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i have a OS 160 FX on a 72" QQ yak with the Bisson Pitts style muffler. wondering how cutting the tips off of the stingers will effect the performance. i'm not worried about fuel pressure due to using a perry pump. it has great power but i'm always looking for a little more and was told that it would give me 400 more rpm. if any of you have done this please let me know how it worked out.

thanks
randy racer

It's a good idea but I think 400 RPM is a little high. More like 200-300 RPM.

thanks joe, have you or anyone you know tried this? i hate to cut the muffler and find out it hurts the performance.

randy racer

Randy,

Think of it this way. Those tips create a small restriction right at the end of the pipe which hurts that exhaust flow to a degree. Cut the tips off and the exhaust has no restriction so the engine breaths better.

Honestly I have done this and I really did not notice that much of a power increase but I also did not check the rpm's before I did it.

The biggest change I made on my 160FX was to remove the perry pump (I had a short fuel run) and change the line to 1/8th inch from the clunk (drilled out the clunk also) all the way to the carb including the little line between the carb and needle. This alone allowed for a cleaner transition in the mid range and really woke the engine up. I do understand that if you have a long fuel run then the pump is needed.

You typically don't see much gain, if any, by chopping the tips off these for glow engines. In fact, the lack of backpressure may be a problem for fuel delivery.
Now, on gassers, it is practically a MUST, IMO. In the past month I advised two guys to chop their tips off their bissons on two Evolution 58's, but to tch it before and after, The gain was 200-350 RPM!!!

thanks again guys, my tank is around 9 inches behind the engine on this bird so the pump is a must. as i said in 1st post the 160 has plenty of power for this plane but i always want more. i have been using JL Smith pipes on almost every plane i have had and love the performance they give. at first i did'nt want to mess up the clean look on this plane, but after you use jerry's pipes it's hard to settle for less.

randy racer

I did this on both of My Moki's (1.80 and 2.10). I have regulators on both of them so back pressure is not an issue. The only way it would hurt performance is if you use muffler pressure for fuel pressure.

Many people cut the tips off and measure a rise in RPM's, but I didn't measure mine before and after.

i have a bisson muffler on my da50. i ended up cutting the tip's to find about 300 + rpm increase

I too have cut the tips off my bisson muffler on my os 160. I'm not sure if I picked up any rpms seems to be around the same. 9200rpm's, kline pump, 18x6 apc, 5/8" muffler extensions. the one thing I have noticed is that I have gotten rid of the anoying pinging sound the muffler makes in the midrange. I've also read it may keep the engine cooler since theres less of a restriction.

hey Badfish mine does have a pinging sound that makes it sound lean, it does'nt run lean so i have been blaming it on the muffler. i would love for that to go away. you don't think there was any power loss? and what do you mean by 5/8" muffler extension... between the head and the muffler or on the tipps?

randy racer

no, there is definitely no power loss. runs good. and the 5/8's tubing is on the muffler tips. I wouldn't cut the tips if your not using a pump of some kind. (I know you are) you need that back pressure for the fuel tank. I think cutting the tips and adding the muffler tip extensions has quieted the engine down a bit. still a very loud engine.

ok, i cut the tipps last night. i'll see sunday how it goes.

randy