Pre Cat Removal - Should I / Shouldn't I

[crazycraig]

I know it's most likley been done before but I see no harm in getting the latest upto date opinions good or bad from everyone.

At the mo I've taken the exhaust manifolds off my 29,000 mile Chim 500 to replace the gaskets (and now the mounts due to heat damage, see pics) and would just like people's opinions on whether to remove the pre cats (manifold cats)or leave them in.

As you can see from the pics, the cats are a nice clean greyish white colour and in an unblocked condition, but I'd just like to know if there is any advantage / benifits in removing them now, or, due to their condition, should I just wait until the gaskets need replacing in the future and review it then.

If the general concensus (sp) is to remove them , then how long / how much and what's involved in removing them and is it worth putting in non reversal cones? and once again how long / how much and what's involved?

A further point as the exhaust is off, I was looking at having the exhaust sleeved / cherry bombed so would it just be worth leaving the pre cats in as it wouldn't make much difference in achieving aural extasy.

ps - I'm not looking at a full ear bleeding sleeved through pipe de cat.









Many thanks.

Craig

pps - is it me, or is it a nightmare to clean up the manifold faces. Any tips?

>> Edited by crazycraig on Thursday 15th December 11:01

[GreenV8S]

I normally start by taking the plugs out, one less thing to break and a little more room to fumble around trying to get at those bolts. I only make a token effort to clean the manifold faces, just to check there are no bits of old gasket stuck on and no damage to the surface.

It would be worth getting a quote from a couple of TVR specialists to remove the precats and fit non-reversal cones. From memory when I had mine done at Tower View (several years ago though) it was about £80. Or you could do it yourself if you're handy with an angle grinder and welder. If you're lucky you can remove the precats with a chissel or they may just fall out when you tip the manifold up, but once you try chisseling them out you're committed and will have to open them up if they don't come out with the chissel.

[crazycraig]

The plugs are just screwed back in to plug the holes.

I put my hand into the manifold and checked for security of the cat and it feels well stuck in there.

As I said, I don't realy want to create extra work by removing the cats if it's of no benifit, especially as 'to me' they look in fairly good nick.

Still abit worried though about how smooth you should get the faces of the manifolds, the engine end is fine, but the manifolds aren't that great, even after using wire wool, then a wire brush, then a wire brush on drill and then finally a file. Maybe it's not so important when using a material gasket but as I was planning on putting on the later steel gaskets (part no ERR6733) I guess it's crucial! (or should I just slap on more exaust sealant?)

Craig

[topsparks]

Craig,I looked at using the P38 type steel gaskets but they are much smaller than the ones TVR use and will reduce the size of your exhaust port and loose you power.
Talk to Tim@ACT as he does a composite gasket to suit the TVR ported heads that last much longer than the standard TVR part.
I took my own precats out,used a masonary drill to drill a large hole then peeled the cats out using long nosed pliers.I then had the manifolds ceramic coated inside and out to reduce the under bonnet temp.

[deeen]

Just to confirm: the steel gaskets are ported too small for a 500.

If everything else is perfect, removing the pre-cats should improve the torque and the noise.

So why not?

[mongoose]

I've never come across one genuinely good reason to keep the pre-cats.The car will still pass the emmissions easily assuming all is well of course.The pre-cats produce so much heat which affects the upper suspension bushes,engine mounting rubber,alternator,air intake,a/c compressor,pas fluid,no more crispy wiring etc etc.Just about everything under the bonnet will have a happier longer life without them.You also get the added aural benefits.I've not bothered with the non rev. cones on either of the griffs i've done this to,to me your better off saving this money towards some shiny new jp manifolds.I wouldn't have the cherry bomb fitted until after the pre-cats are removed though,just in case you decide it then wont be worth the extra cost.
I bought my larger composite manifold gaskets from V8Developments by the way,also they were thinly smeared with wurth rtv before fitting,and the bolts(not s/steel) smeared with copaslip and fitted with locking washers.

[Nuggs]

I had my exhaust sleeved and then 9 months later, had the precats taken out while the EM Gaskets were being changed.

The noise is definitely deeper at tickover and a little louder at revs. It pops and bangs a little more, but it was hardly disappointing just with the exhaust mod. The only downside for me is that it does tend to produce a 'icking' - I even had the car back into the garage to make sure it wasn't the EMGs again...

[crazycraig]

Thanks Guys.

Gutted about my steel gaskets, there's another 8 quid down the drain, but then again, better to know now as I wouldn't want to be removing manifolds very often as it's a pain in the ar*e.

Interesting comments about the heat generated due to the cats, but thinking about how much resistance is there, I can believe it.

As I've said earlier, I've now got to replace the damaged engine mounts before the manifolds go back on so I'll have abit more time to get some of these composite gaskets and the correct size lamda sensor removal tool. Just had one delivered from [url]www.ccw-tools.co.uk/catalogue/product.asp?prod_id=2893&cat_id=81[/url] and found out 22mm it's to bloody big......Tuh

It was also mentioned about not to get the other mod (cherry bombs) done to the exhaust until the pre-cats are out due to the noise. Is there a reason for this?
I thought by taking out the pre-cats there wouldn't be much increase in the noise.

Finally, what's the crack with these cones?


