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Fuel Consumption

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Harleys are said to get really good MPG, your 35 seems like a low guess.  I believe the number I've seen tossed around is 40+, some do 50+.  Harley motors are slow revving low performance engines compared to a XX and that makes them more fuel efficient even tho they're in a less efficient vehicle.

 

The power potential of a naturally aspirated engine will mess with potential MPG; cam specs, RPM, compression, bore/stroke ratio, ports & valves, rod/stroke ratio, displacement,....  The more power potential you add the more likely it'll be to get less MPG and have higher emissions.    If you put the Fit or Harley engine into a XX the MPG would go up.  If you put the XX motor into the Fit the MPG would likely plummet.  The Harley motor might do ok in the Fit.

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Want more MPG?  It's all about reducing.  Reduce wind drag, weight, rolling resistance, and "Pumping losses".  That last one is least understood.  A vehicle going down the highway takes a certain amount of power to maintain a speed, let's say 20HP.  If your engine is capable of 200 Hp, your throttle is barely open at cruise speed, with the pistons having to pull big manifold vacuum (pumping loss).  Plus, friction through the entire drive-train is much higher because the components are bigger to be able to handle 200 Hp when commanded.  If the engine is only capable of 50 Hp, it is much more efficient when producing the required 20.  Of course, it will take much longer to get to a highway speed.  That is the trade-off.

My sister had a 1982 Mazda 626 with a 2-liter inline 4 cyl, rated at 80 HP.  This car was rear-wheel drive, stick shift, and had a carburetor.  Made 38 MPG on the highway.  Imagine what it would do with modern fuel injection, front-wheel drive, and aerodynamics.

Edited by jon haney

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We had a '78 Civic that did mid 30's in mixed driving.  On one trip to Vegas it did 42.5 including 2 days of street driving and a few long stretches at WOT.  4 speed manual and a 52HP 1.5L carbed with points.  No electronic controls and possibly the last car to have a manual choke, and the only car that didn't need a cat to meet emissions specs.

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The Jeep gets 2-4 MPG *less* on road trips than in town.  It gets lower MPG towing a small trailer than my neighbor's 2500 towing a huge trailer.

 

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1 hour ago, superhawk996 said:

We had a '78 Civic that did mid 30's in mixed driving.  On one trip to Vegas it did 42.5 including 2 days of street driving and a few long stretches at WOT.  4 speed manual and a 52HP 1.5L carbed with points.  No electronic controls and possibly the last car to have a manual choke, and the only car that didn't need a cat to meet emissions specs.

LOL.  That was probably the last car to have all those traits.  Points?? In 1978?  Really?

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1 hour ago, SwampNut said:

The Jeep gets 2-4 MPG *less* on road trips than in town.  It gets lower MPG towing a small trailer than my neighbor's 2500 towing a huge trailer.

 

Is your neighbor's 2500 a diesel?  If so, no pumping losses.  One of the many reasons why diesels are more fuel efficient.

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20 minutes ago, jon haney said:

LOL.  That was probably the last car to have all those traits.  Points?? In 1978?  Really?

My 1978 Subaru 4wd wagon also had no cat but did have points.  Great little car that I never replaced one drive line part.  I don't remember the mpg, but it was geared real low and a four speed trans.

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1 hour ago, jon haney said:

Is your neighbor's 2500 a diesel?  If so, no pumping losses.  One of the many reasons why diesels are more fuel efficient.

 

One neighbor has a diesel 2500, the other a gasser.  Both get better fuel economy while towing a 30' trailer than my Jeep with a 20'.  So does the guy with a full-size jap truck.

 

I'm not sure there's a point to be found here other than there are too many variables.

 

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Lets not forget there are gasoline engines without traditional throttle - no pumping losses. Diesel fuel has higher energy content per volume, plus they run higher CR.

 

Anyway, every engine has this https://x-engineer.org/automotive-engineering/internal-combustion-engines/performance/brake-specific-fuel-consumption-bsfc/

 

Swamps Jeep pulling a trailer has to work outside of best efficiency zone while his neighbor`s pick up is in the sweet spot. That's pretty much it.

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4 hours ago, tomek said:

Lets not forget there are gasoline engines without traditional throttle

Modern stuff?  In any vehicles?  Or just old industrial type stuff like hit-miss motors?

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7 hours ago, jon haney said:

Points?? In 1978?  Really?

Almost positive.  And a 3 barrel carb, the CVCC has a unique dual combustion chamber system.  Two barrels feed the main combustion chambers like a normal system and a tiny one feeds the 'pre' combustion chamber where the spark plug is.

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6 hours ago, tomek said:

in the sweet spot

There is much to be said there.

When the federal gov forced Montana to give up it's reasonable and prudent limit, well, actually for a time we were forced to drive 55 the bus companies saw a sharp increase in fuel consumption . They were geared to get best economy at 75, the optimum power band. I know my cummins is best at 1700 rpm.

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Back in those days virtually all buses were powered by 2 stroke Detroits. They had very narrow operating and fuel efficiency range, 4 or 5 speed auto did not help either.

 

They do sound awesome with open exhaust.

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On 9/7/2019 at 8:21 AM, tomek said:

2 stroke Detroits

That's why my ears ring after running them 50 years ago.

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I got one dead-on reading riding up to NeXXt earlier this month. 99 FI with a PC, don’t know the settings, otherwise stock. One rider with moderate baggage weight. 91 octane ethanol-free. Straight interstate, 75-90 mph, no stops. 36.7 mpg. 

 

Oh, and that was over 175 miles. Light came on then, and I was very close to a station.

Edited by RXX
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Actual 175 miles or on odometer ?

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So what's the most you guys are getting back into the tank when bone dry?  And those two pockets on either side at the bottom, is that considered unusable?

Edited by silverbird1100

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