Lynton

I have an FS-120S-E engine fitted with the standard silencer. The engine is disappointingly noisy in a scale Tiger Moth. I recently purchased an FS-91SII-P. Although it is a smaller capacity engine than the 120, it has a much bigger and more effective silencer. I tried to fit the 91 silencer to the 120, but this is not possible because the exhaust outlet diameter on the 120 is smaller than that of the 91- and of course the 91runs much quieter.

How can I reduce the exhaust noise of the 120? Is there perhaps an after-market silencer which is quieter than the standard 120 one?

Any suggestions welcome as my beautiful Tiger Moth is spoiled by the din of the exhaust in flight.

Bax

My Feedback: (11)

The standard muffler for the FS-120 Surpass has a shorter body, but greater outlet diameter than the one on the FS-91 Surpass II. The header of the FS-120 is considerably larger in diameter.

You can, though, install the header and muffler for the FS-120 Surpass III onto any of the FS-120 Surpass engines. Just remove the black reducer fitting and the Surpass III header and muffler will thread right into the exhaust outlet. It may quiet the engine a bit more than the smaller muffler.

Here is the stock number and suggested retail price:

OSMG2859 45525030 MUFFLER FS120 US$70.99

This can be ordered through any hobby retailer who sells O.S. Max engines and accessories. It's currently out of stock in the U.S., though.

Lynton

Hi Bill

Thank you for your response.

How critical are the dimensions of the expansion chamber of the silencer? I know on a 2-stroke the back pressure is very important to extract maximum power - but on a 4-stroke?

If it is not critical then I shall attempt to make my own much larger silencer as there is plenty of room in the cowl.

Your assistance is much appreciated.

Regards
Lynton

Bax

My Feedback: (11)

The amount of back pressure is critical only if it's high enough that it bogs the engine. If you don't need much muffler pressure, then you can go with a larger muffler. If the outlet of the muffler's too large, though, you'll not get much sound reduction. Mufflers work because of two factors: they slow down the passage of the exhaust gasses, and they allow them to expand and cool off. Many people find that a second expansion chamber after the first one adds a lot of reduction. Escept for prop noise, some engines have been made nearly as quiet as electrics.

The expansion/cooling can be very effective...just look at how much silencing is done on automobiles (sure the engines aren't putting out the power they could, but they'd still be very noisy without their exhaust/muffler systems).

Lynton

Thank you, Bax. I'll have a go at making my own muffler as soon as I get the timebearing in mind what you'be told me.

Regards,

Lynton