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Author Topic: Fox .35, mufflers & overheating  (Read 1546 times)

Offline Terry Caron

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Fox .35, mufflers & overheating
« on: February 24, 2015, 03:43:52 PM »
I've read comments that mufflers can cause overheating on Fox .35s.
Old Foxes with old mufflers only or do these apply to current tongue mufflers such as Brodak's, Eric's at RSM or Leonard Neuman's on old Foxes?

TIA

Terry
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Offline Bill Little

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Re: Fox .35, mufflers & overheating
« Reply #1 on: February 24, 2015, 08:55:44 PM »
I have used both bolt on and strap on tongue mufflers on Fox .35s with out an overheating problem. But I make sure to have adequate cooling!

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Offline Terry Caron

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Re: Fox .35, mufflers & overheating
« Reply #2 on: February 24, 2015, 09:02:15 PM »
Thanks Bill -

Seems the older I get the less I can appreciate the unbridled roar of glow engines.
And NO - electric is NOT an option!  H^^

Terry

BTW - any news on the .35 CS NVA?
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Offline Dennis Toth

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Re: Fox .35, mufflers & overheating
« Reply #3 on: March 01, 2015, 08:01:18 AM »
Terry,
The Fox 35 is thin cased with shallow fins. Heat is not it's friend. I have run several Fox 35's in OTS with mufflers and it will work. If you change the head bolds out for socket heads make sure you grid the heads down to at least 0.168" diameter (same size as the Fox bolts) to avoid binding the case as you tighten down the head. Also use crush pads under the mount lugs if you have aluminum mount pads (these are strips of 1/64 plywood that go between the engine and the motor mount hard pad). These allows the draft angle on the bottom of the case mount to crush the wood a little and avoid distorting the case as it is tightened which would cause binding and loss of power.

The basic information on the muffler is to open the exhaust to 5/16" ish diameter on the stock Fox muffler or have the equivalent area in the number of holes in a tongue muffler. Use fuel 5 - 10% nitro with at least 26 - 28% oil (50/50 works well).

Watch the prop load. I have been running 9x6 old Top Flites and APC 9x7 with good results and a nice break. I have tried the traditional 10x6 but that seems to load to much with the muffler for the lap time I want (roughly 4.95 on 59 1/2' C to C) and it goes lean.

If you have the old case with the ears add brass tubing guides (with JB Weld) that are flush with the exhaust flange will reduce case warping. I have used thin aluminum for the gasket (top seal from Tasters Choice instant coffee) that works well for me.

Best,    DennisT
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Offline Terry Caron

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Re: Fox .35, mufflers & overheating
« Reply #4 on: March 01, 2015, 11:39:56 AM »
Thanks Dennis - very good info.
MOF, i have late '50s Foxes in mind.
Anything to choose from among the current CNC tongue mufflers?

On case warping, somewhere I've seen a muffler clamp, I think maybe by a forum member, said to avoid this (and which actually looked much better than the attached drawing).
Recognize it?

Terry
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Offline RandySmith

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Re: Fox .35, mufflers & overheating
« Reply #5 on: March 01, 2015, 12:51:00 PM »
They "can" make em run hot , as can any muffller ,on any engine, you need to make sure they are not too restrictive, and many times it helps to go up on nitro , this allows you to run richer, which mean cooler, most times I see overheat is because people run the engine leaner, trying to get the lost power back.

Randy
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Offline Dennis Toth

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Re: Fox .35, mufflers & overheating
« Reply #6 on: March 03, 2015, 06:15:15 PM »
Terry,
You were on the right track for the pre-muffler era Foxes. I think if you do a search for Fox Mufflers you will come across a posting by Bob Zambelli showing an round the case clamp. This type clamp is similar to what you sketched, it is an aluminum cast clamp that rests on the exhaust stack side bosses not the case bypass. This greatly reduces the squeeze on the case and minimizes distortion of the P/L which would reduce power (and those of us who fly Foxes know we need all the breaks we can get to keep power).  I don't know if there are plans available to get one machined or cast. Maybe Bob Z and give some information on dimensions of the unit.

Best,       DennisT
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Offline Terry Caron

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Re: Fox .35, mufflers & overheating
« Reply #7 on: March 03, 2015, 06:36:21 PM »
Great Dennis, thanks.  H^^
I'm sure that's the one I had in mind.
If Bob doesn't pop in here I'll PM him about it.

Terry
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