Ty,
Are there any markings on the case other than the "40"?
There were several versions of the Max H 40. There was an "S" which was a pretty good stunt motor, a "P" which was an R/C pylon motor and not so good for stunt except with a very low pitch prop. The unmarked engines were, I believe, the standard R/C engine. Nice, well made engines but heavier than an FP with less power.
There was also a Rat Race version that had a huge venturi opening.
Steve