Hi new here, and new again to CL after many many years Lol. I had some experience with Goodyear back in the 70's. This said.

I have an interest in the Fox 35 speed event. I am assembling equipment to put some planes together and hopefully have some fun.

What I am interested in learning is. What can be done to the old Fox 35 to make the most power from it possible? I am aware of the basics, stuffer back plate, hemi head etc. I am wondering more about port timing changes, piston/sleeve swaps, increasing inlet sizing? Next level mods.

Anyone of someone knowledgeable in this area, or may even offer parts? Thanks

SD,
Since you are coming back I think the first steps should be to get you CL legs back with a sport plane like the Flite Streak or Ringmaster then move to something faster like a combat wing. Once comfortable the FOX 35 speed ships are basic rat racer style ships, lots of plan here: https://outerzone.co.uk/browse_plans/category/results.asp?Level=2&Cat1=CL&Cat2=Sport can do a search at the bottom of the page.

As for engine mods, the stuffer backplate is popular but you could just us the stock one with a very thin gasket and get a similar benefit of keeping the rod from moving to far back. The button head is also popular as are other aftermarket heads that raise the compression. Changing to a better NVA is also something that is done but you can't make the spraybar to small as you need to run suction only so need to have a stable needle. Some have changed the piston/cylinder there are some aftermarket ABC units avialable from time to time. Since the fuel is provided at the contest (by rules should be 5%N) no exotic fuel. Also, no carbon fiber props, commercially available wood or nylon reinforced (APC's or Master Airscrew). Trimming diameter of the props, thinning blades and repitch is allowed.

Best,    DennisT

Where can I locate fuel, or something similar to what is required?

Good advice above. Good event that leaves plenty of room for experiments.  Weak point is the crank. Not much to be done but hope you get a 'good' one. There is the Randy Smith unit if you can find one.  Also many parts from other than Stunt .35 will drop in.  TS

Yes, it is a good formula to be able to compete without breaking the bank. What other parts will interchange?

Good advice above. Good event that leaves plenty of room for experiments.  Weak point is the crank. Not much to be done but hope you get a 'good' one. There is the Randy Smith unit if you can find one.  Also many parts from other than Stunt .35 will drop in.  TS

Fortunately, the world is full of worn out Fox 35 Stunts with surplus crankshafts if you generate enough power to blow a crank. 

Before you get all involved in "voodoo speed secrets" the most important thing to know is that piston / cylinder fit is 85% + of the engine performance. The thermodynamic efficiency of a heat engine is directly proportional to the absolute ratio of compression of the cycle. You have to minimize blow-by to the max.

Get the Nelson glow plug head button Dave Rigotti advised and a stuffer backplate. Use the ST needle valve. Build the engine.

Look under the Engine Set Up Tips section for "L&J Fox 35" and follow Larry's break in schedule to the letter for a new P&L set. What you are basically doing is lapping the piston / cylinder to a nearly perfect fit. DO NOT take the engine apart after doing this.

Fuel flow management is also very critical for Fox 35 Speed. The fuel tank position needs to be optimized for the launch and the speed run, especially as the venturi is opened up. Dave mentioned turning down the spray bar. That is a good start. I was able to use a K&B Racing Needle Valve assembly by adjusting my fuel tank in order to prevent the engine from surging on launch.

The devil is in the details. Good luck.

I've got a 35 Stunt with a re-timed Brian Gardner piston/ liner/ rod. Very, very few made. Interested ? PM only.