Removing pre cats

[4Lmike]

How difficult is it? Bearing in mind I've no experience in messing around with cars. Is it something I could give a go, or better to leave it to someone a bit more qualified?

If it's not that hard, would someone mind describing how to do it? With pics preferably! TIA

[Goaty Bill]

I have been told (several times) "don't do it yourself!".
The 'approved' method seems to be; remove the manifolds, cut them open, remove the cats, weld them back up.

I have watched the exhaust manifolds come off a couple of times now, for new gaskets.
I have to say, it's the best couple of hundred I have ever spent; each time!
(to put it in context; I did this kind of thing many times on other cars, and I really prefer to watch else someone do this one)

It's quite obvious however that, with a lift and a collection of all the right length/shape spanners, it isn't too bad.
That said, I always seem to hear an amount of even from the most experienced of 'exhaust system dismantling engineer'
And it's still near to 2 hours per side for someone who's done it before, with the right equipment (excluding cutting, smashing out and welding).

Choose the right person, and it should probably cost you under £400.

[BillC99]

I removed mine earlier this year and removing the pre-cats themselves was not really a problem (1 was moving around anyway!)all you have to be careful of is not damaging the lambdas,its better to remove them if you have the proper socket. As mentioned though it is a PITA to remove the manifolds.The O/S bank took 3 evenings to remove. 2 bolts snapped off and I eventually had to cut a third one as I could only get an open ended spanner on and could not shift it! The n/s came off in less than an hour!although to be fair that had been removed before and on closer inspection a thread had been helicoiled.
I had to remove the head and have the 3 bolts removed. When I re-fitted the exhaust manifolds I was recommended to use the ACT stainless bolts which have a smaller head which allows you to use sockets and ring spanners.

I hope I haven't put you off doing the job yourself but better to know what you are letting yourself in for!!!

[gizzer]

Better still buy a pre - cat griff

[MADMAX2]

4Lmike said:

How difficult is it? Bearing in mind I've no experience in messing around with cars. Is it something I could give a go, or better to leave it to someone a bit more qualified?

If it's not that hard, would someone mind describing how to do it? With pics preferably! TIA

I've taken both sides off I just had the right tools to do it I have left my pre cats in however I have a straight thru exhaust and an ACT y piece it's easier to change the original y piece to a decatted ACT it will be loud enough and you won't have the hassle of the manifolds and it be lighter on your wallet!!! trust me...

[TJC46]

As others have said the hardest thing is removing the manifolds. Once you have, then using a drill, a long masonary bit, a very sharp chisel [an old wood chisel is ideal] its not too bad of a job.

[Mark_S_24]

Several people have done it with the Manifolds on.
Take Y piece off, remove Lambda's, then get big long pokey things into the precats.
It's the way I intend to do it.

Mark

[Harrytsg]

Im sure i have read on here somewhere one solution was;

Remove y piece
Drill out pre cats with a long masonary bit,
Bash the rest out with a broom handle,
Start car to blow bits out
Refit y piece

Not having tried this I cant vouch for the method, but if its viable it certainly beats taking off the manifolds.

Might be worth a search to see what others have done or if anyone actually has done it that way.

Oh and if you do do it that way, let me know if its works.

[MADMAX2]

Harrytsg said:

Im sure i have read on here somewhere one solution was;

Remove y piece
Drill out pre cats with a long masonary bit,
Bash the rest out with a broom handle,
Start car to blow bits out
Refit y piece

Not having tried this I cant vouch for the method, but if its viable it certainly beats taking off the manifolds.

Might be worth a search to see what others have done or if anyone actually has done it that way.

Oh and if you do do it that way, let me know if its works.

hahahahahahahahahaahaahahahahahahaahahahaahaha

[Harrytsg]

I thought I might have to justify my comment, so here


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

And scroll down to 4-5 th reply

[Chimpandtonic]

4Lmike said:

How difficult is it? Bearing in mind I've no experience in messing around with cars. Is it something I could give a go, or better to leave it to someone a bit more qualified?

If it's not that hard, would someone mind describing how to do it? With pics preferably! TIA

My pre-cats came out by removing the manifolds, cutting them open & doing a neat re-weld before refitting with ARP bolts & NordLock washers.

Believe me it's a hassle, but I couldn't bring myself to do the butchery described above.

The thing is after all the work there really wasn't that much (if any) noticeable difference in the way my car performed.

Conversely, a year later the improvement was very apparent after replacing my standard catted Y piece with an ACT de-cat Y Piece.

Based on my experience you are better off starting the process by leaving the pre-cats in there and focusing your efforts and cash on a de-catted Y piece.

As I understand it the ACT replica (de-cat) manifolds have reverse cones to generate the right amount of back pressure.

So it's just possible by some strange twist of fate the pre-cats actually do more good than harm.

The big restriction is not those little pre-cats, in my experience its the big main cat in the Y piece.

Forget the pre-cats & lose that big dustbin, it's not that hard to swap it back in for the MoT & there is a tangible sensation of improved performance that goes with it.

Finally the sound a de-cat Y piece gives you is pure

Edited by Chimpandtonic on Tuesday 13th December 21:37

[Simon says]

Chimpandtonic said:

4Lmike said:

How difficult is it? Bearing in mind I've no experience in messing around with cars. Is it something I could give a go, or better to leave it to someone a bit more qualified?

If it's not that hard, would someone mind describing how to do it? With pics preferably! TIA

My pre-cats came out by removing the manifolds, cutting them open & doing a neat re-weld before refitting with ARP bolts & NordLock washers.

