Chuck, I can understand your position and frustration. I just purchased an OS 91 FS for my Top-Flite AT-6. Sound great on the test stand. I hope the muffler stays in place???? It did vibrate loose on the test stand.
Do you use any special process to keep your's on??
I decided to go with the OS because you van get better deals and service from Tower.
I have not had a problem with Saito service but obviously I have had some problems with the engines. I've had to send them back 8 times[]

On my Dave Patrick Ultimate, first with a 150 and now a 180, I have had mufflers coming loose constantly. I've wrapped the threads with plumbers tape and used red Loctite without success.
The 180 is back for the second time,right now, because the manifold stripped the threads in the head. They replaced it the first time but it's been there 2 weeks and I haven't heard anything this time. I'm probably looking at having to pay for a new head[:@].

There is a definite vibration/muffler problem with the larger engines but they won't admitt it.
When I get it back this time I'm going to use a Slimline Pitts muffler. This is secured in two places and will not unscrew itself. I tried it before I sent it back this time but the threads were so torn up from their muffler it was leaking around the head connection.

I'm getting frustrated with the engines. It seems after about 30 hours they are difficult to tune. Two to three clicks of high speed needle goes from too lean to too rich. That's why I have sent so many back. They always say it's the bearings???
I run them dry and use 4 cc of after run & air tool oil after each flight. I'm not as happy with the 150 & 180 as I am with the 72, 100 & 125 ( which is their best engine) and the OS sounds better.

Put Our Warbirds Over Williamsburg IV on your calendar for June 6, 2009.

Thanks Tom
Nice weather we're having???