IWANASCOOBY

Guys,

I have a Sub Impreza WRX Turbo 93 and I think my cat converter is dead or dying, horrible rattling noise coming from the front end. I originally thought it might have been the exhaust shield or something but it's definelty the cat when you get it up on the ramp everything else is solid.

The exhaust is all standard including the backbox which is the twin exit tailpipe.

I have to admit I don't like the twin exit tailpipe I don't think it looks right on the car and I am considering a bigger backbox to get that deep and sexy Subaru burble.

Question is do I go for a cat back system or the full system from down pipe to back box.

What is the bhp increase for the cat back system and the full downpipe to back box system with 3 or 4 inch tailpipe?

Somebody I know has the full system for £200 and I'm wondering if this is a good price or is it a pain when it's MOT time????

If the benefits between the cat back and full system are marginal then I will just get the cat back system and save hassle but if the noise and performance is better with full system then thats the way I want to go.

Any thoughts please would be appreciated.

funkyspider

You will need at least one Cat to pass your MOT anyway (93 ??). The Cat which will give you most benefit if you replace it is the downpipe one, but unfortunately thats the one that warms up fastest and is more likely to pass an MOT if you only have a single Cat on your system.

People usually do a full decat, downpipe included, then get a second hand centre Cat which is easy to fit to stick on for MOT. You just have to make sure it's sufficiently warm at test time.

Use the advanced search function (dropdown menu on site header) to find pleanty of discussions about performance benefits of replacing either or both cats it will be much quicker than waiting for a response to your thread and you will get a fuller picture. Example, search for "classic decat performance" or "classic decat MOT" etc and you will find more info than you can shake a cat at.

I''m not sure if a 93 classic WRX has an up-pipe cat too as I'm a newage bloke but searching will tell you

BTW I wouldnt hammer if if the cat is breaking up, you dont know where the pieces might go.

IWANASCOOBY

I'm even more confused now after reading previous Classic Performance exhaust posts!

I'm buying the system from a breakers yard is there anything that I should look out for if I buy the system? I think I get the MOT part that if i replace the through pipe with a centre box at MOT time then it should pass?

Come on people I am a real novice here, talk to me like I'm stupid! Ha Ha Ha!

funkyspider

What system is it you have seen in a breakers yard for 200 ? and how much of it are you gettin for your money (backbox and centre, or downpipe/up-pipe as well ?)

Also check if system is 2.5inch or 3inc. If 3inch you will definately have to replace the downpipe anyway as it sounds like you have a standard downpipe at the moment which mates with a 2.5inch centre.

If it's something like Hayward & Scott or ScoobySport (to name but a cpl popular decent ones) and if it's a full centre pipe and back box then I'd say it was about right price, but you could probably pick one up on here for around that (maybe adding P+P). If it's just some generic loud thing then maybe not such a good buy as some of em dont do a lot for your back pressure and you may not run much better. Any decent replacement exhaust should be good quality, so if it's all rusty then dont bother (and I mean rusty, not just discoloured) and find one on here instead. If it's just a standard STi system then it wont really do anythng for performance, just the tailpipe looks nicer.

Are you aware that you have a heatshield just behind the turbo, those often rattle as they are only held with tack welds which can break.

As for performance - and this is in my limited knowledge just from reading around and looking at improving my own performance.

Replacing just the centre cat and backbox will change the noise but performance wise probably wont do a huge amount on its own (maybe 3bhp as the downpipe cat is still the biggest restriction on flow)

Replacing the downpipe cat (and BB) and leaving the centre will probably gain you 5-7bhp without doing anything else. Add a decent panel filter (Green/K&N/Subaru STi) and you'd probably be looking at 10-12bhp. I personally wouldnt suggest going for a full induction system, esp if its on older MAF, but you can read ppls views on that at your leisure.

A full decat and a panel filter possibly 15bhp without any remapping etc - BUT make sure you can get your hands on a centre Cat for MOT or it WILL fail and MOT retest times are very short these days so you've not much time to get it put on and retested before you're paying again. replacing the centre Cat for MOT, 20mins including driving it onto the ramps, replacing the downpipe cat considerably longer with more knuckle skin lost from what I understand.

As for what BackBox you fit it depends on how much you like your neighbours. I personally prefer the scoobysport or H&S 3/4 inch 'normal' box and tailpipe over the big jap style ones. I had a big Jap style and I found it a little too loud on the motorway and when setting off early mornings.

Having replaced, even with a full decat, shouldnt 'force' you to have an expensive remap, but your car would gain extra benefit from it. If it's an import it should have been mapped at some point in it's life for our crappy low RON fuel anyway tho.

There, thats my opinions on the matter.

jaytc2003

iTrader: (1)

a 93 doesnt need its cats to pass the mot, just had mine done, was worried so I spoke with the vosa people beforehand. Its an import so it has slightly different testing rules to uk cars. For whats its worth, mine emiisions were well within limits. (fully decatted, also a 93wrx)
For induction, a panel filter as mentioned is a good upgrade, but the inductions kits are okay as well on the earlier cars as the mafs are quite strong. It was only later mafs where problems of failure started to appear

IWANASCOOBY

Funky spider got a bit more info on the exhaust system.

It's the downpipe, middle section and backbox with 3.5 inch tailpipe. It came from an L reg Wrx Turbo and mine is a K reg so it should pretty much go straight on. Been quoted 60 quid to fit it!

The birds already not happy that I'm spending money on the car given I'm having all new tyres this week, bodywork tidyed up and the exhaust the week after. She keeps whining on about a holiday! They just dont understand. Ha Ha Ha!

Jaytc could you post a little more info about the emmissions test on the early wrx's please!

