Builds for efficiency vs power

[Ken R]

I'm wondering how different builds and/or modifications affect fuel efficiency.  All the talk is about building for power or torque.  What is the effect on efficiency? 
 
Are there builds or modifications that increase fuel efficiency?  Or do they all decrease efficiency? 

[Barrett]

A well tuned, free flowing engine will be more efficient, but it's more fun yankin on the throttle so the MPG's suffer. I heard mopeds get good MPG's.

[PC_Hater]

Barrett got there before me...
A very efficient engine can have very poor fuel economy. But in return for the vast intake of fuel you get a shed load of power!

How about asking for info on 'specific fuel consumption'?
I would love to see that graph for any HD motor.

From memory the best piston engines used in aircraft were something like 0.35lb of fuel per HP per hour at cruising speed. But they put out about 3000 Hp so they still used lot of fuel even though they were the best you could get! I'll see if I can find the actual figures. The figures quoted are now correct.

[Tsani]

I think it's a good question.
I know of a number of guys that have bumped their 88's up to 95's, did the cam, intake and exhaust along with a Dyno Tune and sweaR THEIR mpg IMPROVED. I tend to believe more than anything, the improvement in MPG came along because of the Dyno tuno and even a stock engine tuned by MOCO to meet the EPA's stringent standards would have shown an improvement in MPG.

Still think it's a good question tho.

[Ken R]

I think it's a good question.
I know of a number of guys that have bumped their 88's up to 95's, did the cam, intake and exhaust along with a Dyno Tune and sweaR THEIR mpg IMPROVED. I tend to believe more than anything, the improvement in MPG came along because of the Dyno tuno and even a stock engine tuned by MOCO to meet the EPA's stringent standards would have shown an improvement in MPG.

Still think it's a good question tho.

It's a sincere question.  I'd really like to know if some builds and modifications will gain in MPG and some not.  I have a reason for this question. 
 
I think most of us like to feel the acceleration when the throttle is twisted.  But some of us rarely do that.  I can't remember the last time I went WOT; and I've never tested my modified motorcycle's acceleration against anyone else.  But I do take several trips each year with other Ultra owners.  I don't enjoy always being the first to point to my gas tank.  Bugs the heck out of me. 

[Deweysheads]

That word efficiency gets used a lot usually in conjunction with velocity.
So if you take the sales pitch away.....
Now let's touch lightly (high level) on the topic.
A stock motor has a torque sweet spot of about 2,000rpm (runs at near torque peak). If you run there most of the time you will achieve the maximum mileage. When a good working exhaust pipe air filter and tune are employed the efficiency goes up and mileage has the potential to increase, google BSFC
Add properly ported heads a matching cam without excessive overlap and compression optimized and BSFC can be lowered (more power out of the same ammount of fuel) when operated in or around the sweet spot. Adding the properly ported heads now has the potential to widen the sweet spot, thus increasing the range the motor can operate with maximum efficiency.
In simpler terms, big ports, high overlap cams and big pipes will optimize efficiency in a range we seldom ride. Mileage suffers in lower speed ranges due to reversion and lack of dynamic cylinder pressure.
It's all about choosing a complimentary set of parts that increases efficiency where we spend the most time. On the road that is 2-3k drag racing that is 4-6.5k. Choose your rpm range and go for it. Stock mileage in the 40-45 range is common even with big motors until you roll on hard and use all of that power.

[hotroadking]

Ken was your bike inefficient vis a vis the trips before you
upgraded your engine, or just after...

Have you weighed the bikes with rider to compare to your friends?

My buddy Doug carries a big old tool bag on his evo (theres a good reason too LOL)
and his RK just doesn't roll as easy as others, even with new bearings etc. 

Fact is it feels like his frame is filled with lead but it's not...

You might be heavier on these trips because you have more in the bags weight wise...
Do you lead the pack all the time, so you're the one "breaking wind" LOL

[02roadcling]

Don is correct. 48 at 80-85, and only 37 around 65-70.

cling

[Ken R]

Thank you for the reply.
 
