Quote from: dragonmate on August 06, 2004, 03:59:39 PM
Mga Bossing,
Thanks for the explanation of Stradale and Raymond, which both make some sense.  However, please bear with me because it's not quite clear yet for me.
If I may change the question:  To make one complete revolution of the drive shaft, how much air-fuel mixture will be burned by a 2.4 liter, 4cyl engine, and by a 2.4 liter, 6 cyl engine?  
My answer is 2.4 liters for both.  That is because each piston/cylinder will make a complete cycle, regardless of the number of cylinders.  Hence, the total volume of fuel-air mixture that will be consumed in one revolution of the drive shaft will be the same as the total displacement of all cylinders, which is 2.4 liters. Mali ba yon?  
Note that I'm talking of fuel-air mixture, and not fuel alone.

Yup, engine displacement maybe the same, but different a/f mixture volumes are needed for the 4-cyl and 6-cyl engines.

Puwede ring parehas ang displacement nung 4-cyl at 6-cyl, malalaki naman iyong valves nung isa.

Quote from: Raymond on August 06, 2004, 04:03:53 PM
Yup, engine displacement maybe the same, but different a/f mixture volumes are needed for the 4-cyl and 6-cyl engines.

Puwede ring parehas ang displacement nung 4-cyl at 6-cyl, malalaki naman iyong valves nung isa.

Alright.  So you're saying that between engines with the same displacement, the one with a better aspiration will have the capacity to produce more power.  But that doesn't lead to the conclusion that a 4 cylinder engine is generally more fuel efficient than a six cylinder engine.

If I may change the question again: Between the 4 cyl and the 6 cyl engines with the same displacement, which engine will produce more power with the same amount of fuel burned?  Let's assume that technology for aspiration, transmission and whatever is the same for both.  Wouldn't the answer to that question suggest which engine is more fuel efficient?

Pasensya na for being makulit.  Halata na yatang wala akong ginagawa sa opisina.

Quote from: dragonmate on August 06, 2004, 04:45:52 PM
Alright.  So you're saying that between engines with the same displacement, the one with a better aspiration will have the capacity to produce more power.  But that doesn't lead to the conclusion that a 4 cylinder engine is generally more fuel efficient than a six cylinder engine.

Yes. Try comparing Honda's B16A with an ordinary 1600 engine from let's say Toyota. Let's not focus on VTEC, etc. The fact that Honda was able to squeeze 160 Hp out of it makes it efficient, not in the terms of fuel consumption, but in specific output (Hp/liter).

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If I may change the question again: Between the 4 cyl and the 6 cyl engines with the same displacement, which engine will produce more power with the same amount of fuel burned?  Let's assume that technology for aspiration, transmission and whatever is the same for both.  Wouldn't the answer to that question suggest which engine is more fuel efficient?

Siyempre four cylinder pa rin IMHO.

take into consideration din ang volumetric thermal at mechanical efficiency ng kada engine ang malaking factors. a possible explanation to why a same size engine with four or six cylinders would have more power would probably because it will be more mecahnically efficinet a smaller stroke which should produce less occilations. plus a six \cylinder would produce a power stroke at every 120 degrees providing a more balanced run hth

Quote from: Blackblood on August 06, 2004, 06:57:26 PM
take into consideration din ang volumetric thermal at mechanical efficiency ng kada engine ang malaking factors. a possible explanation to why a same size engine with four or six cylinders would have more power would probably because it will be more mecahnically efficinet a smaller stroke which should produce less occilations. plus a six \cylinder would produce a power stroke at every 120 degrees providing a more balanced run hth

There goes a more technical and detailed explanation. Thanks lloyd

Quote from: dragonmate on August 06, 2004, 03:59:39 PM
To make one complete revolution of the drive shaft, how much air-fuel mixture will be burned by a 2.4 liter, 4cyl engine, and by a 2.4 liter, 6 cyl engine?  
My answer is 2.4 liters for both.  That is because each piston/cylinder will make a complete cycle, regardless of the number of cylinders.  Hence, the total volume of fuel-air mixture that will be consumed in one revolution of the drive shaft will be the same as the total displacement of all cylinders, which is 2.4 liters. Mali ba yon?  

I understand what you're trying to point out - that supposedly equal lang ang swept volume ng air/fuel mix in both cases. You are correct in theory (although the answer is 1.2 liters for both per 1 crank revolution but that's beside the point ).

As pointed out earlier, there are other factors that should be considered.  Lets focus on just one - mechanical efficiency and make an analogy:

Because it has more moving parts (and thereby more friction), the 6-cyl. engine has to overcome more resistance to turn the crankshaft 1 revolution compared to the 4-cyl. engine.  If you have to handcrank both (like with the Keystone Cops cars), mas mahihirapan ka dun sa 6-cyl.  Mas marami kang "susunugin" na calories.

