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Can you run a gas motor with no muffler?

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Can you run a gas motor with no muffler?

Old 11-28-2012, 06:42 AM
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mikes68charger
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Default Can you run a gas motor with no muffler?

Hey guys, Im building a TopFlite P47

I have a DLE55 with a pitts muffler sitting on the shef. But I really want to use a 22X10 4 blade Scale Belia prop. So I got a nice looking used ZDZ80cc not the Super of this site.

Ihave been dispaonted before, Got a Used Qudra 75cc but it only had a tad more power than my DLE55.

Im looking at getting a JTec Muffler $140 and the Belia Prop $110.

So my question is should Iget the prop first, and see what RPMs I can get with out a muffler to make sure the motor can do what I want beforeI spend even more$$ a muffler that I wll not beable to get my money back out of?

Don't nitro motors only lose a few RPMS with out a muffler and a sign of a good muffler is more rpm than with out a muffler?

Thanks Mike (money is not as good as it used to be, We just adopted a little girllast month, and its my first, who a diff in my RC Money)

Old 11-28-2012, 07:10 AM
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chris923
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Default RE: Can you run a gas motor with no muffler?

I have a DLE 55 with a J-tech Muffler and a 19x8 Belia prop on aTF 1/5 Mustang and it flys great! I think you will have plenty of power with the zdz80/jtech muffler/ 4 blade.

That being said, i would not run a gas engine without a muffler. You need the back pressure for the engine to runner properly.

Chris923
Old 11-28-2012, 07:22 AM
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arobatx
 
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Default RE: Can you run a gas motor with no muffler?

While running the engine without the muffler would offer some insight as to whether a given muffler will be hindering its power vs. improving it....exhaust systems can do wonders for engines, especially two stroke engines. That being said, I see no issue at least getting a baseline as to whether your engine is going to operate in the range you desire before spending more money. A bunch of us have done the same thing when new engines are released that there isn't already decent feedback on, regarding props, mufflers...etc.

The DLE 55 isn't going to love a 4-blade 22x10 at all, not even with a VERY good tuned exhaust system hopefully you mean the zdz 80
Old 11-28-2012, 07:50 AM
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mikes68charger
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Default RE: Can you run a gas motor with no muffler?

arobatx Thanks but thats my issue!

I have made 2 post asking for advice with a 4 blade prop for this motor with notmuchhelp. I have read that a DA85 will spin this Belia 22X10 4 blade with good power, but I know this Non super 80 is not as powerfull as the DA.

So with that said now chris923Just posted he uses the 19X8 4 blade on his Gaint P51 with good results Ifeel a little better, WHATAREYOURRPMS Please the world wants to know?

The way I see it I have 3 choses of these nice Belia Props I want to use.

20X10 4 Blade wich says its good for a 50-60cc may be a bit light load
22X10 4 Blade wich says its good for a 70-85cc wich I think will be to much load
Or Im thinking
20X14 4 Blade, wich says its for a 9 cyl 99cc 4c evloution motor, Now I looked this motor up (sexy) but it clames 6hp max rpm 6500, and recomend props of 26X10 wich is about the same numbers I see posted for the ZDZ80 exsept HP

According to my online power caluclator, it takes about .5 less HP to spin the 20X14 at 6000rpms as it dose the 22X10 4 blade.

I cant handle to slow plane. The 14 pich prop will give me around 70mph speed wich is where all my othere war birds are and I would like to be.

Thats why I asked this question about no muff, Ihave a exstra Morepower 20X14 Adjustable 3 blade prop laying around.( dose 10,12,14 pich) I wanted to see if the motor could atleast spin this prop with no issues or with at least more RPM than a DLE 55RA (7200 rpm with it set at 10 Pich)

What you guys think?

Old 11-28-2012, 09:00 AM
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av8tor1977
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Default RE: Can you run a gas motor with no muffler?

The answer to your original question is yes, you can definitely run an engine without a muffler, and it will not hurt the engine. It will be incredibly loud however.

The ONLY muffler that increases power is a tuned muffler such as a tuned pipe, canister, etc. All other mufflers decrease power to varying degrees.

It is a common misconception that an engine needs back pressure. A bit of back pressure helps a glow engine to idle better because it helps keep the glow plug hot, but in all other cases, back pressure is not needed nor desired. And tuned pipes do not work on back pressure, they work with sonic waves.

AV8TOR
Old 11-28-2012, 09:36 AM
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Ernie Misner
 
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Default RE: Can you run a gas motor with no muffler?

