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PostPosted: February 9, 2011, 10:18 am 
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hey guys, I'm looking to build a small bec powered car or trike that would get exceptional mileage around town or on the highway.

I've got a few ideas but I'm looking for your thoughts. I'm leaning more towards four wheels as my goal of a 2 person vehicle always looks odd to me in reverse trike form. I had something like the VW l1 or xl1 prototype in mind. I like the narrow track width, the look of tandem or side-by-side seating.

here is the inspiration:
L1:
Image
Image
XL1:
Image
Image




I have been considering motorcycle engines in the 250-650cc class and was mostly considering the V-twins. I would like to use a standard type differential but out of the front of a quad or a side by side off road vehicle like a razor. The short length of the V-twin configuration would allow me to mount the motor as a mid or rear engine. rear engine would allow me to shorten the car in side-by-side seating or make a tandem car not look "stretched" as much. everything in this car would be minimalistic. basic transportation.

the pro's of the trike configuration are losing lots of things. one less wheel and related suspension, frame, differential. I believe when you go with a trike configuration in Massachusetts you are allowed one headlight, tailight, no reverse etc. I would love to go this route but am leery of balance issues of a side-by-side reverse trike and a tandem would be LONG. any thoughts to overcome these issues?



engines I've been looking at are from v-twin bikes that have reputations of high mileage already, I've read a hyosong 250cc vtwin can get in the 70mpg range and something more standard (and available) like a suzuki dl650 gets in the upper 50s to lower 60's (it's also cheaper, more available, higher torque and better mileage than a sv-650) Any other engines I should consider?? I would look into the small diesel generator type engines but I'm not familiar with diesels and a transmission would be an issue.


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PostPosted: February 9, 2011, 11:04 am 
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Hi Revkev6, glad you still check in on us. Well I think the wing from your oval track car is right out.

The diesels are likely much better on fuel economy. You can look at Jack McCornack's logs, he used a Kubuto turbo diesel from a small tractor. The lack of an intake throttle means no intake vacuum which means way better economy when not making full power. It's a big difference, diesels burn almost no fuel while idling. It's one of the reasons trucks tned to idel rather then turn off their engines.

Consider connecting an engine like that to a VW bug transmission. They can rotate either way and have reverse, the transmission is on the other side of the diff so either way you install it you get a short drivetrain.

THe problem with really small motors is that you have the horsepower to run the car at speed (drag), but the weight of the makes it hard to accelerate. So you need some extra power and that's why the diesel will be good, you don't have to run it at large throttle openings to be efficient.

I think this will be a good thread and the body work you pictured would go nicely on a frame similar to a Locost.

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PostPosted: February 9, 2011, 11:40 am 
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horizonjob,

thanks for the insight to the diesels. that is another reason I'd like to stick with a gas engine, I know them! I'm familiar with bike engines having raced them in mini-sprints for years! I know for a fact this would be a perfect application for a small diesel I just don't know that adding a new engine design to the learning curve of building my own chassis would be smart.

99% of the usage of this vehicle would be my 9 mile commute to and from work. there are plenty of sections with stop and go through town, one large hill and a section that runs about 45-50 mph.

with a smaller engine I can also build lighter.... very few similarities would exist between this chassis and a locost chassis if I built with a 250cc motor! the 650 would be my "extra power" scenario

I did have one other thought on the tad-pole trike and that would be FWD with the engine out in front of the axle.


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PostPosted: February 9, 2011, 1:34 pm 
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I think if your going to stick to a Trike I would recommend a 2F1R type with front engine FWD. It would allow for the narrowest possible design due to the engine being in the front. If you do rear/mid engine the front track would have to get fairly wide to allow for decent tip resistance. I've had this same though numerous times but have never taken the plunge. I to though small Motorcyle motor (maybe as small as Ninja 250) with a light hybrid system (just electric assist to the rear wheel with the ability to kill the MC engine at traffic lights, maybe some regenerative braking). Also keep in mind most states have very simple registration procedures for trikes compared to cars.

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PostPosted: February 10, 2011, 11:10 am 
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I'm building a diesel trike, 2f1r. I have all the expensive parts, but I'm currently putting out smaller fires and creating space to do the work. I have a build log in the nontraditional forum.

If you do a search for "commuter" or "trike", the L1 and trike discussions should pop up.

