15 replies to this topic

[YoungVXer]

Ive used search function but cant quite find what im looking for so maybe you lads can help! Seen recently in some posts about just removing the pre-cat? Is this right and what does it achieve with regards to just a standard exhuast set-up? Does it improve sound and bhp??? and what costs are involved as i wouldnt try this myself! If this isnt right what is a cost effective way to improve sound / bhp with regards to standard exhaust (without having to buy new ones?) Thanks , Dean

[NAP1]

I did search about precat removal and had to go back quite far historically where it was discussed quite alot. I am not sure it has an effect on sound unless you have an aftermarket exhaust (I may be wrong there) but it makes the engine breath much more freely. From the search I did general consensus is its a good mod to do - think its about 100 - 150 labour. If you want more sound I cant recomend an ITG airbox more as the sound is awesome but it is pricey, alternatively a K&N filter is pretty cheap and I think gives plenty of sound for your buck. Night be worth searching airbox mods as well as some people drill holes in the original box - not sure if this is any good though.

[trescoman]

The DIY Car Care section is a good place to start looking, its at the top

<CLICKY>

Any thing that makes the car breath easier is gonna help with the BHP, especially if its a VXT

However unles you want the agro, you can get a front cat replacement part that will save the agro, both Courtenays and TMS (I think) do them

Have fun.

Bob

Night be worth searching airbox mods as well as some people drill holes in the original box - not sure if this is any good though.

Timbo airbox mod , never did my car any harm, other than changing the filter more often, which is never a bad thing anyway

[RichH]

When I removed mine on my old NA there was no change in the sound of the car. It did make the engine feel like it was breathing much more freely and therefore much smoother. I’d say it made the same sort of difference as having the TMS stg 1 remap done. The only way on the NA to get rid of it is to drill it out unfortunately, or replace the whole cat section. The NA doesn’t have a separate pre-cat pipe section like the VXT.

[drpau]

When I removed mine on my old NA there was no change in the sound of the car. It did make the engine feel like it was breathing much more freely and therefore much smoother. I’d say it made the same sort of difference as having the TMS stg 1 remap done.

The only way on the NA to get rid of it is to drill it out unfortunately, or replace the whole cat section. The NA doesn’t have a separate pre-cat pipe section like the VXT.

Unlike RichH in my case after removing the precat there was a definate increase in db and it seemed more 'burbley' (standard backbox K&N filter). Definate improvement in pull. Do it yourself- put aside a fair few hours as the bolts can be a bitch.... I used 1 drill bit which snapped towards the end - you can pick up a load of cheap bits in wilkos though, I got shafted in B&Q - 7 quid for one!

Edited by drpau, 20 September 2007 - 09:55 AM.

[rabidh]

Unlike RichH in my case after removing the precat there was a definate increase in db and it seemed more 'burbley' (standard backbox K&N filter). Definate improvement in pull. Do it yourself- put aside a fair few hours as the bolts can be a bitch.... I used 1 drill bit which snapped towards the end - you can pick up a load of cheap bits in wilkos though, I got shafted in B&Q - 7 quid for one!

On my NA I noticed the exhaust note got a bit more bass, i got more power *and* better fuel economy. Everything else was standard. It took me better part of a day to do myself (my car has done 60k miles and I had to cut off my exhaust bolts and replace them).

[RichH]

I should perhaps add that it did have a VSE and a viper on already so perhaps any increase made from the pre-cat being removed was somewhat dwarfed by the rest of the bassiness and burbling from the other mods. If others have done it to a standard car then that would be a better guide. For saying that though, I can't believe it make a huge difference

[YoungVXer]

Cheers for the replies lads, good help I do have a K&n already, so this may possibly increase sound slightly? When you say labour is £150 is that for them to do the same thing as the DIY job or would i have to give them a pre-cat replacement pipe for them to do? I dont really want to do this job myself as i really dont trust myself ....never worked on a car in my life (apart from fitting an air filter and replacing the header tank )

[davemate]

i am about to do mine myself. if you are around cambridge area we could do a mini meet and see if anyone else wants to get theirs done too?

[robin]

just do it yourself its a easy job to do, i did mine by jacking back of car up and taking exhaust off took a bit of time but did it withno problems, then get the cat section and clamp it in a vice and drill the honeycomb bit out, worth getting a few drill bits as they heat up and melt. i did it with a large masonary bit with the hammer drill turned on went through quite nicely. worth doing i was runing a VSE so really made a lot of change in sound and smoother running.

[chris_uk]

just do it yourself its a easy job to do, i did mine by jacking back of car up and taking exhaust off took a bit of time but did it withno problems, then get the cat section and clamp it in a vice and drill the honeycomb bit out, worth getting a few drill bits as they heat up and melt. i did it with a large masonary bit with the hammer drill turned on went through quite nicely. worth doing i was runing a VSE so really made a lot of change in sound and smoother running.

i can certainly back this up.. i have a VSE and in a tunnel... oh my god!

[JG]

I have done mine to 'protect' the manifold.

[YoungVXer]

i am about to do mine myself. if you are around cambridge area we could do a mini meet and see if anyone else wants to get theirs done too?

Unfortunately im in North East m8. good shout tho

[drpau]

Give it a bash yourself mate - anything is possible if you are persistant. If after having a go you find you cant get the nuts off then you can think about taking it somewhere. Borrow some penetrating oil to free up the nuts from the manifold to precat. Borrow a dremel in case you cant get the exhaust bolts off , get a few drill bits and jobs a good un.

[T5SOR]

Is it worth knocking the cat out at the same time? De-pre cat sounds good. If im there maybe the cat should go aswell?? Mike

[Anarchy]

I would not have a go unless your used to doing a bit of car DIY, something is likely to put a spanner in the works be it a seized bolt or having hard time drilling cat out. In theory its an easy job in practice no guarantees. Puts positve head back on... Its worth it tho, agree with comment above, better sound, similar BHP increse to Stage 1 remap.