I have an OS 1.60 FX engine and is running super BUT! the glow fuel is too much now and would like to swap it for a gas engine in the 25-26CC range and same weight as the OS 1.60 FX. Since this would be my first gas engine and don't know a lot about the products on the marker now (gas), please help me out with a few makes/models I could choose from. Thanks.

You won't find a gasser with the same power output AND the same weight. Just doesn't work that way. What's the airplane the 1.6 is in?

CR

Goldberg Sukhoi SU26MX

the only gas engine that comes very close to 1.60 FX powerwise is the MVVS 1.60 (about 90% power). The modern ICU ignition uses LiPo ignition batteries, so the weight disadvantage becomes real small.
For flight, a 10 oz fuel tank will do. This cancels out the extra weight of the ignition. Add to that the lesser vibration of the gasser, so you need less vibration isolation, and the difference gets even smaller.

Is your 90% power reduction with both motors on pitts mufflers? You are saying that if my OS16FX pulls 18 pounds of thrust the MVVS 1.60gas will pull 16.2 pounds of thrust?
That is about the differnce between my OS160 and my OS108, both on pitts.

I am not comparing with pitts mufflers. They are exhaust gas collectors, not mufflers, and only serve to harm the engine's potential.
the difference between your OS 108 and OS 1.60 should be larger than a mere 10%, and yes, the gas engine will pull about 1 : 1.5 lbs less than the comparable glow engine of same displacement. I have measured 19 lbs pull on my 26cc test engine, using the MVVS tuned pipe.
That is more than enough to adequately hover a 12 lbs plane.

I agree that pitts mufflers are just gas collectors, but it also appears that at least 50% of the people on RCU want to run them--so for practical purposes I think the motors need to be compared like that as well.

I agree that the difference between my OS160 and 108 should be more. My tests show with pitts OS160 pulling 18x6 @8,800 and 18 pounds of thrust and my OS108 pulling 17x6@9,050 and 16 pounds of measured thrust--the 108 does well on a 10 pound 3D plane. The OS108 has a very free flowing pitts that is loud--that may be why it is doing so well.

I agree with you that the MVVS on pipe is good power on a 12 pound 3D plane.

since the question is, gas to glow comparison, I could try to run identical engines, like an MVVS glow on the same pipe as the MVVS gas. That would present a fairly accurate result, though the glow has bronze conrod bearings, and the gas engine has needle bearings. The cooler exhaust gasses also would require a re-tune of the pipe.