Boxer engines thirstier?

[H. Whelply]

I read a review of the Forester--one of many I've read and, sorry, don't
recall where--in which the writer claimed one downside of boxer engines is
that they're slightly less fuel efficient than other more common cylinder
configurations. Can anyone confirm that and, if so, explain why that would
be the case? Thanks.

HW

 

[Bruce Hoult]

I read a review of the Forester--one of many I've read and, sorry, don't
recall where--in which the writer claimed one downside of boxer engines is
that they're slightly less fuel efficient than other more common cylinder
configurations. Can anyone confirm that and, if so, explain why that would
be the case? Thanks.

I can't see why that might be, and in fact it is contrary to my
experience.

My '95 Legacy wagon uses only about 10% more fuel than my previous car,
a '91 Toyota Corona, despite being:

- bigger
- much heavier
- AWD
- 2.5L vs 2.0L
- automatic vs 5 speed
- boxer engine vs inline

My other vehicle is a motorcycle. I used to have a BMW K100RT, which
had an inline 4 cylinder fuel injected 1000cc engine. I now have a BMW
R1100RT, which has a boxer 2 cylinder fuel injected 1100cc engine. On
the open road I used to get about 45 mpg (UK) on the K100, while I now
get around 60 mpg from the R1100.

-- Bruce

 

[UserEddie214]

I read a review of the Forester--one of many I've read
and, sorry, don't recall where--in which the writer claimed
one downside of boxer engines is that they're slightly less
fuel efficient than other more common cylinder configurations.
Can anyone confirm that and, if so, explain why that would
be the case? Thanks.

HW

I've heard somewhere that it is so because boxers produce
a bit more torque at low rpm's than other gasoline engines,
and since people drive mostly at low rpms, it makes for the
slight difference (???).

s.z.

 

[Alan]

I had a 4 cyl 99 Camry and got about 22.5 MPG. My OBW H6 gets 20.1. The
bigger problem is that the gas tank is too small.

 

[null_pointer]

I read a review of the Forester--one of many I've read and, sorry, don't
recall where--in which the writer claimed one downside of boxer engines is
that they're slightly less fuel efficient than other more common cylinder
configurations. Can anyone confirm that and, if so, explain why that would
be the case? Thanks.

HW

Most modern inline engines in the 2.5 litre range need and use balance
shafts to quell vibrations. Because of it's inherent design, the
boxer engine is very smooth and doesn't need these shaft(s) which use
a certain amount of power. I think this fact would help in the
efficiency department

 

[John]

I had a 4 cyl 99 Camry and got about 22.5 MPG. My OBW H6 gets 20.1. The
bigger problem is that the gas tank is too small.

Certainly a 6 cyl will use more fuel than a 4 cyl. My 02 VDC Sedan gets
around 23-25 mpg city.
I think a 15.9 gal fuel tank is more than adequate for a sedan!

 

[null]

Your also comparing front wheel drive and smaller to awd and bigger. That
could account for the difference
a bit.
The boxer design is very smooth compared to a standard v design. You don't
get the side to side rock of
the V design. Also the boxer design allows for a more aerodynamic hood
slant then a V.

I believe the straight 4/6/8 design has less vibration but I think it has
less low end torque. I may be wrong.

 

[John]

I believe the straight 4/6/8 design has less vibration but I think it has
less low end torque. I may be wrong.

Any 6 cylinder is inherently smoother than any 4/8 cyl design. The boxer 6
takes it to an even smoother level.
John

 

[Tony Hwang]

Hi,
6 cyl is smoother than 8? That is news to me.
Tony

 

[Verbs Under My Gel]

Your also comparing front wheel drive and smaller to awd and bigger. That
could account for the difference
a bit.
The boxer design is very smooth compared to a standard v design. You don't
get the side to side rock of
the V design. Also the boxer design allows for a more aerodynamic hood
slant then a V.

