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

[Pepsi90919]

Originally posted by: randay
whats a cylander?

 

[Pepsi90919]

Originally posted by: Colt45
wtf is a cylander

 

[ForumMaster]

well, no cause it uses more gas every revolution.

 

[Vic]

The number of cylinders has very little to do with gas mileage. All things being equal, gas mileage is a function of displacement, volumetric efficiency, throttle position, and rpm. An gasoline engine is an air pump. The more air that flows through the engine, the more gas that is burned, the more power that is produced. The number of cylinders has little to with this. It is more than possible to build a 5 liter 4-cylinder or a 2 liter 8-cylinder if you wanted to.

 

[TheSlamma]

Originally posted by: theNEOone
wow.....just wow.


=|

 

[fbrdphreak]

Originally posted by: 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.

In threads like these there are a few select responses I look for, I don't bother reading the rubbish other idiots post. Zenmervolt is one of the few people whose responses and opinions I trust :thumbsup:

 

[imported_Baloo]

Some funny responses.

OP, you are making a lot of assumptioms about engines based on the number of cylinders.
Does a 6 cylinder work less than a 4? Well, thats 6 pistions, two more sets of valves to overcome the friction for. No, it's actually doing more work right there.

But it's not just about cylinders, it's also displacement. Would a 2.5 liter 6 work less hard than a 2.5 liter 4? Certainly not, the 4 would be doing less work. If this logic were correct, wouldn't an 8 be better still?

And what about the gearing? Are you talking at a given speed, or a given RPM. That can make a very big difference. A 2.5 liter 6 with 3 to 1 axle ration is going to get better mileage than a 2.5 liter 4 with a 4.25 to 1 axle ratio, simply because it is turning slower, and has less of it's own friction to overcome.


If the 4 gives better gas mileage than a 6 in a given vehicle under the same driving conditions, it's doing less work, that is the simplest measure with any accuracy, while still ignoring engine design, tuning and gearing. Efficiency equals workload(i.e. speed) multiplied by fuel consumption -- higher is better. To make it simple, a 4 banger going 35 mph in a vehicle that gets 35 mpg gives a figure of 1225(35x35=1225). a 6 cylinder engine in the same vehicle going 35 and getting 30mpg gives a figure of 1050.

Oh ther is so much more to be said, and has already been said. The simple anser is no.

 

[Inspector Jihad]

Originally posted by: theNEOone
wow.....just wow.


=|

 

[imported_Baloo]

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.

You have stated an opinion here without offering anything to bake it up.

The number of cylinders and arrangment have nothing to do with efficiency.

 

[Zenmervolt]

Originally posted by: fbrdphreak

Originally posted by: 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.

In threads like these there are a few select responses I look for, I don't bother reading the rubbish other idiots post. Zenmervolt is one of the few people whose responses and opinions I trust :thumbsup:

The thing that most people don't realise is that, all else being equal (and most modern engines are pretty close to one another in terms of overall efficiency, close enough to fudge a simple explanation anyway), fuel consumed is dependant upon power produced. If both engines are similarly efficient, then a 100HP V8 (regardless of displacement) should have similar fuel consumption to a 100HP I4 (again, regardless of displacement). (Note that if both engines are indeed similarly efficient and produce the same amount of power, in actual practice their displacements should end up to be similar.)

The reason that in some cases the V8 has better mileage is due to torque curves. If the I4 absolutely needs to be spinning at 3,000 RPM or above while the V8 can live just fine at 1,500 RPM, then the V8 will probably show better mileage. The I4 at 3,000 RPM will be making more HP than the V8 at 1,500 RPM and so will use more fuel than the V8. The V8 can take advantage of gearing and by doing so spin at a low enough RPM on the freeway to actually produce less HP (but more torque) than a smaller, less powerful (in terms of peak power) I4 engine spinning at higher RPM.

In most cases, the lesser overall power of the I4 is enough to keep it making less power at a given speed, but there are times when a V8 is geared right that it can achieve some very good mileage numbers on the freeway.

ZV

 

[ElFenix]

Originally posted by: 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

shouldn't balance shafts 'rob horsepower' the same way friction does?

 

[Vic]

Originally posted by: Zenmervolt
The thing that most people don't realise is that, all else being equal (and most modern engines are pretty close to one another in terms of overall efficiency, close enough to fudge a simple explanation anyway), fuel consumed is dependant upon power produced. If both engines are similarly efficient, then a 100HP V8 (regardless of displacement) should have similar fuel consumption to a 100HP I4 (again, regardless of displacement). (Note that if both engines are indeed similarly efficient and produce the same amount of power, in actual practice their displacements should end up to be similar.)

