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Author Topic: No muffler vs Tongue Muffler  (Read 1568 times)

Offline Cliff Henke

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No muffler vs Tongue Muffler
« on: October 27, 2012, 04:56:45 AM »
At this time I'm running a 20 year old K&B ABC 40 without muffler, starts great, runs great, no complaints.

When I install the factory muffler it becomes harder to start, runs with less power and becomes a little nose heavy.

Would a Tongue Muffler help me, I'm not concerned about noise ( Flight circle is in the infield of a dirt track )

Total dry weight 42 oz. w/ 490 sq. in. without factory muffler.            45 oz. w/ factory muffler.

Thanks in advance,
Cliff
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Offline GregArdill

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Re: No muffler vs Tongue Muffler
« Reply #1 on: October 27, 2012, 05:09:21 AM »
Cliff,

If noise really isn't an issue then keep doing what you're doing. - I guess a K&B 40 isn't going to be as loud as a sprint car.

If it's excessively difficult to start with the muffler there may be other issues, in my experience they only rob a little power. But they do change the balance of the plane. It may be if you need to run a muffler that you need to spend some time working out how the motor behaves differently with muffler.

Greg
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Offline Paul Smith

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Re: No muffler vs Tongue Muffler
« Reply #2 on: October 27, 2012, 07:06:40 AM »
A tongue muffler won't show much decrease in decibels.  But it will shield you from the initial supersonic shock wave when the exhaust port first cracks open. I have found that old engines, not designed for mufflers, won't tolerate a full muffler but will accept a tongue.

You're right about hard starting.  I never liked electric starters, but have used one on muffled engines.  Yes, I have hand-flipped muffled engines, but I always keep the starter handy.
« Last Edit: October 27, 2012, 11:04:33 AM by Paul Smith »
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Offline Bill Hummel

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Re: No muffler vs Tongue Muffler
« Reply #3 on: October 27, 2012, 07:41:05 AM »
Cliff, many of the stock mufflers are very restrictive in order to be "quiet".  Depending on the muffler, it may be possible to drill out the exhaust opening a fair
bit, or add additional exhaust holes to gain back some or much of the power...at the expense of more "loud".  Going to a tongue muffler that is also too restrictive puts you right back in the same predicament.  Don't hesitate to drill out mufflers to gain power, especially since noise does not seem to be a problem for you. 
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Offline Cliff Henke

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Re: No muffler vs Tongue Muffler
« Reply #4 on: October 27, 2012, 10:41:45 AM »
Thanks for the replies guys, I feel better about what going on. I will remain w/o factory muffler on the profiles w/ the K&B.

I believe that the Tongue Muffler would apply much better in the Brodak "Accentor" to get the exhaust out of the cowl and not have the stock muffler to hinder starting inverted.  HB~>

This has been a weak link for myself. After reading many, many past post on SH, I hope to finally finish the "Accentor" this winter.

While I'm on the subject of mufflers, will it hurt to run the OS46LA w/o muffler on the 38 Special Biplane ? I'm just breaking in this motor now.

Do I need to break it in w/ or w/o the stock muffler if I can run it without one on this plane ?

Sorry about bouncing all over the place with these questions, any replies would be greatly appreciated !

Thanks in advance,
Cliff
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Offline Paul Smith

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Re: No muffler vs Tongue Muffler
« Reply #5 on: October 27, 2012, 11:10:54 AM »
Remember, the engine's exhaust port is only open about 20% of the time, but the back end of the muffler is open 100% of the time.  So a muffler doesn't need a very big hole.  The exhaust enters the expansion chamber and waits its turn to go out the back in a steady flow rather than a series of ear-splitting pulses.  If the muffler is wide open the noise just blasts through to your ear drums.

Muffled engines have lower compression to compensate for the back pressure. If you muffle an old engine you would be well to add about .010" of head clearance.
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Paul Smith

Offline Steve Helmick

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Re: No muffler vs Tongue Muffler
« Reply #6 on: October 27, 2012, 08:15:49 PM »
I ran a K&B .40 ABC for awhile in my Humongus, using an RSM tongue muffler (the one that fits Fox .35's and OS .35/.40FP and .40/.46LA). It ran alright that way, but of course it was mounted upright.

I'm not a fan of tongue mufflers...quieter is better for my tinnitus, and there are other advantages. Personally, I'd put on one of Randy Aero's CNC Tube mufflers with a "rubber ducky" on the outlet. If I had to do an emergency shutdown, blocking or pinching off the rubber ducky is uber quick.  #^ Steve
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