RE: Doesn't look like it can be converted
 

Hi,

You have this right. The exhaust systems you speak of on motorcycles are expansion chambers, and they are critical as to sizes, lengths, etc. These little motors don't have the high port timing of an engine used with an expansion chambers, and the sizes of your mufflers, etc. aren't very critical. Do not make the exit pipe small trying to emulate a tuned pipe, (expansion chamber), as it will not work and will reduce power and possibly cause the engine to overheat. If you are not worried about noise, use a large exit for best power.

Good luck,
AV8TOR

RE: Doesn't look like it can be converted
 

Thanks Aviator, I did suspect that would be the case, but wasn't too sure, - makes things much easier.

Steve, I redid my calcs. and got 475.21 sq mm, - (correction 373.23 sq mm [:@] ) = 21.8 mm for reqd. pipe dia. - (near enough to 7/8" dia). - however, as AVIATOR says, things aren't too critical, so I'm probably just nit picking. ;)

RE: Doesn't look like it can be converted
 

hI all , new to all this. :eek:
was working on the final outlet size's 196mm2 as stock.
thought that with no baffles and same outlet this would be about correct ??
Do we make the outlet alot larger than std??
Is this the thing to do ??[sm=confused.gif]
I know you can over exhaust an engine ..is bigger better with these?
As i said am new to all this, so your idea's and help getting this right is appreciated heaps.
Still tight on splayed pipes Wildo because of lead to plug......confident we will sought with all this help though :D
thanks torp;)

RE: Doesn't look like it can be converted
 

Zagnut & Willdo: Good point on holding hub to rotor.
Does anyone have any thoughts on this as a means of additional securement. The bb or lead chip will bind in the threads but once setscrew is loosened it should allow unthreading of the hub.

I have been using red locktite on these hubs and I use heat to soften when replacing/exchanging. Same routine for spinner nut or bolt. Looking for an alternative securement and it may also assist Torp .

RE: Doesn't look like it can be converted
 

Zagnut Exactly no welder, no noise restrictions, materials on hand. The end cap was just a bend over, same for the 90 turn. A few pop rivets and side panels. Compression tubes for bolts- steel brake tubing.
Elegant?? No Deflects? Si.

RE: Doesn't look like it can be converted
 

Mike, i think a better soulution would be three setscrews on the hub flange in the same place you wanted before, instead of threading into the flywheel they just tighten up against it.
they would resist rotation better due to a much longer moment arm than setscrews tightened against the threaded shaft.


dave

RE: Doesn't look like it can be converted
 

Mike,
You could use the common bent over disposable sheetmetal tab so much used today, - anchored to to the flywheel, ( and the prop hub bolted to the starter pawl holes).
Then there's the good old fashioned castellated nut and split pin, ( which in my opinion takes a lot of beating).
Having said all this, the original spring washer works well on the chainsaw!

Do you guys think there's a case for using the original muffler box (gutted, with the outlet holes blocked and 2 exhaust stacks welded on one end) ?.

RE: Doesn't look like it can be converted
 

That's what I do all the time. Good power and lighter than the aluminum mufflers you buy! (Basically free as well!)

On this particular muffler that I just happened to have a picture of, I sectioned the muffler as well because it was quite long.

AV8TOR

RE: Doesn't look like it can be converted
 

Quote , post #20:
Have looked at modifing stock muffler.Std exhaust area 196mm2.
Block up factory holes , rip out internals and put one 16mm id or two 11mm id pipes
onto side or top of muffler.Same area as stock.
Work you think ???
Un quote.
torp:):):):)

RE: Doesn't look like it can be converted
 

Note: The engine that muffler is on is a 23cc, and it turns a 16 x 8 prop at over 8200 rpms at 7000' density altitude. Remember to use spacers inside the muffler for the bolts so that you can tighten the muffler without squashing it.

AV8TOR

RE: Doesn't look like it can be converted
 

Nice muffler Av8tor,:D
what size are your pipes on the 23cc ???
thanks torp;)

RE: Doesn't look like it can be converted
 

Hi,

Thanks for the compliment! The two tubes have an inside diameter of 7/16", or 11mm. The engine is quieter than my .61 size glow engines, but has great power. For a 30cc engine I'm working on, the tubes will be 1/2" each, or just under 12mm.

Good luck,
AV8TOR

RE: Doesn't look like it can be converted
 

Torp,
Just read your post, and checked #20 - but then I did ask you to let me know when you thought I'd lost the plot:eek:.

