[BMWrules7]

Hello, I am trying to compute the number of cycles each piston undergoes within a single revolution.

Question: if my f02 V8 makes a single revolution, does this have any relationship to the number of Pistons that would fire?

For example, is one revolution (in the same context used by the RPM indicator) equivalent to having all eight Pistons fire?

Since my search didn't find this answer, I will post it.

Or, is there simply no way to know how many piston cycles take place within one revolution?

Why? I saw an old Chevrolet commercial that claimed the Pistons fire millions of times within a few months.

I wanted to compute that. If I knew how many pistons fire within one revolution then I could compute this.

[Genieman]

The short answer to your question is that each cylinder fires once every 2 revolutions... So 4 fires per revolution

http://auto.howstuffworks.com/engine1.htm

[ezaircon4jc]

RPM is how many times the crankshaft rotates every minute. The rotating assembly moves with the crank, so each piston moves the same as the crank. Since the engine is a 4-stroke each piston will fire once every 4 rotations. My math says that 1K rpm equals 250 firings per cylinder per minute; or just over 4 times per second.

Off the top of my head...

I could be wrong, just ask my wife.....

[Genieman]

Originally Posted by ezaircon4jc

RPM is how many times the crankshaft rotates every minute. The rotating assembly moves with the crank, so each piston moves the same as the crank. Since the engine is a 4-stroke each piston will fire once every 4 rotations. My math says that 1K rpm equals 250 firings per cylinder per minute; or just over 4 times per second.

Off the top of my head...

I could be wrong, just ask my wife.....

4-stroke yes, but there are 2 strokes per revolution, piston up then down is 2 strokes for 1 full revolution...

[ezaircon4jc]

Originally Posted by Genieman

4-stroke yes, but there are 2 strokes per revolution, piston up then down is 2 strokes for 1 full revolution...

Wasn't the OP talking about the firing stroke??

[Pimpsy]

Originally Posted by ezaircon4jc

Wasn't the OP talking about the firing stroke??

Take a one cylinder engine: one crank revolution is 2 strokes; one up, one down. The piston fires every 4 piston strokes, not every 4 crank revolutions. So, 1 fire per 2 crank revolutions (4 strokes)

4 cycle = suck, squeeze, bang, blow.

Hope this helps.

[BMWrules7]

Originally Posted by AlanM

Take a one cylinder engine: one crank revolution is 2 strokes; one up, one down. The piston fires every 4 piston strokes, not every 4 crank revolutions. So, 1 fire per 2 crank revolutions (4 strokes)

4 cycle = suck, squeeze, bang, blow.

Hope this helps.

All great responses! Thank you!

[HighlandPete]

Originally Posted by BMWrules7

I wanted to compute that. If I knew how many pistons fire within one revolution then I could compute this.

Now you have answers, you can work out some interesting stats.

How about piston distance travelled over the same road mileage? (Stroke x 2 x rpm).

Remember there are two inherent cyclic functions, crank rpm and 1/2 crank rpm for cam shafts, valve gear, etc.

Besides the speed of combustion it always amazes me the effectiveness of the valve work, particularly at high rpm.

Enjoy the maths.

HighlandPete

[BMWrules7]

Originally Posted by HighlandPete

Now you have answers, you can work out some interesting stats.

How about piston distance travelled over the same road mileage? (Stroke x 2 x rpm).

Remember there are two inherent cyclic functions, crank rpm and 1/2 crank rpm for cam shafts, valve gear, etc.

Besides the speed of combustion it always amazes me the effectiveness of the valve work, particularly at high rpm.

Enjoy the maths.

HighlandPete

If each cylinder moves the crank shaft an equal amount of rotation, why do 12 cylinders give you more power than 8 cylinders?

I could see if multiple cylinders could assist in turning the crank shaft simultaneously would increase your power, right?

But, instead, the firing of the Pistons are serialized one after the other. Doesn't that mean at some point adding cylinders doesn't help because they would be sleeping rather than working?

