Thanx Bear, Almost all of my other engines are 4 -strokes This kit called for a .91 as the top end so that is what I bought. I have had one other Thunder tiger ARF and was completely discussed with its quality and performance. This Kit seemed to be a depatrure from their past practices so that is why I thought I would give TT another chance. My major concern was OVER powering this bird which is why I opted for TT's requirements. I am now wondering if this bird will even fly on thier recommendation.