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Old 05-17-2009, 03:02 PM   #1
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mods for better mpg

I own a honda valkyrie, not known for good mpg. however, I average 45 mpg . some mods I have done: cut down the windshield, tilted the windshield back, run the rear shocks on the lowest setting I can without dragging parts in the turns. changed thermostat from stock 180 degree to 195 degree, k&n air filter,advanced the cam timing a few degrees, added air wings to direct wind to the side, rather than over the carbs. hopefully this will reduce drag, and also allow the intakes to run hotter. now I am considering rerouting the fuel tank vent, which vents out under the bike, to have it dump into the air cleaner box. any one have any opinions on this idea?
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Old 05-17-2009, 03:46 PM   #2
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Most of what you've done will increase fe pretty much not at all. Tank vent might be an alright idea though.
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Old 05-17-2009, 04:54 PM   #3
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Most of what you've done will increase fe pretty much not at all. Tank vent might be an alright idea though.
??? most people get around 33 mpg on the valk, I get 45mpg, so why would you think my mods would not effect mpg ? cutting down windshield, and tilting it back reduces frontal area. softer shock setting lowers back of bike, which further tilts windshield, warmer thermostat allows engine to operate more eficiently, advancing cams increases lowend torque, allowing me to run in higher gear at low speeds. one question I have though, is do I run the vent before, or after the air cleaner?
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Old 05-17-2009, 06:01 PM   #4
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I don't know why he would say that your mods won't help FE, but I don't know much about motorcycles. The one thing I do know, or thought I knew, was that a larger windshield is better because the smooth aerodynamically shaped windshield cuts wind easier than the exposed rider.
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Old 05-17-2009, 06:19 PM   #5
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1. Cutting down the windshield doesn't automatically make for better or worse aero. Not only is it a case-by-case basis, the size of the rider figures in too.

2. It can't be tilted back all that much before it smacks you in the face. So the frontal area change is negligible.

3. Shock setting = nothing on a bike. Distance to ground is a factor on cars, but bikes have no bodywork/ground aero interference to speak of. Windshield angle change due to "rear end being lower" = virtually nothing.

4. Hotter t-stat- that might do something, might not. YMMV

5. K&N- now that definitely won't increase fe.

6. change cam timing- could be helpful, especially if you re-gear higher, but you haven't, so that mainly helps you short shift

7. air wings probably = more drag.

"Most people" ESPECIALLY bikers drive like asses too. Let them ride yours and you ride theirs, and see if they still get 33 and you get 45. Biggest factor of all is probably you driving for fe and nobody else is.

I'd vent after the filter.
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Old 05-17-2009, 08:14 PM   #6
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lowering a motorcycle is one of the easiest ways to make it faster at the drag strip frontal area is frontal area, regardless if it is a car or a motorcycle you have obviously not sat on a valkyrie, the windshield is several feet in front of my face .when cutting down a wind shield on a motorcycle, the object is to be able to see over the windshield, and yet still have the wind blast shoot over your head. even after cutting it down 4 " I am still well covered. the lowering the rear by itself might not make much of a difference, but in combination with the windshield mods, it all adds up.motorcycles ,by design are not very aerodynamic, so little improvements can make a difference. my driving style does make the biggest difference, though. the k&n , along with my custom built exhaust, definitely makes the valk run leaner. I really don't want to debate the mods I have made, but I want to be clear on where to route the fuel vent. when you say after the air cleaner, do you mean between the air cleaner and the carbs?
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Old 05-17-2009, 10:09 PM   #7
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Yes - before the air cleaner does no good, after the carbs is just a bad idea period. Closer you get to the filter while still being inside the tract the better off you'll be for even mixing between the cylinders.
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Old 05-17-2009, 10:22 PM   #8
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thanks, I will give it a try
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Old 05-17-2009, 10:32 PM   #9
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Also if you get the impression that it's exposed to too much vacuum there and is drawing too much through, add a restriction to the line.

P.S. I've never done it but it seems to be a sensible mod.
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Old 05-17-2009, 11:04 PM   #10
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thanks again,going to the motorcycle forums and even mentioning mpg usually gets me the ''who cares about mpg, ride it like you stole it" OR "if you want better mpg, buy a moped" responses, so getting a straight answer is kind of refreshing
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