question 'bout engines

[xlr8r]

i have a question about engines and stuff. what is the benifit of having a 2.5 v6 liter engine compared to a 2.5 inline4? or 5l v12 versus a 5l v8? 3.5v6 versus a 3.5v8? whats the difference, if any, between power, fuel economy, etc? just curious. thanks

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<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by xlr8r:
i have a question about engines and stuff. what is the benifit of having a 2.5 v6 liter engine compared to a 2.5 inline4? or 5l v12 versus a 5l v8? 3.5v6 versus a 3.5v8? whats the difference, if any, between power, fuel economy, etc? just curious. thanks<HR></BLOCKQUOTE>

Let's make it easy.
An engine with more cylinders is worthy of higher overall output(when originally built right). ex.. more torque can be derived from stroking a v8 properly than the same cc of a v6.
Now, yes this is a overview and not specific, yet that is the basis.

[Hudson]

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by xlr8r:
i have a question about engines and stuff. what is the benifit of having a 2.5 v6 liter engine compared to a 2.5 inline4? or 5l v12 versus a 5l v8? 3.5v6 versus a 3.5v8? whats the difference, if any, between power, fuel economy, etc? just curious. thanks<HR></BLOCKQUOTE>

Typically, with more cylinders, the engine is smoother. Four-cylinders are notorious for being rough and V8s and, especially, V12s are known for their smoothness.

Since all manufacturers have their engineering differences (and even substantial differences between different engines from the same manufacturer), it's difficult to compare similarly sized engines of different cylinder numbers. It has been my experience, though, that engines with more cylinders will get worse gas mileage than similarly sized engines with fewer cylinders (of similar power).

Emissions from larger bored engines are greater than those of smaller bored engines, which makes the case for more cylinders and smaller bores per cylinder. Chrysler discovered years ago that engines with bores above 4 inches pollute significantly more, even in proportion, to engines with bores under 4 inches. This is the main reason why Chrysler went with a V10 instead of a large bore V8 in their trucks.

Folks, correct me if I'm wrong but the current engines offered for sale (in light vehicles) in the US are in the range of:

3 : 1.0L (Honda/Suzuki)
4 : 1.3L (Suzuki)-2.7L (Toyota)
5 : 2.3L (Volvo)-2.4L (Volvo)
6 : 2.3L (Mazda)-4.3L (GM)
8 : 3.5L (Lotus)-8.1L (GM)
10: 6.8L (Ford)-8.0L (Chrysler)
12: 5.4L (BMW)-6.0L (Mercedes-Benz/Lamborghini)

[Nismo]

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by xlr8r:
What is the benifit of having a 2.5 v6 liter engine compared to a 2.5 inline4? Or 5l v12 versus a 5l v8? 3.5v6 versus a 3.5v8? Whats the difference, if any, between power, fuel economy, etc? Just curious.<HR></BLOCKQUOTE>Most importantly, for a given displacement, more cylinders allows for a higher specific output (more power).

One reason for this is that with more cylinders, each piston has less travel per engine revolution. This allows for higher engine speeds while keeping piston speeds reasonable (when piston speeds get too high, the friction becomes too great to overcome).

For example, the 4 cylinder 2.0L engine in Honda's streetcar--the S2000--has higher piston speeds at 9000RPM than their Formula One racecar engine--10 cylinder 3.0L engine--does at around 18000RPM. (Of course, if FIA allowed the use of ceramic-composite materials in F1 engines, then Honda's V10 would make even more power--but that's another story.)

There are other factors as well, such as vibrational characteritics (an inline 4 cylinder engine will vibrate more than a V-8 engine); packaging issues (an I-4 will fit into a much smaller space than a V-8); and fuel economy (with less weight and less moving parts, an I-4 engine will generally be more fuel-efficient than a V-8 at lower engine speeds).

['97 S14 SE Turbo]

Another good example:

Nissan's own lineup (Japan spec 1st gen VQ engines)

VQ20DE is rated for 170hp
VQ25DE is rated for 190hp
VQ30DE is rated for 210hp

SR20DE is rated for 140hp
QR25DE is rated for 180hp

The big difference is that the engine with more cylinders will offer a better torque range compared to the less 4 cylinder engine. That's why outside of North America, there's BMW 520, 523, 525, 730, MB C200, C230, E230, These are all fairly large car with smaller displacement V6/I6 engines.

[**DONOTDELETE**]

More cylinders with same bore/stroke ratio, displacement, and everything else being equal = more surface friction, but more effective burn. The area scrubbed per unit displacement by smaller but more pistons is much higher than fewer but larger pistons... but a smaller flame spread area is easier to control against hot-spotting, and since the area is small, near-complete progression is rapid... burning more of the fuel, and producing less emmissions. Another advantage of more cylinders is smooth power delivery and responsiveness. Instead of producing 1 power stroke per half-revolution (4-cylinder, 4-stroke cycle), a 12-cylinder 4-stroke cycle piston engine would produce 3 times as many power strokes per revolution... rendering a power stroke every 60 degrees of crank movement (which makes a very smooth engine relatively). This allows the use of a very light flywheel while still maintaining smooth power-delivery... which helps in engine responsiveness.

[Republic]

Another advantage of an engine with more cylinders is that the engine will last longer. An engine with fewer cylinders will have to 'work' harder to give the same performance of a larger engine that can generate the same amount of power more easily.

