1/2" Sports Exhaust system from the DP back,for improved fuel economy and flow......

[rogwick]

I'm just running a 2 1/2" Sports Exhaust system from the DP back,for improved fuel economy and flow......

Oh, yeah, and that obviously goes pretty well I assume. Stock turbo too? The stock MPS exhaust is 2"? I don't have any issues with mine, I can feel increased performance, however, as mentioned I do have dual resonators, a reduction at the Y piece + two mufflers which makes for more back pressure than a typical straight through 3" single muffler exhaust. What's the theory behind a typical WRX straight through exhaust? 3" seems to be the common upgrade size. I assume most WRX's have stock turbo's too.

[magoo]

You will not lose power due to overly large exhausts on Turbocharged vehicles. Exhaust size on N/A vehicles is highly important due to velocity and scavenging.

This talk of power loss due to the exhaust being too large is crap.

To backup my statement please find a quote by a Garrett engineer as follows,

"Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range"

Now this being said and done you will expect very small gains (if any) due to the K04s size if you went from 3" - 3.5".