Hello!
The MVVS.40 GFS/R engine(6,9mm carb) with standard silencer on a 10x6 APC and 20%castor oil and 0-5% nitro will rew 12700-13200 rpm at sea level using a Rossi 3-4 plug and standard headshim.
On the other hand the same engine using the short
minipipe (there is a long minipipe too)rews apr 16500-17000rpm using a 9x7 or a 9x6,5 APC prop.
The MVVS 6,5cc Q-500 engine( 9mm carb) rews apr 17500rpm on the same propsusing a Rossi 6 glowplug.
If you use the longer minipipe expect more trust at lower rpm (10000-15000 rpm.
If you want low noise, get the super quiet silencer which will also give you better throttle respons.
Better still is to get the new "butterflyvalve carb" from MVVS made for the 3.5cc-8.0cc engines.
MVVS engines are delivered with either a Rossi 3-5 glowplug or a Nova Rossi 5 or 7 or their own cold or warm glowplug. The cold plug are use in the bigger engines (3,5cc and up).
Experience have showed that ENYA 3-4 or OS 8 or a Rossi 3-4 glowplug work best if you run on low nitro contents(0-10%nitro)
So ...what prop do you use? What fuel do you use?

Regards!
Jan Karlsson
Importer of MVVS engines
Sweden