Every thing you stated here makes perfect sense to me; considering my layperson's understanding of the subject. 
 
In my "common sense" thinking, if I have an engine build with an aftermarket freer-flowing air filter, Andrews 21N cams, flat top pistons, professionally ported heads, and ride in my motor's highest torque range (sweet spot) of about 2600 to 2850 rpm, then I should get the best fuel efficiency.   
 
Notice I didn't mention exhaust.  It is, I guess, the unknown.  Vance and Hines True Duals with Screamin' Eagle Street Touring mufflers (2005 vintage, I think). 
 
I rarely get over 35 mpg on the Interstate (and I ride like grandma at the speed limits).  I always keep my rpm in the sweet spot. 
 
It just bugs the heck out of me when I'm always the first to point at my tank.  So I'm trying to learn as much as I can. 
 
My tuner, Ed (The Dyno Difference) has my ECU mapped for efficiency in the lower throttle positions, up to 20% I think.  It's kind of buggin' him too, that my fuel efficiency is not what we think it should be.  Everything he learned from the recent dyno tuning  last month indicates that there are no problems evident.  (and the motor is extremely good natured comfortable to ride, and responsive)
 
As soon as the weather warms, I'm going to hook up my Twin Scan and go for a ride, recording cruising data at 50, 60, and 70mph in the Fuel Injection mode.  Then, we're going to put the bike back on the dyno and compare parameters.  (at least that's the way I understand the plan). 
 
Ken
 
 
 
 

That word efficiency gets used a lot usually in conjunction with velocity.
So if you take the sales pitch away.....
Now let's touch lightly (high level) on the topic.
A stock motor has a torque sweet spot of about 2,000rpm (runs at near torque peak). If you run there most of the time you will achieve the maximum mileage. When a good working exhaust pipe air filter and tune are employed the efficiency goes up and mileage has the potential to increase, google BSFC
Add properly ported heads a matching cam without excessive overlap and compression optimized and BSFC can be lowered (more power out of the same ammount of fuel) when operated in or around the sweet spot. Adding the properly ported heads now has the potential to widen the sweet spot, thus increasing the range the motor can operate with maximum efficiency.
In simpler terms, big ports, high overlap cams and big pipes will optimize efficiency in a range we seldom ride. Mileage suffers in lower speed ranges due to reversion and lack of dynamic cylinder pressure.
It's all about choosing a complimentary set of parts that increases efficiency where we spend the most time. On the road that is 2-3k drag racing that is 4-6.5k. Choose your rpm range and go for it. Stock mileage in the 40-45 range is common even with big motors until you roll on hard and use all of that power.

[Ken R]

Ken was your bike inefficient vis a vis the trips before you
upgraded your engine, or just after...

Have you weighed the bikes with rider to compare to your friends?

My buddy Doug carries a big old tool bag on his evo (theres a good reason too LOL)
and his RK just doesn't roll as easy as others, even with new bearings etc. 

Fact is it feels like his frame is filled with lead but it's not...

You might be heavier on these trips because you have more in the bags weight wise...
Do you lead the pack all the time, so you're the one "breaking wind" LOL

Steve, from my memory, the bike was about like everyone elses.  Seems like I used to occasioinally get 200 miles from a tank of gas, almost always at least 170 before heeding the 1-gallon-left warning. 
 
No, I haven't weighed the comparison bikes.  But I only weigh 156 pounds soaking wet .  Even if I packed a little heavier, my all-up weight wouldn't be much different from the others.  Comparing to other Ultras, a Road Glide, and some Road Kings in my travels.
 
I even did a little coasting experiment with a friend while on a ride a few weeks ago.  At 70mph, we pulled in our clutches and coasted down to 40 as we came into a town.  The difference was insignificant.  We decelerated at about the same rate.  To me, this eliminated anything dragging (brakes).  Also indicated that our "wind-breaking" (aerodynamic drag) was about even.  That day, we filled up before heading out and again when we returned.  Granted, it was only one tank of gas, but I was still 5 mpg down from him.   
 
