I currently have a 94 WRX Sti - sporting a few mods, including HKS induction kit and a HKS Hiper exhaust - however, this is from the CAT back.

A few people have suggested the replacement of the down pipes and CAT would give great BHP increases (which is nice!)

However, what are the MOT issues?
also, what sort of cost should I be looking at?

H

 

Keep your old downpipe and swop them when you go to get MOT'd.
The HKS downpipe is not too expensive [I have a straight through Super Drager].
I don't know about bhp differences as the car has never been tested for such foolishness.
Audibly you get a lot of burbling and popping, the occasional flame [cool] and can hear the turbo spinning.
The car becomes a lot more responsive [placebo]. You really sense it doing things a lot quicker/better.

 

No work, Ian?

Cem

 

Catching up with the five and a half months I missed spending time in autobahn land.
What are YOU doing here anyway.

 

I am busy stirring, wooden spoon and all...basically causing trouble.

I can confirm that Baije's set up is pretty hardcore. It sounds very nice and flameouts are, off course, a great bonus.
Bbut u must maintain back box polish frequently, or you may suffer upto 40bhp loss.
Cem