(I could google this, so please forgive me)

[HighlandPete]

Originally Posted by BMWrules7

If each cylinder moves the crank shaft an equal amount of rotation, why do 12 cylinders give you more power than 8 cylinders?

I could see if multiple cylinders could assist in turning the crank shaft simultaneously would increase your power, right?

But, instead, the firing of the Pistons are serialized one after the other. Doesn't that mean at some point adding cylinders doesn't help because they would be sleeping rather than working?

(I could google this, so please forgive me)

Every power stroke adds to the output, so no issue adding cylinders. Good engine design is all about how you arrange the combustion cycles. Some engine designs are inherently more balanced in torque pulses, simply by the crankshaft and cylinder block configurations.

We are getting more technical, as we need to examine the engine balance, understand the implications of flat and cross-plane crankshaft designs and the various cylinder counts and engine block configurations.

Google is your friend if you want to take it further, as there are some good sites which explain it well.

A grasp of the principles involved, help explain why the BMW "in-line six" is such a good engine design. Or why a V8 can give that lovely burble from the exhaust.

HighlandPete

[The X Men]

Originally Posted by BMWrules7

Hello, I am trying to compute the number of cycles each piston undergoes within a single revolution.

Question: if my f02 V8 makes a single revolution, does this have any relationship to the number of Pistons that would fire?

For example, is one revolution (in the same context used by the RPM indicator) equivalent to having all eight Pistons fire?

Since my search didn't find this answer, I will post it.

Or, is there simply no way to know how many piston cycles take place within one revolution?

Why? I saw an old Chevrolet commercial that claimed the Pistons fire millions of times within a few months.

I wanted to compute that. If I knew how many pistons fire within one revolution then I could compute this.

What do you mean by cycle? Do you mean combustion cycle as in a 4 cycle engine or do you mean firing cycle. Here is a good explanation of a V8 engine's combustion cycle and firing order:

C. 90 degrees *V Eight-cylinder Arrangement

with Two-plane Crankshaft
This arrangement of cylinders provides the firing at
equally phased intervals of 90 degrees. The cylinders are
arranged with numbers 1, 2, 3, and 4 in the left-hand
band and numbers 5, 6, 7, and 8 in the right-hand band
as shown in Fig. 2.30. The two-plane crankshaft uses
pairs of crank-throws phased at intervals of 90 degrees.
Each crankpin incorporates two separate connecting-
rods, hinged to pistons in different cylinder banks. A
main journal and bearing is provided at each end and
between adjacent crankpin. Since two connecting-rods
share a common crankpin these five-main-journal-
crankshafts are extremely short and less complicated.
The two-plane crankshaft has a dynamic balance far
superior to that of the single-plane crankshaft and hence
is more popular.
Consider the order of cylinder power strokes occur-
ring as the crankshaft rotates as shown in the Fig. 2.30.
With piston 1 at TDC after its compression stroke and at
90 degrees V eight-cylinder
Fig. 2.30. 90 degrees V eight-cylinder
arrangement with two-plane crankshaft.
the beginning of the power, piston 5 is at mid-stroke on compression. Piston 3 and 7 are then at
mid-stroke exhaust and at the beginning of exhaust respectively; pistons 4 and 8 are at the
beginning of the compression and at mid-stroke on induction respectively; and pistons 2 and 6
are at mid-stroke power and at the beginning of induction respectively.
With subsequent first, second, third, fourth, fifth, sixth and seventh 90 degrees of rotations
of the crankshaft provide the firing order in this case as 1, 5, 4, 8, 6, 3, 7, 2. A final eighth 90
degrees of rotation completes 720 degrees of crankshaft displacement.

[Noggie]

Originally Posted by BMWrules7

If each cylinder moves the crank shaft an equal amount of rotation, why do 12 cylinders give you more power than 8 cylinders?

I could see if multiple cylinders could assist in turning the crank shaft simultaneously would increase your power, right?

