4 cycle engine and number of cylinders

[Clevy]

Originally Posted By: ZeeOSix
Originally Posted By: Clevy
I cannot say for sure that every manufacturer is the same as far as firing and position however I did work on a triumph tr7 and I'm positive that engine had the 2 center cylinders in the exact same position and the 2 outside cylinders also in the same position. So the outsides would fire simultaneously and so would the center pistons.


Just because two of the four pistons were at the top or bottom at the same time doesn't mean they both fired at that same time. A piston is at TDC twice and BDC twice in it's 4-stroke process. Multi-cylinder engines typically do not fire two or more pistons at the same time because it causes too much vibration. The pistons are usually fired by (720 degrees/# of cylinders) apart to give as many power pulses into the crankshaft as possible per crank revolution.







Ohhhhhhhh.
Ok. So one of the pair was firing while the other was compressing.

Gotcha.


I stand corrected. Thanks zo6

 

[ZeeOSix]

Originally Posted By: 29662
Originally Posted By: ZeeOSix
Originally Posted By: 29662
V4's use a 90 deg crank. They fire 1 cylinder every 180 deg of crank rotation, 720 deg in a 4 cycle rotation.


Yes, just like an I4 does. Like I said, 720/4 = 180.

Engine designs that fire multiple cylinders at the same time are odd-ball designs.


You're forgetting that an "L4" Flatplane has 2 pistons at the same position but in different cycles. In a v4 with a crossplane crank the pistons are not aligned like that because of the separation of the "v".


Unless it's some odd-ball engine design, a typical 4-cylinder engine - regardless if it's and inline 4 or a V4 - will have a piston firing every 180 degrees. And that means two pistons will be at TDC and two will be at BDC ... all on different phases of their 4-stroke process.

 

[29662]

Originally Posted By: ZeeOSix
Originally Posted By: 29662
Originally Posted By: ZeeOSix
Originally Posted By: KevGuy
In an 8 cylinder engine is it safe to say 2 cylinders on intake, 2 on compression, 2 on combustion and 2 on exhaust???


No ... as said before, each cylinder by default has to be 90 degrees apart, so no two cylinders can be on the same part of the 4-cycle process at the same time.


Yes they would as each cycle encompasses 180 deg of rotation and the firing order is separated by 90 deg of crank rotation. They would just be in a different phase of any given cycle with the "paired cylinders" changing continuously, in regards to a v8.


Read carefully what KevGuy asked. The answer is no. On a typical V8 there is no way that there are a pair of cylinders on the same exact part of their 4-stroke process.

Each 4-stoke cycle comprises 720 degrees (2 crank rotations), not 180 degrees. At any give time, all 8 pistons are in a different phase of the 4-stoke process ... they are all out of phase by 90 degrees of crank rotation (720/8 = 90).


I think you misunderstood. I said each "cycle" encompasses 180deg of crank rotation. so on a V8 there are 2 pistons in the same cycle but in a different phase (position) at any given time for a complete power/otto cycle(720 deg of crank rotation).

A v4 is not an oddball design as there are millions of them out there. Just look at all of Honda's v4 engines.

 

[29662]

Originally Posted By: ZeeOSix
Originally Posted By: 29662
Originally Posted By: ZeeOSix
Originally Posted By: 29662
V4's use a 90 deg crank. They fire 1 cylinder every 180 deg of crank rotation, 720 deg in a 4 cycle rotation.


Yes, just like an I4 does. Like I said, 720/4 = 180.

Engine designs that fire multiple cylinders at the same time are odd-ball designs.


You're forgetting that an "L4" Flatplane has 2 pistons at the same position but in different cycles. In a v4 with a crossplane crank the pistons are not aligned like that because of the separation of the "v".


Unless it's some odd-ball engine design, a typical 4-cylinder engine - regardless if it's and inline 4 or a V4 - will have a piston firing every 180 degrees. And that means two pistons will be at TDC and two will be at BDC ... all on different phases of their 4-stroke process.


