360 to 180 degree crank

pieeater · Post by **pieeater** » Tue Feb 17, 2015 6:15 am

Why did Honda make two engines so similar.
Is one smoother and one faster?
There must be some reason.

hondauser · Post by **hondauser** » Tue Feb 17, 2015 7:00 am

hi ;

the answer is in the question !!!

the smooth for the utilitary C77 and the CL77

the fast for the sporty CB 72/77 !!!

pieeater · Post by **pieeater** » Tue Feb 17, 2015 8:23 am

I can see why the ca77 might be smoother firing every second stroke but I fail to understand how the cb77 firing on two stokes then missing on two strokes develops more power.
please enlighten me.

G-Man · Post by **G-Man** » Tue Feb 17, 2015 11:32 am

The CB series was designed as a more powerful engine with two carburettors (and inlet ports) and more sporty cam profiles. The 180 crank makes it a little smoother mechanically but gives the odd firing order. The engine revs a little higher too.

The CA77 has only a single (small) carburettor and the 360 crank is mechanically less smooth but has an even firing interval.

Just to complicate matters Honda made 360 crank CBs for some markets. You're right that the crank spacing doesn't actually make more power in an engine that is otherwise identical. If you cut the engine in half the two halves would behave identically.

G

OldScrambler · Post by **OldScrambler** » Tue Feb 17, 2015 5:47 pm

Based on a LOT of reading and insight from active and past racers, both road and dirt, the 270-degree firing cadence of the CB and CL cranks (and hundreds of others including H.D. XRs) provides a distinct traction advantage and possibly transfers more power through the tranny.

Like G-Man said.........it allows the motor to rev higher and I will add that it also allows a high-performance motor to start easier.

pieeater · Post by **pieeater** » Tue Feb 17, 2015 6:24 pm

mmm I can see that the cb engine would have better balance with one piston working on the opposite stroke and therefore have the ability to rev higher. Cant see why it would have better traction though.

OldScrambler · Post by **OldScrambler** » Tue Feb 17, 2015 9:25 pm

Its not opposite...............piston #1 fires near TDC...........piston #2 fires when #1 is near BDC. Then there is a long pause before the next firing sequence.

BTW.........a performance cam (Megacycle) and a custom extended intake manifold to adapt a 28mm carb (from CB750) will make a CA model perform very sprightly.........but no better than a stock CB.