>> Edited by crazycraig on Friday 16th December 09:12

[mongoose]

Craig,the lambda sensors dont have to be removed if your carefull/sensible,both of mine were done with them left in situ.The cherry bomb comment was simply a warning that,yes,things will get louder when youve removed the pre-cats,so you might want to hear what it's like first,depending on how loud you want to go,you can always get the cherry bomb done later if you still want more!The cones are fitted to prevent gasses going back up the manifold,some say worth it,others say not.My personal veiw is that as these manifolds will never be any use if you want to get the best from your engine,then theres no point in flogging a dead horse.Save the money for some better manifolds.

[pjac67]

Hi Craig,
very interested in this thread - As you know I have just had a straight thru SS sports exhaust but still not 'aural ecstacy' (even when reducing the size of the silencer!). I have just (yesterday) had a quote from my Bristol based TVR mechanic to remove the 2 small cats (is this what are referred to as 'pre-cats'?) - c.8 hrs/£200 - does this sound about right? Hoping this will acheive an even better soundtrack!
PS Will you be ready for Sunday??
Cheers, Paul.

[zippee]

crazycraig said:

Thanks Guys. It was also mentioned about not to get the other mod (cherry bombs) done to the exhaust until the pre-cats are out due to the noise. Is there a reason for this? I thought by taking out the pre-cats there wouldn't be much increase in the noise.

craig,

I had my manifolds replaced with ACT stainless De-cats back in June due to a crack in one of my originals. This was done before my cherrybomb conversion at Offords.
TBH I didn't notice much of a difference though it was a little deeper at tickover, the biggest diff was the main exhaust mod.
If it's noise your after removing the pre-cats will not do it.

[mongoose]

zippee said:

If it's noise your after removing the pre-cats will not do it.

This is the problem,its all very much a subjective thing.Personally i find that just removing the pre-cats is very nice,which is why i'd recommend you do things in stages.Do the non cat manifolds sound any different out of the rear of the exhaust,when compared to de-catted originals?I have a shiny new completely cat-less manifold and 'y' piece set,ready and waiting to go on,and wondered what this is going to sound like.I hope it's not going to be too loud!

[zippee]

mongoose said:

zippee said: If it's noise your after removing the pre-cats will not do it. This is the problem,its all very much a subjective thing.Personally i find that just removing the pre-cats is very nice,which is why i'd recommend you do things in stages.Do the non cat manifolds sound any different out of the rear of the exhaust,when compared to de-catted originals?I have a shiny new completely cat-less manifold and 'y' piece set,ready and waiting to go on,and wondered what this is going to sound like.I hope it's not going to be too loud!

Are you saying the Y-piece is also Catless? This is what holds the main cat so will make a HUGE difference to the sound, pre-cats alone will only make a marginal diff. Removal of the main cat though will cause emission problems at MOT time, though being able to spit flame from the exhaust should more than make up for this once a year hassle.

[mongoose]

zippee said:

Are you saying the Y-piece is also Catless? This is what holds the main cat so will make a HUGE difference to the sound, pre-cats alone will only make a marginal diff. Removal of the main cat though will cause emission problems at MOT time, though being able to spit flame from the exhaust should more than make up for this once a year hassle.

Yep,the whole lot is catless,the mot wont be a problem,i've got two options on this.I'm not sure i want it to spit flames though

[crazycraig]

Hi Paul.

The pre-cats or manifold cats are the ones I'm talking about.

I wouldn't dream of consider myself as being in the same league as a full time mechanic, but I'm fairly competant with a set of spanners and 8 hrs sounds to be a fair time for someone at my level, 1 hr per manifold to remove, 1 hr per manifold to remove the cats, 1hr per manifold to put back on and 2 hrs for cleaning, filing, swearing, cursing, struggling and putting on plasters where you rip you hands and forearms to shreads, so 8 hrs (or a days work) for a mech is doable, especially with a post lift, but at a cost of £200.00, it sounds well worth it, I'd hate to imagine what a cuffufel I'd be in if I'd have sheared off a bolt or 2.

Anyway, comments taking in about having the non reversal cones fitted, the exhaust mod and how the look of a cat doesn't nescisarilly mean it's not blocked, so a de cat with non reversal cones maybe the way to go ?????

So just the gaskets to deal with.(oh, and the exhaust mounts and the refiting of the manifolds)

I've posted another pic below of the ones I've got at the mo and the hole in them are the same size as the manifold ports.



I've looked at other topics and people seemed to have used them no bother so I think I'd better give ACT or V8D a ring just to check.

[GreenV8S]

The gaskets you want are twin steel gaskets, which look like the ones in that picture. They're composite gaskets with steel wire reinforcement, hence the name. You can get them from ACT, RPI etc.

[crazycraig]

But not the ones I've got at the mo? Even though the hole sizes are the same as the manifold and head?

[GreenV8S]

I couldn't find a socket slim enough to fit inside the mounting boss, so in the end I resorted to a box spanner. I don't think the box spanner would be strong enough to break the thread on a seized-in sensor after it has a slot cut down it, so I left the spanner intact and just take the plug off the lamba sensor. Takes an extra minute or so, but it's not the sort of thing you have to do very often and far less hassle than trying to find the right spanner.

[Nuggs]

Quinny said:

I found that a 3/8 drive socket from Halfords fitted down the recess no problem

I found that Austec's spanners (and mechanics) did the job superbly!

[crazycraig]

Worst case scenario, if I can't get the lamdas out, will they be robust enough if I was to start on the cats will a hammer/drill bit, Mongoose seems confident, but should I ?????