The International Cessna^® 170 Association

I am headed down to San Diego this weekend in 67D (and I even got the wife to go along - probably the thought of seeing her son back from overseas overcoming her tendency to avoid light planes). I planned to stop in Hemet and talk to the Aero Propeller folks - holders of the so-called Air Flow or California Prop STC. I gave them a call to introduce myself and make them aware of my plans. Not very friendly folks, or talkative about the STC. However, the person I spoke to did say, regarding the question of eight versus six bolt props, if you have the six bolt brought you probably "already have the upgrade, or the 172 prop". In what little further discussion he would allow, I gathered that the Air Flow STC just turns the 8 bolt McCauley into the later version that came out with six bolts and was used on the C-172. Does that make any sense to anyone?

Yeah, makes sense to me. I think they called it 'jet flow" tho. Cessna was trying to recover the performance they lost when they put the nosewheel on. Anybody have one? How much speed and climb improvement?

It's not clear to me what is meant by all that. The original McCauley prop (DM7653) was later modified to a thinner blade to improve efficiency and called the MDM7653. This blade was married to a lighter weight hub (the 6-bolt hub) for use on O-300-C/D/E engines and re-designated the EM7653. The improvements allowed an increase in pitch to 54 (thereby making the prop specified an EM7654) in order to approximate the performance of the MDM7653. (This had the additional positive effect of improving specific fuel economy....more miles per RPM.)

Thinning the blades of the early DM series will increase efficiency but requires approval...which presumeably is taken care of by the STC. It's still an 8-bolt prop and heavy hub, however.

the dm props for the 170 were reprofiled to get better performance to help the 172..
I have a mccauley prop overhaul manual and it shows that the blades were thinner and the blades angles down the lenght had a greater inboard angle then less outboard on the mdm than the dm props.
I talked to a prop shop who said they could reprofile my dm blades to the mdm profile . they were going to see if there would be a problem with the FAA.
The way the manual shows is a 7652 mdm should give better takeoff than the 7651dm and not hurt your cruise .
I am going to do a little more research into it let you know what i find.