Longest reported life of an engine
I got 4-5 gallons through a new TMAXX 2.5 before it started to lose performance. The only way the engine seemed to make good power though, was to tune it relatively hot (250-280). I suspect I might have gotten a gallon or two more if I could have gotten it to run cooler....
I am now running .21 OS RZVBO1 big block and am on gallon #4 running 25% nitro, with temperatures more along the lines of 220F-250F. MAX (measured accurately and frequently). The performance is as good now, as at any time during the previous 3 gallons, so I suspect I am around the engines half-life, perhaps less.
I personally attribute the higher volume of fuel, until engine failure, with the bigger displacement engines, compared to the small blocks, to a number of variables:
1. More fuel consumption=more lubrication.(a .21 goes through 150CC of fuel TWICE as fast as a .15!)
2. larger heat displacement due to larger heatsink design, and big blocks commonly have webbing around the block which works as a heat-sink.
3. The big blocks have the ability run at 100% potential while maintaining a cooler temperature(200-250) where the .12-.15 seem to constantly be running close to 300F when making their full power
Of course these are just my observations. I intend to try one of the RB products next, either the WS7 or the C5. I don't have a problem believing a .21 with the proper tune (200F-250F.MAX)could run 15 gallons. At the same time I don't think 4-5 from the 2.5 is bad either.
Personally I always simply replace the piston/sleeve/rod and maybe crank at engine rebuild time. The bearings on the Connecting rod cannot be replaced and if they are worn they need to be replaced to get max. performance. Re-sizing maybe works for some but nothing works as well as a new OE piston set. Besides of course the piston/sleeve is the most expensive part of the engine-it the most important, and highest tech part of the engine!