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".

[240MPS]

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".

You would know Magoo for some reason.. I have the proof that's all that cares to me.... Not saying you are wrong but I've seen it and the techs have answered it when I asked...... I don't know myself personal, I just get from the professionals who do I also read a lot of documents and see a lot of different answers go figure, I see it in my own profession, everybody have different answers....

[RedDjinn]

Unless u are running a large turbo there will be no gain in it. 3' dp and 2 1/2' cat back with straight through mufflers will do the job.

[Onyx]

Sorry for the late response. (Crazy monday in the office!)

The MPS is currently all on stock. I haven't done anything to it since I got it 6 months ago and it's kinda getting bored to drive. (Almost sold it!)

My plans for the car are to get a FMIC & exhaust done before 2011. Maybe a HKS BOV for Xmas? (hopefully!) Well, depending on how these 2 mods goes on the car a
I have a CS FMIC coming next month from MPS Garage (Thanks to Daniel!)
I was meant to get the downpipe from CP-e initially. But I was looking at the cost of $1,000. Might as well get a whole custom system including downpipe, high-flow cat, 2 mufflers & fatter pipings for a bit more.

My mate knows this old Aussie man who have been working on exhaust systems for at least 35 years and he now works from home in his 4 cars shed. I went over to see him yesterday and had a chat with him regarding what suggestions he have for the MPS. (He seems to be a really nice bloke, has those trustworthy face and is really knowledgeable in his field.) I saw one of his client's Ford GTS and when he start it up all I did was drool. That dragster was beautiful and he did all whole exhaust system for it and the welding on the headers was close to prefect! Should have taken a pic!...

ANYWAY... long story short! Here is what he suggested - 4" downpipe, Hi-flow Cat, 3½” straight then spilt into 2 X 3" mufflers and a resonator somewhere. When he told me that I was like wow - overkill? My concern is noise level. I hate drone (full stop). He suggested to install an exhaust control valve. I prefer a quiet exhaust system when I'm not driving like a mad man in & around the city and has a deep tone when I hit on the throttle. The main reason why I'm after a exhaust system is to get the power and not just for the noise.

So you guys are pretty sure that 3 ½” is overkill and will drone for sure? How bout 3"? And stainless steel causes drone??? How about mild steel?

Depending on how well these 2 mods make on the car and how much smile I have on my face driving the car after these 2 upgrades, I might lower it with a set of coilover, sway bars (Front & rear), upgrade the turbo along with all the usual internal upgrades and the biggest project of all will be to try make it from AWD to RWD.



Off topic - Does anyone know how much boost is the stock 6MPS running on and how much boost can the stock turbo handle before going KA-BOOM! ?

Many thanks!

[rogwick]

Not to sure I'm sold on a 4" Dp mate. I doubt you will find many members on here with the exhaust pipework in excess of 3". Don't forget CP-E (for example) has also done extensive testing on their Downpipe design. You know it's reputable work when there are hundreds and thousands of MPS6's and Mazdaspeed6's that are running that same DP. There is information on power curves etc on the CP-E website which has been tested.

With regards to stainless steel pipework, for one it will be more expensive but secondly it will be generally louder and have more drone. To think about it, if you were to grab a spanner and tap a SS exhaust what you would hear is a "ting.....ggggg" it carries sound. Tap a Mild steel exhaust and you hear more of a blunt "clack" and the sound deaden's within a second. The same with air flow and resonance, a SS exhaust will carry more air flow noise through it. Don't quote me on that, but that's my understanding and logic.

I would go coated mild steel if I was you which is what I have. Cheaper, looks reasonable and low noise. I think 3.5" would be overkill to be honest mate. Not to mention a little heavier and sit slightly lower than a 3" which means, more prone to hitting things if you lower the vehicle at some point. Coilovers will be fairly low just to mention.

Why would you want to convert it to RWD? That's one of the best things in the MPS6 is the AWD capability! lol

MPS6 is running 15psi boost stock however first, second and I believe third gear is also limited boost. Stock turbo is only effective to 18psi

[Nepharius]

Sorry for the late response. (Crazy monday in the office!)

Depending on how well these 2 mods make on the car and how much smile I have on my face driving the car after these 2 upgrades, I might lower it with a set of coilover, sway bars (Front & rear), upgrade the turbo along with all the usual internal upgrades and the biggest project of all will be to try make it from AWD to RWD.

Not to be cruel, but I'd suggest giving up on the RWD thing unless you have serious money to burn. I know it is possible in soemthing like a WRX and from that you can guess it might be similar in the MPS6. My understanding is that it isn't really feasible without replacing pretty much the entire drivetrain etc. etc. Good luck with everything else though, I just feel that if you want a RWD car your better and cheaper option would be to just buy one.

[Onyx]

You guys have just reassure my initial thoughts of getting a 3½” exhaust. It's too big. Looks like 3" is the way to go.

In your own opinion, would you reckon that having a custom downpipe will gives a CEL?

Not to be cruel, but I'd suggest giving up on the RWD thing unless you have serious money to burn. I know it is possible in soemthing like a WRX and from that you can guess it might be similar in the MPS6. My understanding is that it isn't really feasible without replacing pretty much the entire drivetrain etc. etc. Good luck with everything else though, I just feel that if you want a RWD car your better and cheaper option would be to just buy one.

I see your point, Nepharius. It's gonna cost a lot of R&D, Cash & Time! But a RWD car is a more fun car IMO...
That's just a idea I got in in my mind right now. Wouldn't be planning to make the MPS6 into weekend warrior just as yet.

P.S I hate drones!

[rogwick]

Have a look here mate CP-E 3" SS Downpipe. CP-E specifically designed the downpipe with the MPS (Mazdaspeed6) in mind. CEL's are virtually eliminated although have been known to still occur. Many people with the CP-E unit experience no CEL. I got a CEL light on first fire up after installation, then a restart and it was fine. Just the ECU a little confused or a cold cat in conjunction. I doubt you will have any problems at all with it. A custom Downpipe may/may not give you issues. Depends on how much preparation and research was put into the design and fabrication prior to installation. CP-E has done this for you. Hence they're in the business.

Actually, I think you can have more fun in the MPS. To be honest I haven't had a comprehensive drive with a RWD vehicle but on the MPS the potential for grip is amazing. You can corner much, much faster and with more control. Depending on how intense you want to corner the vehicle can slip but maintain limited control as I have done before. Virtually a sideways yet controlled drift. I've also had the MPS6 completely sideways before when turning out a corner. So you can still have plenty of fun with it trust me. IMO you would quickly grow bored of straight line performance RWD. Get the best of both with the MPS6.

[Onyx]

I had a chat with the exhaust guy last nite and decided that 3½” exhaust will be too big for the car. He then suggested 3½” downpipe follow by a hi-flow cat and 3" coated mild steel straight back & spilt into 2 X 3" Difillipo mufflers.
Downpipe being the most restrictive part of the engine, he will try to squeeze as big downpipe he can.

What do you guys reckon? Sounds reasonable ya?

[Scaredycrow]

Sounds more like it anyway. Be aware that you will almost certainly generate a CEL. You'll have to look at other ways to make that go away.

[Onyx]

Sounds more like it anyway. Be aware that you will almost certainly generate a CEL. You'll have to look at other ways to make that go away.

CEL is my 2nd concern. What are the usual method of getting rid of the CEL?

Thanks!