Hi,
Since a few months I have a CB450 K0 1965, I want to share some info on this bike.
Got the bike with 1533 miles on the speedo, now it is showing 2187 miles. I did two complete dyno runs (one in the beginning), including gas analyzing for both cylinders, and some re-jetting. The second run I did a few weeks, and showed increased power and torque curves (was 21 HP on the rear wheel, but is 32.5 Hp on the rear wheel). It pulls easily to 85 miles / hour, and with a high speed test on the highway it did hit 100 miles / hour (on my GPS 94 miles / hour).
For now, the bike is everything what I expected from it, but in comparison with my cb72 it's vibrating violently, much more then I expected (I lost already one bolt from my taillight glass).
The first run showed 21 Hp, the second run 32.5 Hp. This second run is done in the same climate conditions, and on the same dyno, so both runs are comparable. The 11 extra horse are gained from riding it as it should, moderate (5000 to 6000 rpm) alternated with pulls to 8500 to 9000 rpm for short times. This way the engine isn't overheating, but the pistons and piston rings are braking in nicely this way. I had the feeling that the engine was very, very lazy.
A vid of the first run you'll see here : http://www.flickr.com/photos/40215250@N04/4758364418/
Next to that I have the engine getting used to the much thinner oil (Castrol Power RS Racing 4T / 10W-50), it's also a detergent oil. I cleaned the oil filter before chancing the oil, and I did that again after 250 miles, and again after another 250 miles. As usual (when switching over to powerful detergent oils) some oil seals started leaking a bit, but that says more about the condition of the oil seals. Also the packing material isn't up to the detergent power of the oil, so the dynamo side cover started leaking too (all bad gaskets and oil seals replaced now).
The 43 HP of Honda isn't much exaggerated I think, the transmission, and bearings from these periods are not known for their efficiency, neither the chains. A 10% loss is normal with the old bikes, that would mean that (my) Honda is 38.7 - 32.5 = 6.2 Hp off. I think I will gain another 2 or maybe 3 Hp after 500 miles or so, but I don't see this bike hitting 43 Hp ever, leaving it as it is (standard). Also Honda doesn't give any info how these figures where established, or on what type dyno they used, or climate conditions or..... etc.
The dyno for me is a measurement tool, to see in what shape the engine is, I'm not really interested in max HP or Torque. I'm more interested in how these curves are build up.
The torque curve shows that the max torque is reached at 2700 and around 7000 rpm, but after the 2700 rpm point it falls down at 3250 rpm. This doesn't seem to be that important but this gives away the character of the bomber. First it pulls, then it feels like is doesn't like pulling, and then it pulls again. Maybe this is the reason that you think you need an extra gear.
Before I took the bike out the first time, I knew that the gap between the low gears was a weak point, and in the first rides I agreed with it. After 500 miles I got used to this and with the torque curve interpreted, I ride the bike in a different way, and I'm not missing the extra gear anymore.
Furthermore the air to fuel ratio is shown, and it's clear that the mixture is just right above 4500 rpm to 9000 rpm. When it's getting colder (this measurement is done at 29 degrees Celsius), I might switch the main jet for a bigger one, and put the needles a little higher to stay on the safe side. Maybe it's a little on the rich side, and not fuel economic, but a top-end rebuild is expensive too.
It's the same with the CB72 / 77's, these bikes are all on the lean side, especially in the higher rpm regions. I don't know why Honda did this, but when I look and read old advertisements, the good fuel economics is mentioned often as an advantage .
The big hump in the beginning of the fuel-air ratio curve is caused mainly by the carburetors. Although these are vacuum controlled carburetors, the damping isn't perfect. In more modern vacuum controlled carburetors this bump is less heavy seen. This bump was worse in the first runs, and probably due to friction in the carburetor.
When I got the bike, the first dyno run showed the mixture was lean in the higher rpm regions, and I directly switched to a bigger main jet. Now I understand why there are so many top end issue's with the bomber. The lean mixture is overheating the head, combined with mineral oil that burns away instead of lubricating the cams and followers. The results of that are very predictable.
