Shouldn't a 6 cylander engine get better gas mileage than a 4 banger?

[acemcmac]

Originally posted by: Sukhoi
I see you failed high school physics.

forget that... the OP failed 5th grade spelling...

 

[Raduque]

Originally posted by: Crescent13
OP Just got owned big time.

Man, the chanting in that thing is annoying.

 

[randay]

Originally posted by: Ktulu

Originally posted by: Garet Jax

Originally posted by: Accipiter22
To achieve a certain speed, say on flat terrain, a 6 cylander would have to work less than a 4 cylander, correct? So why not get better gas mileage?

Assuming all other things equals (weight, wind drag, etc...), it has to ignite more gas to operate the extra 2 cylinders so no.

Yes, but it most likely won't have to rev as high to achieve the same amount of work thus actually using less gas PER CYLANDER.

fixed.

 

[Colt45]

wtf is a cylander

 

[feelingshorter]

Originally posted by: randay

Originally posted by: Ktulu

Originally posted by: Garet Jax

Originally posted by: Accipiter22
To achieve a certain speed, say on flat terrain, a 6 cylander would have to work less than a 4 cylander, correct? So why not get better gas mileage?

Assuming all other things equals (weight, wind drag, etc...), it has to ignite more gas to operate the extra 2 cylinders so no.

Yes, but it most likely won't have to rev as high to achieve the same amount of work thus actually using less gas PER CYLANDER.

fixed.

lol, just wow but not nearly as funny as the self ownage on the infamous "eBay/Fraud/Legal advice needed"

 

[randay]

Originally posted by: Colt45
wtf is a cylander

I thought I was the only one who didn't know?

 

[Cloud Strife]

Too many variables to account for; I'm not even going to mention them. Just look at the car's MPG if you want to compare car A and car B.

 

[Ktulu]

Originally posted by: randay

Originally posted by: Ktulu

Originally posted by: Garet Jax

Originally posted by: Accipiter22
To achieve a certain speed, say on flat terrain, a 6 cylander would have to work less than a 4 cylander, correct? So why not get better gas mileage?

Assuming all other things equals (weight, wind drag, etc...), it has to ignite more gas to operate the extra 2 cylinders so no.

Yes, but it most likely won't have to rev as high to achieve the same amount of work thus actually using less gas PER CYLANDER.

fixed.

Corvette (400 hp 6.0L v8)- 18/28 mpg

Solstice (177 hp 2.4L i4) - 20/28 mpg

As i've said before, i'm not necessarily for the OP's idea, I just don't think he deserves the flames he's getting.

 

[EarthwormJim]

It's possible that a 6 cylinder engine will use less gas to get up to a certain speed, however once at that speed it will probably use quite a bit more fuel than a 4 cylinder to maintain that speed.

A better comparison would have been a V6 truck vs a V8 truck, in which case the V8 can get better gas mileage.

Mostly because it can make better lower end torque and have anemic gearing to take advantage of that.

 

[funboy6942]

My wifes 98 Jeep with an inline 4.0 6 banger gets worse MPG then my 88 Firebird with a 5.0 V8. On the highway her car at 70 is at 2300 rpms where as mine when goes in to od converter 1:1 lock down is at 1800 rpms at same speed.
Areo dynamics (hers is nothing more then a brick with wheels) and gearing is the diff between hers and mine.

 

[CraigRT]

The 3.5V6 in my Altima gets similar gas mileage to the old 2.0L I had in my 2001 Neon.

The costs to fill are different, but the Altima gets more per tank by far, as well as costs more to fill.. Thus making it actually very close. At least these are my experiences...

 

[Stunt]

A 6 cylinder *can* have a better fuel economy than a 4 banger. Depends on the number of litres the engine is and how efficient it is.

 

[xanis]

Dear Lord there are a lot of flames. V6s have more moving parts which equals more weight, friction and reduced gas mileage compared to an I4. Also, I've seen some V6 vehicles that get just as good if not better mileage than I4s. Aerodynamics plays a HUGE part in fuel efficiency as well. Less drag equals better fuel economy, and more drag equals worse fuel economy. I have a Chevy Cavalier with a 2.2L I4 and my dad has a Dodge Intrepid with a V6. We both get similar gas mileage, but part of it might be due to the fact that the Intrepid is more aerodynamically efficient since it's shaped like a bullet.

