I have a 2011 r56 Cooper s. I have A 3 inch straight pipe cat back exhaust with no mufflers or resonator. So from the catalytic converter to the tips it is a 3 inch straight pipe. How much horsepower would you say this adds?

 

On stock boost and tune, maybe 5hp

mQubed Motorsport, Manic Tuning Dealer

 

I also have Alta CAI if that matters

 

With the CAI, maybe 6 hp total.

 

More than you can handle

 

hahahahaha

 

Not enough to be worth the hassle of driving the annoyingly loud car...

 

Tune it. Make it worthwile. But I'd have to agree with richardsperry, 3" is too loud for very little gain. 2.5" would be better with a stock turbo.

 

The issue is not the size of the pipe (2.5" vs. 3"), but the lack of a muffler!
Either pipe will be bearable with a functional muffler, but that's not what the OP is aiming for (no muffler or resonator) !

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ditto what others have said. it will still be bottlenecked by the smallest diameter area of the exhaust anyway, and without a tune it wont do much

 

Here's the link to the "annoyingly loud exhaust" that "isn't worth the sound"

 

FYI,

Just opening up the exhaust without any other changes will result in a loss of torque, typically in the part of the power band where it's needed most.

 

A cold startup, idle, and 3k rpm rev in a garage is in no way an accurate representation of what that particular setup sounds like.

 

+1. How does this sound above 3k full throttle, and then at 70mph on the highway?

 

I wouldn't want to sacrifice any torque. I like my smaller quick little cars to have nice torque response for quick bursts in the twists. I don't really think of my MINI as a high horse power making project, rather a super sweet, torque powered corner gobbler. Just my feeling.

Too much free breathing and you will lose nice torque balance. I would understand if you were strictly racing the car, but on the street torque is often forgotten about in the horsepower pursuits.

I like balance.

 

Exactly.

I used to run a 300+HP fox mustang on the street and only ran a 2.5" exhaust.

For a street MINI I would think 2.5" is plenty. If you wanted to do a 3" downpipe and then neck down, but 3" all the way out seems a little self defeating on the street. Unless of course everything else is in line to support it. And by that you'd have to have a very specific tune to take proper advantage.

 

For just a few more horses?
A sage wit on the forum once said: "If you can't go fast with 90HP, 900 won't help you."
And that video...sounds just like the ricers running around town. I'd sure hate to be associated with that.

 

Fly'n Brick i would like to hear your car. I simply started this thread to see how much horsepower it adds. I didn't need to hear you unnecessarily ripping on other people's cars.

 

Couple of quick points:

1. Where is this lack of back pressure coming from by adding a 3" exhaust on a turbo car? The turbo exhaust housing is tiny and creates all the backpressure you need or don't want. This happens BEFORE the exhaust be it big, small or titanic. You want to have zero back pressure after the exhaust housing. This encourages air to flow through the turbo easily which creates power and torque not reduce it.

2. As for horsepower added. We measured the back pressure before the cat and after the cat when running standard bhp. The cat is the creator of backpressure in the std exhaust. There was nearly no back pressure after the cat and quite a bit before the cat.

We removed the cat and therefore reduced the back pressure in the system and whilst the back pressure reduced we saw ZERO horsepower increase over stock on a stock engine over several runs on the dyno.

So the conclusion is zero horsepower can be expected by increasing the standard exhaust size on the standard car.

When you get higher up the bhp range maybe you will see some increase in bhp but not the lose in torque people are claiming. The tiny exhaust housing creates all the back pressure you may need (or not want, as is the case).

Cheers
Steven RW