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  • September 21, 2017, 10:02:08 AM

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Author Topic: A question for all of you LA-46 fans (and engine lovers everywhere....)  (Read 982 times)

Offline Scott Richlen

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Okay, so I wanted a little more ooomph out of my LA-46, so I take the muffler apart (yes, I'm using a stock muffler, or was) and remove the internal baffle (a little cone with a hole in the middle).  So, now I got a little more power.  "Hmmm", I thinks to myself "if a little is good, a lot should be even better!"  So, I further de-constipate it by cutting off the muffler stinger.  Now I notice that the stinger pipe itself seems to be a bit constricted at the inner end, so I drill out the hole in the muffler to the outside diameter of the stinger (that I had just removed - follow me so far?)

So, I go fly it today.  Ooooh!  You immediately know that something is changed as the sound is much sharper and the engine runs faster on the unchanged needle setting from last week.  More power, but I notice that it seems harder to needle - much touchier.  First flight: too fast; 2nd flight: too slow; 3rd flight: just right.  Also, I noticed that the engine seems to be surging (but the guys outside the circle didn't notice that.)  Fuel use went up from 4.25 ounces to 5 ounces.

So what do you think?  I stuck the baffle back in tonight and hope to fly it again tomorrow to see what that will do.


Offline peabody

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #1 on: September 08, 2017, 05:34:27 PM »
Hi Scott
I wager that you'll be happy with the baffle back in....
A wise engine guy once told me to open the exhaust on LA's or FP's to 3/8"...

On the stock OS muffler that means you'll lose the stub .....

Have fun!

Offline Scott Richlen

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #2 on: September 08, 2017, 06:14:51 PM »
Rich:

I'm pretty sure that the hole in the muffler (where I excised the stinger tube) ended up being about 3/8ths dia.  I think the hole in the baffle is slightly smaller.

I'm also wondering if the removal of the baffle would also affect the muffler chamber pressure which, in-turn, affects the pressure feed-back to the uni-flow tank?

I did get it running at a reasonable speed for the 3rd flight, but the needle valve just seemed a lot touchier than previously.

Offline Keith Miller

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #3 on: September 08, 2017, 07:55:25 PM »
Less restriction at the exhaust doesn't necessarily mean more power. A small (3/16") stinger on a muffler can actually increase power.

Offline Matt Spencer

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #4 on: September 08, 2017, 08:24:27 PM »
Somebody in a post somewhere I hit earlier today said use the baffle ( Holes smaller than 3/8 ? ) and knock outlet to 3/8 , which means its knocked off . or half of .015 thick if 10 mm .
reputed to be a knowledeable chaps advice ! ( must be right then  S?P  )

A lot of those differant makes / models of rear housing interchange , theres even an OS one short , long rear - that matches a long front , short rear . Nearly . Slight detail dosnt .

SO you could mix n match Cone Baffles . The Cone goes AFT Not Fwd like one I looked inside ! , and tail housings . The permutations are endless .  VD~

Offline Carl Cisneros

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #5 on: September 08, 2017, 10:40:58 PM »
Scott

Bring out a screwdriver that fits the screws for the muffler tomorrow.

I have an OS muffler I would like you to try on teh motor also.

Carl C
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Offline Scott Richlen

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #6 on: September 09, 2017, 06:01:08 AM »

Quote
Less restriction at the exhaust doesn't necessarily mean more power. A small (3/16") stinger on a muffler can actually increase power.

Keith:

That may be true in some cases, but not this one.  The stock muffler greatly restricts the power of the LA-46 so when you de-constrict it, the power really comes on.  However, it appears that it may be possible to open it up too much and then lose some consistency in the engine run.  Not sure that that is what is happening here.  Hopefully Carl will help me get it sorted out today.

Scott

Offline Chris Brainard

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #7 on: September 09, 2017, 07:11:44 AM »
What size venturi are you running?
Chris

Offline Carl Cisneros

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #8 on: September 10, 2017, 07:57:35 AM »
He is running the large OS venturi in it as usual.

I got him sorted out with one of my OS mufflers.