 

[Zenmervolt]

6 cylinder has higher internal friction and while it does make more power, it takes more fuel to make that power.

At 60 mph, most cars only need about 20 hp. Drag increases with the square of speed, so to double speed you need 8X the power (2X power to double speed times 4X the power to overcome the drag associated with the higher speed), so a car that needs 20 hp to go 60 mph would need 160 hp to go 120 mph, which is roughly on track with where a 160 hp car would be hitting top speed (actually, it's over-estimating the required HP slightly as 160 hp should carry a car to about 130-135 mph).

So, at cruise speed, if the 4-cylinder is making 25 hp at 3,000 RPM while the 6 cylinder is making 35 hp at 2,000 RPM, the 4-cylinder is still using less fuel.

Even if both engines were sending 25 hp to the transmission at the same RPMs as above, the 6-cylinder is still using more fuel because of higher internal friction. (E.G. the 4-cylinder may only need to make 27 hp total to send 25 hp to the transmission while the 6-cylinder, due to greater friction, needs to make 30 hp total to send 25 hp to the transmission.)

ZV

 

[Zenmervolt]

Originally posted by: infestedgh0st
actually, the most efficient internal combustion engine design is the i6 and v12. Friction counts very little in terms of efficiency (motor oil anybody?). Newer engines now usually have lighter internals, which is a big contribution to engine efficiency.

Wrong. Those are the best balanced, but they are not the most "efficient".

ZV

 

[raptor13]

Size does have something to do with efficiency.

There are simply way too many factors at work to reliably say a 4 cylinder automotive engine does or doesn't get better mileage than a 6 cylinder automotive engine.

Reference: Here.

 

[DivideBYZero]

Originally posted by: Zenmervolt
6 cylinder has higher internal friction and while it does make more power, it takes more fuel to make that power.

At 60 mph, most cars only need about 20 hp. Drag increases with the square of speed, so to double speed you need 8X the power (2X power to double speed times 4X the power to overcome the drag associated with the higher speed), so a car that needs 20 hp to go 60 mph would need 160 hp to go 120 mph, which is roughly on track with where a 160 hp car would be hitting top speed (actually, it's over-estimating the required HP slightly as 160 hp should carry a car to about 130-135 mph).

So, at cruise speed, if the 4-cylinder is making 25 hp at 3,000 RPM while the 6 cylinder is making 35 hp at 2,000 RPM, the 4-cylinder is still using less fuel.

Even if both engines were sending 25 hp to the transmission at the same RPMs as above, the 6-cylinder is still using more fuel because of higher internal friction. (E.G. the 4-cylinder may only need to make 27 hp total to send 25 hp to the transmission while the 6-cylinder, due to greater friction, needs to make 30 hp total to send 25 hp to the transmission.)

ZV

:thumbsup: First decent, honest, non-flame response.

 

[Xyclone]

Originally posted by: Crescent13
OP Just got owned big time.

My brother showed that to me... lol.

 

[loic2003]

Just dumb on so many levels (if, of course, this isn't a prank post). Here's some things you've not considered:

Increased mass of larger block
Increased mass of more moving parts.
Pison masses
Friction increases
Overall port volumes
Burn speed of fuel in same volumes
Torque vs power (think 1000cc V-twin ducati vs 1000cc straight-4 Honda)
Engine design: port shapes & sizes, cam shaft profile, aspiration methods, exhaust system, ignition system, etc etc etc
Everything else that affects engine performance...

Basically there's so much else other than 'cylander' numbers to take into account...

 

[b0mbrman]

Originally posted by: Thraxen

Originally posted by: iwantanewcomputer
i don't know anything about the relationships of torque produced, cylinder number, and fuel consumption of an internal combustion engine, but i am going to post something I just made up based on my limited scientific knowledge that sounds technical.

What's funny is that despite all the snide comments people are actually having a hard time accurately explaining why.... and the people with the snide comments didn't even try to explain.

Exactly...

 

[thescreensavers]

Originally posted by: GagHalfrunt
And an aircraft carrier should be able to outrun a cigarette boat because the propellers are bigger.

