Those blue head #s look similar to mine. I used the MA prop and got just slightly less on the 7-5 at 17,600 and 17,900 on different occasions open exh. Just for interest's sake The turbo plug head that I made up got 20,500. A 7-6 was 17,600. I later opened up the carb to a control line type with F2D prop which was about a 6.3 - 5" and it went about 25,700. Really that was not a lot better than my AP .15 on that prop. I think the blue head one likes a bigger load. Just to confue you more. The AP .09 with a 7-5 was 12,800 and the same prop on the AP .15 was 15,700. The muffler sucked the .15 down to 13,300. The AP .09 7-4" 15,200 and the AP .15 with the same 7-4 is 21,400 and 22,100 with a pipe.