I have these heads and am not impressed. I was reading an article from a magazine (cant remember which one, may have been the MM&FF comparison a while back) and these $900 185cc cast iron heads only barely beat out a set of stock $400 ~145cc cast iron gt40 heads in terms of horsepower. In my case, I didnt know the spark plug angle was similar to the gt40P, which does not clear any Falcon headers that I know of. IIRC, that same article also mentioned they ran into valve float because of a heavy valvetrain that comes in these heads. In my oh-so-humble opinion, if youre going to spend a bunch of money on good heads, spend a little more and get a lot more with something with a smaller port, yet produces more power, such as the AFR 165.