When riding with others, I almost always ride tandem (side by side) with my different riding friends.  But for some reason, I'm always the first to point to my tank; usually at 130 to 140 miles.  I'm running consistently 5 mpg or worse gas mileage than others, either next to me or in other pairs in front of me or behind me. 
 
 

[FLTRI]

Don is correct. 48 at 80-85, and only 37 around 65-70.

cling

You sure the 48mpg @ 80-85 wasn't downhill and/or with a tail wind? 
What kind of bike did you do this test with?
Bob

[BAKON]

Stock mileage in the 40-45 range is common even with big motors until you roll on hard and use all of that power.

I agree. I can get 200 miles out of a 5 gallon tank, or 125 miles out of the same tank with a .650 lift Woods cam. Depends on my throttle control, or lack of control.

[FLTRI]

Stock mileage in the 40-45 range is common even with big motors until you roll on hard and use all of that power.

I agree. I can get 200 miles out of a 5 gallon tank, or 125 miles out of the same tank with a .650 lift Woods cam. Depends on my throttle control, or lack of control.

Yep, it's hard to know what do say when someone says they only averaged 35 mpg on a long trip....until you find out they were hauling ass in the mountains above 6,000 ft for most of the time/miles.

[akajjmon]

Ken R
"I rarely get over 35 mpg on the Interstate (and I ride like grandma at the speed limits).  I always keep my rpm in the sweet spot."

Ken
Just for comparison. my 106" r/g with 42 mm magnetti,rhinehart true duals, 2 up with overnight goodies got right at 35mpg coming home from New Orleans on hwy 55 at 80avg mph. this wasn't any kind of scientific test just gallons in miles out with stops and speed traps etc. just the "usual" highway riding. not sure what your build is but seems like you should be getting more than 35mpg something in the build didn't quite click? maybe post your build sheet and some of the pros here can pick it apart and make suggestions. good luck to you ken.
 

[Ken R]

Stock mileage in the 40-45 range is common even with big motors until you roll on hard and use all of that power.

I agree. I can get 200 miles out of a 5 gallon tank, or 125 miles out of the same tank with a .650 lift Woods cam. Depends on my throttle control, or lack of control.

Yep, it's hard to know what do say when someone says they only averaged 35 mpg on a long trip....until you find out they were hauling ass in the mountains above 6,000 ft for most of the time/miles.

The actual mpg number isn't as important to me as is the fact that I'll be the first one to run out of gas 25 or more miles before everyone else.  That's significant.  It's only then that we compute and compare mpg figures. 
 
Having said that, I think some of the really high mpg numbers I've seen posted may be high because of speedometer error.  A 4 to 6 percent speedo error will produce the same mpg error.  I've seen plenty of speedo errors in that range (reading higher than actual).  When I DO compute my mpg, it's using my GPS-calibrated speedometer.  THe dyno agreed with my speedometer to within a needle width when on the dyno last month.  From the factory, the speedometers can be way off. 

[02roadcling]

Don is correct. 48 at 80-85, and only 37 around 65-70.

cling

You sure the 48mpg @ 80-85 wasn't downhill and/or with a tail wind? 
What kind of bike did you do this test with?
Bob

FLTRI,

Well I see you are still being a smartass to me and doubting everything I say... as usual.    It wasn't a test. It's my '02 FLHR, 95", flattops, 204's, Scottsman, K&N, carb with 46 slow, Sporty needle, 195 main, 337 gearing, vpc, T-header. Btw, Scurvy is the guy who brought the great mileage to my attention so I checked it. We were in Montana and not going downhill, just rolling it on. I have checked my mileage at least 90% since I first got my bike. When it was new and had 203 and stock gearing with the 48 slow I only got 25 mpg. Then I hit 33 after fixing the carb and 37 after going 337 on the gearing. I also got 48 going 85-90 in Eastern Washington 2 years ago. But of course since I'm a car salesman I must be lying to you.   

cling
 

[Max Headflow]

All you guys need to do is get rid of all that chrome and your mileage will got up.. Max

[dunbarton]

How much effect do you think oil viscosity has?  Over the last 8-10 years cars have moved from 10w30 down to 0w20? mainly for efficiency reasons. Of course there were no doubt lots of internal design changes that allowed this.
If the v-twin ran 10w40 instead of 20w50...? Might be ok in moderate temps.