Get it?

Quote from: stradale on August 06, 2004, 08:01:00 PM
I understand what you're trying to point out - that supposedly equal lang ang swept volume ng air/fuel mix in both cases. You are correct in theory (although the answer is 1.2 liters for both per 1 crank revolution but that's beside the point ).

As pointed out earlier, there are other factors that should be considered.  Lets focus on just one - mechanical efficiency and make an analogy:

Because it has more moving parts (and thereby more friction), the 6-cyl. engine has to overcome more resistance to turn the crankshaft 1 revolution compared to the 4-cyl. engine.  If you have to handcrank both (like with the Keystone Cops cars), mas mahihirapan ka dun sa 6-cyl.  Mas marami kang "susunugin" na calories.

Get it?

As pointed out earlier, there are other factors that should be considered.  Lets focus on just one - mechanical efficiency and make an analogy:

Because it has more moving parts (and thereby more friction), the 6-cyl. engine has to overcome more resistance to turn the crankshaft 1 revolution compared to the 4-cyl. engine.  If you have to handcrank both (like with the Keystone Cops cars), mas mahihirapan ka dun sa 6-cyl.  Mas marami kang "susunugin" na calories.

Get it?

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Stradale,
I think I got you this time.  So it's really just the mechanical inefficiency, i.e., more moving parts and friction, that makes the 6 cylinder engine consume more fuel.  But given that these engines are finely-tuned and well-lubricated machines that can run for a good number of years, I would imagine that the inefficiency wouldn't be too significant.  Is it?

Ano bang recent 4 cylinder production engine ang may displacement na equal to a 6 cylinder (2.2 or 2.4 liter?)? Perhaps we can compare the actual fuel consumptions.

Thanks for the replies.

yung inneficiency nyia nareresolve naman through as what i said earlier sa more powerstrokes per crank revolution. so give or take lang per factor, mechanical, thermal at volumetric

check out mo mga nissan na rb engines, rb20 2.0 rb25/26 rb30? hehe di ako sure dito sa huli hekhek pero straight six ang pinaguusapan ko, a v6 or a boxer layout would be different

Agree.  The 6-cyl will more than make up for the disadvantage in mechanical efficiency thru as you said, more power strokes per crank rev (3 versus 2) and more rpm (due to proportionately lighter reciprocating mass).  The question kasi was which engine would consume less fuel, not which engine would make more power.

gack mali pala basa ko hekhek sori medj bangag na kasi ako nun

Quote from: stradale on August 04, 2004, 05:14:35 PM
This is the correct formula but you have to multiply this by the number of cylinders pa .

and how is thermodynamics involved in this question/answer?

mga folks, it's pointless discussing this in the sense that there are about a thousand (million?) factors which will determine fuel efficiency, power, etc. of an engine.  but the basic generalization is that larger engine displacement would result in higher power and fuel consumption (assuming all things equal -- which hardly is).

all this talk about volumetric, stoichiometric, and thermal efficiencies is just noise.

Quote from: aranetaj on October 21, 2004, 11:19:20 AM
mga folks, it's pointless discussing this in the sense that there are about a thousand (million?) factors which will determine fuel efficiency, power, etc. of an engine.  but the basic generalization is that larger engine displacement would result in higher power and fuel consumption (assuming all things equal -- which hardly is).

all this talk about volumetric, stoichiometric, and thermal efficiencies is just noise.

ditto

Quote from: aranetaj on October 21, 2004, 11:12:22 AM
and how is thermodynamics involved in this question/answer?

We got a bit carried away talking about efficiency and friction (nothing about thermodynamics at all) but the post you quoted is the wrong example because that wasn't OT at all.  But since you have now spoken after digging up this old thread, I guess we will just have to STFU then huh?  

I think engine displacement has been pretty much defined. Now talking about fuel consumption is another thing altogether.

I see people pointing to same volume for 4 & 6 cylinder engines of exact same displacement. But no one, say COMPRESSION RATIO ?. This makes a difference as well as chamber design, head design, value design, lift, timing method of timing. Pretty complex.

The comparison between HP is also not that useful. Cos the Torque part is what gets you accelerating!. Also, the "how fast" your RPM climbs. My old Accord 2.3 manual takes forever to get to 5K RPM while my new VIos 1.5 can rev from 2K to 6K very quickly delivering the much needed torque for great acceleration. Its light too so picks up pace real quick to deliver a very spirited drive.

Manufacturer's claim for fuel comsumption is typically very very optimistic. However, one can even better that by driving lightly and very accurately. Looks at Poncholo Ramirez winning the Civic Challenge. He clocked in over 45 MPG in the thing. Most people would be lucky to get 40 MPG!!!.