inline 4 vs inline 6

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s3cf
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inline 4 vs inline 6

Postby s3cf » Thu Apr 17, 2014 10:28 am

for the same displacement let say 2.0L, which engine gives better fuel efficiency?

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SidekickChuck
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Re: inline 4 vs inline 6

Postby SidekickChuck » Thu Apr 17, 2014 10:30 am

I would assume the i4 due to the additional weight of the i6.
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yoshimitsuspeed
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Re: inline 4 vs inline 6

Postby yoshimitsuspeed » Thu Apr 17, 2014 7:41 pm

Completely depends on everything else.
Compression, cams, bore, stroke, number of valves, combustion chamber design, port size, intake and exhaust design and many other things.

I4 will tend to have less parasitic loss from the internals but on the other hand the 6 will have more ports and more valves per displacement which will help airflow and efficiency.

Jimmee1990
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Re: inline 4 vs inline 6

Postby Jimmee1990 » Thu Apr 17, 2014 7:44 pm

The 6 cylinder will also have a greater piston surface area. Are you comparing two engines in particular?

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yoshimitsuspeed
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Re: inline 4 vs inline 6

Postby yoshimitsuspeed » Fri Apr 18, 2014 9:08 am

Jimmee1990 wrote:The 6 cylinder will also have a greater piston surface area. Are you comparing two engines in particular?


Not necessarily. Like I said it completely depends on bore and stroke.

s3cf
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Re: inline 4 vs inline 6

Postby s3cf » Fri Apr 18, 2014 9:24 am

Thanks for the inputs and I understand there are many other moving targets/factors that need to be taken into accounts.
So if we assume all being equal (# of valves, compression and etc), is I4 more fuel efficent than an I6?
(i m sorry for making it too general....)


I was comparing the engine from IS200 and RS200 (altezza) but thought both engines were designed for different purposes so it might not be a good comparison.

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Re: inline 4 vs inline 6

Postby yoshimitsuspeed » Fri Apr 18, 2014 5:15 pm

s3cf wrote:Thanks for the inputs and I understand there are many other moving targets/factors that need to be taken into accounts.
So if we assume all being equal (# of valves, compression and etc), is I4 more fuel efficent than an I6?
(i m sorry for making it too general....)


I was comparing the engine from IS200 and RS200 (altezza) but thought both engines were designed for different purposes so it might not be a good comparison.


Well for one all else can't be equal.
For example a 3SGTE has a bore and stroke of 86.0 mm 86.0 mm

A V6 with the same bore and stroke would be a 3 liter.

You could shrink the bore and the stroke equally but you would still have different properties. Piston speeds are different, piston surface area is different. Combustion chamber size is different which also limits valve size.

Number of valves is going to be different because 4 valves per cyl on a 4 cyl gives you 16 valves, on a 6 cyl gives you 24 valves.

These variables are exactly why there are so many different engine combinations. If one was all around best then there would only be one engine in any car.
It's the reason why Toyota makes a 4.0 V6 and a 4.0 V8.
They are going to have different characteristics. One might have it's BSFC peak at 4500 RPM and one might have it's BSFC peak at 3500 RPM.
One might get better gas mileage in one chassis/trans combination in one driving environment and one might get better gas mileage in a different chassis/trans in another driving environment. One might get best gas mileage at 65 mph in fifth gear, the other might get the best gas mileage at 55 mph in 4th gear.

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Re: inline 4 vs inline 6

Postby yoshimitsuspeed » Fri Apr 18, 2014 5:17 pm

Not sure what you are looking for but I'll bet the better and more important question is what engine will do better for your particular goals. In which case we would need to know those goals.
Even then it can be a complicated question.

BlueDeathTrap
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Re: inline 4 vs inline 6

Postby BlueDeathTrap » Fri Apr 18, 2014 7:40 pm

yoshimitsuspeed wrote:
Jimmee1990 wrote:The 6 cylinder will also have a greater piston surface area. Are you comparing two engines in particular?


Not necessarily. Like I said it completely depends on bore and stroke.


Also don't forget piston design. Rod to stroke ratio will also play a factor (which alters deck height, affecting COG and PMI as well as allowances for piston skirt design). A long stroke, middling length rod engine with small pistons will require more structure around the barrel of the piston to maintain it's integrity with side loading, whereas a short stroke, long rod, middling piston diameter engine will have far less side loading, allowing for a smaller skirt design (either offset barrel or minimal tang), reducing heat generation and frictional losses. Oiling systems also will change engine efficiency, not to mention ring placement, combustion chamber design and finishing, port angles, etc.

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