Does anybody no if the harvey slip pipe is supposed to slightly blow when cold?????!

 

Slip-pipe?

If you mean the up-pipe, ask Alyn.

 

As Jeff said above are you referring to the up-pipe? If so then no its not suppose to blow, or at least ours don't any leakage before the turbo can result in loss of power, get it looked at would be my advice

 

As it's a slide fit there could be a small amount of leakage when cold and the metal has not expanded to it's working fit.
Have you got tubular headers combined with this? These often make a different sound when cold.

JohnD