But, instead, the firing of the Pistons are serialized one after the other. Doesn't that mean at some point adding cylinders doesn't help because they would be sleeping rather than working?

(I could google this, so please forgive me)

The firing order is set up different to have a smoth load on the crank.
For a 4 cylinder the common firing order is Cyl 1-3-4-2.
Because it only has 4 cylinders the load on the crank is not evenly spread through the revolution but turns the crank in pulses and these engines vibrate a lot because of this.

for an inline 6 cylinder engines its 1-3-5-7-2-4-6. funny thing here is that cylinder 3 and 4 are both on top at the same time but in opposite stroke.
because of the extra cylinders there load "pulses" are more frequent and the engine vibrates a lot less than a 4 cylinder one.

For V engines the firing order jumps between banks.
V8's essentially being two 4 cylinder engines has much the same vibrations as a 4 but not quite as bad, though not as smooth as a straiht 6.

A V12 is typically 1-7-5-11-3-9-6-12-2-8-4-10. Cylinder 1-6 is on one side and 7-12 on the other bank.
Since this is two inline 6 engines this thing is silky smooth, you can balance a coin in a running V12 its so smooth. just check out this video.

Adding more cylinders means you get more pulses delivering power to the crank and the more cylinders the smoother the engine will run, and the power delivery is more constant.

Looking at the V12 balancing a coin, imagine what a V16 Bugatti Veyron engine will be like

[dadysev]

Remember spark only fires once every two times the pistons hits Top Dead Center so don't forget that in your math calc. Intake - Compression - Power - Exhaust.

N63 (550i) motor and S63 (M5 ) motor have the same block but different firing order do to the fact the cross link the exhaust banks to the turbos to get more pulses (makes turbo spin faster with more power).

Point is the more Pistons the easier it is to ---->>>

[lsturbointeg]

Originally Posted by AlanM

4 cycle = suck, squeeze, bang, blow.

LOL... I chuckled when I read that.

[The X Men]

Originally Posted by lsturbointeg

LOL... I chuckled when I read that.

No sexual innuendo there

[Pimpsy]

Originally Posted by The X Men

No sexual innuendo there

I swear...this is how I learned it as a kid when I was a Harley mechanic!

[BMWrules7]

Originally Posted by The X Men

What do you mean by cycle? Do you mean combustion cycle as in a 4 cycle engine or do you mean firing cycle. Here is a good explanation of a V8 engine's combustion cycle and firing order:

C. 90 degrees *V Eight-cylinder Arrangement

with Two-plane Crankshaft
This arrangement of cylinders provides the firing at
equally phased intervals of 90 degrees. The cylinders are
arranged with numbers 1, 2, 3, and 4 in the left-hand
band and numbers 5, 6, 7, and 8 in the right-hand band
as shown in Fig. 2.30. The two-plane crankshaft uses
pairs of crank-throws phased at intervals of 90 degrees.
Each crankpin incorporates two separate connecting-
rods, hinged to pistons in different cylinder banks. A
main journal and bearing is provided at each end and
between adjacent crankpin. Since two connecting-rods
share a common crankpin these five-main-journal-
crankshafts are extremely short and less complicated.
The two-plane crankshaft has a dynamic balance far
superior to that of the single-plane crankshaft and hence
is more popular.
Consider the order of cylinder power strokes occur-
ring as the crankshaft rotates as shown in the Fig. 2.30.
With piston 1 at TDC after its compression stroke and at
90 degrees V eight-cylinder
Fig. 2.30. 90 degrees V eight-cylinder
arrangement with two-plane crankshaft.
the beginning of the power, piston 5 is at mid-stroke on compression. Piston 3 and 7 are then at
mid-stroke exhaust and at the beginning of exhaust respectively; pistons 4 and 8 are at the
beginning of the compression and at mid-stroke on induction respectively; and pistons 2 and 6
are at mid-stroke power and at the beginning of induction respectively.
With subsequent first, second, third, fourth, fifth, sixth and seventh 90 degrees of rotations
of the crankshaft provide the firing order in this case as 1, 5, 4, 8, 6, 3, 7, 2. A final eighth 90
degrees of rotation completes 720 degrees of crankshaft displacement.

