Best exhaust diameter for KO3

[GTI_Kyle]

Thanks for advice mate 

Anyone elses opinion on this?

[AJP]

Thanks for advice mate 

Anyone elses opinion on this?

Just another thing to mention - I'm on a Stage 1 map at the minute, with a full Powervalve (200 cell sport cat). It's a 3" system all the way from the turbo to the y-piece at the rear bumper (I went for the R32 style).

I'd read about the theory of a larger bore, such as 3", potentially losing low end torque and response, especially at modest K03 power levels. However, I can confirm that there's been zero loss in low end torque, in fact off boost it's miles more responsive on the throttle. The turbo spools sooner, and on boost it's doing what you'd expect.

There's theory, then practice. In practice, reducing back pressure is massively the priority. Don't get hung up on the idea of losing torque with a larger bore. As long as the design is right, It'll sing at 2+.

[pudding]

That's really good to hear /\

As you say, a really good exhaust system can work really well.   The 3" thing boils down to how much the gas speeds slow down.  In theory, a turbo needs absolutely zero restriction post turbine, so a 5" system should be brilliant.... in theory     It's kind of the hose pipe analogy.  Squeeze the end of it and the water comes out faster, which is fluid dynamics 101, so restrictions are good for torque if things have been designed properly.  I have in past experience dabbled with bigger bores than standard and not always had the desired results, so I'm glad you've found a system than works for you 

Is the standard GTI bore 2.5"?

[AJP]

I was chatting to them about this once it was all fitted and I'm sure they said the standard downpipe is actually slightly less than 2.5"!

Easy to see why we get so much more out of these TFSIs with so much more room after the turbo!!

[r5gtt]

Thanks Dan_FR  would a different backbox increase power in any way?

No. Spend your money elsewhere if you're after power.

Wont the stock catback/backbox restrict power at stg2+?

IMHO yes they do have a little restriction on any stage as not having them let's your car breath better and adds a better throttle response.

[AJP]

.

[Dan_FR]

Small amount yes, but £ per hp it's not worth buying a cat back for performance alone unless you want the noise. WMI makes an awesome difference though, even on the baby K03