The curves in the first image are taken while shifting and are showing that the transmission is in perfect working order, the clutch doesn't show drag, and isn't slipping (in this test the used oil is the full synthetic as described before). Maybe the chain and sprockets show some wear (hence the little spikes on the curves).
I hope that these explanations of the curves are helping you out to interpreting the results, please ask questions if you want to know things I didn't mention yet.
I put my bikes on the dyno every year, or every 7500 km whatever comes first, the costs are relative low and the results say a lot about the state of the bike is in and what to do in wintertime. It's better to put the bike on the dyno with moderate temperatures, I personally don't like to measure at these temperatures, and the results are somewhat unpredictable and incomparable. Most of the times I use the dyno in the autumn, or spring, when the temperatures are around 18 to 20 degrees and the humidity is normal.
I tried to visualize the behavior of the transmission in figure 1, having the crank speed at the left and the road speed (in km/hr and mls/hr) in all gears. When compared with the dyno results it is shown that at 2700 rpm the max torque is reached in the lower regions., let’s say the first max torque peak (the second max torque peak is at 7250 rpm).
I also stated that when the torque curve is falling, it feels that the bike loses power, and so you will shift automatically to the next gear, that is at around 3000 – 3500 rpm. And if this isn’t worse enough, the engine starts to vibrate in first gear around 3500 to 4000 rpm, and that doesn’t feel right at all, so shifting it is. And when shifting at 3000 3500 rpm to second gear the engine will do around 2000 rpm, and that's way to low. This shift pattern is the red arrow between the first and second gear.
I have the feeling that the engine runs nice from 2500 to 3000 rpm, below this rpm, the engine behaves like a bad running one cylinder.
Looking at the figure the red arrows shows the automatic shift pattern, when first riding the bike, you’re mind tells you to, because the input from the bike “demands” it. Shifting between second and third and third and fourth gear is given by a orange arrow, becuase while touring, this is acceptable.
I forced myself to behave different on a bomber, this is visualized with the green arrows, it requires a different mindset, and that’s hard when you used to listen to the bike and feel the bike. If I’m in a hurry I shift according to the pattern given by the yellow arrows, the bike accelerates fast and can cope with modern traffic.
If you force yourself to ignore the character of the bike, and use the shift pattern in the figure, you find that the bike is really quick, and that the gap between the first en second gear isn’t that annoying anymore.
But I admit, it’s against the “nature” of the bike, but once used to it, it is a fast bike, and you don’t have to play the clutch at low riding speeds.
Jensen
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CB450 K0 dynojet and why it doesn't need a five speed trans
CB450 K0 dynojet and why it doesn't need a five speed trans
Last edited by jensen on Tue Sep 07, 2010 2:45 am, edited 4 times in total.
assembly of Japanese motorcycles requires great peace of mind (Pirsig)
Jensen, I had a '70 model CL450 scrambler years ago and loved it.
It gave the local 650 Triumphs and BSA's a fit. It was a five speed, and I installed large diameter TT exhaust under the engine. I once gave a ride to a stranded Kawasaki 500 triple rider (broken chain). The Kaw was supposed to be the fastest production bike made at the time. His remark when he got off was "damn, this thing has some torque". I'm keeping my eye out for another one myself. I used to ride mine in the front door and park it in the living room of my apartment when I was in school. When I moved out, there were two perfect K70 impressions in the vinyl flooring......just rambling now Keep us posted and pics.. 66 dream, 78 cb750k, 02fz1, 09 wing
Hi,
Yes, I'm also on the hondatwins forum, just recently, becuase I got the bomber a few months ago. This is a summarize of the thread I started there, maybe also interesting to the people on this forum. But the hondatwins forum isn't so lively as the honda305 forum, I thinks there much more CB72 / 77 and dreams out there then CB450 K0's. It's hard to find lot's of info on these bikes, I didn't find anyone yet who can verify the dyno results I gathered from the runs I did lately. I guess I'm the only one who's interested in the technical background of these Honda's in this way, and like sharing the results on the net. I can find lot's of technical info on highly tuned CB450 engines (team Hansen), including dyno results, but not from standard bikes. Brewsky, nice story, and yes, look at the dyno results and you'll understand why he said that isn't it ? (but I guess you did already) Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
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