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[icy]

looking for a little help with a power vision. i have a couple questions regarding a log. fuel milage seems to take a severe dive at 75-80 and im just wondering if it can be tweaked a little..

[Para Bellum]

It's possible your PV map can be improved, but there's a larger factor at work here: air resistance.  The air resistance that works against your bike, or anything else, is much higher for higher speeds.  The math equation (simplified to leave out other factors that don't depend on speed) is force = speed x speed (aka f = V²).

For example, the resistance posed by the air at 30 mph = 30 x 30, or 900.  At 60 mph, it's 60 x 60 = 3600, or 4 times as much, even though your speed only doubled.  The resistance from 60 mph to 80 mph increases from 3600 to 6400--which is why gas mileage drops off so badly at higher speeds.

That's also why it takes huge increases in horsepower to get fairly small increases in top speed, and why streamlining the shape of a vehicle is so important to fuel economy and top speed. 

[skratch]

just how bad is your fuel mileage?  I know that when I rode from Louisiana to va a couple years ago, we would run anywhere from 75-85 mph and averaged over 40 mpg.

what, if any, mods do you have on your bike?  if your setup is similar to mine, could share my map with you for comparison.

[icy]

running a t124 S&S with 585 cams. gets 42avg going down the hwy as long as i stay under 70. running 80-85 down the interstate she drinks the fuel . like 23-26 mpg. huge change.

[grc]

running a t124 S&S with 585 cams. gets 42avg going down the hwy as long as i stay under 70. running 80-85 down the interstate she drinks the fuel . like 23-26 mpg. huge change.

Was it tuned by a respected professional dyno tuner?  If yes, have him re-examine the tune.  If no and you just used a canned map, seek out a respected professional tuner.  The folks at TTS Power Vision/Fuel Moto can give you names of tuners they recommend in your area.  You should expect a significant drop off in fuel economy at 70 - 90 mph, but your results seem worse than usual. 

Jerry

Edit:  fixed my mistook on name of tuner

[rigidthumper]

My sons CVO gets 10 less at 85 than it does at 75. 

[sadunbar]

Was it tuned by a respected professional dyno tuner?  If yes, have him re-examine the tune.  If no and you just used a canned map, seek out a respected professional tuner.  The folks at TTS can give you names of tuners they recommend in your area.  You should expect a significant drop off in fuel economy at 70 - 90 mph, but your results seem worse than usual. 

Jerry

Point well taken and good advice, Jerry.  The OP is using a Power Vision (not TTS), but the same applies.  The folks at Fuel Moto can help him out...

[grc]

Point well taken and good advice, Jerry.  The OP is using a Power Vision (not TTS), but the same applies.  The folks at Fuel Moto can help him out...

Oops.  Thanks for catching that, my mind must have wandered a bit. 

Jerry

[Fullsac Performance]

looking for a little help with a power vision. i have a couple questions regarding a log. fuel milage seems to take a severe dive at 75-80 and im just wondering if it can be tweaked a little..

Your situation is real common. The closed loop area will yield good fuel milage in a moderate steady load cruise scenario. At 75-80 MPH, level ground no head wind, your on the edge of closed loop. As load increases with incline and headwind, KPAs rise beyond 80, closed loop ends and fuel gets added real quick and as more power is demanded to maintain that 80 MPH cruise. This is your dive. You may be able to lean it a hair and tweek a few more MPG out of it at high load. Be carefull what you ask for. Leaning it down up there is good recipe for higher temps and pinging. Pulling timing to reduce the ping will kill milage too. Double edged sword.

Good luck with it!

Steve@fullsac.com

[icy]

Steve thanks for the reply. that makes more sense to me now.

[icy]

Just a little update. Talked to Jamie over at fuel moto. He made 2 small changes and it made a acceptable difference thru 2 tanks. Puts it in the mid 30s down the interstate now.