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Low Redline, Why?

22K views 27 replies 11 participants last post by  Thump 
#1 ·
Something has dawned on me. The CB 500 line was aimed at the 47 horsepower limit of the learner class European market.

I thought it odd that the limit of the engine was only 8500 rpm. Other parallel twins have much higher red lines.
So is this how Honda has restricted the HP?
And could we get more hp out of this bike with an aftermarket ECU which would allow for more rpm?

I understand that a manufacturer considers the mechanicals of a motor when it sets the red line but I don't believe this is the case here. Any modern MC engine is more than capable of 10,000 rpm.

Has anybody ridden the CB above the factory limit?
 
#2 ·
Actually it's 9000 or 9100 stock. I raised mine by 500 after @tothezenith told me about the rev X-tend feature on the PCV. But yeah, Honda really neutered this bike, in typical Honda fashion. It can certainly be pushed more, but I suppose this is why Hondas have the reputation of "lasting forever"....they over-design stuff for reliability and longevity. tothezenith is getting like 56-57 hp at the wheel out of his 500. I need to get a custom fuel map for mine after I replace my exhaust and get a different air filter, then I'll see what it puts out. It won't be as much as his, but I'm hoping it will be in the upper 40s at the wheel.
 
#4 ·
So is this how Honda has restricted the HP?
this is how honda makes the engine almost bullet proof!

if you look at the 2012 nsf250r aka moto3 racer, it produces the same amount of power as the 500s @13k rpm, but the engine has to be rebuilt every 2k km of racing.

so it's actually a sacrifice of power to get longer engine life.
we can actually get a little more power and a little shorter engine life.
 
#5 ·
All engines are made like that, because despite being sport bikes meant for racing, manufacturers know that the majority of the people who buy them will buy them for street riding, and the great majority of people don't want to spend thousands of dollars rebuilding engines every year. Even the 600s typically put out around 110-115 hp at the wheel these days (stock) at best, but in WSS they build them up to where they're putting out about 150 hp at the wheel...but they also go through a few engines in a season. The Moto 2 bikes, although custom for the most part, they all have CBR600RR engines on steroids in them. The Moto 3 bikes are 250s (not sure what configuration, but I don't think they're twins) and they're pushing close to 60 hp at the wheel!
 
#6 ·
Yes, I'm not going as far as Zenith but was just wondering about the electronic approach along with the standard exhaust and filter mod.

I'm mechanically sympathetic and seldomly take my bikes near the red line though once there it's amazing how smooth they are.
 
#10 ·
An economy engine with a relatively long stroke (the CBR500R has a 66.8mm stroke; compare with the CBR600RR's 42.5mm stroke...) is going to equate to a low redline to keep mean piston speeds below the threshold for more "exotic" (read "expensive") engineering.
 
#13 ·
My thoughts are they cut off the HP at the appropriate level with the electronics for the beginner class.
I believe for high rpm action a special spring or springs are used which resonate (?) differently at higher RPMs. Not just a stronger spring.
In the end I'm concerned with high mileage reliability.

I wish they would use hydraulically adjustable valves like they did in the 750 Nighthawk engine.
Does anybody know what the red line in that one is? I think it's around what our engines are.
 
#14 ·
I have a 95 Nighthawk 750 and the redline is 8500 too. My 500 cuts at 9000rpms, or so, but I haven't tried that on the 750 yet, not sure how that works on a carbureted model. I will say the 750 has 58,000 miles, still runs like a champ and I love those hydraulic valves.
 
#15 ·
I would settle for a lower power for the hydraulic valves but only on a larger more powerful bike such as the 750.
But I do enjoy the beasty power of my ZRX which is a shim adjustable valve train. It has finger followers which move to the side to get at the shims so you don't have to remove the cams or the followers themselves.
 
#18 · (Edited)
You are thinking of exhaust resonance which only affects two stroke reed valves.
4 stroke valve speed depends only on the strength spring, the weight of the valve and exhaust pressure.

High rpm and engine life are always a compromise.

Going by the feel of the engine, I don't think the engine is restricted much at the higher rpm, but I would expect more torque out of it down low, I've had 125s with more torque below 4k rpm.

That may be to stop learners spinning out at lights.

End of the day, it's a cheap bike, not much new technology or R+D on it. But it will last.
 
#19 ·
Nah, I'm thinking about sympathetic somethingorother something. It's been a long time since I took mechanical engineering.
Oh, I forgot, I never took it at all :grin:.

Notice the double springs on one side. This is a BMW engine. I'm really surprised to see the cam followers as they add a lot of mass. I think the new R1 uses them as well. My ZRX has them.
https://youtu.be/nsa6kq-qqIE
 
#20 · (Edited)
You're right about spring resonances: Seat pressure is important but at certain engine speeds the excitation of the valve spring by the cam can set up standing waves in the spring itself and the seat pressure can fall dramatically; at that point, the spring has lost control of the valve.

You can get a feeling for the phenomena looking at this video:



and



Older techniques to control this include dampers inside the spring and multiple-springs with different resonance characterstics. Some modern valve springs have different pitches along their length, beehive winds and other techniques to produce a spring with minimal tendency to resonate badly at any one point within the expected operating RPM of the engine.
 
#22 ·
Which model was it?
 
#24 ·
even with the raised rpm, it's only netting increased engine speed, as torque states declining around the 8K mark even with my mods.
Stroke is one aspect, also relatively low compression (for a bike) is another factor for lower rpm cut off; both also a positive point for engine longevity.
I'd be inclined to think the valvetrain from the bike would be able to handle quite a bit higher rpm given other factors addressed. Given most of their bikes are higher revving, I'd imagine economies of scale would supersede cheaping out on valve springs that'll only 'just' do the job.
Even then, Honda is known for a fairly high threshold, so an additional 15% raise to even 10500 would still be within scope; though not much point unless one can do mods to have the torque curve still strong in the upper revs.
 
#27 ·
Honda does want to keep their reputation for reliability for sure but to be honest I'm perfectly happy with the way it is.
But also I wouldn't mind the extra HP your bike has. Can't help it.

Maybe someday somebody will come out with a big bore kit. They have to, they do it for scooters for cry eye.
 
#28 ·
It's all about what the customer wants - a 750cc engine, for example, could make 60 horses at 6,000 rpm or at 12,000 rpm, that's up to the engine developers. A higher revving engine usually has a bigger bore and a shorter stroke, otherwise a too high piston speed would result into vibrations. That's why long-stroke cruiser engines have a lower rev ceiling while short-stroke Ninjas have way higher ones.
Personally I prefer low revving engines with more torque, they simply handle city traffic better. I don't like to rev a bike to get to the power which is somewhere between 8,000 and 14,000 rpm.
Of course there are lots of other factors at play.
The NC750S has a lot of grunt down low, the redline is somewhere around 6,500 rpm and that would be just fine for me. I don't like to wring out an engine so that it screams at 12,000+ rpm. Lower revving engines are also more economical.
But check out this video and hear the rider change gears at low revs:
 
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