andyp

If I were starting from a std exhaust system and wished to increase performance, which component should I replace first??

I ask this question because everyone (including me!) starts with the backbox. Would it not be better to to start with the downpipe because this would reduce turbo lag the most and hence make the car more drivable?
I also thought that you might be able to keep the centre Cat and still pass an MOT. Has anyone done this - or has an opinion as to whether this is a valid argument or not?

Cheers,

Andy

Ian Sutton

Well i'm certainly not the expert but I think the down pipe is where you gain most BHP then its the back box, if you change the mid section I believe you gain limited power but it enables you to spit flames and deafen the neighbours.

I changed the back box first at Scooby Sport then went back a year later for the down pipe.After that i knew what id been missing , they should definately have been changed together from day one.

This month hopefully the Catless,res boxless Magnex midsection goes on.

Never did like my neighbours anyway!

Hope it made some sense...Ian

andyp

Ian,

it sounds more like Downpipes are THE best performance upgrade to your exhaust system, while BB offers a nice sound and some improvements!!!
I've got an older MY95 with the larger turbo and on some days the excessive turbo lag gets a bit tiresome. I'm hoping a new downpipe would reduce the lag.

Does anyone know if keeping the mid-section cat would allow the car to pass the emissions test?

Andy

Ian Sutton

I obviously lost a cat with the fitment of the down pipe ,i was told that the car will not pass its MOT unless it has both cats in place, hence thats why im getting a replacement midsection and not having the Scooby Sport adjustment (cat cut out) thus I can keep the old catted one for my MOT in 18 mths.

...Ian

Doc

The car *MAY* pass the MOT on the centre cat, if you get it very hot and they test the emissions straight away, but I wouldn't bet on it. If you have the cat in the downpipe the second cat is not required for it to pass the emissions test.

Lee

biggest gains are to be had from removing the main restrictions.

hence downpipe, then mid, then backbox.

most change the backbox for aural/visual reasons..the perf. difference to the driver is negligible.

strictly speaking the best performance increase is purely to raise boost.

RaymondH

I have a Scoobysport downpipe and backbox on my MY98 and it passed on emissions check which was carried out for curiosity's sake. However, a MY99 with PE downpipe and Scoobysport backbox failed the same check (both cars have centre cat still in place). Make of that what you will but it must be marginal.

MorayMackenzie

Lee,

Surely getting the timing and fueling spot on for your setup is as important as jacking up the boost in performance terms? You can gain extra go by sorting the fuel and timing without touching the boost... then just add a bit more boost and you are laughing/constantly grinning.

Moray

andy p

So it sounds like a downpipe is a performance "must-have" not just for power boost, but more importantly (to me anyway) so-called responsiveness.
It also seems that people have had varying success with the dreaded MOT emissions test; as Ray says it must be marginal.
Has anyone had experience of Performance Catalysts? How do thay keep their free-flow nature and still work?

Andy

grief

Ok, stupid question time, so be gentle.

Where are the 2 cats on the standard MY99 exhaust ? Mid section and backbox sections ?
Or downpipe and mid section ?

If I change the downpipe only, what could I hope to gain ?

Ian Sutton

Mid section and down pipe are where the cat's are.If you read back on this thread you will see the answer in full about the improvment gained by a free flow down pipe.

Its the way forward.

...Ian

andyp

I agree with you Ian that it must be the way forward. However, how I deal with the MOT seems a little unclear!
It's okay if you've got a newish car and the MOT is 2-3 years away, but folk like me who aren't so lucky will find it difficult (and costly) to keep swapping the cats in and out.

Is the truth out there?

Andy

Jay m A

iTrader: (2)

Andy P

I have the same dilema as you, I read in other threads that the mid section is a doddle to swap over. Does anyone know how easy/hard it is to replace the downpipe?
Is there any ill-effects on cats that are stored for a year then used for a day then stored again?
Any help appreciated - cheers.

Steve Howat

The initial change over of the downpipe is a bit of a bu99er due to stubborn bolts, heatshields etc. It can take anywhere from 2 hours onwards to change (plus removal of skin on knuckles). However the subsequent changes for MOTs are alot easier, mine took about 30 minutes to change back to the original for the MOT and 30 minutes to put the SS one back on. This is because the bolts were easier to remove and I knew what I was doing.

One thing is that if you do change the downpipe back fot the MOT you appreciate the improvements even more

The alternative is to find an MOT station that will turn a blind eye to the emissions on the count that you will change it back anyway.

Hope this helps! Its well worth fitting it

BPM

The downpipe...


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GavinP

I have a 94 WRX and have a MRT downpipe with a high-flow cat.

Breathing is definately improved due to the improved design from the OE part and the 3" diameter.

I also considered a cat-free downpipe but didn't like the idea of getting the pipe changed every year for the MOT.

As it is the Link has to be swapped out but I can do this myself in about ten minutes

There is a much more limited choice in cat downpipes - MRT, GGR , err... and they do tend to be expensive but paying for the labour to remove and re-fit annually will soon recoup the cost.

I dare say that the cat-free pipe breathes better and makes more noise but there are disadvantages as well.

Incidentally, Power Engineering do a central section "super cat" which may be a better solution (?)

Thanks

Gavin