Excellent help/feedback! I really appreciate it.

To answer a few questions:

W8ye – Of course I’ll baseline the thrust before, so I’ll be able to compare the final results. If you don’t hear back from me, it means I screwed it up big time! <Joking>

ProBroJoe - No – It won’t be a wild porting job. I’m pretty cautious, because I’ve seen epoxy patches where the porting went through the wall. <ouch!>

Jeffie8696 – thanks for the boost of confidence that the GP-42 responds well to porting.

The comparison to heads is how I think about it. I did mention porting, not port and polish. I’ve never polished anything except piston tops and one set of exhaust ports. I’d love to knife edge the crank, balance the entire rotating assembly, etc., etc., etc., but I think that’s out of my home workbench capability. I probably won’t do much to the crank or rotating parts for the reason you mention – balance, except that smoothing the flow into/through the crank and bell mouthing the air/fuel exit from the crank sure looks appealing and since it’s very close to the centerline of the crank, the weight is not so much of an issue.

Proptop – Wow, thanks for the link. There is a lot of great stuff in that thread.

DarZeelon – Wow, some of what you write is surprising, especially the part about a step caused by a smaller passage at the muffler opening not being an issue. That is almost hard to believe – sorry. Fortunately, my muffler is not a concern, as the ports match perfectly. My primary concern is where the case shrouds some of the sleeve opening, and sharp edges/flashing, etc.

Lots of great stuff here. It’s nice to know there are some like minded folks on the board. I’m a long time car guy, relatively new to RC. I’ve rebuilt car engines, trannys even fuel injected one carbed car (megasquirt EFI – www.msefi.com) My 13 year old was the driving force into the hobby, but once I opened up my first nitro engine, I knew I’d be doing work inside. I guess I just don’t know when to leave well enough alone. <Blush/Grin>

Over the weekend I finally fired up the used PRO-46 I was planning to upgrade to. It was a used engine from an estate sale that I disassemble and cleaned up. It vibrates badly at higher RPM’s, so I may not be willing to start cutting on our primary engine, the GP-42 until after I figure out what is going on with the bigger one. In either case, it’ll be a mild porting job. This is for a fun plane and just like my cars, I want a reliable engine with a nice fat power band.

Thank again for all the pointers and input,

Jack