Carl R Cisneros, Dist IV
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Offline Scott Richlen

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #9 on: September 10, 2017, 04:28:19 PM »
What Carl had me try was an OS stock muffler but with the stinger pipe reamed out to 8 mm (I think that's what he said.)  The stock muffler stinger pipe is a bit more restricted than it looks, thus the reamer.  Turns out that the stinger actually does something and isn't there just for looks, so when I cut mine off the engine exhaust was essentially just dumped into the air with little pressure restriction.  That is probably what I detected as engine surging and difficult needling.

I think the venturi is a .281.  I'll probably put the venturi from my Fun-51 on it to see what that does.  I think that it is a .312.  More fun!

Offline Carl Cisneros

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #10 on: September 10, 2017, 10:40:58 PM »
just make sure to use the same NVA from the motor as well off the Fun 51.

Carl R Cisneros, Dist IV
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Online Brett Buck

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #11 on: September 10, 2017, 11:04:00 PM »
I think the venturi is a .281.  I'll probably put the venturi from my Fun-51 on it to see what that does.  I think that it is a .312.  More fun!

     If you enjoy one screaming melt-down after another, then yes!  One way to find out, of course.

     Brett

Offline Scott Richlen

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #12 on: September 11, 2017, 07:00:34 AM »
Brett:

Actually, here is the set-up on my Fun-51: it has an earlier model (not stock) muffler #762 with the stinger cut off and a .312 venturi with an ST needle valve.  It really runs great!  It has never had a run-away and has very consistent needling.  If I don't get the engine run I want, it is my fault for not setting it right in response to weather change or location change.  This LA-46 probably has around 350 flights on it.

So, I assumed that I could do similar with the LA-46 stock muffler and get similar results.  However, the #762 has the stinger on the centerline of the muffler at the end of the cone while the stock muffler has the stinger on the side of the cone coming out at a approximate 30 degree angle to the centerline of the muffler.  The #762 is smaller than the stock muffler.  So what do you think is the reason for the difference? 

Offline Scott Richlen

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #13 on: September 11, 2017, 07:05:56 AM »
Just to clarify - the #762 is on my Fun-51 (the cartoonish D) while the stock muffler (that I butchered) is on my P-51 B. 

Offline Al Ferraro

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #14 on: September 11, 2017, 11:01:38 AM »
[quote  so when I cut mine off the engine exhaust was essentially just dumped into the air with little pressure restriction..

I think the venturi is a .281.
[/quote]
  Drill out the muffler to 3/8, then JB weld .375 brass tubing the same length as the part you cut off, after you cleaned and scuffed each surface, it should be a close fit. When you have it all glued up, heat the bottom of the muffler a little, with the 3/8 pipe pointed down using a heat gun to get the glue inside the muffler to flow around the brass tubing and let it dry in than position.
    I would use the .281 venture with .156 spray bar and cover it with one layer of panty hose, just hold it in place with a rubber o ring. This should cure you problems and give you better fuel mileage.
Al
« Last Edit: September 11, 2017, 08:24:19 PM by Al Ferraro »

Offline RandySmith

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #15 on: September 11, 2017, 06:05:28 PM »
use the  .281 venturi  with  the  .157 spraybar   or  use  the  .252 venturi  with the  .135 OS spraybar

Randy

Offline Carl Cisneros

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #16 on: September 11, 2017, 08:40:42 PM »
Scott;

IF memory serves, you are going to have to DRILL out the NVA hole in the case for the Fun 51 NVA.

I would leave well enough alone and work on the present set up. The present set up has more than enough power to get things done and is
very close to getting the set up you want.

REMEMBER, the new motor is NOT an X year old motor with Blue paint and then oil built up on it over the years and years of running.


Carl

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Offline Steve Helmick

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Re: A question for all of you LA-46 fans (and engine lovers everywhere....)
« Reply #17 on: September 13, 2017, 09:32:52 PM »
Read through Randy's pinned engine tuning articles at the top of the page. He says that restricting the exhaust works like a smaller venturi, while reducing exhaust restriction acts like a larger venturi. Basically, it allows more pumping efficiency. The reverse is also true.

That aside, the only engine I've run a stock OS .40/.46LA muffler on was a Magnum XLS .36. Other than adding a rubber ducky, it worked exceptionally well. On my .46LA, I ran a MACS Muffler, a borrowed Big Art tube muffler (so I was told), or a Randy Aero CNC Tube muffler. All those also worked well with .271" to .285" venturii with Randy NV Assy. or similar of .156" diameter.    D>K Steve
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