Believe me it's a hassle, but I couldn't bring myself to do the butchery described above.

The thing is after all the work there really wasn't that much (if any) noticeable difference in the way my car performed.

Conversely, a year later the improvement was very apparent after replacing my standard catted Y piece with an ACT de-cat Y Piece.

Based on my experience you are better off starting the process by leaving the pre-cats in there and focusing your efforts and cash on a de-catted Y piece.

As I understand it the ACT replica (de-cat) manifolds have reverse cones to generate the right amount of back pressure.

So it's just possible by some strange twist of fate the pre-cats actually do more good than harm.

The big restriction is not those little pre-cats, in my experience its the big main cat in the Y piece.

Forget the pre-cats & lose that big dustbin, it's not that hard to swap it back in for the MoT & there is a tangible sensation of improved performance that goes with it.

Finally the sound a de-cat Y piece gives you is pure

Edited by Chimpandtonic on Tuesday 13th December 21:37

Those cones are anti-reversal ie gas flow and nothing whatsoever to do with back pressure we don't want back pressure

[SILICONEKID340HP]

Get rid of the lot ! remove the manifolds and then it`s a piece of ps. .Its worth doing if you need to replace the manifold gaskets.

I have pre cats out ACT Y piece and a standard exhaust..

[TV8]

I agree with Chimp(what am i called this month)nic. The ACT y-piece certainly made my car feel crisper to drive. The noise was good at full beans but it sounds even better with the ACT Cherry bomb system as well.

[SILICONEKID340HP]

TV8 said:

I agree with Chimp(what am i called this month)nic. The ACT y-piece certainly made my car feel crisper to drive. The noise was good at full beans but it sounds even better with the ACT Cherry bomb system as well.

Now your being greedy

[Chimpandtonic]

Simon says said:

hose cones are anti-reversal ie gas flow and nothing whatsoever to do with back pressure we don't want back pressure

You do want back pressure if it aids scavenging the combustion chamber when the exhaust valve is still open.

There's a lot more to exhaust tuning than a big pipe.

In the simplest terms back pressure is just a pressure drop that if used correctly can be utilised to great effect & benefit, the best examples of this can be seen in two stroke exhausts.

Tune the exhaust shape correctly to generate a pulsed pressure drop at the right point in the cycle and you can use it to evacuate the exhaust gasses and initiate a momentum that actually assists the drawing in of the fresh mixture into the combustion chamber.

Kind of a free back to front supercharger if you like.

First developed and properly demonstrated by the East German motorcycle manufacturer MZ on their highly successful race bikes over 40 years ago.

Although used in slightly different way the fluid dynamic principles are as relevant in a four stroke as they are in that two stroke race bike.

So the truth is, if used correctly, some times back pressure can be your friend not you enemy, FACT!

[TV8]

SILICONEKID340HP said:

TV8 said:

I agree with Chimp(what am i called this month)nic. The ACT y-piece certainly made my car feel crisper to drive. The noise was good at full beans but it sounds even better with the ACT Cherry bomb system as well.

Now your being greedy

I know and it sounds good as well. Not sure the neighbours agree though!

[Milk Tray]

I replaced my manifold gaskets and removed the pre cats in the summer, it is definitely a character building exercise, but I have not noticed any difference what so ever with the pre cats being removed, so act y piece will be purchased soon. I'm taking the body off over Christmas to replace the outriggers and what ever other little surprises I find, so I will get that done before the y piece

[Simon says]

Chimpandtonic said:

Simon says said:

hose cones are anti-reversal ie gas flow and nothing whatsoever to do with back pressure we don't want back pressure

You do want back pressure if it aids scavenging the combustion chamber when the exhaust valve is still open.

There's a lot more to exhaust tuning than a big pipe.

In the simplest terms back pressure is just a pressure drop that if used correctly can be utilised to great effect & benefit, the best examples of this can be seen in two stroke exhausts.

Tune the exhaust shape correctly to generate a pulsed pressure drop at the right point in the cycle and you can use it to evacuate the exhaust gasses and initiate a momentum that actually assists the drawing in of the fresh mixture into the combustion chamber.

Kind of a free back to front supercharger if you like.

First developed and properly demonstrated by the East German motorcycle manufacturer MZ on their highly successful race bikes over 40 years ago.

Although used in slightly different way the fluid dynamic principles are as relevant in a four stroke as they are in that two stroke race bike.

So the truth is, if used correctly, some times back pressure can be your friend not you enemy, FACT!

But the cones are not in those manifolds for back pressure FACT and comparing a piston ported 2 stroke to a 4 stroke is not a fair comparison if we are talking tuned pipe lengths and port scavenging, I was into bikes long before cars and around the time of piston ported & rotary disc valve 2 stroke and before the reed valve was widely in use, this is why 2 strokes use expansion chambers and pee shooter exhaust systems for that very reason, these do not even resemble what a 4 stroke needs exhaust wise you was saying.....

Edited by Simon says on Wednesday 14th December 09:47

[spend]

Cones just aid the transition in flow of 4 small pipes into 1 big chamber to keep the speeds up rather than a big transition at the merge point creating a loss in momentum, which would impinge dramatically on the subsequent pulses from adjacent headers. They will in fact reduce back pressure IMHO.

I don't see the cones would have any effect on back pressure or reversal due to the large expansion chamber formed at the pre-cat collectors or dustbin (they are practically like atmosphere to the engine after the headers IYSWIM). Smoothing the flow by cunningly avoiding drastic instant changes in cross sectional area is a very smart fix to the flaw in the standard manifold design.

Thats only for you Simon not Mr. Chimopelagic