[akajjmon]

All you guys need to do is get rid of all that chrome and your mileage will got up.. Max

BLASPHEMER!!!!! STONE HIM!!!!!

[Max Headflow]

Too late, I already been stoned..    Max

[akajjmon]

Too late, I already been stoned..    Max

Yeah I figured that!! but ""Blaspemer!!! Stone ME!!!"" sounded so.......Selfish

[strokerjlk]

My tuner, Ed (The Dyno Difference) has my ECU mapped for efficiency in the lower throttle positions, up to 20% I think.  It's kind of buggin' him too, that my fuel efficiency is not what we think it should be.  Everything he learned from the recent dyno tuning  last month indicates that there are no problems evident.  (and the motor is extremely good natured comfortable to ride, and responsive)

ken
PC III tuner?
I have seen this.
I dont know what was wrong with the PC  because the guy didnt send it back. But I had the bike 3 times on the dyno. trying to get better mileage and it never bested 32mpg even as low as 25mpg. swapped it to a TTS  tuned it,now it is up in the 38- 42 range.
If it isnt a PC well......never mind

[Ken R]

Thanks for the try Stroker, but no.  It's Direct Link tuning; modifies the parameters in the ECM, no piggyback needed. 
 
Ken
 

My tuner, Ed (The Dyno Difference) has my ECU mapped for efficiency in the lower throttle positions, up to 20% I think.  It's kind of buggin' him too, that my fuel efficiency is not what we think it should be.  Everything he learned from the recent dyno tuning  last month indicates that there are no problems evident.  (and the motor is extremely good natured comfortable to ride, and responsive)

ken
PC III tuner?
I have seen this.
I dont know what was wrong with the PC  because the guy didnt send it back. But I had the bike 3 times on the dyno. trying to get better mileage and it never bested 32mpg even as low as 25mpg. swapped it to a TTS  tuned it,now it is up in the 38- 42 range.
If it isnt a PC well......never mind

[Deweysheads]

I would guess there is a tuning issue and it is rich, simple as that, no need to get too deep into motor theory.
Many times tuners run into issue with accurate sampling and this may be one of them. Also some like to tune rich and build in a ping cushion and keep the heat lower. Problem is worse throttle response and wasted fuel. Worse case excessive carbon buildup and pinging anyway, what they were trying to prevent.

[FLTRI]

Don is correct. 48 at 80-85, and only 37 around 65-70.
cling,

Well I see you are still being a smartass to me and doubting everything I say... as usual.    It wasn't a test. It's my '02 FLHR, 95", flattops, 204's, Scottsman, K&N, carb with 46 slow, Sporty needle, 195 main, 337 gearing, vpc, T-header. Btw, Scurvy is the guy who brought the great mileage to my attention so I checked it. We were in Montana and not going downhill, just rolling it on. I have checked my mileage at least 90% since I first got my bike. When it was new and had 203 and stock gearing with the 48 slow I only got 25 mpg. Then I hit 33 after fixing the carb and 37 after going 337 on the gearing. I also got 48 going 85-90 in Eastern Washington 2 years ago. But of course since I'm a car salesman I must be lying to you.   

cling

Please do not take my comments personal. I would have questioned anyone claiming 48 mpg @ 80-85mph from a 900lb bagger that has the aerodynamic drag of a side-by-side refrigerator.

Definitely have heard of 45-50mpg from Dyna owners, but that bike is 1/2 the frontal area of a bagger.

Getting 5-10 mpg better @ 5-10 mph faster than mpg results from an average stage1 EFI bagger tuned for best performance/mileage, is well just hard to swallow. Sorry
Bob