The top dog of Vespa moped kits. This improves further on the D.E.P.S. design with a proper 4-stud cylinder and better exhaust. These are all 12 pin and will fit all Vespa moped frames like Ciao, Bravo, Si, Grande, etc. The new cylinder head design will fit them all.
THIS ONLY WORKS WITH THE 4 STUD MP-ONE CASES. This will NOT work with any other cases.
From Malossi themselves-
The cylinder kit Ø 47 BIG D.E.P.S. 4 MHR combines the best aspects of the Big D.E.P.S. with absolutely innovative and unique features. Designed for all the Ciao, Si, Bravo, Boss and Grillo mopeds, it is at the top of the range of the already extensive family of tuning kits for Mopeds. The drilling, unlike the other components in the range, involves fixing the cylinder exclusively to the Malossi MP-One casing by means of 4 studs thanks to which, in addition to distributing the forces during operation in a much more efficient manner, our technicians have finally created an exhaust that is perfectly centered with the axis along which the entire washing process develops, with, at the same time, a much thinner and profiled crosspiece.
- Material: primary aluminum alloy with a high content of tempered and stabilized silicon.
- Exhaust flange connection.
- Updated intake ports.
- Completely centralized exhaust port with re-profiled crosspiece!
- Single ring piston.
- New annealed aluminum head gasket.
- Fixing to the casing with 4 studs!
- Completely redesigned head.
- High precision coupling between head and cylinder thanks to an external centering.
The cylinder draws its peculiar characteristics from the BIG D.E.P.S. range: the same aluminum alloy, barrel with nickel-chromium coating, the same redesigned central core and identical ring washing strategy. The support surface in the front part of the cylinder continues to be worked with high precision diamond tools and has 4 holes for fixing of the exhaust flange. The result has translated into a further and significant increase in performance! Finally, the most reliable and safe strategy of coupling and centering between cylinder and head has also been applied to these cylinders: external centering! Using this technique, the same used in our range of racing cylinders, the relative centering of the two components is obtained thanks to a high precision coupling created on a diameter external to the cylinder fixing studs. This strategy is successful because it does not require any interface component, such as, for example, bushings, and moreover, being created on a diameter external to the studs, it can be used to exploit areas of the cylinder normally free from further tensions, typical of the geometry close to the barrel, where combustion takes place, without dangerously overloading the resistant structure. The position makes the machining more agile and allows greater precision of the couplings.
For the correct sizing of the entire cylinder kit, our technicians have designed a new version of the historic Ø 47 piston equipped with a single sealing band, also created with ultra modern technologies. The single band is used to maintain the same standard of sealing and pressure insulation, but with lower friction, all to the advantage of performance and durability.
The exhaust outlet uses the same strategy as the other versions: a steel fitting with housing for OR fits into the seat created in the cylinder and is held in position by a flange also in aluminum, made by high precision laser cutting and fixed with 4 screws. With this system, no matter how much power the engine can produce, our exhaust will not unscrew and will not fail even in extreme conditions!
An absolute novelty: the detail that makes the new cylinder kit even more unique! The Malossi technicians have invested a great deal of energy in creating an innovative head with unique features.
- Profiled fins to channel the flow of cooling air and to make it flow along the hottest surfaces, thus optimizing the heat exchange and, consequently, the outflow of heat from the combustion chamber to prevent dangerous temperature levels from being reached.
- An additional lateral fin to direct as much heat as possible from the combustion chamber towards the outside of the cylinder and to maximize every fin, including the external ones, further away from the heat source and therefore less efficient and less involved in the disposal action.
- A central radially strengthened structure, starting from the center of the combustion chamber, to significantly increase the general resistance of the structure itself and to contain the deformations due to elongation of the aluminum at engine operating temperatures. By decreasing the deformations, the contact between the head and the cylinder is always and constantly on one level and guarantees insulation of the combustion chamber from the external environment, eliminating any possible source of outward loss or leakage.
- A spark plug perfectly centered in the combustion chamber. By centralizing the spark and keeping the entire washing chain (intake and exhaust ports) symmetrical with respect to the cylinder and directed along a single axis, without damaging curvatures of the flow of fresh and burnt gases, an exceptionally regular combustion was obtained, developed in a straight line across the top of the piston crown. The higher performances, due to optimization of the washing, trapping and combustion performances, have been coupled with optimization and an optimal distribution of the stresses derived from both the pressure of the expanding gases, and the inertial forces of the crank mechanism kinematics, better tolerated by the supporting structures of the engine.
- In the lower part there is an additional fin which, facilitated by a fin extended to the opposite side to create a bulkhead, is able to channel the flow of air towards the finned part. This solution is used to exploit every surface of the head, directing the heat flow away from the combustion chamber.
- Domes adequately sized and integrated into the geometry of the head with a surface for supporting the fixing nuts machined in order to obtain surfaces with low roughness.
- The old fastening system with nuts and washers has been improved with the use of modern flanged hex nuts which are much more comfortable and functional.
- The central dome houses a flanged hex head screw with which the valve lifter for the decompressor supplied in the kit is fixed.
- A groove created in front of the seat for the valve lifter and a stop integral with the structure of the head, located in the rear part, allow the housing and correct fixing of the cable for handling of the decompressor on the Ciao, "Si” and "Bravo” type vehicles.