muffler for fox35

i found some tounge muffler stock at the hobby shop i want to make custom mufflers for some fox 35s that dont have mounting lugs. how long should i make them and how many holes should i put in them?
thanks again

Two rows of 3/32 each row 6 holes.

You r making a strap on right?

Scott (not a porno question) Riese

yes it will have to be a strapon i have no muffeler lugs they were ground off how long should i make it i can cut the muffeler stock down to what i want.

Drill more than you need, and plug them up one by one until you balance performance and db reduction to your individual needs. Use ordinary engine mounting screws, a bit oversize for the hole. It will tap itself. Then cut off the excess.

Is this the extruded Du-Bro stuff? Can someone confirm that it will fit a fox exhaust?

yes it is dubro 6" aluminum exhaust ext. stock, cat no. 213 and it does fit a fox im cutting what i need and cap the end with some 1/16 flat aluminum.

While it's more money, if the internals are in real good shape, I would consider just getting a new case, one with mounting lugs molded in.

The light-case Fox 35 can be quite sensitive just to bolting on either a stock muffler or a tongue muffler, the RSM tongue muffler being my choice. I think you will find the potential for squeezing case and cylinder out of round to be much higher with a strap-on arrangement.

To the point where I simply would not consider using such on anything other than an old, trashed motor. Any maybe not even then...

LAST EDITED ON Feb-09-04 AT 04:34 PM (CDT)
 
>While it's more money, if the internals are in real good
>shape, I would consider just getting a new case, one with
>mounting lugs molded in.
>
>The light-case Fox 35 can be quite sensitive just to bolting
>on either a stock muffler or a tongue muffler, the RSM
>tongue muffler being my choice. I think you will find the
>potential for squeezing case and cylinder out of round to be
>much higher with a strap-on arrangement.
>
>To the point where I simply would not consider using such on
>anything other than an old, trashed motor. Any maybe not
>even then...
>
>Dan
>

Ron B.
F4Fguy

What Dan said,but(I just can't stop myself),if you're determined to do this any way.................

Make it long enough to at least (with the stack volume)equal the displacement.Longer is better up to ~ 1 1/2xDispl.,any longer and you 're better off with a tube(assuming it's properly done).I recommend much smaller holes and many more of them.I usually do .015to.032 holes and drill as many as it takes to equal or slightly exceed the area of the port(not the stack,the cylinder).
The reason for the smaller holes is to increase the energy loss through higher flow losses and more direction change.I must warn you ,this is a lot of holes but you'll get more silencing with less power loss.With this method,the procedure is usally to drill more holes until the noise is excessive,then plug the last one.Don't deburr the holes the sharper the edge,the higher the energy loss.
I only go to .032 holes when I just can't get enough area otherwise.If .032 isn't enough,increase size in small increments(say .010).You can do most of this on paper,so it doesn't cost a dime until you start cutting metal.
Before doing this,or any other engine work,run and tach the engine several times in stock form,this engine,not one "just like it".Without doing this you have no basis to evaluate your work.

Ron B.

Wow, I can't imagine going to as small of a size of holes as Ron says here. That would take a ton of holes. The .015 would take over 500 holes to equal the exhaust area in the sleeve for a 35 size engine. And it would still take over 100 using .032 holes.

In comparison, Art uses ten number 43 (.089) size holes in his, and the ones I had made use fifteen number 46 (.081) size holes. Art's then have an exhaust outlet area of .062 and ours have an exhaust outlet area of .077. I don't know what the Fox 35 exhaust outlet in the sleeve measures (and I am too lazy to dig one out) but a 20 FP has an exhaust outlet area in the sleeve of .068, a 25 FP of .078, and a 35 FP of .095. The Magnum 53, just as a comparison, has roughly the same exhaust outlet area in the sleeve as the 35 FP. Our muffler body, by the say, has a volume of .377 which would be right in the ball park for Ron's recommendations for a .35 or .40 size engine.

I didn't measure or calculate anything here, however, as everything was done by trial and error. We started with 12 no. 43 size holes in the muffler and then worked up to 15. Every additional hole boosted the available power, but the more that were added, the less the increase in power grew. Ultimately it is a compromise, again, between available power and lowering of noise. These work quite well, however, and we have them available in both bolt on and strap on varieties.

LAST EDITED ON Feb-10-04 AT 02:24 PM (CDT)
 
Ron B.
F4Fguy

Len:
You're right,it's a ton of holes.The number of openings for a given area is the sound attenuating factor.It all depends on how much sound reduction you're happy with,and how tired you get drilling holes.
I guess I wasn't clear,.015 is where I start ON PAPER.As you point out,as the engine size goes up ,it becomes a matter of practicality.I don't usually end up at .015 on a 35.By the same token ,I seldom exceed .040.Remember,if you double the diameter,the area goes up four times.The real point is,smaller holes/more of them gives better sound attenuation with less power loss for the same area than bigger holes/fewer of them.
As I said you can do most of this on paper.Iterate it until you're satisfied before cutting metal.