Odd you should ask that as I'm just in the process of breaking in a GRP tuned .21 buggy engine with the turbo head for a mate in our club..it's in his brand new mp9 ..ahem but he's never done anything but bash with a savage truck before so he's spent some serious money..anyway bit early to tell really what the GRP is like but first impressions are its very very steady on the idle but seems to lack the full on top end of my GO 7-port..(MM stage 5 mind you not stock)..it's also bloody finicky on the lsn setting..fraction + or - seems to wreck the tune.Wouldn't like at this point to say I do or don't like it without watching it race once the run in is complete..what I will say is it lost it's really really tight pinch after only 2.5 liters of fuel and would start no problem from then on without preheat..my GO was much tighter until at least 7 litres..but that's what GO's are famous for..I would just buy a MM5 and sod the rest! I have the 3 and 7 ports from mark and get all my spares from him as well..never a problem EVER! Just order your spare rods,wrist pins and clips at the start so you don't have to worry about stock when you NEED to change them..Thats it really..go for it..make mark richer and get a great motor!