Hi, I had been thinking what would limit max engine rpm ? I have a rcmk evo with a 1mm stroker crank lightend piston increased compression, the engine has also been blueprinted to match all parts so there's no overlapping of parts, it also has a tuned length on the exhaust of 300mm the carb is a walbro wt 1048 the inlet duration has been increased.
I seem to have reached a barrier at 16080 rpm. Thanks

It would be very helpful if you knew what durations your ports are open for. Pick up a degree wheel so you can measure them. After you are sure the port time is decent enough, pike up a QD hot pipe and enjoy over 18,000 RPM.

Before considering if any engine can be pushed to higher RPM's, a determination should be made as to; can the engine in question survive mechanically at the higher RPM? The only way to determine the RPM limit is to run the engine faster & faster until something fails. Many posts on other sites clearly indicates that sustained RPM's approaching 20,000 + can cause bottom end roller assembly failures such as blueing & retainer breakage, no matter how much or what type of lubricant is used.

Modified bottom end roller assemblies available from some engine manufactures can raise the RPM limit to 22,000+. Higher sustained RPM limits, 24,000+, require re-engineering of the standard bottom end roller assemblies used, including; the retainer's design & metallurgy; the connecting rod's design & metallurgy; the crankpin's metallurgy & the total radial clearance amount.
Jim Allen

I would listen to this guy. It's not going to do you any good to get higher RPM if you start breaking parts

.Ok thank you I think i'll leave it at 16000 rpm

Well Jim is right for substained high rpm - most of my Zens and MK's will run to 18,000 all day long will no issues

Not saying thats where they run all the time but 18 is usual for a slightly modded Zen or MK - I don't have much stock stuff

Beyond that is stretching it unless it's a Quickdraw

A stock G290PUM with the quick draw pipe should do way better than 16,000 rpm all day long. You might have to play with the coupling length of the QD pipe a bit, but that pipe likes to drag out more RPM from engines. That pipe is so good IMO, it has made many Zen engines with poor porting work pretty good. The Zen engines can hold up to 18,000 or 19,000rpm's IMO, with no reliability issues at all if a good oil is used.

zenoah 26 and 30cc engine with porting only on cylinder. what is the max of top RPM we can get?
can we reach 20,000?

We've run 26 cc Zenoahs over 20,000 on our dyno, but whats the point? The peak power comes around 16,000 rpm ant there's almost none above 20,000 rpm for the best mod engines. . Our Quickdraws would run to 25,000 rpm and still have some power. That's because they have considerably wider ports, especially the intake port. Zenoahs have serious intake port restrictions so increasing the duration over stock pays big dividends.

Durability of the stock rod big end starts to be an issue over 20,000 rpm. Our Quickdraws had factory modified rods and would run reliably, at least for SAW durations. The M&D cast cylinder engines will also turn over 20,000 rpm with reasonable power, but the stock Zenoah rod big end bearing won't last long. The only gas engine rod failure I've ever had was on an M&D cast cylinder engine. The same was true for a 30 mm stroke, 36 mm bore engine rod bearing. It turned blue after a very short period. The solution was a 5 mm longer rod. Even so, I would not expect long life from a rod and crankshaft that was designed for under 4 hp weadeaters that turning less than 10,000 rpm.

Lohring Miller

Lohring, if there is possibility to increase intake width, how width it is needed?