I have just been for a test run and it is noticeably quicker, especially after the top end of 3rd. This is where the original sysyem is fully saturated with heat.
I installed a digital temp sensor on the output side of the Intercooler, as it flows through the hose to the V6 plenum.
On the original, this temp would be around 33-35 while idling, now it is 29-30. It used to stay the same while crawling along at 30mph, now it falls to about 27.
From a standing start at the bottom of a long hill, I can be on boost for a long time going up this hill, I would see 72 degrees by the time I hit the top end of 3rd and I think the IC is working well as the temp would not go any higher. It would take a couple of minutes of free running for the temp to slowly fall again to the thirties.
NOW, I cant get to see the temp rise more than the low forties, so I am 30 degrees better off. If it is .8hp per degree, I'm not loosing that 24bhp any more PLUS the ignition will not retard as soon or start to over fuel. The car is still pulling really hard all the way through 3rd and through 4th on boost all the time and still only 42/43 degrees.
What is more, withing about 3 seconds of free running the temperature is back down to the low thirties again.
I am so glad I used clear pipes as there were quite a few little bubbles to vent out, this took quite a while to complete.
Thanks again to David G for his help and support.
Off sprinting tomorrow, who cares if it is hot, I'll have a well cooled charge

PS: if anyone needs spares for any Mountfield mowers, I have all sorts available.