Hemi Heads and Stuffer Backplates

What are some sources of stuffer backplates and hemi-heads for Fox Stunt .35's? Having read some criticism of the Fox brand hemi- heads, what is a better choice?

Fox for the stuffer and the Blue Magic from Tom Muggleton for the head.

What is the criticism on the Fox heads?? Another source is L&J (larry Foster.

Bigiron

Actually, I read what I took as critcism on the Flightlines Forum by someone going by the name of Bigiron 13. Did I misunderstand? Is the Fox head ok?

OH!.. You mis-read what I thought I wanted to say. Or something like that. As comes from the factory, both the Muggleton AND the Larry Foster heads are probebly a little bit better. There is nothing wrong with the Fox hemi-head system, it is just NOT in the configuration that I wanted it to be in when they decided to put it into production. If you get one, and want it to work like I wanted them to, just send me the button and I will modify it to meet my specifications (at no cost to you other than shipping costs) and it will be as good as , or a little bit better than the other two. (Muggleton and Foster will probably disagree with that last statement though).

Bigiron

Bigiron,

Thanks for the info. I think I will try the Fox head.

Don, give it a try, and if you don't lke it, or want a little better performance, drop me a line and send me the button and I will modify it to my specifications. No charge, just shipping costs,
Bigiron [email protected]

I got a Fox .35 from Brodak when he was offering the one with a hemi head and stuffer backplate already installed. I would assume that is a Fox head.

> Don, give it a try, and if you don't lke it, or want a
>little better performance, drop me a line and send me the
>button and I will modify it to my specifications. No charge,
>just shipping costs,
> Bigiron [email protected]

Hello BigIron,
Could you tell us here on the forum exactly the mods you do to the stock Fox hemi-head, a photo(s) maybe too? I have two of the stock Fox ones and would not mind fooling with one myself just to test against the remaining stock one. I am a capable tinkerer of model engines, see attached photo of my latest inline TWIN Cox engine, it runs great too ...... THANKS!

LAST EDITED ON Apr-09-04 AT 11:20 AM (CDT)
 
Injun... I am a bit reluctant to give the alterations as Fox mfg is "supposed" to incorporate the changes (they told me they would) in future production runs. If I say what I do, and someone does it on one that has already been changed by the factory, .... Well you can see that it wouldn't be nice.
If you have one and are SURE that it hasn't been corrected, here is what I do.

1. Machine off 0.020" from the bottom side of the flange (where the gasket goes) so the squish band goes down into the cylinder that much further.
2. Machine the slot 0.020 inch deeper to assure clearance of the piston baffle.
3. Flatten the bottom of the dome (at the plug) out 0.035" and then start the curve of the dome there and blend it into the present dome 1/2 way up the side of the present dome.
4. Enlarge the present dome radius by 0.020" at the edge of the squish band and blend it into the surface of the present dome at the 1/2 way point that you ended the dome in step 3.

That will give you a very slight double bubble flat bottomed combustion chamber. Install it with a single 0.010 stock head gasket. I recommend 7 1/2% nitro and 25 % castor oil

I get this mix by mixing Fox Super Fuel and Dukes Fuel 50/50 and add 1oz klotz per quart just to keep the engine clean.
Bigiron (you asked for it---you got it)

> Injun... I am a bit reluctant to give the alterations as
>Fox mfg is "supposed" to incorporate the changes (they told
>me they would) in future production runs. If I say what I
>do, and someone does it on one that has already been changed
>by the factory, .... Well you can see that it wouldn't be
>nice.
> If you have one and are SURE that it hasn't been
>corrected, here is what I do.
>
> 1. Machine off 0.020" from the bottom side of the flange
>(where the gasket goes) so the squish band goes down into
>the cylinder that much further.
> 2. Machine the slot 0.020 inch deeper to assure clearance
>of the piston baffle.
> 3. Flatten the bottom of the dome (at the plug) out 0.035"
>and then start the curve of the dome there and blend it into
>the present dome 1/2 way up the side of the present dome.
> 4. Enlarge the present dome radius by 0.020" at the edge
>of the squish band and blend it into the surface of the
>present dome at the 1/2 way point that you ended the dome in
>step 3.
>
> That will give you a very slight double bubble flat
>bottomed combustion chamber. Install it with a single 0.010
>stock head gasket. I recommend 7 1/2% nitro and 25 %
>castor oil
>
> I get this mix by mixing Fox Super Fuel and Dukes Fuel
>50/50 and add 1oz klotz per quart just to keep the engine
>clean.
> Bigiron (you asked for it---you got it)

Thanks BigIron, I'll give it a go and see how it compares to the early stock Fox insert. What exactly is the advantage supposed to be .... I mean will it have more power, or just run better for CL Stunt flying (4-2-4), or what? It sounds like you are basically changing the head geometry (to double bubble with lesser squish band) while keeping approximatly the same original compression ratio?

The intent of the Hemi was to get more torque in the hard 4 cycle range without runaway when it converts to the two during maneuvers. The earlier versions that I didn't like had a problem with missing a beat or two when flying level in the "4". It would sound like it would go to a six cycle and would startle the pilot.
The combustion chamber that Fox came out with was very close to the right size, but to eliminate the "6" stutter, they raised the squish band. I lower it and get the chamber volume back by flattening the bottom and adding the second bubble. The single dome that Fox does is more simple to manufacture. A single ball end mill, ond cut and it is done. I had a special cutter made so I also only make one cut. But with my system, I have to worry about keeping it sharp and/or replacing it which is more expencive. My very low production keeps me from having a lot of head ache with that problem.
Bigiron

LAST EDITED ON Apr-10-04 AT 08:51 AM (CDT)
 
To all,

It's very difficult to give an A-B-C comparison unless you have all available variations to test on the same engine. I just know that my Fox 35ABC with Marvin's hemi-head and a factory stuffer back-plate runs superbly. I fly against Marvin every year at SIG and his Foxes run just perfect. Any comment from people who have seen Marvin's work perform?

Fred

Would you believe this!!! I used to ENVY Jim Lee as his Fox 35s ran SOOOO GOOOODDD. I just couldn't get mine up to his level of performance. That is what started me on my quest for better performance out of the venerable old Fox 35. Now I will put mine along side of any 35 and even some 40s. Glad ole Jim prodded me a mite.

Bigiron

What do you think of the plasma P&C assy from OZ? I got the last one available with his special head.

"SAVE ALL THE PIECES"-Phil Brown

The OZ Plasma sleeves for the Fox 35 are very good for sport flying and for profile mounting where vibration is a problem. They wear very well (long life). But their draw back is that when you install one in a 35, you will wind up with a .31, not a 35. Less displacement relates to less power. So what you gain in less vibration and less friction, you lose in displacement. You use the one you want. I prefer POWER! I got my OZ on my granddaughter's skyray 35 and it works nicely there. I have heard that Fox mfg may be comming out with something similar.
Bigiron

Don't forget to buy one of those Randy Smith crankshafts.

I'm no Fox guy, but if I had one I would...

Ion, I already got one and am going to get two more. They are GGGGRRRREEEEAAAATTTT as Tony the Tiger would say.

Bigiron