Problems under hard acceleration

[Matt Skillett]

Hi all,
Last night i went out in a friends Subaru Impreza, I don't know much about Imprezas but I know its a 1994 car, STi, and it was one of only 100 built or something like that. She has owned the car 3 months and the guy who owned it before her has fitted an aftermarket exhaust, alloys, turbo timer and boost guage. He may have done more but I havent looked under the hood and she doesnt know too much about it.

We were driving round yesterday when she started to give a bit of juice. everythings cool until u hit about 4500-5000 RPM when it starts to kind of lose power and then gain it again very quickly, like a juddery kind of thing. (technical terms here!) Anyway, she seems to think that it gets better when the engine warms up a bit and she says it only does that when she hasnt driven the car hard for a while (our speed limit in Guernsey is 35mph so it doesnt get driven hard too often). I dont know what the problem is at all and could only guess that its pinking or detonating or something.

I'm also not sure whether the turbos been upgraded because the boost guage says were getting just above 1 somethings?! yes i dont know what its meaured in because im stupid, I'd guess its bar but 1 is quite high for a standard car isnt it? I though most turbo'd cars put out 0.65 bar or something?

Any ideas on anything i've just said would be handy. I'll try and find out more about the car.

Cheers
Matt