hii all i am looking to buy mvvs .25 combat engine or os 25 fx i need some advice from the pros on which one to get for open b combat
thanks

Get the OS.

The MVVS might or might not be more powerful in theory, but the OS is far more reliable and will last longer.

It's no accident that the most common engine seen in B and 2610 class combat is the OS .25FX.

If you want more power, look at the Webra .25, it's probibly the most power for the money out there. Some guys have said the needle value is prone to damage, but it's not hard to hack the carb in to a remote needle arragement that is less prone to damage.

I agree with Kirk 100% on this - go with the OS.25FX. It is durable, powerful and very user-friendly.

D

THank you for your info
I bought a os 25fx today and i have couple of questions. do i break it in with the original muffler or the musse-can, than i heard there is a special way to get them broken-in for power.

I usually break them in with the mousse can, but I've seen it done both ways.

The break-in itself is important. There are some different thoughts on how to do it though. Basically, you want to run the engine rich enough to ensure enough lubrication to the conrod, bearings, etc. But you need to get the engine up to normal temperature FAST, so you never want to run it so rich that it "four cycles" or spits fuel. Running at too cool of a temp results in the piston/liner wearing for a good fit at that lower temperature. When the enging actually heats up fully, you wind up with a loose fit and a loss of power.

Some guys set the engine rich, then put on a prop with the same pitch, but one inch smaller diameter, then do a short series of very short (10 seconds or so) runs, with a complete engine cooling in between. The small prop allows the engine to turn at the RPM expected later on when leaned out, but the rich setting provides the necessary lubrication. This temperature cycling, in theory, reduces the internal stresses in the metals, and can allow you to break in an engine fairly quickly. At some point, they put on the flying prop, run the engine a bit more, and that's it. But you can also wreck your engine if you do this wrong, and over-rev a new engine. If you want to do this technique, I suggest you read more about it. I think the Jett Engineering website had info on this, and if you search on here or on the RCCA forums at rccombat.com you can find more info.

You can also just do some short runs on the rich side, 2-cycling, but not leaning it way out. A couple of short 10-second or so runs, cooling in between. Followed by longer runs, leaning the engine out a bit at a time, or leaning in then backing out a bit and so on. Usually done with the flying prop.

The key is to avoid running the engine at lower than operating temp for any longer than you have to. No extended rich running, no extended idling, etc.

Wreck your engine?? How? or what goes wrong? I ran an OS 15 up to 24,000+ rpm at break in and it seems to be OK and turns 18,600 with a blue prop?

Depends on the engine and what you do with it. Most likely failure is a broken conrod if you have it set too lean with too small of a prop. Another possibility is a bearing failure on some engines. (never heard of an OS bearing blowing up, but it's possible) When new, there is more friction in the conrod connections than after the engine has broken in. Also, new engines often have burrs or very small bits of metal left over from the manufacturing process. These all go away pretty early on in the break in, but if you don't have enough lube, it could lead to problems.

The smaller engines can generally turn up higher than larger ones as well. So 24k on a .15 is not the same as 24k on a .25.

Although the OS is quite reliable the Irvine 25 is faster and as reliable. A good MVVS wil be quicker than anything else on a mini pipe [ the black silencer ].

IMOH I would not buy an OS for combat in the UK best 15 is the OS CVA best 20 is the rear exhaust mini pipe MVVS and for a 25 I would buy an Irvine.

The unmodified Irvine's that I've seen turn almost exactly the same as the OS's when run on mousse cans. What are you using in Europe for an exhaust system on the OS? If you're comparing the MVVS on the pipe to an OS on stock muffler, well, no kidding the MVVS will turn more RPM. Try putting a mousse can or ultrathrust muffler on the OS. You'll pick up between 1,200 to 2,000rpm.

The Webra .25 puts out noticeably more power than the Irvine or OS on the mousse can.

My advice is to stay away from the Norvel and MVVS for combat. You don't want a combat engine with that type of muffler mount. Your best bet is Webra, Irvine or OS. All three are about the same. Pick one a stick with it, that way you can salvage and swap parts from engine to engine when necessary(and it will be).

Oh, yeah, what Jimbo said about parts swapping. I've swapped parts around on engines several times. Espeically carb or carb parts, but also prop hubs and muffler/pipes.