I've got a 1979 Honda CB650 motorcycle that I would like to rebuild to increase my engine's efficiency. It's got a classic Hemi-shaped chamber (a nice big dome), with 2 valves per cylinder. The ports look decent to my eyes, but I have virtually no hands-on experience with porting. I know the downfalls of the hemi chamber and the slow-burn characteristics of the head. I don't know how to correct these downfalls, however. And here's my question. What can I do to this chamber to be able to run higher compression and get a faster burn? I won't be able to replace pistons, as there are no aftermarket options for this engine. I may be able to deck the cylinders, shave the head, and do some mild porting if I can see what the ports
should look like. However, being a poor college student limits the amount of money that I can spend on the project.
Engine: Air-cooled, 8-valve, SOHC inline-4
Bore x Stroke: 59.80 x 55.80 mm (2.354 x 2.197 in.)
Capacity: 627cc (38.2cu-in)
CR:9.0 : 1
Carburetion: 4 Keihin PD50A or PD50B Mechanical
Ignition: CDI (Capacitor Discharge Ignition)
I'm going to try to incorporate the carburettor mods that David mentioned
here. It has 4 Kei Hin carbs.
I will also incorporate
PowreLynz and
Surface Turbulence Valves to help with fuel vaporization. I might try
Metric Mechanic's Grooves to further increase chamber turbulence, but I worry about the depth, width, length, and all things that are unknown about this particular mod.
I
may be able to incorporate
Singh Grooves if the piston sticks out of the cylinder far enough to create some squish around the perimeter of the chamber. This area will be very small, however, so gains will probably be minimal. But adding a lot of small changes can add up to one big change.