I have 4 or 5 Webras and a gaggle of FX's.

On a mousse can, the Webra blows away the FX. One of mine turned a MAS 9x4 at over 22k, which is stupid-fast for that prop, it starts flexing and such. so I use an APC 9x3 combat on the Webras (except for one, which ate serious dirt and needs the smaller MAS 9x4 just to get up to a solid 19.5k).

Most stock OS FXes on the MAS 9x4 can hit a bit over 19k on 15% nitro.

The problem with the Webra is that spare parts are unobtainable as far as I can tell. And that's bad because the needle and fuel nipple assembly that is pressed into the side of the carb breaks really easily. sometimes a hit will cause the spray bar to crack internally, and you can't see the damage, but suddenly the engine won't run right.

The Webra also has a massive carb intake, which means it doesn't draw fuel well, so it's critical you get the tank position right (or use a bladder, which I don't, I just get my tank right). You also need to launch a mousse can equiped webra really rich, because set up right, it will unload like crazy in the air, come on the pipe and start sucking fuel like mad. If you lean it like an OS, it WILL be too lean in the air, and RPM will drop.

When my Webras in my old 2610 planes were set and running, when I pulled a high-G turn, the engine would lean a tad, pick up RPM, and the plane would actually accelerate through the turn and was faster turning than flying straight, which was amazing, and a great advantage in the air. But you can only get that if you set the engine a little rich on the ground. Use the pinch test to get that right.

Oh, and a Webra will empty a 6oz tank in less than 6min. So in many combat contests, I'd wait 30-45 seconds after start engines to fire up, launch at part throttle (or full, then pull back right after I released the plane if it was windy), and not go full power until "start combat". Sometimes I'd still run out of fuel before the end. That's using a hayes 6oz.

Also, the Webra use a press fit prop hub over the front bearing, which is hard to clear if you eat string. I find that annoying on a lot of engines (Magnums are the same way, only OS has a prop hub that just comes off in your hand)

Anyway, the OS is MUCH easier to get working and keep working, parts are more available, power is solid, and so many guys have them that help or parts is usually for the asking at a contest. I don't run my Webras much anymore because if one is damaged, it's done.

now, for 2548, the Webra is junk, don't bother with it, you want the OS FX, it's really hands-down the best engine for 2548 and Limited B right now. The Webra is designed to run at high RPM, and wants a small prop and high RPM to make power. When I put a standard non-tuned expansion chamber muffler on my Webras, and bolted on the mandated 10x3 APC or 10x4MAS, the Webra just couldn't make any power and was a sitting duck, the OS FXes clearly have more low-end torque to turn the bigger props.

My impression of the AX is that it's designed for low end torque with bigger props, but I don't know how that translates to the 2548/LimB props at this point, those props might still be too small for the AX to really produce the power. I don't have an AX, so beyond theory, I can't commend.