[DannyG]

I have a r33 gts with a boost controller. It runs very well when set on 0.5 bar of boost but it just makes a loud hissing and goes no faster when boosting at 0.8 bar,

Could this be spark plugs?
It also emmits a little black smoke at gear change is this o.k?

 

[Stan]

I had this a couple of weeks ago & the pipe from the turbos to the intercooler had come loose. Same symptoms as yours. Refitted it & sorted straight away.
Might be worth a check.

 

[DannyG]

Cheers mate, will check it out, someone else said it could be over fueling - is this likley?

 

[Stan]

Not sure about that - my knowledge is limited to whatever goes wrong on mine !!