Ah ok, i found 20% loss to be more realistic figure when converting fom crank power to wheel power.
Cheers

I did have a similar setup. going bigger now.
im pretty sure 2 inch pipe is the size of the standard exhaust. why would you use the standard size on a modified engine?
even with a 2 inch outlet from the extractors the 2.25 inch system will flow more air. if you want you could get the outlet changed to 2.25.
couldn't tell you the difference in torque from just changing the system, I went bigger exhaust when I modified lots of other things, and torque was very much increased.
 

Thanks for all the advice guys. Looks like fate has played a part tho... Stumbled across a cheap pair of ph4310 pacemakers on gumtree the other day. Went and picked em up (quicksmart) and the seller was also willing to part with the 2 inch system incl. s/s muffler box and silencer for a nominal price. He was going the whole hog with a complete ashley system on his new build. It gets me on the road and it was a deal I couldn't ignore!