Originally Posted by finchy

I heard it might be based on the older XZ-R design. The person that told me information said it would be in close spec's to the Maxpower engines. The only thing I could think of is the older XZ-R engines had a slightly different bore and stroke. I know the stroke of these older engines where 16.80mm and the bore was 16.27mm. Honestly I've have personally run both the Speed XZ-R and the current Speed R21 family of engines and haven't had any troubles with either. But I haven't tried any of there newer 9 port designs except for the GiMar Saturn which I had no issues with piston or sleeve damage that the R2104 and R2105 seem to be having.