de-pre-cat sound difference...?

[darkcat]

So im finally back on the road, which is nice, just in time for the snow...

anyway im interested to hear thoughts on the perceived difference after removing pre-cats. TBH i cant hear much of a change.. if anything its given a bit more of a metallic twang to it, and possibly a little more bass throb but this might just be because ive been been driving a smart car for 6 weeks......

im thinking i might sleve the silencer next, i assume this makes more of a difference?

[dogbucket]

I agree that all I got was metallic ringing which I then had to try and deaden with exhaust wrap. Not one of the best mods I have done tbh

[spend]

I suspect the exhaust port - header mating is closely related to aural results when removing the pre-cats.

It's kind of like blowing horns / trumpets etc. with so great an effect from the mouthpiece I guess?

[Alexdaredevilz]

Mine growled slightly louder on idle, my main cat will be coming out as soon as I can find one to chop about

[Chris71]

Can't comment on the difference, but mine is fully decatted and the main thing that strikes me is the idle - it's a very percussive US muscle car sort of sound (more so even than the normal Rover V8 TVRs I think).

I actually preferred the sound of the S3 on the move though. The RV8 has more 'blood and thunder' to it, but the V6 had more tonality. Having getting on for twice the power is nice though.

[ralphy12345]

Chris71 said:

Can't comment on the difference, but mine is fully decatted and the main thing that strikes me is the idle - it's a very percussive US muscle car sort of sound (more so even than the normal Rover V8 TVRs I think).

I actually preferred the sound of the S3 on the move though. The RV8 has more 'blood and thunder' to it, but the V6 had more tonality. Having getting on for twice the power is nice though.

How do you get on at MOT time - is it a question of replacing the cat just for the test - or something else?

R

[dogbucket]

spend said:

I suspect the exhaust port - header mating is closely related to aural results when removing the pre-cats.

It's kind of like blowing horns / trumpets etc. with so great an effect from the mouthpiece I guess?

My theory was as the manifold rings like a bell when struck after removing the pre-cats, the exhaust pulses were setting it off. Maybe the peoples that dont have cracks in them :-)

[Chris71]

ralphy12345 said:

Chris71 said:

Can't comment on the difference, but mine is fully decatted and the main thing that strikes me is the idle - it's a very percussive US muscle car sort of sound (more so even than the normal Rover V8 TVRs I think).

I actually preferred the sound of the S3 on the move though. The RV8 has more 'blood and thunder' to it, but the V6 had more tonality. Having getting on for twice the power is nice though.

How do you get on at MOT time - is it a question of replacing the cat just for the test - or something else?

R

I'm hoping for 'something else'.

I only picked it up a few weeks back and I plan on finding a friendly garage (think it's due in March). If anyone knows of one in the Herts/London area please PM me.

[AJs Cerbie]

Well I started changing mine from the back towards the front.

Had it sleeved first of all (on way home from buying car).

Then went for ACT decat y-piece, then finally had precats taken out.

If you want to hear the difference at all three stages, I did small vid's at each stage so you can compare.

http://www.youtube.com/watch?v=eMOaXt6Uapg

(sleeved with main cat and precats still in place)

http://www.youtube.com/watch?v=-SrXrymuw8A

sleeved and new decat y-piece but precats still in)

http://www.youtube.com/watch?v=WNj40-FQ9kk

final mod with precats out and straight through.

Personally I don't get any ringing or resonance with precats out, and this is the sound I was looking for from the start.

More than happy with the results.

Each to their own I guess.

Alan

[BliarOut]

http://www.youtube.com/watch?v=jtTerU8TfmI

Doesn't come across that well on the vid but notice how far away you can hear her in the second clip.

[ralphy12345]

Chris71 said:

ralphy12345 said:

Chris71 said:

Can't comment on the difference, but mine is fully decatted and the main thing that strikes me is the idle - it's a very percussive US muscle car sort of sound (more so even than the normal Rover V8 TVRs I think).

I actually preferred the sound of the S3 on the move though. The RV8 has more 'blood and thunder' to it, but the V6 had more tonality. Having getting on for twice the power is nice though.

How do you get on at MOT time - is it a question of replacing the cat just for the test - or something else?

R

I'm hoping for 'something else'.

I only picked it up a few weeks back and I plan on finding a friendly garage (think it's due in March). If anyone knows of one in the Herts/London area please PM me.

;-)

But that's raised another question for me: is the removal of the pre-cats likely to turn a MOT test into a fail?

(Can't you tell I've had company cars for most of my life!!!)

R

[darkcat]

only if theres something wrong with the main cat

[dogbucket]

ralphy12345 said:

Chris71 said:

ralphy12345 said:

Chris71 said:

Can't comment on the difference, but mine is fully decatted and the main thing that strikes me is the idle - it's a very percussive US muscle car sort of sound (more so even than the normal Rover V8 TVRs I think).

I actually preferred the sound of the S3 on the move though. The RV8 has more 'blood and thunder' to it, but the V6 had more tonality. Having getting on for twice the power is nice though.

How do you get on at MOT time - is it a question of replacing the cat just for the test - or something else?

R

I'm hoping for 'something else'.

I only picked it up a few weeks back and I plan on finding a friendly garage (think it's due in March). If anyone knows of one in the Herts/London area please PM me.

;-)

But that's raised another question for me: is the removal of the pre-cats likely to turn a MOT test into a fail?

(Can't you tell I've had company cars for most of my life!!!)

R

Pre-cats are only there to control emissions during initial warm up. As the MOT only tests a hot engine in this country they are not needed.

[SILICONE KID]

I had pre cats out ,main cat in and two cherry bombs fitted , the silencer box removed,it sounded sweet..I then fitted the ACT de cat Y piece and it was just to much.I now have a standard exhaust pre cats out and the De cat Y piece , its not as nice as the sports exhaust but ok.The only thing idon`t like is the resonance from the Y piece..

[SILICONE KID]

Yes bit they are a arm and an leg

Edited by SILICONE KID on Wednesday 15th December 18:33

[Jonny_uk]

Is it not just easier just to cut out the silencer all together rather than sleeving?? And replace with a length of off the shelf pip either welded in or reamed and clamped each side?

I cant see the advantage of leaving the silencer on ?

[BliarOut]

Looks completely standard come MOT/Nosey time

[richtvr]

the silencer is left on as the exhaust is mounted by the silencer box

Rich

[Jonny_uk]

Right....thats my winter project sorted! Assume you just replace perforated pipe with solid