>>> they work with sonic waves. >>>

Yes, they work with alternating waves of: vacuum / backpressure, that help to draw the exhaust charge out, / keep the new raw fuel charge in place. The timing of these waves is everything. That is why the header length and pipe design are so important. It all has to happen when the exhaust port is open.
Old 11-28-2012, 02:37 PM
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Default RE: Can you run a gas motor with no muffler?

Well, you can certainly test run a engine without a muffler on it. It'll be loud. But it'll work. Now as to performance, it may depend on the engine design. Many engines need at least a little back pressure to work off of so they get best all around performance. The intake fuel charge may tend to exit out of the exhaust without a muffler thus causing a slight performance loss. Some engines tend to not want to idle as low without a muffler as they will with one too.

I would say try it and log your results. Then repeat when you have a muffler to put on the engine and log those results too.

Old 11-28-2012, 03:13 PM
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Ernie Misner
 
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Default RE: Can you run a gas motor with no muffler?

Some intake charge may be lost without backpressure and no muffler. The spent exhaust charge may exit more quickly without a muffler though. My experience has been tons of noise but a small rpm increase with no muffler compared to a stock, non tuned muffler. I thought engines were great before they had mufflers or throttles..... but that's when my hearing started to go.

Running a 4-stroke without a muffler or header pipe I've heard can lead to a warped exhaust valve when cold air hits it right after a shut down.
Old 11-29-2012, 07:11 PM
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Default RE: Can you run a gas motor with no muffler?

I ran a DLE 20 with out a muffler because the pitts muffler in the tight cowl (KI-61 Tony) was causing to much heat to carb and vapor lock. Gained about 300 rpm over the pitts. But it was very LOUD. Solved the vapor lock problem. I put in baffel from Troy Built Models. It toned it down a bit. Still loud, and cost 300-400 rpm. I had to retune slightly. Didn't affect idle or transition. Ran fine without the muffler.
Old 11-30-2012, 10:27 AM
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apalsson
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Default RE: Can you run a gas motor with no muffler?

In response to your question, yes you can run your engine without a muffler but a full open port setup will be unacceptably noisy.
Another way is to get a suitable flex header and run it outside the cowl underneath the plane.
If you coat the header with high temp silicone and then a fibreglass cloth, you will somewhat reduce the "twing" noise but it will still be noisy (possibly too noisy for many flying sites). The length of the header piece matters somewhat but I haven't done anything to adjust it. I just used a standard cheap stainless steel header like you get them from SDS Hobby or similar sources.
By propping the engine down, you further reduce the noise somewhat.

I have a 93" Zero where I have an MVVS80 set up this way (it is one of the new 80cc with a starter on it).
I have a 3-blade 26x10 Xoar prop on this setup and get around 6000 RPM on the ground but it unloads nicely once in the air.
Peak torque from my 80cc is at around 6200rpm so this load isn't excessive. Being a warbird that I fly for scale, I don't really mind if the somewhat slower spool-up isn't what you would want in an aerobat.
You will have to be careful with cooling if you go down this path because the engine works quite hard with such a big prop.
I suspect my 80 has similar or slightly more power as the ZDZ80 or a DA85 so the comparison may be valid in your case.

I hope this is of some help



ORIGINAL: mikes68charger

arobatx Thanks but thats my issue!

I have made 2 post asking for advice with a 4 blade prop for this motor with not much help. I have read that a DA85 will spin this Belia 22X10 4 blade with good power, but I know this Non super 80 is not as powerfull as the DA.

So with that said now chris923 Just posted he uses the 19X8 4 blade on his Gaint P51 with good results I feel a little better, WHAT ARE YOUR RPMS Please the world wants to know?

The way I see it I have 3 choses of these nice Belia Props I want to use.

20X10 4 Blade wich says its good for a 50-60cc may be a bit light load
22X10 4 Blade wich says its good for a 70-85cc wich I think will be to much load
Or Im thinking
20X14 4 Blade, wich says its for a 9 cyl 99cc 4c evloution motor, Now I looked this motor up (sexy) but it clames 6hp max rpm 6500, and recomend props of 26X10 wich is about the same numbers I see posted for the ZDZ80 exsept HP

According to my online power caluclator, it takes about .5 less HP to spin the 20X14 at 6000rpms as it dose the 22X10 4 blade.

I cant handle to slow plane. The 14 pich prop will give me around 70mph speed wich is where all my othere war birds are and I would like to be.

Thats why I asked this question about no muff, I have a exstra Morepower 20X14 Adjustable 3 blade prop laying around.( dose 10,12,14 pich) I wanted to see if the motor could atleast spin this prop with no issues or with at least more RPM than a DLE 55RA (7200 rpm with it set at 10 Pich)

What you guys think?


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