[llaprad1]

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by Republic:
Another advantage of an engine with more cylinders is that the engine will last longer. An engine with fewer cylinders will have to 'work' harder to give the same performance of a larger engine that can generate the same amount of power more easily. <HR></BLOCKQUOTE>

Is that a legitimate, documented answer or is this based on personal or anecdotal experience? Hope that doesnt sound smart ass, but Ive heard other logic that fewer cylinders results in fewer moving parts, therfore lasting longer.

But I believe that information I recieved was either anecdotal (i.e. I had a Toyota that ran forever and a Ford that blew up in a week..) or pseudo-common sense.

Just curious.

[Republic]

That was written in an older issue of either Automobile or Car & Driver. The editor was commenting on how French car manufacturers always used low-liter/low-cylinder engines, and mentioned that since the engine with a higher displacement and more cylinders wouldn't have to work as hard to generate a reasonable amount of power, they'd last longer than engines with smaller displacements and/or less cylinders. Seeing that he was a car editor, I trusted what was published...

It's a totally fair question, and doesn't sound smart-ass in the least. With all the **** that gets posed on message boards, I totally understand you asking.

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less cylinders = more work = more friction = more heat = probable lower life span, although it seems that most of the high millage cars around are 4cyl., this could be due to better engineering to begin with.

[thearabian]

with all this talk about work and friction, im asking myself, what kind of Thermal Efficiencies do internal combustion engines get?

Diesel Powered
Octane fuel engines and the diff between efficiencies of 4-6-8-12 cylinders
Race engines such as a BMW V10

[**DONOTDELETE**]

Quoting
_______
That was written in an older issue of either Automobile or Car & Driver. The editor was commenting on how French car manufacturers always used low-liter/low-cylinder engines, and mentioned that since the engine with a higher displacement and more cylinders wouldn't have to work as hard to generate a reasonable amount of power, they'd last longer than engines with smaller displacements and/or less cylinders.
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That is simply because he/she is talking about different displacement engines. Given the same relative structural strength, this shouldn't matter.

[Hudson]

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by zbeast:
less cylinders = more work = more friction = more heat = probable lower life span, although it seems that most of the high millage cars around are 4cyl., this could be due to better engineering to begin with.<HR></BLOCKQUOTE>

Assuming the same total engine displacement, more cylinders would provide more surface area (piston to cylinder wall) and would (all things being the same) generate more friction than an engine with fewer cylinders.

Some of the highest mileage cars on record have been four-cylinder engines (the record-setting Volvo, for one, is a four-banger). Large over-the-road trucks are large-displacement sixes. Wouldn't it make sense that if an eight were more durable than a six, Class 8 trucks (vehicles that need to generate income for a million miles or more) would have them?

[Nismo]

Regarding friction: Twice the contact area amounts to twice the friction at any engine speed. However, it doesn't stop there. Friction is generally a cube of speed; therefore, an engine running twice as fast would have to overcome EIGHT times more friction.

At lower engine speeds, it's better to have less moving parts--for example, 4 cylinders would be better than 8. However, as engine speed increases, piston speeds become more and more important, and there's really only two ways to keep piston speeds low (for a given displacement): (1) decrease stroke while increasing bore or (2) use more cylinders to give the same displacment. Both methods have their advantages/disadvantages, and real-world designs are a combination of the two.

To keep things simple: for a given displacement, less cylinders usually is better for fuel economy while more cylinders usually is better for higher specific output (more power).

On a side note, one of the reasons small lightweight--yet powerfully high revving--engines are gaining popularity nowadays is that in normal driving they can offer very good fuel economy. But when you want to cut loose, you can rev it up to stratospheric levels and still be rewarded with excellent power. Sure, if you wanted that kind of power ALL the time (like when towing a big load) you'd be foolish to attempt it with a high-revving engine because the combination of stress and friction would bring the engine to a premature death. Instead, for heavy hauling duty, vehicle designers use high-torque engines (diesel and/or big displacment) which provide good power at lower engine speeds where friction and other stresses are much lower.

[hiwayman17]

Another way to think about the "less wear" for engines with more cylinders is this...even if a 4 and 6 cylinder engine "works" the same, the stresses of the wear are divided over 6 cylinders. If you have only 4 cylinders and it works as hard as the 6, the stresses are only spread among 4 cylinders. So in this respect, the 4's will get more wear.

[Hudson]

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by Nismo:
..On a side note, one of the reasons small lightweight--yet powerfully high revving--engines are gaining popularity nowadays is that in normal driving they can offer very good fuel economy. But when you want to cut loose, you can rev it up to stratospheric levels and still be rewarded with excellent power. Sure, if you wanted that kind of power ALL the time (like when towing a big load) you'd be foolish to attempt it with a high-revving engine because the combination of stress and friction would bring the engine to a premature death. Instead, for heavy hauling duty, vehicle designers use high-torque engines (diesel and/or big displacment) which provide good power at lower engine speeds where friction and other stresses are much lower.<HR></BLOCKQUOTE>

Finally, someone has stated a reason for BOTH big and small engines. It irritates me to no end when "American muscle car fans" overuse the cliche "no replacement for displacement," but on the other hand, the four-cylinder drivers think the former group are just "stuck in the 1960s."

Bravo!

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And Here, I thought I was strange because I owned a Turbo Deisel for Hauling. A 360 Hi-po for local runs and lighter loads and I run around in my 240sx for fun and fuel economy.
Yet then again, this may have nothing to do with my mental state http://66.96.198.147/forum/images/icons/wink.gif
RZ