stiscotty

have been saving up parts to put on my 2001 bugeye jap spec sti now have new manifolds decat down pipe decat centre section green cotton filter an walbro 255 ltr fuel pump allready fitted cat back and hope to get new adjustable regulator soon but would like to know can i fit any of these lovely shiney new parts with out remap or would i do damage an does any one have an idea of much gian in power i should hope to get thanks in advance for any reply

TonyBurns

iTrader: (3)

Dunno why you even changed your fuel pump, the JDM cars have a perfectly good one already.
As for the decat, well it will spike the hell out of itself and self destruct the engine, that should answer your question

Tony

KenS55STI

Scotty
I have the same car, mods as follows:
Scoobysport decat downpipe, centre and backbox
Walbro 255 fuel pump
Green panel filter

If you fit a decat exhaust and better headers then this will improve the airflow through the engine. The result will be that the turbo produces more boost than it should and you get boost spikes as Tony says. The boost will overshoot the target and the ecu will try to correct it, so it will fluctuate up and down causing the car to surge under acceleration. I had this on my car and it is a right pain when you try and overtake.

I don't know if the jdm fuel pumps are any different to the uk ones, but I did see a big difference when I had the walbro fitted. The car is more responsive particularly off bost and at lower revs. I suspect this may be because the car is slightly richer than before because of increased fuel pressure, I have not changed the regulator. If you fit the pump and regulator at the same time and have it set at standard pressure then you may not notice any difference.

It's difficult to say how much power improvement you will get by fitting these parts without remapping but it is likely that whatever gains you have will probably be caused by the car producing more boost than it is mapped for. As Tony says this is potentially dangerous and having gone through the boost control issues with my car as a result of the exhaust I would probably not fit the exhaust parts without remapping.

My advice would be to get a knocklink and fit that before you change anything else. Then have your exhaust and fuel bits fitted along with a remap. Then you will get a massive performance increase and be safe.