fitting a pipe instead of gutting

[rtd]

most owners when modifying their downpipes have the cats gutted - however, has anybody just had them removed and replaced with a pipe?

[Stigter]

yeah, talk to Grizz as he can get Miltek catless downpipes for "off road use only" due to tree huggers.

[N11LS_J]

Will be bloody loud though!

Are you sure you wanna do this???

better off gutting or sports cats?

Nils

[Blue_Thunder]

The problem with gutting the pre-cats is that you're left with a large empty chamber with a bigger diameter than the rest of the DP's, so you get resonance and it changes the exhaust note. Some people like the slight rasp, but I reckon it would be nicer with a single sized pipe.
Imagine it would be slightly less restrictive as well as there wouldn't be a reduction in pipe diameter (this is not 'cancelled out' by the initial increase in diameter where the gases enter the pre-cat chamber).

[Jules]

I agree with Scott

[N11LS_J]

I retract my previous comments, perhaps straight through pipe is the way to go...

[drjones1]

I retract my previous comments, perhaps straight through pipe is the way to go...

It would be interesting to understand the dynamics. You want the pipe to increase behind the turbo to stop the waste gasses spinning.

When they are spinning they are going round and round and not out (if that makes sense) If it enters a larger pipe (gutted pre cat for example) it will stop spinning and go out as intended which helps with back pressure and flow.

Lots of tuners talk of larger down pipes and reducing down to a smaller system. Part of this reason is to help the gasses lose the momentum of spinning from the exit of the turbo and to go out..

[Doug_S2]

Gutted precats are very good for these cars as the pressure on the exit of the turbo is really low.

There are no strange resonances on gutted rs4 DPs - if anything it is quieter than the miltek DPs as you don't strangle the gasses as soon as they are exiting the turbo.

Miltek nocat DPs are louder then the 3" nocat downpipes. The 3" DPs are quieter,deeper sounding with less resonance.

[andream88]

So, Doug, would you suggest to upgrade the DPs on K04s or are gutted RS4 ones good enough?

[Doug_S2]

Preferences:
RS4 DPs with no precats (cheapest option - left with 200 cell main cats - ok flow - legal)
Miltek DPs with 100cell (most expensive option - good flow - legal)
Miltek No cat DPS (cheapest/best flow option - not legal)
Miltek 3" DPs with no cats and 3" link pipes (the best you will get without going fully custom dual 3"- not legal)

[andream88]

http://www.wagner-tuning.de/produkte/50 ... wnpipe.php

what about these Doug?
i can have them for a very good price.....

[Nige_RS4]

As Doug says, the cheapest option i.e. gutting the pre-cats gives you 95% of the performance of the 200cel milltek solution for around 10% of the cost, so unless you're planning on huge HP, spend you're money elsewhere?

[Jules]

i think rtd is asking,if its as easy to replace the cats with a stainless straight through pipe,
Its got to be better than just gutting the cats,and still much cheaper than race cats.

[Stigter]

yeah, talk to Grizz as he can get Miltek catless downpipes for "off road use only" due to tree huggers.

Miltek catless downpipes as advised

[juice]

can you gut the precats (cheap option) and have no cats what so ever