The reason that in some cases the V8 has better mileage is due to torque curves. If the I4 absolutely needs to be spinning at 3,000 RPM or above while the V8 can live just fine at 1,500 RPM, then the V8 will probably show better mileage. The I4 at 3,000 RPM will be making more HP than the V8 at 1,500 RPM and so will use more fuel than the V8. The V8 can take advantage of gearing and by doing so spin at a low enough RPM on the freeway to actually produce less HP (but more torque) than a smaller, less powerful (in terms of peak power) I4 engine spinning at higher RPM.

In most cases, the lesser overall power of the I4 is enough to keep it making less power at a given speed, but there are times when a V8 is geared right that it can achieve some very good mileage numbers on the freeway.

ZV

All things being equal, like displacement, bore/stroke ratio, camming, etc., then the torque curves should be similar as well. Usually I4's are made to rev higher because of smaller displacement and NVH issues. A large displacement I4 under load at 1500 rpm is not exactly going to be very smooth (which could also be detrimental to engine life), but otherwise there's no reason why it couldn't make the same power/torque.

 

[Zenmervolt]

Originally posted by: ElFenix

Originally posted by: 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

shouldn't balance shafts 'rob horsepower' the same way friction does?

Not all I4 engines have balance shafts. A balance shaft is less an issue than extra pistons though as rotating mass is not as bad as reciprocating mass.

ZV

 

[Zenmervolt]

Originally posted by: Vic
All things being equal, like displacement, bore/stroke ratio, camming, etc., then the torque curves should be similar as well. Usually I4's are made to rev higher because of smaller displacement and NVH issues. A large displacement I4 under load at 1500 rpm is not exactly going to be very smooth (which could also be detrimental to engine life), but otherwise there's no reason why it couldn't make the same power/torque.

Absolutely true. My V8/I4 example was assuming that it wasn't equal, which I didn't make clear enough given the paragraph that preceded the example. The first sentence of the second paragraph should read, "The reason that in some cases a larger V8 has better mileage is due to torque curves."

ZV

 

[bob4432]

Originally posted by: 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

those are just the speeds they want you to know about

 

[Rogodin2]

As noted earlier-too many variables to make a generalization.

This is why the EPA gives milage rankings for each individual car model-not just a ranking for all 4 cylinder vechicles.

Here's some conspicuous variables.
1. Gross weight of vehicle
2. Drag Coefficient of vehicle
3. Size of contact patch (of tires)
4. Gear Ratios at crusing speed
5. Transmission type

Rogo

 

[ballmode]

LOL at op

 

[SophalotJack]

I just put a 16 cyclinder engine into my honda accord and I cruise 80mph on the highway at 10 rpm....

I get 300+ miles to the gallon.

OP... thank you for your insight.

 

[Ktulu]

Originally posted by: SophalotJack
I just put a 16 cyclinder engine into my honda accord and I cruise 80mph on the highway at 10 rpm....

I get 300+ miles to the gallon.

OP... thank you for your insight.

How funny, i just put a 3 CYLANDER Geo Metro motor into my Silverado and my mpg busted up to 60 mpg, i'm in total disbelieve :roll:

 

[Ilmater]

Originally posted by: theNEOone
wow.....just wow.


=|

My thoughts exactly.

 

[Ilmater]

Originally posted by: Dacalo
Going by your concept, 12 cylinders or 16 cylinders are the most efficient.

EDIT: Oh and LOL!

I'm making a V24 production vehicle that has roughly 2,500bhp and gets 65mpg. It should be the greatest car ever invented.

 

[Pepsi90919]

CYLANDER

 

[Paddington]

Work is exactly the same. A V6 does the same amount of work to propel a car to 60 mph that a V4 does.

Typically you see V6's getting worse fuel economy than V4's, because V6's tend to be in bigger cars which are going to be heavier, less aerodynamic, and thus more energy losses due to friction.

Work means something very specific in physics. It's how much energy it takes to get something moving, or elevated, or whatever. That doesn't change, no matter what.

 

[waggy]

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?

have not read the thread.

but with this logic sholdnt say a 12 cylander be better? etc? wouldnt we all be driving 24+?

 

[Ktulu]

Originally posted by: waggy

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?

have not read the thread.

but with this logic sholdnt say a 12 cylander be better? etc? wouldnt we all be driving 24+?

So then wouldn't a 3 CYLANDER be even better than a 4?