If you have those engines, share your experiences with us. I have no knowledge at all with the collari. The mega engine (I don't have one) seems to be very very fast. Probably one of the fastest stock 12 engines available. It also seems to very tempermental and has had (I don't know if they corrected this problem) a history of bad con rods. If you get one to run properly, they are very fast. The other issues with the engine have caused me to steer away from one despite the horsepower. I have been considering trying one anyway, but have not as of yet.