I have a 97 12 valve with a 270 plate and K+N air filter and a BD clutch. I have 270000 km's on it and drive about 200 km/day. I would like more power but still get good fuel econemy when I behave. I do need exhaust so should I jump to 5 inch or go 4.

 

Which clutch is it? BD sells many levels of clutches.

Okay so you have an #11 plate...you can use which ever exhaust you want, there's no performance difference between a 4"and 5". If you want more power then look at injectors, like DDP stage 2 or 3, and have your timing bumped up round 15.5* to 16* to get your mileage up.

What do you mean by K&N filter? Like you're still using the stock airbox?
Get rid of it, and get a performance intake kit.

 

BHAF, HANDSOME fill out your sig

 

gsk 3k or 4k depends on what you want to do down the road. if you just want a little more pep get a 3k but if you want to do more mods and push more than 350 hp i would do the 4k. dont forget the valve springs with the 4k. the gsk itself is easy to do and it takes maybe 1.5 hours to do yourself. if you can change a fuel plate you can do the gsk.