Re-cating!

[StreetDragster]

Hi All,

As i'm not having a great deal of interest in my car, probably due to its appearance and mileage i'm considering finding a way to keep it.

Now, i'm wondering, has anyone re-fitted the cats to their car? And what effect did it have on the sound of the exhaust?

Mine is fully decatted, and cherry bombed, and i'm just wondering whether the main cat would make the exhaust noticably quieter, or would it change the tone of the exhaust, make it tinny'er etc?

I'd just like to add that i'm not thinking about doing this, i love the decatted sound, i'm just curious.

Thanks

Matt

[MADMAX2]

oh dear sounds like you are falling out of love with ya chim whats up with it?

[Pupp]

StreetDragster said:

Hi All,

As i'm not having a great deal of interest in my car, probably due to its appearance and mileage i'm considering finding a way to keep it.

Now, i'm wondering, has anyone re-fitted the cats to their car? And what effect did it have on the sound of the exhaust?

Mine is fully decatted, and cherry bombed, and i'm just wondering whether the main cat would make the exhaust noticably quieter, or would it change the tone of the exhaust, make it tinny'er etc?

I'd just like to add that i'm not thinking about doing this, i love the decatted sound, i'm just curious.

Thanks

Matt

Never re-catted (nor had to)... the main cat is the biggest 'silencing' component of the system in my experience. Otherwise stock exhaust on decatted manifolds and link is still pretty raucous (but nothing like the sleeved mod admittedly)

[daz the plumber]

why not swop ypur exhaust for my standard one .don`t you think you have gone over the top ,removing the pre cats , main cats and changing the exhaust , you must not have any back presure

[Littletidnock]

I agree its probably nothing to do with the car its the economic climate, its time for buying not selling

[Littletidnock]

Quinny said:

Why would you need back pressure Daz??

The faster the gasses get out the better. Thats why drag cars have short wide open pipes

I think a bit of back pressure creates swirl and a better combustion

[thenick]

Can't remember why but back pressure is very important on rover v8s especially. This is why the decat ACT manifolds I have run smaller bore manifold pipes - or you end up losing lots of torque. I'm sure someone like Trackcar will be along to explain shortly!

Edit: Matt if I were buying a chim again, I would buy yours like a shot, its a great looking car and at a reasonable price I think. It should sell given some time don't worry. Why are you selling it though? All it needs is a charger..!

Edited by thenick on Monday 7th July 21:18

[daz the plumber]

to get the most from a supercharger you need low comp heads eather by porting or spacer , concave pistons and a very flat cam .

[daz the plumber]

read the steve heath bible , before and after rolling road sesions have proved tht a noisey exhaust can lose 30bhp

[That Daddy]

daz the plumber said:

to get the most from a supercharger you need low comp heads eather by porting or spacer , concave pistons and a very flat cam .

whats that got to do with back pressure Daz?

[Pupp]

Think there's some confusion of restriction to flow (ie 'back pressure'), with pulse tuning due to header lengths and collector configuration etc (which actively scavenges gas from the chamber when it all comes together at whatever revs suits the cam etc). One can be beneficial, one isn't

[Pupp]

That Daddy said:

daz the plumber said:

to get the most from a supercharger you need low comp heads eather by porting or spacer , concave pistons and a very flat cam .

whats that got to do with back pressure Daz?

And how do you lower the compression by porting?

[That Daddy]

Pupp said:

Think there's some confusion of restriction to flow (ie 'back pressure'), with pulse tuning due to header lengths and collector configuration etc (which actively scavenges gas from the chamber when it all comes together at whatever revs suits the cam etc). One can be beneficial, one isn't

[Littletidnock]

what I was thinking of doing was a total decat, with the spare main for MOT and then leaving the exhaust standard, has anyone seen this done?

[Pupp]

Littletidnock said:

what I was thinking of doing was a total decat, with the spare main for MOT and then leaving the exhaust standard, has anyone seen this done?

Yup. Moi at present. Toying with re-doing my 'old' sleeved (ahem 'bombed' ) system by inserting short perf tubes for maybe half the length of the stock ones... know someone has done this and would imagine it results in a pleasant half-way house as full sleeve-job is a bit OTT with no cats

[StreetDragster]

Wow this thread has grown haha!

I'm not thinking of doing this un-mod, i was just curious how the noise of the exhaust could be tweaked with different exhaust component combinations.

Cheers for all replies

Thanks

Matt

[clive f]

That Daddy said:

Pupp said:

Think there's some confusion of restriction to flow (ie 'back pressure'), with pulse tuning due to header lengths and collector configuration etc (which actively scavenges gas from the chamber when it all comes together at whatever revs suits the cam etc). One can be beneficial, one isn't

I think this one covers what you are on about

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[Littletidnock]

TVR Moneypit said:

Littletidnock said:

what I was thinking of doing was a total decat, with the spare main for MOT and then leaving the exhaust standard, has anyone seen this done?

Yep. Thats what I have done.

Sounds like this; http://uk.youtube.com/watch?v=m5FKfGgN0AY

I like that! I asumme yours was the second car,whats it like at tickover please

[Pupp]

clive f said:

That Daddy said:

Pupp said:

Think there's some confusion of restriction to flow (ie 'back pressure'), with pulse tuning due to header lengths and collector configuration etc (which actively scavenges gas from the chamber when it all comes together at whatever revs suits the cam etc). One can be beneficial, one isn't

I think this one covers what you are on about

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

A fair attempt; certainly

[TVR Pablo]

StreetDragster said:

Hi All,

As i'm not having a great deal of interest in my car, probably due to its appearance and mileage i'm considering finding a way to keep it.

Now, i'm wondering, has anyone re-fitted the cats to their car? And what effect did it have on the sound of the exhaust?

Mine is fully decatted, and cherry bombed, and i'm just wondering whether the main cat would make the exhaust noticably quieter, or would it change the tone of the exhaust, make it tinny'er etc?

I'd just like to add that i'm not thinking about doing this, i love the decatted sound, i'm just curious.

Thanks

Matt

I did exactly that. Was running decatted ACT manifolds and Cherry Bombs. Great combination with lots of extra power but wanted to try to turn it down a tad on the motorway and save some trees
Didn't want to lose any performance though, so went for some ACT racing cats.

Result - all good. If anything it's a bit deeper and angrier, as you get a bit less noise from the central section under the car (so quieter in the cabin with roof on), but possibly a bit more out of the back (so just as good if not better roof off). Recommend it. Best combination I've tried so far, and I've had cats + sleeved (too thin and reedy) and no cats + sleeved (hearing damage territory on long fast runs).