First off, I have new OS 40 FX, it has been broken in, but has not logged much flight time, how long should I wait before piping it? Also I have been told that the mount for the muffler is the same for the 40FX and the 46 FX, is this true, because I cant find a Header on Towers web site that specificaly calls for the 40, but they have one listed under the 46, by the way Im looking for the MACS setup, for my Shrike.

Thanks

Tony

HI ONYTAY, I only have experience with the .32, but if the .40 holds a good high speed needle setting, don't waste any time piping it if you want more rpm. I am curious to find out how well it turns a 7.2-8.6 and a 8-8 APC.

I was planing on turning a 9x8 APC Ill give you some tach readings this weekend

I don't know about the header size... I haven't bought an OS for the last ten years...

But as far as running it with or without pipe goes... run it with the pipe from day one. Just keep the pipe set on the long side for the first gallon or so. After that, start cutting things up until you reach peak. When you reach peak, run it for a couple more gallons without tinkering... and after that, start tinkering....

Just don't go for the max right away! Run the engine in, then look for "a" peak setting, but not "THE" peak setting... you know? Don't go for the kill setting right away... give it some time... but keep it screaming anyway (that means a small prop)...

thank you, very helpful

anyone know about the header size?

That's a "loaded question" because much depends on your airframe and intended prop size. If you get a baseline reading with open exhaust, then a reading with just the header you will at least have a starting point. A 9" diameter prop on a hot .40 is like having a 2 barrel carb on a 454, it acts like a governor. I think a 8" prop will give adequate low speed thrust to get your average speed model in the air, and give the .40 a chance to unwind.

Why not put a JettStream or UltraThrust exhaust on your OS. So simple, no tuning, just bolt it on. A full length pipe won't give you that much more and it needs to be tuned when you change prop size. A 9x8 works well on a Jett 50 but is too much prop for a 40 FX IMO. I would use a 9x6 and maybe a 9x7. I would not go much smaller then 9" on a 40 size Shrike or your launch thrust would be marginal IMO.

I found the ultratrust, but where do I get the jettstream?

Try this link.

http://www.jettengineering.com/accy/accy.html

I just ordered one for a Webra Speed .32... I hope it's all they crank it up to be...

I might give one of them a try

Thanks

Tony

Rude.......

I think you will be particuarlly happy with the Webra 32 application

I have one running on an older helicopter version Webra 32.... sings quite nicely. Don't over prop it......Let it turn up... the more the merrier.