Thanx

jaytc2003

iTrader: (1)

go to the vosa website and do a search on there. It tells you about the different tests. Because of the age of the car they will probably do whats called a BET which is Basic Emissions Test. Funnily enought though my emissions were low enough to pass the cat test as well! I did get my car well upto temperature though before the test

IWANASCOOBY

Thanx for the input! Jaytc does the above exhaust system sound like a good deal to you? It's supposed to be in very good condition, should be going to see it at the weekend!

funkyspider

Like I said, depends what system it is but assuming it's ok then for a full system and the decat downpipe 200 sounds like a good enough price yeah. It should be stainless steel (but dont expect all of it will shine like your knives and forks lol) so shouldnt be any flaky rust on any of it. It's very difficult to tell what downpipe/centre pipe it is from looking at it as they all look pretty much the same looks wise. Have a search in the for sale section here for "classic back box", "classic downpipe", "classic exhaust" etc and see what stuff has previously been sold for as everyone on here (including me ) likes a bargain so its about as cheap as you'll get stuff.

My 'guess' is for that money it's probably a prodrive or STi back box as they tend to sell a lot cheaper than the aftermarket ones like H&S, ScoobySport etc so have a look what different back boxes look like (prob find pics in for sale and members gallery) then you'll have some idea what you're looking at when u go see it.

Use the search, the search is strong

The 60quid to fit it will probably be mostly for fitting downpipe and you'll probably find the nuts connecting it to turbo are rusted tight. Dont forget a new gasket between turbo and downpipe as you really dont want it blowing there, so find out if they gonna fit one.

IWANASCOOBY

I'm going to have a look at it tonight aft work to decide whether or not Iwant it, the guy has somebody else interested in it. It is an aftermarket system and not a standard subaru system, the guy says the centre pipe bore is 2.5 to 3 inches and the tailpipe is 3 inches! Can go have a look for nothing and decide whether or not I like it! Will post more tonight when I have had a look at it to let you know!

jaytc2003

iTrader: (1)

chances are it will be a 2.5 system (specially for £200) then 3 inch is probably just the outlet from the backbox. You can get downpipes that are 3 inch but taper down to a 2.5 inch to mate up with the centre. Either way it should fit no problem and for £200 does sound like a bargain (decat downpipes on their own are nearly that price)
good luck, let us know how you get on.

IWANASCOOBY

That exhaust was complete junk, not worth £100 never mind £200, a few dints in it no particular make that I could see, decided against it!

I don't know whether or not to get the full system?

I mean don't get me wrong I love the burble of the subaru with a full system on but then I think it would probably do my head in after a while.

Anyway on just increasing the noise a touch on my car without having to put full decate system in?

What would a cat back system be like volume wise or what about just changing the backbox from the standard twin pipe I have to a 3 or 4 inch one?

Any thoughts guys or ideas????

thedeester1

That noise you described could be a damaged heat shield right at the front of the system. I had the same thing. They get hot then wet and crack around the bolt holes. They then vibrate giving a noise like a damaged turbo or CAT. I fixed mine by putting a big washer on the bold to clamp the heat sheild. Check this before you shell out your cash!
I know you said everything is solid but it is really hard to see since its quite rigid till the car is in motion. The crack is hardly visable.
Took me weeks to track it down. Get the car ramped up with the engine running and get a screwdriver. Get someone to rev the car since thats when you hear the noise. Push the screwdriver onto all the mounts of the heat sheilds and see if the noise stops.
If IT IS the cat you can get someone to make you a through pipe!
However the cat is usually under the gearstick area of the car and you said it was at the front!

[Davey]

Middle cat should get you through the MOT no problem..

jaytc2003

iTrader: (1)

there is only one cat on a 93 import and it is in the downpipe. The centre section is just a resonator but it does look like a cat.

you can always remove the heatshield and go for a run, if the noise disappears you know where the problem is, you can then refit it and make sure it is tighter etc

funkyspider

I'd still recommend a scoobysport back box with 3 /12 inch tailpipe. Gives the lovely burble but is not overly intrusive inside the car and isnt any more noticable than the tyre road noise when on the motorway, but considerably better than the standard twin.

You should be able to pick one up for no more than 100quid and as it's 2 1/2 inch it will mate to your current centre pipe. I believe the haywood and scott box is very similar. Just dont go for a jap style back box if you dont want big noise.

Remember if you stick to 2 1/2 inch components you dont have to replace all of em at the same time as the aftermarket stuff will fit the standard, so centre pipe/down-pipe/up-pipe can come later.

IWANASCOOBY

Guys you have been great with the advice, really helped me out alot! I will put a post in the wanted section for a backbox then either scoobysport or haywood & scott backbox with 3.5 inch tailpipe.

I understand the down pipe leads to centre pipe and then to backbox but what is the up pipe???

Also if I take the downpipe cat off and put a through pipe on and leave the resonator on will it pass the mot????

My baby is in the garage as I type for new front anit roll bar bushes and a set of 4 new tyres and tracking.

It's in ther body shop on monday to get the bodywork tidyed up because some jobless scumbag nicked it a few months ago and scuffed the front passenger wing and bumper and mangled my back bumper to. Hopefully by the time it comes back next thursday it should look like a new motor! Yay! until then im stuck driving the bird 1.4 mg zr or my mates crappy rover metro 1.1. What a joy!

Many Thanx

jaytc2003

iTrader: (1)

mot will be fine with a catless car if it is a 93 import! Mine a smentioned above has none, and it passed the emmissions easily. It also passed the noise as well (no silencers on it at all)

funkyspider

http://www.scoobysport.co.uk/images/exhaust/flow.gif

Answers your question about the up-pipe