Any problem with using another type of muffler and exhaust manifold then the stock RCV one supplied; Performance specialties at www.pspec.com sells a 4 stroke muffler and exhaust elbows that are used on YS engines which have the same thread on the exhaust port as the RCV 91CD.

Hi

No there is no problems with using an alternative muffler on your 91CD. The thread size is M11 x 0.75

Best regards
Laurenne

Just be aware that the M11 X 0.75 metric thread form is as rare as rocking horse...... I don't know where its used, but maybe the USAF copied them off fastners found on the UFO that crashed at Roswell New Mexico in 1947, which is now hangered at Groom Lake at Area 51?!

You have more chance of winning the lottery than finding a M11 X 0.75 die to make your own header pipe. In fact you will be doing extremely well to find any tube that you could cut a thread on for a header pipe. Which explains why the exhaust with the RCV engines are apparenly machined down from a larger diameter, THEN, have the M11 X 0.75 thread put on them using a CNC lathe, prior to bending. This saves RCV themselves from actually looking for a supplier of M11 X 0.75 dies!

Why do they, RCV and OS Engines, do this? Because they know members of the oily hand brigade are suckers, who will pay loopy amounts of cash just to see their pride and joy take flight. Go and price an optional exhaust header / muffler from engine makers? You will pay for it, and it might be close to a third the price of the engine!

For example, several fellow fliers of mine have lost the rear part of OS two stoke muflers in flight (not recoverable), and one has been quoted that a replacement, for an OS LA40, will be...$90 dollars! This is an OS LA 40 we are taking about! You ever wondered why they come in two parts? Its so you stand a good chance of having to buy a new back part!

However, if you own a Saito four stroke, you can walk in to almost any hardware store and buy a lenght of alluminium pipe that will last you a whole fleet of models, and a M10 die, for less than $30.

How did I find this out? I bought an RCV engine for a scale model, and I wanted / needed to make a custom header pipe. And I found out all about the top secret nature of M11 X 0.75 thread much to my chagrin.