Kelly,

Noise regulations would explain this, but only half the way.

When MVVS designed their larger glow engines (.61-.91), they intended them also, to be used for low RPM, low noise operation.
So they used a 15mm o/d crankshaft (like the OS.46FX/AX and much smaller than most high power .40-.53 engines, not to mention other .61-.91 engines), with a small gas passage, modest timing numbers and relatively small intake bypasses, to maximize low RPM torque.

Their tuned exhaust systems are likewise tuned for the below 10K to 13K (.61 - 12K for the .77 and 11K for the .91) RPM range.

And they do excel with very large props in the intended, low RPM range (the .61 out-revs the OS.61FX, on a 14x6, by 2,000(!!) RPM).

Even if you cut their header down, the engine's design would not allow it to make Rossi/Picco/OPS/YS/Jett type, 14K++ RPM power.


The OS.46FX/AX are still rated at 16,000 RPM, yet are intended to spin, as they come from the factory at only 10,000-10,700 RPM?
Isn't there something wrong here? Shouldn't they have been designed to maximize their low end power?


The AX is new (but utilizes many FX parts). This is (was?) a great chance to redesign the engine for its intended, low RPM purpose.
Yet OS failed to do so.