Drop in replacement for a Fox 35

[Ara Dedekian]

      The Magnum 25 has the identical bolt hole spacing as the Fox 35. The muffler lugs also have the same spacing as the Fox. The engine in the photo was originally an RC version and flown C/L with the throttle wired open. I made a venturi and replaced the Fox 35 with the Magnum on a Buster. Only one flight the first time out as I had my wife and dog with me but it was spectacular.

      The venturi has a .250 bore with a K&B needle/.162" spraybar. I picked up an ounce overall with the Magnum/Fox tongue muffler and came in at 33 ounces without fuel. The Buster has a sealed hinge line with no rudder offset. The engine ran a rock solid 2 cycle throughout at about 4.9/5.0 sec per lap on 60' Spectra lines, GMA 10/22 fuel and a 9-4 prop. Response to the needle adjustments were instant. It went wherever I pointed it. A great little engine, AND, no Fox burp! (I'm still uncomfortable putting a stick inside an engine!)

      Ara

[Brett Buck]

      The Magnum 25 has the identical bolt hole spacing as the Fox 35. The muffler lugs also have the same spacing as the Fox. The engine in the photo was originally an RC version and flown C/L with the throttle wired open. I made a venturi and replaced the Fox 35 with the Magnum on a Buster. Only one flight the first time out as I had my wife and dog with me but it was spectacular.

      The venturi has a .250 bore with a K&B needle/.162" spraybar. I picked up an ounce overall with the Magnum/Fox tongue muffler and came in at 33 ounces without fuel. The Buster has a sealed hinge line with no rudder offset. The engine ran a rock solid 2 cycle throughout at about 4.9/5.0 sec per lap on 60' Spectra lines, GMA 10/22 fuel and a 9-4 prop. Response to the needle adjustments were instant. It went wherever I pointed it. A great little engine, AND, no Fox burp! (I'm still uncomfortable putting a stick inside an engine!)

      Ara

   A Magnum 25 is much better than a Fox 35, even when the Fox is running perfectly.

    Brett

[Dennis Toth]

Sounds great. If you go to a wood prop and a plastic tank (setup for uniflow, vent in free airstream above fuse side) you might be able to offset the extra ounce of weight. Did you rebalance the ship? Other option is to get on Brain Gardner's list for the ABC piston/cylinder/rod set for the Fox 35 and change out the iron/steel one. This change makes the Fox a whole different engine not the old 4-2-4 but more like a 2-2-2 running a 9 1/2 x 5 (with muffler), runs smoother and is still lighter (but still needs at least 24% total oil 50/50 for the plain bearing).

Best,   DennisT

[Motorman]

Very nice. That Magnum is true ABC, BB and bushed rod I believe. Should last for years.

MM

[Jim Svitko]

I side mounted a Magnum 36 and it had the Fox burp on outsides.  Not as severe as the Fox, but it was there.  I am somewhat surprised that the 25 has no such burp.

Burp or not, the Magnum/ASP engines are very good right out of the box.  Originally intended for RC, they are quite suitable for CL use, needing only the proper venturi and needle assembly.

[john e. holliday]

Ara, sounds like you have a combination that works for you.  Just get out and practice.

[Colin McRae]

Not an 'exact' drop-in but I did put an Enya 29-5224 on my Shoestring replacing a Fox 35.

Mounting holes in one direction (I forget which direction) were only a bit off. Maybe a 1/16". I had to ream 2 holes slightly. And the engine case was a bit wide between the hardwood mounts. But just had to shave them a bit. And the Enya's are heavier, so had to add a bit of tail weight to maintain CG location.

But after the adjustments it flies better than with the Fox.