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Old 07-27-2012, 06:54 PM   #1 (permalink)
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In-Line or V-Twin As Basis for Streamliner

After riding with the MPG pioneers at Mid-Ohio I've decided to get in on the fun and one of the bikes I'm considering is the Yamaha 250 V-Twin that's been around since '88. This pretty much insures parts availability for a long, long time and while not as simple as a thumper it's long-stroke motor delivers some incredible mileage in stock form. It's as narrow as a thumper and it's riding position is already there for a feet-forward setup. The single carb setup is nice and simple to work on as well.

There's a line of thought that says streamliners ought to be water cooled. Can air cooled motors survive with proper ducting of cooling air, especially one with a rear cylinder that's going to get a lot of heat from the front?

While we're discussing air cooled motors another possible candidate is the small Honda 185-250cc twins. They too use a single carburetor, deliver great mileage stock and at least in my mind might be easier to cool than a V-twin. The 185 & 200cc versions of these motors used breaker point ignitions, too which appeals to my flat-world Luddite mentality (I'm not a big fan of black boxes that work on the "FM Principal" and leave you walking when they quit).

Another consideration is that all these bikes are available for pocket change around here.

Anyway I'd appreciate your thoughts about these bikes and how they might work for such a project.

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Old 07-27-2012, 08:52 PM   #2 (permalink)
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I played around with a 1995 CB250 nighthawk. It might as well be thought of as a 1960's bike, old school technology. Ambient temp in TN gets HOT. I found the same thing Alan did = air cooled motors will overheat unless you have some extra way to cool them. Once shrouded you will need extra fans to get the air across the cooling fins. The little motors don't have much electricity to spare so will have to watch amperage draw if you use auxiliary fans.
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Old 07-27-2012, 09:19 PM   #3 (permalink)
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I just found that the 185-200 Twinstars are 6v. motors. Much as I like simple motors a 6v. system ain't gonna be for me. That leaves the 250cc motors for consideration.

Any pictures of the bike you built from that '95 Nighthawk, TedV?
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Old 07-27-2012, 09:34 PM   #4 (permalink)
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In the end all motors transfer the heat to the air. John Bradley in his book The Racing motorcycle points out that an air cooled engine can get more than enough cooling with proper ducting. However under fuel economy contest conditions that would have to be tested, to conferm. I am of the opinion that and air cooled engine with an oil cooler that could be enlarged is a good candidate with proper ducting, however I have not demonstrated this myself so it is nothing more than a two bit opinion. What ever the cooling system; ducting is the key. One area that I have noticed is that in stop and go trafic even a liquid cooled engine heats up and the cooling fan comes on, this would suggest that an over sized or expandable sytem would be advised. one of the big cooling problems with behind the front wheel radiators is the large wake caused by the front wheel even inside a dustbin fairing, this suggests that in order to assist cooling the front fender should cover as much of the front wheel as posible even inside the fairing. An even better option is to duct the hot air into the wake behind the bike.
Some form of duel sport bike with a radiator high and on the side mit be an other idea, so that the radiator can be moved around... to optimise cooling.
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Old 07-27-2012, 10:28 PM   #5 (permalink)
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The whole purpose of your streamlining is to decrease the load on the engine. Then you lower the final drive ratio to increase speed at any given RPM. The same amount of work done by the engine gives you a greater speed. Based on that it seems obvious to me you will have higher velocity air to cool the engine and aerodynamic bodywork to reduce the CD. While water cooled engiens may have a coolant stability advantage, air cooled engines have no cooling system other than fins. Many may consider this their only cooling but oil cooling also helps the air cooled engines and some have greater oil capacity to assist with oil cooling. Obviously the addition of a separate oil cooler would improve cooling.
I would monitor temps on any air cooled aero-bike and compare them to temps in stock configuration. You may be surprized at how cool thay can run, but one thing is certain. They do NOT suffer from overcooled liquid coolant entering the engine and sucking more heat from the cylinder walls.

regards
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Old 07-27-2012, 10:53 PM   #6 (permalink)
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Quote:
Originally Posted by woodsrat View Post
I just found that the 185-200 Twinstars are 6v. motors. Much as I like simple motors a 6v. system ain't gonna be for me.
The 6v system works quite well for this bike... I should know... put 10000kms on mine.

But if it's really not your style you could always find an old 1980 CM200... Honda switched to 12v.

These engines are near indestructable, can take redlineing for hours at WOT while still delivering good mileage!
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Old 07-27-2012, 11:26 PM   #7 (permalink)
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At least according to the on-line parts diagrams the '81-'82 Twinstar 200's were 12v. units which puts them back in the running as a potential starting point. They're also a breaker point ignition motor as well which again satisfies my inner Luddite. I like the simplicity of these little bikes and I've heard they're as reliable as a claw hammer.

The only reason I want to go with a 12v. system is the ease of adapting automotive components as needed as well as finding bulbs and such on the road. 6v. stuff is getting hard to come by.

I haven't seen a spec on the wattage output for these bikes but I'm sure it's not much.

Thanks to all for your responses.
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Old 07-28-2012, 12:04 AM   #8 (permalink)
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It all depends on what type of riding you will do. If you don't spend too much time standing in a spot or at very slow speeds than you will not need much air to cool the air cooled motor but if if it's going to idle at low speeds than even a water cooled motor will constantly overheat.

If you do engine off coasing than that will cool the motor even more
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Old 07-28-2012, 12:46 PM   #9 (permalink)
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Sorry, I never got around to doing any aero work on the CB250. I was doing base line testing watching mpg, cylinder head temps, etc. with the bike in mostly stock configuration. I did gear it up, added HID headlight, trailtech vapor, ran it in a saddle sore 1000. It has trouble going up hills in TN. I then purchased a 2007 BMW F650GS Dakar single cylinder. The Dakar is able to carry more gear, maintains speed better, more comfortable, etc. etc. etc. all while getting the same or better fuel economy. When the ambient temp gets over 100, the air off the motors on both bikes just about burn the insides of my legs even with the riding pants I wear. Lots of detail will be needed for both external aero and ducting of the engine cooling air.

Vetter has said it is all about truth in what will work. The truth is a motorcycle will not work for me. The conditions I have to ride in where I live, extreme heat, humidity, rain, hail, tails of hurricanes, dodging animals, being hit by people texting, being socially presentable when I get to work, a motorcycle will not work for me other than a recreational vehicle. For that reason I have stopped developing much on bikes.

If I could carry 4 people with 16 bags of groceries in the Vetter competition with My 98 Jetta TDi, at 48mpg I would win the competition with an equivalent 192mpg in air conditioned comfort. The car will fit 5 people and 20bags if folks are friendly in the back seat.
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Old 07-28-2012, 06:40 PM   #10 (permalink)
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Well said. My buddies have pushed me for years to get another "real" street bike to ride with them on their ST-1300's, Gold Wings and the like. For that kind of money I'd rather drop a few bucks more and buy a convertable that will allow me to put the top up when it rains, have heat/air conditioning as needed and depending on the car haul four in a pinch plus luggage--and get better gas mileage using the same computations as above.

I agree with Mr. Vetter in that motorcycles get embarrassing mileage relative to modern cars and it might be that they'll just remain an expensive toy rather than practical transporation.

Regardless I still enjoy riding a lightweight, fun to ride motorcycle and if it can be developed having a bike that gets double what a car can do with lots of carrying capacity and still cruise at real world highway speeds--and do it with 16 horsepower, saving you money on insurance and other costs--I'd like to have one.

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