pre -cats

[daz the plumber]

i removed the pre- cats , the car seems to rev better and a deeper noise and the odd crackle from the rear , what i dont like is the constant noise like a fine clatter from the exhaust manifold . as any one had the same problem ?. not sure if it was a good move .

[Chimjunkie]

I've done the same and also have a clattering which seems to come from around the main cat area? Initial thoughts were it may be a loose bit of material. Also got more blowing where the 4 tubes go into 1. Tip here is dont buy second hand exhaust manifolds! Cant be arsed any more with my exhaust woes so may spend a small fortune on the Sports manifolds with Sports cats from ACT.

[redkarla]

Mine was de-catted when I brought it I hate the sound I keep checking the manifold to see if there leaking. Gonna zap the a cat back for MOT to see what it sounds like then may not take it off again !!!!!

I'll wait and see what happens to the performance as well.

[That Daddy]

The manifolds do ring more with precats removed,but if you have the right cam fitted it sounds more like a tuned small block and there is nowt wrong with that like the rest of you will have to do with manifolds that sound like they are blowing only kidding,yes they are louder but you get used to it,what it does prove is that you get used to the way your engine should sound and anything that changes you notice which is a good thing i bet removing the maincat sounds alot worse though drainpipes anyone?

[Zippee]

I have ACT stainless manifolds with no pre-cats and have no problems with ringing sounds etc, I'm guessing most of you have the OEM manifolds with cats manually removed?
Also having heard a few cars with the main cat knocked out the Y piece dustbin they sound awful - more like a tractor TBH. The ACT de-catted Y-piece on the other hand sounds fantastic as the neck is a lot narrower.

[im]

Isn't there a perfectly valid reason (other than the sound 'improvement') for removing the pre-cats though?

Something about them having a tendency to melt in the manifolds as they get older and it then turning into a bd of a job to get them out - not to mention expensive if done by a garage.

It's just something I heard - I can't remember where.

[That Daddy]

Zippee said:

I have ACT stainless manifolds with no pre-cats and have no problems with ringing sounds etc, I'm guessing most of you have the OEM manifolds with cats manually removed?
Also having heard a few cars with the main cat knocked out the Y piece dustbin they sound awful - more like a tractor TBH. The ACT de-catted Y-piece on the other hand sounds fantastic as the neck is a lot narrower.

Agreed Zippee,i was referring to the stock set/up i should have made that clear your system is proper getting back to what "Im" said,yes they are a pain when they shift and take the tip of your Lambda probes off(it happened to me)and removal of said precats lowers the under bonnet temps a touch.

Edited by That Daddy on Friday 27th June 10:10

[WazzaL]

I've got the ACT ones in mine as well. Along with an upgraded cam and ECU the car does now rev a lot better.

It does sound a bit louder with the manifod change than it did before. Sounds a lot better, but I am a little worried I may have a headache with the drive up tonight.

[chrispitman]

It also depends on wether reversal cones were fitted to the manifolds, the ACT one's have these.

I have std manifolds with pre cats removed and cones fitted. I fitted a de catted Y 'Dusbin' for some tuning work and it is quite a lot louder, just pottering along there is'nt much noise difference from the cabin but soon as you give it some right foot it get pretty loud.

[blitzracing]

Can anyone verify from experiance that removing the pre cats helps to elliminate the low speed shunting issues ?

Mark

[Zippee]

blitzracing said:

Can anyone verify from experiance that removing the pre cats helps to elliminate the low speed shunting issues ?

Mark

No it doesn't.

[hiltonig]

Zippee said:

I have ACT stainless manifolds with no pre-cats and have no problems with ringing sounds etc, I'm guessing most of you have the OEM manifolds with cats manually removed?
Also having heard a few cars with the main cat knocked out the Y piece dustbin they sound awful - more like a tractor TBH. The ACT de-catted Y-piece on the other hand sounds fantastic as the neck is a lot narrower.

Have you got the normal replacement manifolds from ACT or the ACT performance manifolds the 1200 quid jobbie ?

