Pre-cat Gutting Tool

[MarkB]

It's high on my list of mods to do (myself) when I can spare the car incase I don't get it all back together in time for work

[ajsl]

Jim is the owner of Starperformance, which is quite well respected up here.

[rolskii]

@ajsl .... cool.... can you elaborate on the claim made then please..... as being darn sarf .... we all may be too far away to know .... thanks
Like to know what plays up ... on what build models affected also .......

[ajsl]

As mentioned I didn't talk to Jim directly... here's the full cut and paste :

Spoke to Jim @ Star on Saturday. £300 for the swap of downpipes. Jim says he's done it before but it can take between 6 and 8 hours! Hence the high price tag.

He also recommended that you fit the Milltek ones as they not only produce more power but aparently some cars don't run right when the OEM downpipes have the CATS knocked out.

I was surprised myself. I'm intending to get Jim to do my timing belt etc so I'll ask him directly then

[s4woody]

the thing is the precat is after the lambda sensor so the exhaust gases are measured before they reach the precat ..the milltek dwnpipes are set up the same with the lambda in front of where the precat would be except they have different cell main cats..cant really see how it would effect the engine management and cause a prob...brett collins and sum others have even removed there main cats and there lambda still sorts out the ecu and there car works well...the mind boggles...

[S2tuner]

I can't see an issue with running no cats, apart from very very rare 2001 models with Hitachi MAFs (and lambdas after the precats, just before the main cats) and RS4s, where the ECU would throw a code because of no cats being there, but that is only if you don't know how to disable the ECU cat check routines.

HTH,

Mihnea


PS: I've ran my car with no cats and apart from the fun factor that was increased and the nice smell of burnt fuel coming from the tailpipes there were no downsides at all..

[MarkB]

With no cats how does it fair at the MOT station?

[S2tuner]

They like to see cats on our cars.... and I think a good cat is a dead cat

With no cats how does it fair at the MOT station?

[MarkB]

Served 'Gutted'

So can the main cats be gutted in the same way, or are they best replaced with a pipe and leave the pre-cat shell in place for effect?

[Paulm]

I would say you are always best with just a straight pipe. But for the cost involved and prob very little power gain gutted cats is fine. You will need main cats for the MOT though.

Not quite sure what happens to exhaust gasses when they get to expand into the cat shell then get compressed agian as they leave the shell and got back into the exhaust.

My very basic understanding of flow is.

As gasses enter the cat they will slow and cool(very slightly), then as they leave they will speed up and heat up. What does that do to back pressure and pressure waves? I would say it may well produce some back pressure but to what degree I have no idea. Small to nothing is my guess