Adam555

I still have the stock centre section with cat fitted on my STi2 - Will changing it to an after market section with high flow sports cat improve power at all? (backbox and twin downpipe minus cat already fitted +19bhp/16lbft)

If so, can anyone recommend one?

It has to be with a cat as I would want to pass a roadside emission test if ever needed...

[Edited by Adam555 - 1/1/2004 5:38:07 PM]

Turbo_Steve

Adam,
before you change your exhaust you should consider remapping the car. These are already set for 100RON fuel, and running leaner than they should be on UK fuel. Changing the exhaust for more flow can lean the map out further, and potentially damage your engine At the very least you should couple your exhaust upgrade with a Knocklink or remap.


As I understand it with exhaust pipes, changing your downpipe will help your turbo spool quicker, changing your mid-pipe and back-box are for peak power.

A friend of mine recently had a powerflow exhaust made, and had a Dodge Viper cat put in the middle (secondhand cat) to the tune of about £390 all in. This cat will flow a substantial amount over the factory setup.

Adam555

I'm putting OB in on top of Optimax so I thought fuel would be fine without a remap (I've only got stock ECU anyhow, is this remapable??)

So a high flow sports cat in the mid section would give more power than stock then?

The only one I could find was an Afterburner mid section with hi-flow sports cat for apporx £430

Any ideas on power gains with this?

Turbo_Steve

Not sure about power gained from exhaust. To be honest, it really depends on the car.

As your car is one of the older STI2s, I _think_ it should accept a scoobyECU. Visit http://www.scoobyecu.co.uk/ for more information. If they have mapped an STI2 before, then I would guess you are looking at less than £100. If you need a custom map (which I'd reccommend) you are still looking at less than the price of your catted midpipe.

There are sports cats out there that claim to have no perfomance decrease over a straight through system. What you will probably find is that a straight through system will be enough: if you still have the cat in your downpipe fitted, and the car is nice and warm, most cars pass their MoT emmissions check anyway. SOME cars even pass it with no cats at all, though this is a lot more unusual.

My experince with 'sports cats' is that they have a tendency to come apart inside under high exhaust flow conditions....I know of two and have had this happen to me once. For the hassle of borrowing a midpipe and getting it fitted and having an MoT centre run an emissions test, you might save yourself £300 to put towards a remap for better power delivery and safer running


NF + Opimax has been shown to be very good, but is not guaranteed, especially once you start modifying your car, which will cause it to run leaner and leaner the better you make it breathe (i.e. exhaust and airfilter). I would urge you to spend £140 on a Knocklink, just to make sure you get that big flashing Red light that stops you blowing your engine. Consider it this way: £140 kocklink against a £2000 or so engine rebuild. Looks like a good investment to me

Adam555

So your are saying a remap would bring on power gains without the sports cat mid section...

How about if I got the sports cat mid section and then a remap? I take it the gains would be greater?

Turbo_Steve

Gains will be available with a good remap. I think you will be amazed at how much better the car will run.

Gains will be better with a sports cat and best with a straight through pipe.

And yes, you will have to remap after fitting the pipe to get the full benefit.

Manufactures software is heavily compromised to allow for poor servicing, fuel, arctic conditions, desert conditions etc etc etc etc. Removing these compromises will get you more power and better driveability. Also, the Jap Maps are not known for their driveability anyway.

Adam555

Thanks Steve - I have emailed them to get prices

I understand about the straight thru mid section but as I have no cat in my downpipe then it would defo fail MOT and roadside emmissions test - I really would find it a hassle to get the mid section changed around every year so it would have to be a high flow sports cat for me!

Also Knocklink - I understand why I need it - improved breathing = leaner running = det but what could I do about it? If i'm adding optimax + OB in and still the Knocklink was going all Christmas tree on me, what would I do to correct it?

As far I can see having it remapped would stop the need for a Knocklink sensor

The only advantage I can see is that if problems arose in the future then it would show me but to be honest I think I would know simply from the cars performance!

Adam

Turbo_Steve

If the knocklink lights up, you stop driving like a nutter, as you'll blow your engine.

Then you go away and find out WHY it lit up (bad petrol, ECU probelm, sensor failed, ETC).

It's a just a catch all, and it's a damn sight better than waiting for a check engine light or a £2500 crunch.

Jolly Green Monster

iTrader: (4)

STi centre section doesn't contain a cat..

just a resonator bubble to reduce noise a little..

Get a downpipe instead.

But as said you would need knock link and afr monitors or a remap to ensure you were not under fueling.

JGM