Exhausts

[GT3]

...then its free flowing to the rear muffler and twin pipes.

The rear muffler isn't free-flowing, it has 3 chambers so it's definately a restrictive muffler.

[Kai]

Hacksaw!..

[Blitzen]

The rear muffler isn't free-flowing, it has 3 chambers so it's definately a restrictive muffler.

Like I said in my original post "...It is free flowing to the muffler..."
Not the muffler itself...

[Timbo]

The most restrictive part of the stock exhaust system is the dump pipe bend into the cat. It's 2.25", and at that bend, the width is effectively less than 2". That's why installing a custom dump pipe (say, 3" to the cat) or something like the APR dump and hi-flow cat liberates good power on chipped cars.

[hkogti]

So that the middle silencer can be ignored and just get a dump pipe and rear exhaust? Isnt that bigger middle pipe helps too? As the stock one is only 2.25", a 3" would be nice isnt it?

[h100vw]

So that the middle silencer can be ignored and just get a dump pipe and rear exhaust? Isnt that bigger middle pipe helps too? As the stock one is only 2.25", a 3" would be nice isnt it?

You don't need to go as big as 3inch, in the system, it doesn't help. Then you can start to experience booming, I have a 3 inch turbo back system on my A3 and I wish I'd not gone so big.

The std turbo spooled quick mind!!

Gavin

[Timbo]

So that the middle silencer can be ignored and just get a dump pipe and rear exhaust? Isnt that bigger middle pipe helps too? As the stock one is only 2.25", a 3" would be nice isnt it?

IMHO, just a dump is all you need, but others seem to think otherwise

[GT3]

You don't need to go as big as 3inch, in the system, it doesn't help. Then you can start to experience booming, I have a 3 inch turbo back system on my A3 and I wish I'd not gone so big.

I've upgraded the exhaust systems on both a Polo GTI and A3T using different configurations on each. Here's what I've learnt:

If you're going for a full system, then 2.5" from start to end will give you the best balance between low/mid/high end power. ...any bigger than 2.5" on a KO3(S) turbo and you'll lose power and drop boost. This is why Milltek, APR etc etc don't go bigger than 2.5", and their R&D and testing confirms this.

The biggest challenge (and compromise) in designing performance exhaust systems is containing drone. That's why most full systems come with resonators and longish rear mufflers - to keep them quiet. The problem with performance exhausts and "what's the best" is that it's highly subjective, ie the level of noise that's acceptable or desirable. Most performance exhaust manufacturers have little choice but to make them as quiet as possible. This may not suit some where the custom route gives them the freedom to try something else.

In terms of the Polo GTI, the stock system is pretty good (for a stock car). VW were raunchy enough to even remove the middle muffler/resonator after 2006. What keeps it reasonably quiet is that it's 2.25" from start to end, coupled with a rear 3 chambered (restrictive) muffler. For more power and flow, you either can upgrade the down pipe and/or rear muffler. Most opt for the DP which provides the biggest gains power wise, but the rear muffler shouldn't be entirely overlooked as a restriction either.

[Timbo]

Here's some data for people to contemplate. Yes, I know, it's from a dyno -- but it's an Aussie dyno..in fact, I used the same dyno, same fuel,same operator...just different days.

Here's the sheet for my car, stock apart from Revo flash, running on V-Power Racing (which doesn't make much difference anyway...no wonder Shell is pulling it)



This second sheet shows my car, as above, with the addition of a custom 3" dump pipe, fabricated for me by Fyshwick Exhausts (they're technician who know all to know about exhausts -- don't just get any pipe bender to do this work for you)



By any measure, the dump liberated 13KwATW. That's more than I have seen even from a full 2.5" system. The biggest restriction is in the dump!

[binnyvo]

Timbo,

How much did it cost you for the 3" downpipe, if you don't mind me asking? Is it similar to the APR one? cause I'm thinking of getting one done.

Cheers, Binh.