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PostPosted: February 10, 2011, 11:50 am 
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An old article but it also lists a couple of other "Major Manufacturer" concept cars in a similiar vein.
http://www.gizmag.com/go/4990/
Of interest, I think, is that one could use a typical transverse engine FWD and create a pretty hot little number out of a commute crash (sandwiched) donor.
Use an aftermarket upper strut brace for the top beam, a factory subframe and the factory suspension on light springs. ..

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PostPosted: February 10, 2011, 1:22 pm 
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Miatav8,MstrASE,A&P,F wrote:
I'm building a diesel trike, 2f1r. I have all the expensive parts, but I'm currently putting out smaller fires and creating space to do the work. I have a build log in the nontraditional forum.

If you do a search for "commuter" or "trike", the L1 and trike discussions should pop up.




just went and looked at your diesel setup. i've always wondered about cvt reliability and efficiency. interested to see how this turns out.

i've been trying to come up with ways to lighten or increase efficiency, what would the groups thoughts on using scooter wheels tires and brakes be?? I was looking at the 12" rims and tires and they are rated at 560lbs each! more than enough for a super light setup. Think not much more than a go-kart with suspension wrapped up in an aero package.....


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PostPosted: February 10, 2011, 3:04 pm 
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The problem with bike/scooter tires is they are very soft, lasting only 2 or 3 oil changes. Thats why I went with 3 wheels and a wide track/non tilt to use Smart tires. There is a fellow that has a cruiser with the same engine as me but hydrostatic drive. Very easy to do since the motor was setup for that but there is still slippage at speed compared to a mechanical drive and the noise (think low powersteering fluid noise) would drive me crazy.

CVT is more efficient in gearing but friction is high at the belt compared to a chain.

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PostPosted: February 10, 2011, 8:03 pm 
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How much economy do you need? Curious what numbers your aiming at.

Jack McCornack has been getting over 80 MPG on his diesel locost that he has moved to a Lola inspired body. Picture below. He says he's working up to 100 MPG. That's pretty decent and it's more or less a real car, no roof so maybe not so great for the winter. He entered a "no petroleum" race and won it on vegatable oil :) .

I think that will be hard to beat with a motorcycle 250cc. Maybe not...

When I said locost chassis, I meant loosely but here's one that's done well. A lot more effort on body to look like the volswagen in your pictures would get you more mileage.

The stuff your talking about at the relatively extreme end of the spectrum could do better. I don't mind adjusting my thinking that way, but the amount of effort goes up with fancy bodywork.

I think drag is the big issue, motorcycles don't weigh much but most don't get more then 50 or 60 mpg. I've never owned a bike intended for mileage though :-)

Before they got into downforce racecars in the sixties were designed to be low drag. So some of the old Lotus, Lola etc. were pretty slippery.

A last thought was I saw a Chinese company selling little off road vehicles that had 5 speed transaxles. JUst because your going to be economical doesn't mean you have to stop having fun!


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PostPosted: February 11, 2011, 9:58 am 
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I don't have a target MPG as of yet. I do want a roof, as I am in new england there are plenty of days of bad weather. I Haven't run numbers for estimated weights and power requirements yet either so I don't know if something like the 250cc engine would be sufficient power. the korean hyosung engine I mentioned is right around 30hp @ 10k rpm and is fuel injected if 2010 or newer. because the bikes are low volume here they are hard to find though. my reading has put these bikes at a low of 50mpg when ridden hard up into the 70mpg range. I'm guessing if I built the car very efficiently around town I could probably get the 50mpg and on the highway I'm thinking I could exceed the bikes efficiency with increased aerodynamics


other 250cc bikes I've read about don't seem to get the mileage of the hyosung V-twin 250. I've also considered larger sized 2wd sport atv engines as they come with reverse and are more suited to higher torque applications. I do have reservations with these engines as I don't think they are designed for higher mileage with low maintenance. I really would like to stay away from diesels though.

Can anyone chime in here who has a BEC that could give me an idea of the mileage they are getting at this point? might give me a starting point.


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PostPosted: February 11, 2011, 12:01 pm 
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Not really trying to push the diesel, Jack's just happens to be one. I am not sure that high performance, in terms of power per displacement, produces a good "fuel specific" number. Your looking for a high performance in lbs. of gas per horsepower number. Dynos can plot those curves as well, it's just that everyone is interested in the other numbers.

