Topic: Oil pressure at 2k rpm on oil cooled motors.

[yesplease]

Would there be enough oil pressure for cooling/lube if an oil cooled bike were geared to cruise at 55mph/2000rpm instead of ~6000rpm? Specifically I'm wondering about a CB650SC, but I'm guessing other oil cooled bikes would be similar.

[merc2dogs]

 seriously aiming for some mileage there?

I don't think there would be a probl;em with the oil pressure, it works fine at 200rpm in town.
 I think the issue would come down to having enough power at 2000 rpm to hold 55mph, a hill or headwind would kill ya.

gearing for that RPM would mean long runs need for getting up to speed, making the bike about useless for town driving.

Ken.

 

[yesplease]

Definitely. In terms of utility, it's no problem imo if I only top out at ~100mph on flat ground, and 70mph going uphill into a head wind, but if I could get the bike's engine out of that ~1000-700g/kwh SFC area, I should be able to see some huge improvements in efficiency. Granted, if I go too far, it'll just be slow, but I figure having half throttle at ~75mph would be a good compromise. Ideally, this would be a very tall OD gear, and the first four would remain the same so off the line it'd be just like a stock version. Thanks for the info btw!

[mlinder]

cb650 makes about 9 HP, 20ish lbft at 2k rpm.
That MIGHT be enough to get you to 55mph. I kind of don't think so, though.

[Gordon]

I don't even think you'd be able to get the bike moving with that kind of gearing, unless you were facing down a pretty steep hill.  Also, wind resistance will probably prevent you from reaching 55mph because the engine wont be making enough power to overcome it. 

[mlinder]

I was also under the impression that these bikes didn't start charging the battery until about 3k rpm.

[yesplease]

Regarding the charging, I think the 84s were better, but who knows? I figure I can really cut down on current use w/ LCDs and a newer headlight, or maybe even go the other way and grab a larger battery.

1984- Minor changes only in 1984; the alternator design was improved to provide a little more charging current at idle and low speed

In terms of power, assuming the motorcycle has a Crr=.65 then I should only need ~6hp at 55mph. Of course, it could be worse, but I would hop not considering Semis have Crrs=~.4-.6. In any event, cutting the power needed at a given speed shouldn't be much of a problem, if I don't mind it looking different. And like I said before...

Ideally, this would be a very tall OD gear, and the first four would remain the same so off the line it'd be just like a stock version. Thanks for the info btw!

[merc2dogs]

only way I can see to do it without massive engineering is to use a jack shaft with a sliding dog clutch, one way to direct couple the I/O sprockets, other way through planetary gearset from a car automatic at 1:2 maybe 1:3

 sure there are other ways, interesting excercize though, got me curious may draw up a few ideas.

ken.





 

[yesplease]

I had a fire lit under my ass after I saw this write up. I dunno how much machining and fabrication would be required, but I'm gonna pull apart a spare transmission I have and find out. There's also converting to FI and running lean, or maybe even cylinder deactivation too, but this seems to be the best bang w/o busting my balls.

[mlinder]

Most unfaired motorcycles, with a rider, have a CD of something in the .8 to 1 or higher, range.

[yesplease]

So they literally have the drag coefficient of a brick? At least there's plenty of room for improvements... 

[mlinder]

So they literally have the drag coefficient of a brick? At least there's plenty of room for improvements... 

That's correct. With all the nooks and crannies to actually catch air, as well as the irregular rear end throwing all the already turbulent air willy nilly,it can be worse than a flat surface.
Remember CD isn't just a function of of aerodynamics, its aerodynamics + frontal area.
A hayabusa has a CD of mid .5's with a rider (.55, .56, rider tucked in). A naked 650.... well, yeah.

[yesplease]

I think you mean CdA.  Cd's just a function of how well something moves through the air iirc.

[mlinder]

I think you mean CdA.  Cd's just a function of how well something moves through the air iirc.

Yes, sorry.
Still, youa rent going to get that 650 anywhere near .65 without crazy aero. Suzuki spent a lot of money streamlining the hyabusa.

[yesplease]

Yeah, it'd need to be decidedly streamlined, but I'm pretty sure ~100mpg and functionality could be possible w/ the right fairings/gearing.

[mlinder]

Yeah, it'd need to be decidedly streamlined, but I'm pretty sure ~100mpg and functionality could be possible w/ the right fairings/gearing.

If it was enclosed, yes.
Then you run into trouble keeping the engine cool. And it really isn't much of motorcycle if it's enclosed, other than it has two wheels.

[yesplease]

If it was enclosed, yes.
Then you run into trouble keeping the engine cool. And it really isn't much of motorcycle if it's enclosed, other than it has two wheels.

Well, everyone's version of what is and isn't something varies, but semantics aside, there are huge gains from even partial fairings. 100+mpg highway is np from a sleek design. having a nose that will allow for a relatively even pressure differential and a decent approximation of a boat tail to avoid the low pressure area behind a bluff body. Even in bicycles this is seen on trikes. Routing the exhaust helps to fill in that area and detach flow farther away from the vehicle. I suppose I could go balls out with a fully enclosed version, but after ~100mpg, the fuel savings really dwindle. No need for some 500mpg streamliner. $300 versus $50 isn't nearly as big of a jump compared to $600 versus $300, and the initial jump isn't as extreme.