I believe the straight 4/6/8 design has less vibration but I think it has
less low end torque. I may be wrong.

Can you get "side to side rock" with a transverse-mounted V-6?

 

[no mas panzon]

Certainly a 6 cyl will use more fuel than a 4 cyl. My 02 VDC Sedan gets
around 23-25 mpg city.
I think a 15.9 gal fuel tank is more than adequate for a sedan!

I believe you missed his point entirely, but I'd say you repeated it!

 

[Rob Munach]

Most modern inline engines in the 2.5 litre range need and use balance
shafts to quell vibrations. Because of it's inherent design, the
boxer engine is very smooth and doesn't need these shaft(s) which use
a certain amount of power. I think this fact would help in the
efficiency department

Inline sixes are inherently balanced and do not require balance shafts.
My 2.5l 6 in my BMW is as smooth as any boxer 6!

 

[Edward Hayes]

The term thirsty boxer engine came from the days when VW (air cooled H4)
engines used a single pot carburetor and no plenum to even out the intake
pulses. Porsche (flat four) used a two pot carb for each bank of cylinders
or one pot per cylinder. Porsche spent the extra money and VW didn't. Modern
Subaru's with fuel injection eliminated any problem. Inline one pot four
cylinder engines have the same problem. ed

 

[Edward Hayes]

Right on John. In I6 has 2 pistons up, 2 pistons down and 2 in between for
perfect balance. The flat 6 is a small step better. The I4 engine is very
bad but, OK up to about 1.8L. Above 1.9L they are trying to tear themselves
apart so counter shafts are used to help. Two wrongs do not make a right
but, an I4 is cheaper to build. eddie

 

[Alan]

The Camry had a 17.5 gal tank. There was never any urgency to get to the gas
station. Once a week whether it needed it or not. WIth the OBW, I *have* to
get to the station at least once per week.

 

[Alan]

Yes, he did. Thanks. Getting only 2 MPG less with the 6 is nothing to
complain about. Now, if only I could use regular instead of premium...

 

[null_pointer]

Inline sixes are inherently balanced and do not require balance shafts.

My 2.5l 6 in my BMW is as smooth as any boxer 6!

OOPS....I meant to say "Most modern inline 4 cylinder engines in the
2.5 litre range"

Gee...since I thunk it in my head, y'all surely musta known whut I
meant to say.....

 

[John]

I did indeed miss Alan's first point. However, don't you find 15.9 gal tank
large enough?
I don't always use premium gas though. I can only find 93 around here. They
recommend 91 for the H6.
I get premium 2/3 of the time and regular the other 1/3.
John

 

[John]

Hi,
6 cyl is smoother than 8? That is news to me.
Tony

Tony,
Check this out. When the cylinder firing and angles and everything else is
taken into account, the 6 cylinder is the smoother design from
http://autozine.kyul.net/technical_school/engine/smooth3.htm :

What about vertical / transverse forces? like 3-cylinder engines, the
vertical and transverse forces generated by individual cylinders, no matter
first order or second order, are completely balanced by one another. The
resultant vibration is nearly zero, thus inline-6 is virtually a perfect
configuration.
Inline-6 is not the only configuration can deliver near perfect refinement,
but it is the most compact one among them. All boxer engines are perfectly
balanced, but they are two wide and require duplicate of blocks, heads and
valve gears. V12 engines also achieve perfect balance, but obviously out of
the reach of most mass production cars. Automotive engineers knew that long
ago, that's why you can see most of the best classic engines were inline-6,
such as Rolls-Royce Silver Ghost, Bentley Speed Six, Mercedes SSK, many
Bugattis, Jaguar XK-series and BMW's various models.

 

[Guest]

The 2003 Camry has an 18.5 gal fuel capacity. Once, I went a month between
refueling. Now, my 2004 Forester XT is gobbling fuel at an average of 19.5
mi/gal, with a 15.9 gal tank . . . you talking about requent gas station
trips.