It really doesnt matter as long as you buy a quality engine. Usually more ports mean harder tuning. You will be safe buying almost any Novarossi based .21 (RB, Max, Top, Rex,ect..) Tuning should be easy on any of those as long as you break it in properly. V-specs are good too, but I've seen some bearing problems lately. That is fixed when you put a ceramic in, then they last 4ever.
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