I just finished my "Corvette" (Old School) sport pattern plane 72" wingspan with an OS .61FX with a Mac Pretuned Pipe on the business end. My question is, the pipe did not come with a presure fitting or anywhere on the pipe indicating where it might go. could someone tell me where would be the best place to put it and since the wall is so thin, how to secure it. Also, I'm goings to use the presure fitting off of the stock muffler and I need to know what size to drill the hole and the tap size.

Try here: http://macspro.com/pressure.asp

As far as what bit to use.... Use one that matches the shank (the bottom part of the thread where the "V" is). I like to rough up the pipe and solder the nipple in for added insurance.

Thanks impactiq, I have no way of soldering the fitting in so you think JB weld will work ok?

I have a OS 61.rf (rear exhaust) with macs quiet tuned muffler, on macs website they recommend you dont put the pressure valve on the header. I had to do this due to the length of the tuned pipe anywhere between 2-3 centimeteres back from the motor it worked perfectly. Also used a 3mm drill and tap (dubro) the valve went in tight but worked perfectly no leaks at all.

JB weld will work also.

The best place to put the fitting is in the largest diameter of the pipe. I do not remember the brand of fitting we used but it was one with a nut that you put inside the pipe.You should be able to get one at your LHS. This is a tricky job, but with a piece of wire and CA ,it can be done.

I use a coat hangar and tape, to slide it in the pipe, works ok

Thanks for the info guys.