Small displacement can be bad for these numbers because a lot of heat is lost into the motor from the small combustion space. Slower, larger displacement may be better. Running the engine hot also helps, that's why so many 200+ thermostats instead of 180 now. The cam grinds are also wrong on high performance motors

People used to cut down VW bug motors to 2 cylinders for airplanes. That would be about the same power and the transaxle is 75 lbs. Not so good for heat and defroster though, so water cooling is probably what you want.

Small industrial motors from things like gensets might be good and tuned more for economy/reliability. No water cooling again though...

Would be interesting to get some fuel specific dyno curves, but the only motors I know with dyno runs are built for horsepower. I can ask though...

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PostPosted: February 11, 2011, 1:18 pm 
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I'm also looking for smallest physical engine size and weight. i'm not using the specific output of this engine as an indicator of mileage but throwing it out to give others an idea of it's ability to pull the load of a "car"

for it's displacement in a bike form it seems to perform very efficiently. the V-twin configuration gives the smaller displacement more torque than similar CC engines. it's size is larger though. the kawasaki ex250 engine is a parallel twin that is physically smaller (and watercooled unlike the V-twin) but is apparently unhappy at lower RPM.


right now anything would be better than the 12mpg I get with my f150. that's regardless of what it's doing. around town, highway, towing whatever! it costs me about $25 to drive back and forth to work for one week. if I got 50mpg I'd be looking at less than $6 a week, 70mpg would cost me $4. that's going from $100 a month to $16! ahhh and I think this would be much more interesting to drive!


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PostPosted: February 11, 2011, 1:45 pm 
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Considering the useage I think you'll be more interested in to torque curve, having to rev to 3k just to pull away with alacrity due to an extra 400lb of roof and etc with a small engine and bike gearing might be a bother.
Interesting thought, the diff can be centered and the engine off-center with a chain (belt) running almost straight down. ..
I'd use something a bit bigger though just to get some low end grunt. Maybe a V45 or a Vulcan 800?
Find an old drop tank for a body and have the roof lift up to open. .. Bonneville here you come!

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PostPosted: February 12, 2011, 8:59 am 
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A cvt allows a smaller displacement engine to pull like a larger one, similar to modern small engined vehicles with 4/5/6 speed transmissions accelerating like a muscle car with 2 or 3 gears.

Use an engine that provides the required amount of power at the torque peak, then adjust the final drive gearing for the desired speed. BSFC is lowest near the torque peak. Since the torque peak is usually near the middle of the rpm range, the higher revs can be used to get to the cruising speed at a reasonable rate, pass when necessary, climb hills, etc. This means a heavier engine with more displacement and excess peak power. Additional weight affects acceleration and braking but has very little to do with required power to maintain a speed. It will also be more durable. Consider a 750 nighthawk engine, turning 1500-2000 rpm at cruising speed. It will also be easier to drive. Down shifting burns more fuel than opening the throttle more to maintain speed.

Check out Craig's site:

www.craigvetter.com

Also, consider that CD is a measurement of drag per unit of area. An aerodynamicaly shaped bus could have the same drag as a bike per unit, but the bus has a lot more units / frontal area so it still has more drag.

I assume you've read my scooter build (Chet moved it so it shows him to be the author).

For a way to save money right now, spend $500-1000 on a good running 5spd Ford Aspire. Accel is slower than most everything else but the overdrive is deep, so it will go with the flow at highway speed. Drivers of slow, small cars have the same driving priviledge as those with faster equipment. Drive it like a tank.

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PostPosted: February 12, 2011, 11:49 am 
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revkev6 wrote:
that is another reason I'd like to stick with a gas engine, I know them!
That's one thing cool about small diesels--you don't have to know them!

Seriously, all I've done for my Kubota is change the oil, and occasionally (very occasionally) put fuel in the tank. Even the veggie oil conversion was entirely external to the engine. Gosh, with no throttle and no ignition, what's to know? I suppose a serious diesel knower could have some hot cams ground for it, but I wouldn't go to that much trouble even on a gasoline engine. Anyway, I too know scads about gasoline engines, and figured I could learn enough about diesels to get me by, but no dice: I haven't learned a darn thing about them, except they run and there's nothing to adjust.

Now making your body, well, that's a different story...

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