CB 350 2-2 vs 2-1

teazer said:
180 cranks make less low end than 360 (degrees)so maybe they wanted more traction or pulling power. A friend of mine ran a CB72 as a 360 but as a twingle. Don't ask me why. :) Dream 305s were 360 of course. Haven't heard of a 360 degree 350 or a 350 degree 360 if it comes to that. ;-)
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180 Cranks only have a rocking couple vibration, compared to a 360 with both piston masses going up and down together. The CM400/450 etc put a balance shaft in to handle the increased vibes of the 360 crank.

Twingles are even a little worse for vibration with both pistons on a power pulse..... But they are good for traction in the dirt....
 
Just curious if anybody knows for sure, but i was thinking that since the 350 crank is a 180 degree crank, the uneven exhaust pulses would make the 2 into 1 unable to fully take advantage of exhaust scavenging. One cylinder might benefit a little while the other cylinder might even suffer.

just a theory, could be crap. ::)
 
Yep, uneven exhaust pulses can really hurt at certain rpm
2:2 is best for max high rpm power
 
I would (and did) stick with a 2:2 system. But (someone correct me if I'm wrong) it would make sense that a 2:1 system would still be the best performance option provided that the headers were of unequal length (or diameter).

The idea would be that the pulses would arrive at the collector at the same time. The left header would need to be longer and/or larger in diameter to make this a reality. I suspect this goal is what helped design the CJ exhaust, which is a stock 2:1 system. You'll notice that the CJ's headers are larger in diameter than the other 360 variants and that the collector is located on the right side of the bike, necessitating a longer header for the left cylinder.
 
Sonreir said:
I would (and did) stick with a 2:2 system. But (someone correct me if I'm wrong) it would make sense that a 2:1 system would still be the best performance option provided that the headers were of unequal length (or diameter).

The idea would be that the pulses would arrive at the collector at the same time. The left header would need to be longer and/or larger in diameter to make this a reality. I suspect this goal is what helped design the CJ exhaust, which is a stock 2:1 system. You'll notice that the CJ's headers are larger in diameter than the other 360 variants and that the collector is located on the right side of the bike, necessitating a longer header for the left cylinder.
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The CJ had larger diameter pipes? The engine ports are the same.... That is interesting if you are correct (not doubting your veracity). I have a MAC (over 30 years old) that has 2 into one. the OD is the same as stock , but the pipes are single wall. In addition, the bending and routing are made equal. If you look at my build pictures, you can see I exit on the left, and the pipes are routed to equal lengths.

I have no dyno tests, but I can tell you that performance was better then stock. However, the ID is larger, so maybe I don't have all the performance available, but it is definitely better then stock. A fast start in first gives me a little wheel lift (no wheelie, just an inch or so). the stock system did not have that kind of power at all.

Still, it runs out of breathe about 8k RPM or so, and maybe the 2-1 system is exascerbating the high end power delivery.

My future plan is to use the MAC 2 into 2, so I may have a back to back review when that happens.
 
Thinking about it a bit more, the Cl has unequal length pipes with the right pipe being longer.
The 2:1 on Brendon's bike has a longer right pipe as well, that made 40bhp on my 378 motor
Maybe the right pipe needs to be longer for max power? (counterintuitive but seems to work)
 
crazypj said:
Thinking about it a bit more, the Cl has unequal length pipes with the right pipe being longer.
The 2:1 on Brendon's bike has a longer right pipe as well, that made 40bhp on my 378 motor
Maybe the right pipe needs to be longer for max power? (counterintuitive but seems to work)
Click to expand...

Actually... that makes a bit more sense. Firing order is left and then right, correct? Delaying the pulse from the right cylinder would make for an even distribution by the time it got to the collector.
 
Ignore the discussion on a CJ360 which had a power curve as flat as a witches tit. That 2 into 1 pipe was just a style thing for a very boring motorcycle IMHO. :)

Race bike 2 into 2. End of story. :)
 
teazer said:
Ignore the discussion on a CJ360 which had a power curve as flat as a witches tit.
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Are they flat? How are you sure of this?

Mixed metaphore here....The saying is "As cold as a witches Tit" I never heard anything about flat... ;D
 
It's common in Britain, used to describe lots of flat stuff ;D
Flat as a fart is another one ;)
 
Flat as a Dover Sole if you prefer :) I don't think there are any mixed or confused metaphores in there but I could be wrong.

Now had I said "flat out like a lizzard drinking" you'd know I was on a hiding to nothing and telling porkies if I said that was the same thing. Well oiled beef hooked as a mate of mine used to say......

As you can tell, I was using a colloquialism to suggest that the CJ was not overly endowed with power and that the exhaust was unlikely IMO to be very scientifically designed to boost power at particular RPMs. A most disdainful comment, I have to admit.

I was brought up with the CB72 and 77 and the CB250/350 that followed were soulless and the were followed by the even more woeful 250/360 and the CJ was shameful. How low had Honda sunk over a few short years? And I have no intention of letting facts get in the way of a good story ;-)


I could have just said - flat as a stale bottle of piss, but that needs more translation than the image of a skinny flat chested witch. :)
 
I think the CJ exhaust was designed to make you fall down, don't think I knew anyone who hadn't accidentally had it lift rear wheel?
Eve though I like the engine design, I must admit they really were a total turd before being worked over
 
I'm pretty fond of my PJ special CJ378 and the pipe hasn't killed me yet :)

Need to post a video of it, its a right mean bastard


_MG_9683_1.jpg
 
For now I bought some megaphones im going to strip the packing out of and run on the stock pipes,

Going to look into building something lighter, with better flow from the head after I port it, but for now its out of my budget.
 
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