Red Clone Vs Yellow

Really depends on which yellow clone your talking about. There is a big difference between the yellow Box Stock Project engines and the other yellow or red clones you see out there, the difference in quality is obvious, and much better. The only difference iv seen in the other yellow and red clones you mentioned, is the casting of the heads, and tolerances of the engines.
personally I used all the engine in the past but I only uses the engines that dyno cam sell now I like them the best. But that just my opinion