3" Exhaust Too Big for your Turbo Mini?

There seems to be a cyclical debate about 3" exhaust on the 1.6L Mini Turbo cars being too big, or too heavy, or not "Needed". My favorite argument is "its not needed so why do it?" That could be said about any aftermarket part. None of these things are needed so why do it at all! Simple, people want to have more fun with their cars, which involves tinkering, customizing, making more HP and making the car handle better. In a world where people do the tiniest things to get a few extra HP, it should be obvious why you would want a 3" system for the R56 over a 2.5" system.

Proven Wheel HP from 3.0"

Of all the things I see on the fourms, the one comment that stuck out was, "3in may make more HP, but there is a point of diminishing returns." I 100% agree, and for sure this is the case, but the point of diminishing returns is where? All I see are people guessing, people saying "I heard this or that", "Well this tuner SAYS 2.5" is best", but again ZERO proof of this. We feel the answer to that question is 3" for virtually any turbo car. How can we say this? Simple, experience.

Here is a dyno graph showing our 3" dual cat system ran on our otherwise stock JCW and MCS.

First off, we are dealing with turbocharged cars not normally aspirated. So the rules of sizing really get thrown out the door. Its a given in the forced induction world that bigger is better. Read any book about turbo vehicles, they say if it fits and its not too loud put on a biggest size you can afford. Turbos don't want back pressure as this slows the turbos response. Because turbo cars have lower compression, the sooner you get it making boost the sooner you have torque, the more torque at a given RPM means more HP. For the last 10 years we have seen this over and over again, and today continues to be a rule of thumb. We have actually done a test on 2.25", 2.5" and 3" exhausts on a 1.6L forced induction engine. We did dyno testing on our R53 with 15% SC pulley comparing stock to threes sizes. The 2.25" exhaust made about 3-5WHP, the 2.5" system made about 10WHP, and the 3" made about 12-13 WHP. On this car we opted to push normal customers to the 2.5" system because of sound more than anything. These cars are much louder than the R56 because there is no turbo in the exhaust killing some of the sound. Keep in mind that during these tests, the boost on this engine was only 10psi at 3000RPM and 14psi at 6800, making only 190WHP. On the R56, we are running 18-ish peak boost at 2000 and 16 or more at 6500 making around 220WHP. The turbo cars are making 50-80 more WHP at 4000 than the SC cars. More HP means more airflow. If the 2.5" theoretical exhaust system is good enough, then why do we still gain more HP on cars removing a high flow 3" cats from our 3" exhaust system? Simple there is still a slight restriction on our 3" (too big) turboback exhausts using two high flow cats. When the JCW R56 came out we had customers asking for a single cat exhaust for them and of course some dyno numbers to see how much better it is. You can see below the results we found. Keep in mind this is showing the ALTA 3" Turboback dual cat system versus the ALTA turboback single cat system.

This above graph was done on our JCW with intercooler and intake installed. We did nothing but swap out one of two cats for a straight pipe.

Lets take a fabricators approach. Company X has been making exhaust for normally aspirated Euro cars for a long time. Now this new turbo Mini comes out and they are not tooled up for 3". The 3" 304 SS tubing is about 25% more expensive than 2.5" 304SS tubing. Also its a big step up to be able to bend 3" over 2.5", this could require a new machine or new tooling. Welding on flanges takes more time as there is 20-ish% more welding to be done. The system needs to be finished somehow, and with 20% more surface area, you might have 20% more time wrapped up in finishing it. Now add to that the overall system weighs more an cost more to ship materials from place to place. All these things add up to more that just a couple of dollars. Since its easier and cost less, the choice must be made to make a more affordable system, or make a higher performing system. Lets take the "Engineers" approach to this for a second. We always get told (by engineers) that the engineers designed this car perfect for the HP it makes. So if the stock exhaust was perfectly designed for this engine making around 160 Wheel HP stock, then shouldn't a 2.5" system (13% bigger by internal volume) only be suited for 13% more airflow/horsepower?? So that means they are only good on cars up to 180 WHP? So then a 3" system (65% bigger internal volume) is necessary to hit the 220+WHP we typically get from MCS?? So if it was designed perfect then why do we gain more HP from installing bigger exhausts? If the OEM exhaust is way undersized (proven by our 10+WHP gains) are you saying an exhaust only 13% bigger is good enough? You can see how those arguments look silly to us.

3" Is Too Heavy

We hear its too heavy going to a 3" system. Lets use the stock JCW catback exhaust as an example. This system connects at the factory downpipe and is one really long single piece that weighs 31.2lbs. The ALTA JCW catback (AKA downpipe back system) weighs in at 34lbs. So adding 2.8lbs is too heavy? If we made our system in 2.5" tubing for a weight savings we would only loose 3.6lbs. So is that still too heavy?

Turbo is Only 2.5" So Why Make It Bigger?

The other argument we hear is, the outlet on the turbo is only 2.5" so why make it bigger. Using that argument, then why make it any bigger than 2" as the turbine wheel is smaller than 2"?? Same goes for the turbo inlet or outlet. Why make any part of the system bigger? Yet we see making a bigger intakes, bigger boost tubes and of course bigger exhaust all make HP. These rules just don't apply. I don't understand why so many customers out there that just don't believe us. On one hand, we constantly see competitors being shot down because they do not have dyno results. Since 2005 we have been providing all our Mini customers with dyno graphs backing up claims we make, yet still its not good enough. We are all here because we want more power and to have more fun with our cars. We all want that little edge over the other guy, so even if you don't want to believe us, you at least should understand that 3" will make more power. Even if its a tiny amount, its a more than the guy with the 2.5" system. If we can offer you a system that makes more HP, quiet enough to keep you happy and at a reasonable price, then why not buy it? By far the Mini customer has been the toughest customer to please over the years, but also the most rewarding. We feel like we have an opportunity to teach Mini customers about new things make the very happy. Everyday we make more and more customers happy. Everyday we get customers that call us thanking us for continuing to stick to our guns and have the constructive online conversations. It shows how solid we are planted in the Mini world and that we know what we are talking about. In these discussions, we keep talking about our downpipe yet it has been discontinued. We made this decision a while back because there is no way to keep it form throwing a Check engine light on stock cars. After we discontinued the part, we have been getting lots of people asking about it. It could be because customers cars are finally coming off of warranty are looking for these once again. If you are interested in buying this from us, please let us know! If we get enough people asking we will offer this once again.

3" Exhaust Too Big for your Turbo Mini?

Proven Wheel HP from 3.0"

Here is a dyno graph showing our 3" dual cat system ran on our otherwise stock JCW and MCS.

This above graph was done on our JCW with intercooler and intake installed. We did nothing but swap out one of two cats for a straight pipe.

3" Is Too Heavy

Turbo is Only 2.5" So Why Make It Bigger?

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