HI.
Yesterday i tested my OS 91 FX so as to see if it fits in the cowm of my Corsair.
Unfortunately it wasn't.
The reason is that the muffler has a part that adds to the overall length.
So i thought if i can remove it and use my engine without it.
But firstly i would like to hear some oppinion from the experts of the RCU forum.

Hi! I asked about this in the OS support forum and Bax said that it would make the volume of the muffler too small and he advised against it.

A pitts style muffler from bisson or slimline will solve your problem.

this engine requires a good back pressure so i wouldnt mess with the stock muffler.

zain

I agree....the muffler with the center section removed would work OK
on a .60 size engine. It would be restrictive on the .90 without it.

FBD.

Hi!

I bought my .91FX about 3 years ago and at that time did not exist a muffler with this center section.
I flew with this short muffler and had never problems, my FX turned ~8.600 RPM with APC 14x8 and CoolPower 5% fuel.



I think it wouldn't be a serious problem when you take this section out.

Hi xcarlos!
Thank's for your awsome pic!
I like so much OS engines when they are packed!!!
So,i must admit that removing this part will result in a bit loss of power,but this loss is not too much to consider it.
So,xcarlos your engine without this part is working good?
Also can you tell me with an APC 14x6 prop. what rpm idle you have?

-->Zain: I must tell you that no other muffler will be better than the one that OS supplies with the engine!
I think all people are with me...
So,yes i know that OS 91 FX needs enough back pressure (which the original muffler provides),but....
Many paople in RCU complain for problems with backpressure and not good fuel feeding![]
BUT....
OS 91 FX NOW comes with new needle valve and cover plate.
And these new things work and minimize ANY problems to minimum.

Hi!

I bought and used my .91FX with this original short muffler and also tried it with a tuned pipe and never had any running problems.
Unfortunately I don't have an APC 14x6 and have not tried yet.
With a 15x6 MARO wooden prop it turns about the same RPM as with the 14x8 APC.
I also have an APC 15x4w but cannot remember what it turned...

kostas, just try it and if it is to restrictive, if the engine overheats or is weak you can remove the baffle and open up the outlet a bit to "derestrict" the muffler. I run the 91 fx with these mods even though I have the mid section in place and it made my engine a whole lot quicker to spool up my prop.(wasn`t to impressed with the performance in stock form) have no tachreadings before and after, but it certainly has more power now and no issues. trottles fine, runs great and never a deadstick as long as there is fuel in the tank

Yes,ok,but i think that power loss will not be a too much problem!

OS does make 1/2 inch extensions for the muffler. Been there , done that

I've already ordered one of these extensions (35mm) and i will have it in some days.
So until then do you have any other option for this darn muffler?