Prodrive [TSL] Sports-Cat - Emissions Sorted!

The last thing on my MOT list was the exhaust emissions, my total de-cat pipe was desperately in need of a catalytic-converter. A standard one would be £140 new and the right length to meet the joint on my Peco, but joining a pipe of less than 2 inches to a 2.5 inch big-bore would be an interesting challenge. I then found out the OEM system relies on 2 cats, doubling the price and forcing me to buy a whole new back section as the 2-piece Peco would have to be fully removed.

If I was going standard then I'd need a full system. The simplified design of the straight-through Peco replaces 4 OEM parts on my 98 model and tracking one down that looked as if it would fit was a pain. Although I could find used 'full systems'

on eBay for as little as £80, they just didn't seem to be everything I needed [from the back of the turbo, right to the tailpipe]. I'm not sure if the exhaust differs much from year to year on the WRX as most upgrade parts fit all classics, but some sets had both cats under the car, some had one cat on the downpipe and some had no downpipe at all. To guarantee the right fitment I turned to new exhaust suppliers, the cheapest quote being from Kwik-Fit @ £850!, so that was right out.

I'd heard about sports-cats, which fit onto a big-bore system and replace both cats with a single concentrated one, but at around £250-300 they seemed too dear. With the price of an OEM system sky-rocketing though it now seemed like a good idea. The ones in my price range looked pretty naff though to be honest, but I stumbled on a second hand TSL one, highly recommended and used by Prodrive, which was a snip @ £235. Of course there's always the worry that a used cat off eBay might be wrecked, but the guy selling it was none other than scooby-leicester who supplied me with the fuel-filler pipe in April, so I figured it was worth the chance just to keep everything on the car top-notch.

The sports-cat is excellent. Not only did it more than half the emissions figures and pass the MOT, but it's reduced the noise a bit too and got rid of the racing-car crackle and the pops when letting off the gas, which is great news for my neighbors and passengers, even if the car has lost a wee bit of character. The engine seems to be ticking over much more smoothly and evenly too, there's less vibration in the cabin and there even seems to be a little increase in power at low-revs - the car seems peppier anyway and I'm finding myself pulling away in 2nd now at times when I would have reached for first. The only downside to the sports-cat seems to be a loss of power at high-revs. Where the car would scream the entire way up the rev band before, there's a feeling now like something is tugging on the power when you get right to the top. It's not a great loss, the car feels just as quick where it counts and it's a bit more useable day to day now and at least I still have the de-cat front pipe there, ready for trackdays...

FITTING: [This covers replacing the front-pipe of a big-bore system (de-cat to sports-cat or vice versa), although the standard front-pipe (1st cat) is very similar to fit.]

It wasn't a lot of work to fit the sports-cat, just undoing a handful of bolts and the pipe is a doddle to replace, provided you can safely get right underneath the car, as a few of the bolts are too hard to reach otherwise. The exhaust bolts are constantly heating and cooling and they shouldn't have seized on too tight, so the job should be over in 2 hours.

1. Lift the entire front of the car, but don't use axle-stands - you'll need to do some heavy bolt twisting right underneath the car and axle-stands just aren't sturdy enough with both front wheels off the ground. The wheels don't need to come off so use ramps if you have them. Be sure to get the handbrake well on and chock the rear-wheels front and back. [We have no ramps and drove the car onto a couple of large concrete-blocks, which worked really well and large wooden blocks would be just as good, but I wouldn't advise using house-bricks or breeze-blocks.]

2. Get the front under-tray off by removing the two 12mm bolts on the cross-member and front-lip, then the two 10mm bolts on either side.

On my 97/98 model, among others, the Lambda oxygen-sensor is located on the right side of the down-pipe collar, just behind the turbo.

3. Unplug the Lambda sensor from its wiring-connector, by inserting a slim flat-head screwdriver into the sleeve that runs along the bottom of the plastic-clip. Slide the screwdriver down the length of the sleeve until the connector-plug can be slid from the socket.

4. Unscrew the Lambda sensor from the front-pipe collar using a mm open-ended wrench.

5. Remove the 2 large bolts and the 3 guiding-stud nuts that run around the collar and fix the front-pipe to the back of the turbo, using a 14mm wrench [although one of our stud-nuts underneath was a 13mm fit, but I don't think this is standard]. The upper ones are easy enough to get to, though all but the bottom right one can still be accessed, just, from under the bonnet. That last nut can only be reached by lying flat under the car and reaching up into the engine, [quite scary if the nut is hard to budge at first]. The guiding-studs will hold the pipe up when you unfasten it from the centre-pipe so there's no need to leave any of the collar-bolts on to hold it.

6. Remove the 2 long bolts from the bracket that joins the front-pipe to the centre-pipe, halfway down the underside, using a 13mm wrench.

7. Remove the 13mm bolt from the pipe-bracket, just behind the front wheels. The front-pipe should now be free to lift off the studs on the turbo and out under the car.

8. Wipe off around the back of the turbo and the centre-pipe inlet, as well as each end of the new pipe. Give the metal gasket from the back of the turbo a good wipe, apply a little exhaust-sealant paste [we did, but not essential if your gasket is in good nick] and replace it.

9. Lift the new front-pipe up from underneath and replace it over the studs on the turbo. Re-insert the 2 top collar-bolts and tighten them enough so that the pipe moves up to align with the centre-pipe. The gap in the rigid cross-member is a tight fit, so the pipe is confusing to align without guiding it with the collar-bolts.

10. Seat the front-pipe into the centre-pipe and replace the two 13mm bolts onto the bracket. The big-bore system has a resin gasket so no need for sealant, but make sure the bolts are wound tight. Then replace the 13mm bolt to the hanging-bracket behind the front wheels.

11. Replace the 3 nuts onto the collar-studs on the turbo using a 14mm wrench and fully tighten them along with the 2 bolts at the top.

12. Give the Lambda-sensor a quick wipe and screw it back into it's hole on the collar of the new front-pipe using a mm wrench. Plug the sensor wiring-connector back into it's socket and you're done.