Bought the old style when they first came out & put out fair power. Ran very hot so needed lots of oil in fuel to help cool. The longer I used it the better it ran & the less fuel it used. We found that we had to remove some cover in back & drain excess oil out of it ( if my memory is right?).New ones have a drain. Use only the Wankel PLUG. The best prop I found for it was an 8/6 three blade, it likes to turn. Have one of the new type mounted in an original Goldberg Sailplane maybe get around to fly it this summer? Buy the way paid $68.00 for it new in LHS in 70`s. >>>>>>big max 1935