Aircraft carriers go up to a speed of 35+knots that is the fastest ship in the US navy at this time. Destroyers go up to 30knots. Cruisers go up to 32.5 knots.


its all true go look it up in WIKIPEDIA

 

[Calin]

Originally posted by: infestedgh0st

Originally posted by: desy
more moving parts means more friction mechanical loses etc.
The gas engine isn't 100% effecient to start so muliplying cylinders magnifies the loses.
Added vehicle wieght unless you remove something elsewher to keep the GVW the same and on and on

actually, the most efficient internal combustion engine design is the i6 and v12. Friction counts very little in terms of efficiency (motor oil anybody?). Newer engines now usually have lighter internals, which is a big contribution to engine efficiency.

Rotating masses have a negative impact on engine efficiency - and alternative-moving masses (like pistons) have an even greater effect. Increasing the mass and/or number of the pistons will decrease overall efficiency.

 

[Calin]

Originally posted by: desy
there seems to be a break point around 10 or 12 cylinders, after which addition of cylinders becomes an overall detriment to performance and efficiency, although exceptions such as the W16 engine from Volkswagen exist.
http://en.wikipedia.org/wiki/Internal_combustion_engine#Cylinders

As you add more and more cylinders, the length of the crankshaft must increase. This is a real problem, as it must be made stronger and stronger to withstand the tendencies to twist.
The W16 engine is a V, but in each side of the V the cylinders are forming a smaller V. The smaller V (at 15 degrees I think) allows packing the cylinders closer to each other.
This technology appeared (I think) on the VW Passat VR6 of 1990 - the VR6 is a transverse engine, just like the inline 4 used on other models.

 

[Stumps]

hmmm, while it really does depend on the vehicle, there have been a few cars in which some of the larger engine options have had better fuel effiency under certain conditions.

A few Australian examples

1972-1979 GMH Kingswood and 1978-1985 GMH Commodores were a good example, standard they came with a pretty sad 66-85kw(depends on year model) 3.3litre (202cu) Inline six, but the next engine option for these cars was a 4.2litre (253cu) V8 which generally had around 100-115kw and offered 10-12mpg better fuel economy at cruise than the smaller six cylinder.

But both engines were outclassed by the 4.1litre (250cu) inline 6 cylinder used in the 1971-1987 Ford Falcon which offered 92-127kw's (depends on year model)and miles more torque, had much better fuel economy than both of the GMH engines and was used in a heavier car the average weight for Kingswood sedan 1400kg's, Commodore sedan 1200kg's the falcon sedan varied between 1450kg's (most models after 1979) and 1800kg's (1976-78 XC Fairmont GXL).

I'm sure there are plenty of US examples but I don't know enought about them to comment

 

[zephyrprime]

I'm not expert on this at all but here's my explanation:

The flaw with the op thinking is that he is considering one dynamic while forgetting about a coincident dynamic that negates the first dynamic. To attain a given speed, having more cylinders means they need to "work less hard" (as defined as working at a lower percentage of maximum output) than fewer cylinders. But you forget that you now have more cylinders working less hard and the presence of more "workers" compensates for the fact that each one is working less hard.

Basically, it's like this: 6 cylinders * (Workload/6 workers) = 4 cylinders * (Workload/4 workers)

Although this explanation is simple and profound mathematical explanation, there is actually a more complex physical effect that occurs in engines that is the actually reason why V6s have worse gas mileage.

The real answer is because engines do not operate at a fixed efficiency over their torque curve. Engines efficiency is a rough bell curve and engines have low fuel efficiency at the low and high end of the curve. A 6 cylinder will operate lower on it's torque curve than a 4 cylinder in a typical empty card driving at typical speeds. Since it's operating at the lower end of its curve outside the power band, it will operate with lower fuel efficiency.

However, I guess if you were to load the 6 cylinder down with 50% more weight and 50% more aerodynamic drag, both cars should get the same fuel economy on a (miles*tons) per gallon basis.

Friction has an effect too of course but I believe it is much weaker effect than the one given above. In a V6, there is more surface area suffering friction but those surfaces are also moving slower than in the I4 when driving at the same speed so that partially compensates.

The same sort of thing is happening with the additional reciprocating/rotating masses. There is more such mass in a V6 but they would be traveling slower and that would partially compensate.