Hello Pete:
Sadly, nobody advertizes that the Brodak Super Fly (as kitted) makes for a pretty lousy racer when equipped with a Fox. (ANY other engine is fine)
The stock Superfly even when well built, has a serious vibration problem. I'm SURE it was never intended to be that way, but it is... What you notice is that it's hard to hang on to & hard to set the needle (because it's shaking a lot) & also the nose will start cracking away from the center section right away. Again, none of this was intended. What to do?? During constuction there is some beefing up that should be done per other posts. ONE reason for the excessive vibration is the long nose moment. IF there is any way to mount the engine as close as possible to the wing L.E. that would be of major benefit. Of course that might mean a custom short tank & maybe means having to mount the shut-off on the tank. If tail heavy then possibly the stab size might need to be decreased...( this part I'm guessing at). I will offer that mounting the engine directly onto wood & NOT aluminum mount plates will help, in this case.
The whole point is to get the engine vibration down to a managable level... somehow.
I have found with a Fox that even mounting a given prop 180 degrees sometimes results in MORE SPEED /less vibration for no apparent reason, so I mark my props at the hub to try this.
I have not completed tests as to weather a vibration reducing material under the motor mount lugs will work. I HAVE seen this done on a russian Doreschenko combat model. He used 1" lenghts of silicon fuel tubing that was split with a razorblade. Easy to try though...
I have not tried out of balance props, or a counterweighted spinner /prop hub.
My solution was to use a short nose "mongoose" airplane & be done with it. But that's no use if you have a perfectly good Super Fly kit, is it?
Regardless, your set up will work even if you do nothing. The Super Fly is rock steady. I guess I'm just trying to advise you in advance of what to expect. Getting the Fox vibration situation down to a reasonable level just makes your model go faster & tank run much steadier which makes it re-start faster, too.
I find a 1.5 oz uniflow vented tank works well, just like in stunt. I use foam tape between the tank & the fuse. I think Todd Ryan is very recently offering tanks for clown & Fox sport race. I think one of his tanks is well worth it, if you don't care to make your own. (He holds all the NWSR records)
Go out there & race Pete, Fox racing is GREAT FUN (just like you remember, only the pull & noise is less) I'm sure there's lots of help available.
Best of Luck,
Paul