I was thinking of modding the Mac star engine. It has a screw in the side just below the carb for a boost bottle it came out of the factory as a bump start engine. I did try getting a good tune with a number of plugs and found the R4 to suite it the best any hotter and it started to pre ignite (Bad for the conrod) so I tryed to tune it with that and also found it to be inconsistant but that might be the fuel tank. I didn't check to see if it had any shims in the head it is completely standard so I'm not sure if it would have. I have just got a new centre diff and set the oils at 5,000wt in the front 7,000wt in the centre and 3,000wt in the rear. I Also got new suspension pins wishbone and anti roll bars to take away all the play. And new MG995 servos and a 1500mha 6v battery. I'm going to go with the 16 tooth clutch bell and see how it goes. Also got a new shell and new bearings and wheels and tyres will post pics as it won't take me long to get it all dirty and scraped again.