[daz the plumber]

do you think useing exhaust wrap around the pre- cat area may help.

[Zippee]

hiltonig said:

Zippee said:

I have ACT stainless manifolds with no pre-cats and have no problems with ringing sounds etc, I'm guessing most of you have the OEM manifolds with cats manually removed?
Also having heard a few cars with the main cat knocked out the Y piece dustbin they sound awful - more like a tractor TBH. The ACT de-catted Y-piece on the other hand sounds fantastic as the neck is a lot narrower.

Have you got the normal replacement manifolds from ACT or the ACT performance manifolds the 1200 quid jobbie ?

Normal ones - around £500ish a pair IIRC.

[That Daddy]

Zippee said:

blitzracing said:

Can anyone verify from experiance that removing the pre cats helps to elliminate the low speed shunting issues ?

Mark

No it doesn't.

No Mark def not seconded.

Edited by That Daddy on Friday 27th June 12:40

[Dave81]

Had my Pre-cats removed by Neil Garner yesterday.....(Excellent Service it was too). The pre-cat removal has made my exhaust noise slightly louder, and i have no issues with any clattering. The main benefit (except the extra bit of noise) for me was the reduction in temps. I got stuck in traffic on the way out of Cirencester, before my car would go up to around 100 deg, It did'nt move above circa 92!! It also has the added benefit of slightly reducing inside cabin temps, (the misses was happy when i picked her up). The throttle response has also greatly improved!!

All round for me a very worthwhile job and Neil's price was significantly cheaper than anywhere else!!!

+1 Mr Garner!!

[blitzracing]

That Daddy said:

Zippee said:

blitzracing said:

Can anyone verify from experiance that removing the pre cats helps to elliminate the low speed shunting issues ?

Mark

No it doesn't.

No Mark def not seconded.

Edited by That Daddy on Friday 27th June 12:40

OK fair enough, Id been told by "those who know" more about the ECU than me that this was at least part cause of the over lean condition, by destorting the composition of the exhaust gas the lambda probes see. It does (or at least did) makes some sense technically, although id be much happier to get some measurements to back this up. Not that easy to do however unless you had an extra probe before a pre cat' and you could compare the signal levels with the post cat probe. I think I might try reducing the Lambda probe outputs slightly (This will richen the mixture overall) and see if I can still get it to switch reliably, and reduce the lean period. Anyone tried running the non cat fuel map on a shunting car, as this runs much richer low down? (somewhat dependent on the CO setting on the AFM however).

Mark

[daz the plumber]

dave 81 . how come you have no clatter? so why do mine make that noise .

[Dave81]

daz the plumber said:

dave 81 . how come you have no clatter? so why do mine make that noise .

I have no idea Daz??

I met you at Chatsworth complaining about you car making noises after you'd just had you Cam done!!!!

I'll be honest with you....... You car sounded fine then, i'm sure it does now!!!

I'm not sure if its the fact you've bought a TVR you expect there to be problems with it, but to me your car seemed fine. The cars 10+ years old now mate and i think you need to realise that the cars gonna have a character....make strange noises...and every now and then confuse you. I'm a great believer in, if it aint broke don't fix it. From what i remember your cars far from broke.....so just go out and enjoy it! This is what TVR ownership is about. You could spend thousands trying to track down misc noises, but never find the culprit.

[Veg]

Dave81 said:

Had my Pre-cats removed by Neil Garner yesterday.....(Excellent Service it was too). The pre-cat removal has made my exhaust noise slightly louder, and i have no issues with any clattering. The main benefit (except the extra bit of noise) for me was the reduction in temps. I got stuck in traffic on the way out of Cirencester, before my car would go up to around 100 deg, It did'nt move above circa 92!! It also has the added benefit of slightly reducing inside cabin temps, (the misses was happy when i picked her up). The throttle response has also greatly improved!!

All round for me a very worthwhile job and Neil's price was significantly cheaper than anywhere else!!!

+1 Mr Garner!!

Beiing a Ciren lad myself, how much did garner charge?