The new Arrow-Racing GTR-21 Ver III .21 engine is now in stock at Hobby Pro USA.

The engine has been redesigned to have less mechanical pinch to make engine break in easier and allows the engine to be started the first time with less effort. This also puts less stress on the con rod and allows a race tune to be put on sooner.

He is the explaination from the manufacture:
We have done a number of minor adjustments to help with the initial start-up process for end-users. But ultimately this was done without affecting the engine's overall lifespan. The idea was brought up long ago but it was only until the beginning of the last production schedule, we were able to bring this element in. From our drawings and the actual sample, we were able to locate a slight increase of 20 microns in tolerance at 2 points of the surface between the sleeve and piston. The tightness has since been eased off by 0.1 mm with standardized insertion pressure. In the end result, the engine is easier to start and this slight increase also promote a more sufficient clearance during operational heat expansion. Thus, in general the new engine requires less time, effort and money to complete the breaking-in process.

I have not had time to break in my new one yet, but I took it apart and the piston can now be pushed up into the sleeve much farther. I compared it to a new OS XZ-B piston and sleeve and I was able to push the piston up the same distance on both engine (both new never started). So it should break in much easier now, probably half the time (.75 gallons vs 1.5 gallons).

Hobby Pro USA has sold out of Ver II engines, so all engines ordered as on today will be the new Ver III engine.