- sorry about that, - didn't read it properly [8D].

I'll always have an excuse ready though ( I was crook :D).

RE: Doesn't look like it can be converted
 

Sweet as Wildo,
don,t think you have lost the plot any more than the rest of us !!!!!
ha ha :D:D
torp.

RE: Doesn't look like it can be converted
 

Hi everyone,[8D]
Just another idea to run past you people on the muffler question:
On modding the stock unit.Twin pipes a problem because of plug and lead.
Depth problem because of proximity to firewall etc.
Pics show possible solution fixing one pipe to side of muffler.
Av8tor suggest two 12mm pipes.
How big would you make the single pipe in this setup.
As usual big ups to you chaps help :D:D
torp;)

RE: Doesn't look like it can be converted
 

Steve,
Another method would be to fit the pipes with the required length protruding, and the rest inside the muffler ( straddling the exhaust port), leaving a bit of space between the end of the pipe and the bottom of the muffler.

I have heard of something like this being used with expansion chambers on karts and motorcycles, where the stinger is pushed right into the chamber, ( seems that it also enhanced the muffling a lot), with no loss of power.

What I mean is, that if you look at your second picture, - just imagine the pipe inside the muffler, - this could solve your pipe length problem neatly.

If my description isn't too good, I'll try to wind up my old scanner, and send a sketch!

RE: Doesn't look like it can be converted
 

Yes Will, good idea.:D
Depends on the size of the pipe though,If we have enough room to clear plug etc. out top right side
Av8tors two 12mm pipes is the only size we have too work too at moment.
Need to get a size from someone for one pipe and we 'Will' be away laughing.
Can you calculate this from the info we have been given.Can anyone !!!!!!????????
I worked it out at a 16mm i/d , but am not sure now at all :eek:
thanks to all , torp;)

RE: Doesn't look like it can be converted
 

Torp,
I am talking two pipes! - one each side, - Plenty of room now? ;)

RE: Doesn't look like it can be converted
 

Two pipes nice , what about that plug and lead ?????
cheers torp;)

RE: Doesn't look like it can be converted
 

2 centavo worth.... Area of exhaust gasket ID x 1.25 to 1.75 is a ballpark for the combined ID area for 2 pipes. No restriction.

I have a bunch of 'trial muffers/deflectors' Read somewhere that beyond a certain point ID you really don't gain anything but weight.

I have a friend with DA50 who I'll see later today. I'll try to get an ID on its pipe.

RE: Doesn't look like it can be converted
 

Torp,
Plug lead doesn't have to be at that angle, it can be re-routed straight over the head.

You may have to fit it with a metal cap (to lessen radio interference) anyway, + maybe some braid covering the lead.

Pipes can still be splayed a little too.

RE: Doesn't look like it can be converted
 

Hi,

You guys are really making this way too critical. But...

A=PI X R squared.

My math shows that one 17mm outlet will equal two 12mm outlets in area. If you have trouble fitting that size pipe to the muffler, you could squeeze it gently in a vise to oval it a bit.

Good luck,
AV8TOR

RE: Doesn't look like it can be converted
 

Yes, I think you're right, - I may be getting a little too complicated, so I'll try and settle down a bit, :D and listen to you guys a bit more,
I've messed with engines all my life, but this aircraft stuff is quite new to me, and I see that it has problems and solutions peculiar to RC aircraft. - and this is Torp's thread of course! ;)

RE: Doesn't look like it can be converted
 

I know, it's easy to get carried away. I too, have a lifetime of engine tinkering and experience, and I also get carried away. I find myself tweaking, porting, tuning etc. on an engine, when it would be easier to just go to a bigger motor. With most of these conversions, that doesn't cost anything, as often a bigger engine is close to the same weight as the one you are working on. As they say; "The only substitute for cubic inches, is more cubic inches!" But it's all fun, and it's part of the hobby. It's a personal challenge to get the most out of an engine and engine/plane combination. I love it!

As I re-read the above before posting, I got a chuckle. On one of the combos I'm working on, I decided to do just that; go to a bigger size engine. Now, of course, I'm modifying the bigger engine before I even install it!!! And on it goes...

Have fun!
AV8TOR

RE: Doesn't look like it can be converted
 

Well , looks like muffler soughted.:D
Two 12mm pipes on the std unit.
[that didn't take long] ha ha lol
Will take another pic on plan for you wildo to get prop hub dimensions,etc
cheers torp;)