[IMG]http://lh3.googleusercontent.com/_Ii...mage004102.jpg[/IMG]

Fantastic explanations from all of you.

Okay, to me, one cycle is one complete revolution of the crank shaft.

It would seem to me that there has to be a point of diminishing returns, right?

Can you get to a point where adding cylinders has no effect in increasing the raw power?

Or, is it true that there is no upper limit to the number of cylinders you can add to keep increasing power?

[BMWrules7]

Originally Posted by Noggie

The firing order is set up different to have a smoth load on the crank.
For a 4 cylinder the common firing order is Cyl 1-3-4-2.
Because it only has 4 cylinders the load on the crank is not evenly spread through the revolution but turns the crank in pulses and these engines vibrate a lot because of this.

for an inline 6 cylinder engines its 1-3-5-7-2-4-6. funny thing here is that cylinder 3 and 4 are both on top at the same time but in opposite stroke.
because of the extra cylinders there load "pulses" are more frequent and the engine vibrates a lot less than a 4 cylinder one.

For V engines the firing order jumps between banks.
V8's essentially being two 4 cylinder engines has much the same vibrations as a 4 but not quite as bad, though not as smooth as a straiht 6.

A V12 is typically 1-7-5-11-3-9-6-12-2-8-4-10. Cylinder 1-6 is on one side and 7-12 on the other bank.
Since this is two inline 6 engines this thing is silky smooth, you can balance a coin in a running V12 its so smooth. just check out this video.

Adding more cylinders means you get more pulses delivering power to the crank and the more cylinders the smoother the engine will run, and the power delivery is more constant.

Looking at the V12 balancing a coin, imagine what a V16 Bugatti Veyron engine will be like

Cool video! The sound of that engine is similar to a jet when starting.

[HighlandPete]

Originally Posted by BMWrules7

Fantastic explanations from all of you.

Okay, to me, one cycle is one complete revolution of the crank shaft.

It would seem to me that there has to be a point of diminishing returns, right?

Can you get to a point where adding cylinders has no effect in increasing the raw power?

Or, is it true that there is no upper limit to the number of cylinders you can add to keep increasing power?

One cycle is two revolutions, in a four stroke engine. Only two stroke engines cycle in one revolution.


Clearly there are limits to multiple cylinders, for many a reason, costs, size, complexity, etc., also depends on how an engine is tuned. Often the larger the capacity/more cylinders, the engine is tuned to be less stressed.

On the efficiency front, a smaller engine capacity with less cylinders is usually the preferred option. Hence the down sizing we see these days, where engines work more efficiently in real world driving. But even that is a complex design issue, computer control for functions like valvetronic, are tuned to assist efficiency.

HighlandPete

[BMWrules7]

Originally Posted by ezaircon4jc

Wasn't the OP talking about the firing stroke??

The OP is clueless. I can understand if all cylinders must complete its power strokes within a single revolution of the crank shaft.

If true, then adding more cylinders will always add more power to my way of thinking.

I think that's all I need to know: regardless of the number of cylinders, will all cylinders complete their power stroke within a single 360 degree revolution of the crank shaft?

Is that a 100% true statement?

From the responses I see here, I think this is true.

Do I have it correct?

Ugh!

I obviously don't have this correct according to Pete and others.

I am going to re read the responses here again.

[HighlandPete]

Think of the four stroke engine cycle this way... a single cylinder engine can't run unless it completes two revolutions.

HighlandPete

[HighlandPete]

Originally Posted by BMWrules7

I think that's all I need to know: regardless of the number of cylinders, will all cylinders complete their power stroke within a single 360 degree revolution of the crank shaft?

Is that a 100% true statement?

No, however many cylinders you have, it still takes two revolutions (720 degrees) to sequence all the power strokes. That is whether there is one cylinder or up to twelve or more.

HighlandPete