here is what Malossi.com says about them...
The replica:
MHR REPLICA CYLINDER KIT
The MHR Replica line of cylinder was created especially for the International Scooter Trophy * 70cc Automatic Class. These cylinder kits were designed to guarantee maximum performance in this category, while at the same time assuring extremely long product life.
In order to guarantee these special characteristics, Malossi MHR Replica cylinder kit have pistons with two chrome-plated rectangular segmants and a compression ratio of 13.8:1, plus torque value of 7.35 N.m. (o.75 Kgm) at 8.000 rpm and power of 6.6 Kw (9 C.V.) at 8.500 rpm.
The MHR line is the results of Malossi's many years of experience in European and National competitions. These new cylinder kits are composed principally of cylinder- piston * ring * head.
The MHR cylinder:
ALUMIN-CYL. KIT Ø 47 pin Ø 10 MHR
TECHNICAL FEATURES cylinder kits
CYLINDER
- Material: special aluminium alloy with high percentage of silicon and titanium that guarantees exceptional strain strength even at high temperatures.
- Heat treatment: special quenching and stabilizing treatment that gives the material increased toughness and strength, guaranteeing that mechanical and size specifications will remain unaltered for temperatures of up to 250 °C.
- Chip-forming machining: carried out on NC machining centres with extremely-limited size and shape tolerance (roundness, perpendicularity).
- Inner surface coating: effected using silicon carbide on a nickel matrix with heat treatment that guarantees extreme hardness (around 600 HVO, 1/5) and excellent resistance to wear.
- Internal machining of cylinder: using special machines that allow a degree of finish on the cylinder barrel walls whose roughness corresponds with the angles set at the design stage (grinding process using special stone).
- Port and exhaust diagrams: designed and manufactured especially for racing. The definition of the port and exhaust diagrams has requested considerable effort on the part of our engineers both on engine test stands and the circuits on which the trophy is held.
PISTON
- Material: special aluminium alloy with a very high percentage of silicon and titanium that guarantees both excellent heat resistance and strain strength upon temperature variation.
- External coating: graphite coating that guarantees a very low friction coefficient
- Structure: reinforced in order to offer resistance to the stress suffered by cylinder units used for top-level competition, but at the same time light enough to reduce inertial force.
- Ring: 1 mm nodular-cast-iron single ring with rectangular cross section and hard-chromium coating on outer surface.
PISTON RINGS
- Rings in very strong modular cast iron with ground, wear-resistant, hard chrome metal-spray coating on the contact surface.
HEAD
- Material: special alluminium alloy with a very high heat exchange coefficient.
- Geometry of heat exchange surfaces recalculated and increased.
- Combustion chamber completely-designed to obtain a high compression ratio (15.8:1) with a very high turbolece.
- Machining: numerically controlled machines.
obviously the actual MHR kit is a better kit... however you are paying the additional money for it as well as apparently there is more issues of them lasting longer due to the tighter clearances on them and higher compression...
I went with the MHR Replica due to not having to change the stock crank... however I can't find the part number for it, but it appears there might be a MHR kit that is set up for the 10mm stock crank... Water under the bridge... anyway...
The compression is 13:1 on the rep and 15:1 on the mhr... so higher compression by far... then again the stock motor is only 8:1 or something like that... Get a kit w/ a head
