PA 18 air intake on a PA 12

Purchased a new bottom cowl from Clyde for my 12 that is getting an engine upgrade to a 320 from a 235. Clyde indicated that the carburator is located differently on an O-320 compared to an O-235, so I ordered it without the scoop installed or the hole cut for the intake. I have my original bottom cowl and the bottom cowl that came with the firewall forward O-320. Appears to be some slight differences between the two and also some rubbing issues that have damaged both cowls. Makes me think there might be a better way and was wondering if converting to the PA-18 style with the domed air intake and round filter might make for a better install. Any ideas or input would be appreciated if it is an option in the form of an STC or FA.

Thanks.........Rod

Rod, I had a rubbing issue with the bottom of the carb heat box and the square bottom cowl opening on my SC. Resolved it by shimming the bottom rails away from the boot cowl brackets with the addition of a few washers between the rails and brackets. That moved the cowl away from the heat box just enough to provide some clearance. Jim

On my rebuild, I wanted the round airfilter due to its larger filter surface. No issues with rubbing, allthough the shimming-by-washer idea is brilliant.

Rod---take a short drive to see Randy Rubbert. He is a genius at this sort of thing.

I recently installed one of Clyde's lower cowls on my -12. Clyde didn't say anything to me about this issue. I have the engine stabbed into place now but without the airbox on it. All I can say is that it looks like it would line up with the hole. I'm using a Kenmore STC. The STC says to cut a new hole in the lower cowl and gives dimensions on where to cut. I measured my dimensions of the opening of the cowl from Clyde and it was off a little. I held the airbox in place with my hand and it looks like it lines up. My engine is an O320 A2B. I'm not sure if the model of O320 would have anything to do with this. As of this time I can not comment on the rubbing issues because I haven't permanently installed the airbox. Clyde builds the parts directly from the original Piper drawings.

I thought about installing the Supercub style box/filter. I think it really gives more air but to me, it looks like a speedtrap and it doesn't look like a stock Super Cruiser (I'm going after that look). I have a friend who has a -12 with O320 and stock airbox. His thoughts are that when the airplane is in level flight, the air filter is just about horizontal to the ground and thus could reduce airflow.

I second on Randy Rubbert. He is a super nice man and definately knows his stuff. Keep us posted on your outcome because I'm right behind you. Thanks.

Kevin

Thanks for all the ideas guys. I might just give Randy a call as he is just up the road a ways... As I have 18 gear on my 12 I am not too concerned on keeping the original look, so something like an air intake change, if there is good reason to pursue that avenue I feel now is the time to do it. I ordered the new bottom cowl since I went with a Sutton exhaust and Atlee 18 cabin air box which eliminates the need for the two large holes in the back of the cowl. Also both cowls have age and vibration issues better addressed with a replacement. Enclosed photos show the 235 original cowl with a bump out that seemed to address the rubbing issues which is evident on the 320 bottom cowl that came with my engine.


I guess if Piper changed to the design to what is on the 18 there must be good reason for doing so. Ill have to take a good look at an 18 to see if its even possible.
Again I really appreciate the input.........Rod