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Author Topic: Custom made exhaust extensions and mufflers  (Read 1833 times)

Offline Matt Piatkowski

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Custom made exhaust extensions and mufflers
« on: November 05, 2015, 08:02:21 AM »
Hello,
Please see the attachment and comment.
Thanks,
Matt
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Offline Tim Wescott

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Re: Custom made exhaust extensions and mufflers
« Reply #1 on: November 05, 2015, 10:45:15 AM »
You have an engine setup that's "locked" at a nice steady RPM and you want to change it?  Why not find a prop pitch that works well with what you have and be (really) happy?
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Offline Matt Piatkowski

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Re: Custom made exhaust extensions and mufflers
« Reply #2 on: November 05, 2015, 11:43:20 AM »
Interesting thought, Tim.
I will give it a try with 11 x 6 or/and 11 x 5 APC or/and use larger diameter with 7", 6" and 5" pitch.

Having said that....I do not really understand why the existing setup is not reacting to the rotation of the needle when I want to enrich the fuel-air mix.

Any ideas..?

Regards,
Matt
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Offline M Spencer

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Re: Custom made exhaust extensions and mufflers
« Reply #3 on: November 05, 2015, 04:52:38 PM »
See what it does unmuffled .  >:D

MIGHT find is ' natural ' characteristics .

I prefer say ten 1.5 mm holes in a muffler as theres maybe not ONE shock wave hitting all at once, so quiter for same area outlet ,
and maybe a lengthed tuned effect ?
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Online Steve Helmick

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Re: Custom made exhaust extensions and mufflers
« Reply #4 on: November 05, 2015, 09:28:17 PM »
The maximum rpm is easy enough to understand...engine goes too lean and stops at 11k. That's a lot of prop, specifically in pitch. I still think that engine might be happy with a 12-4 or 12-5 APC. Further, I suspect the current cute little muffler is too restrictive, limiting the top rpm limit by limiting the pumping ability of the engine. Read Randy's pinned articles about engines and note the part where he talks about venturi size and muffler flow having similar effect on the engine run. I'm not sure how this might limit the lower rpm range, but there may be something in Randy's writings that will explain it. I'm pretty certain that it's not a resonance thing like a tuned pipe or the OS "Cone of Silence" mufflers.

It's getting a wee bit cold here in the last few days. How deep is the snow there?  LL~ Steve
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Offline Matt Piatkowski

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Re: Custom made exhaust extensions and mufflers
« Reply #5 on: November 06, 2015, 05:13:48 AM »
This is what I will do:
1. Remove my "cute little muffler" and put back the tongue muffler.

If the engine can reach lower RPM and 2-4-2 cycling ( it could do it before the change) the "cute little muffler" will be permanently retired in my waste basket.
At the same time, I will experiment with different props.

Comment: the original configuration had 11 x 7, BYO prop. from Brodak and the tongue muffler. Everything else ( glow plug, venturi, needle, fuel ) is unchanged.
With this configuration, I could reach 7,600 RPM and even less and full 4 stroke with heavy smoking on the ground.

In my never ending quest to experiment, I decided to try the exhaust extension similar to the one I have on my EVO 36 C/L.

Perhaps this that worked for .36 size engine does not work IN FULL RPM RANGE for .45 size engine?
     
2. I will adapt the light expansion muffler shown on the second photo in my attachment to be installed on Magnum Pro 45 and run tests.

If the lower RPM are unlocked with this expansion muffler, the main problem is solved.

Hi Steve,
I suspected too much exhaust flow restriction and you suspect this.
By the way: EVO 36 runs 11x4 APC prop in full 2 cycle mode at ~10,500 RPM and this is good for 5.0 s laps on 60' lines with my Parrot.
I have found a moment ago in my notes that I could not go below 9,000 RPM with EVO 36 and 11x4 APC prop but Parrot did not need lower RPM as it flies well in full 2 cycle mode on 11x4 APC.

Toucan needs lower RPM with Magnum Pro 45 and 11x7 APC and this is how I discovered the RPM restriction. I will run this engine with lower pitch prop, what you suggested, the RPM will be higher and the engine will be in the full 2 cycle mode.

Perhaps if I started the entire exercise running lower pitch props, I would have never discovered the lower RPM restriction?

Re:weather in Toronto: no snow on the ground and the weather was recently fantastic.

Regards,
M
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Online Steve Helmick

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Re: Custom made exhaust extensions and mufflers
« Reply #6 on: November 06, 2015, 09:33:17 PM »
Matt, I think you really need to stop thinking of the NV as a throttle! It isn't. Use it to adjust your launch rpm a bit and rely on your prop pitch to set the speed of the plane, and the prop diameter to adjust the load on the engine. Again, these notions are covered in Randy's pinned articles. Very much worth reading! 

A useful exercise is to start your engine and block off the tank air inlet, whether muffler pressure or uniflow inlet. Pinching off the muffler pressure hose responds much faster; probably why I like it better. Assuming it's on the rich side as usual, the engine will pick up rpm and start to sag as it goes past peak. When the engine drops back (rich) to the same rpm two or three times (using the tachometer!) when the pressure line is released or uniflow unblocked, then you know the engine has reached a stable temperature.

That's when I adjust the NV to desired launch rpm. Whether I know what the desired rpm is or not, this is the only way I can think of to get a grasp on launch rpm by experimentation. SO many times, I've seen guys start their engine, quickly adjust the NV and head for the handle...while they are on the way, the rpm very often drops off. They pickup the handle and are perplexed as to whether to launch or not. Sometimes they signal for the launcher to make an adjustment. Which then results in launching at an unknown rpm. They don't know if it will be too lean or too rich and can't learn much from this flight. Bad news, IMO.

Some guys just start their engine and head for the handle. This makes a lot more sense to me than a quick adjustment to a cold engine. At least this is a NV setting that is known to work sometime in the past. Maybe not right now, today, but sometime or other, it worked. I suppose that there are some climates where this approach might work fine...one where the weather is steady and temperature is steady through the day. That's not ours, and I doubt that is yours.  H^^ Steve

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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

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