Cylinder Port Timing

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Port Timing Table

Variator Equipped Transmission

1987 SE 50 83-84 Aero 50 85-87 Aero 50 88-93 Elite SA50 94/2001 Elite SA50 Urban Express NU50 1982 Express Sr NX50
BBDC Exhaust Open 78 71 76 80 79 67.5 67
ABDC Exhaust Close 78 71 76 80 79 67.5 67
BBDC Scavenge Open 57 52 57 56 56 47.5 47
ABDC Scavenge Close 57 52 57 56 56 47.5 47


Fixed Ratio Transmission

Spree 84/85 Spree 86/87 Iowa Spree 84/85 Iowa Spree 86/87 Elite SB50 Elite SB50P 1977-81 Express NC50
BBDC Exhaust Open 71 73 70 71 77 74 65
ABDC Exhaust Close 71 73 70 71 77 74 65
BBDC Scavenge Open 52 54 50 52 60 57 47
ABDC Scavenge Close 52 54 50 52 60 57 47


Port map measurements

A degree wheel may be utilized to generate data similar to above using reference points of TDC or BDC. Another method to mapping port timing is to take measurements of the ports. A piece of paper may be cut, and installed with it's edge at a reference point, such as the cylinder top.

  • Each port is rubbed to emboss the port shape
  • The paper is removed and rubbed with a pencil, charcoal etc to reveal the embossed edges
  • Measurements can then be taken
  • The rubbings are of immediate value in comparing or duplicating a given design.
  • If desired, knowing stroke and rod length (check the web for calculators) this info can be converted back to degrees


Member donaudi provided port info for Mallosi MHR and Polini Corsa cylinders shown below:


Polini Corsa port map

PortMap 1.jpg

PortMap 2.jpg

PortMap 3.jpg

PortMap 4.jpg



Malossi MHR port map

PortMap 5.jpg

PortMap 6.jpg

PortMap 7.jpg

PortMap 8.jpg

PortMap 9.jpg

PortMap 10.jpg

Full thread of donaudi


Author: mousewheels

Measurements: Donaudi


Fabrizi portmap

Member DirtyE mapped a Fabrizi 50mm bore as captured below:

Fabrizi Portmap 1.jpg

Fabrizi Portmap 2.jpg


Full thread of DirtyE


Author: mousewheels

Measurements: DirtyE

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