You're forgetting that an "L4" Flatplane has 2 pistons at the same position but in different cycles. In a v4 with a crossplane crank the pistons are not aligned like that because of the separation of the "v".

 

[ZeeOSix]

Originally Posted By: 29662
I think you misunderstood. I said each "cycle" encompasses 180deg of crank rotation. so on a V8 there are 2 pistons in the same cycle but in a different phase (position) at any given time for a complete power cycle(720 deg of crank rotation).


No ... each 4-stroke "cycle" comprises 720 degrees of crank rotation (ie, 2 crank revolutions). If people don't use the correct terminology all thoughts are jumbled.

There are never two pistons in the same part of the 4-stroke cycle on a typical, common V8 engine.


Originally Posted By: 29662
A v4 is not an oddball design as there are millions of them out there. Just look at all of Honda's v4 engines.


I didn't say a V4 engine was "an odd ball design". I said if a V4 fired two of the 4 pistons at the same time then it would be odd ball. Just like any muti-cylinder engine that fired multiple pistons at the same time.

 

[29662]

Originally Posted By: Clevy
Originally Posted By: ZeeOSix
Originally Posted By: Clevy
I cannot say for sure that every manufacturer is the same as far as firing and position however I did work on a triumph tr7 and I'm positive that engine had the 2 center cylinders in the exact same position and the 2 outside cylinders also in the same position. So the outsides would fire simultaneously and so would the center pistons.


Just because two of the four pistons were at the top or bottom at the same time doesn't mean they both fired at that same time. A piston is at TDC twice and BDC twice in it's 4-stroke process. Multi-cylinder engines typically do not fire two or more pistons at the same time because it causes too much vibration. The pistons are usually fired by (720 degrees/# of cylinders) apart to give as many power pulses into the crankshaft as possible per crank revolution.







Ohhhhhhhh.
Ok. So one of the pair was firing while the other was compressing.

Gotcha.


I stand corrected. Thanks zo6


No. I think he meant that each piston was in a different cycle. one compressing, one firing, one on the power stroke, and one exhausting.

 

[ZeeOSix]

^^^ You guys are getting all wrapped up on the axle here.

Listen, on a "normal/typical" 4-stroke engine design, the pistons fire apart by the formula: "720 degrees divided by the number of pistons". This also tells you how many degrees each piston is out of phase in the 4-cycle process.

UNLESS, it is some "odd-ball" engine design (ie, "big bang") where it fires multiple pistons at the same time. I could design a V8 to fire 4 of the 8 pistons at the same time, then the other 4 at the same time, so it would essentially be a gigantic "2-cylinder" engine in terms of piston firings.

 

[29662]

Originally Posted By: ZeeOSix
Originally Posted By: 29662
I think you misunderstood. I said each "cycle" encompasses 180deg of crank rotation. so on a V8 there are 2 pistons in the same cycle but in a different phase (position) at any given time for a complete power cycle(720 deg of crank rotation).


No ... each 4-stroke "cycle" comprises 720 degrees of crank rotation (ie, 2 crank revolutions). If people don't use the correct terminology all thoughts are jumbled.

There are never two pistons in the same part of the 4-stroke cycle on a typical, common V8 engine.


Originally Posted By: 29662
A v4 is not an oddball design as there are millions of them out there. Just look at all of Honda's v4 engines.


I didn't say a V4 engine was "an odd ball design". I said if a V4 fired two of the 4 pistons at the same time then it would be odd ball. Just like any muti-cylinder engine that fired multiple pistons at the same time.


A "cycle" is a 180 deg rotation of the CRankshaft. An Otto cycle is 720 deg of crankshaft rotation. I think youre the one who is not using correct terminology. That's why it's called a 4 cycle engine.

A v4's pistons don't line up like an L4's pistons do. you're forgetting the separation in piston plane alignment due to the V.

A BIG BANG does not fire multiple cylinders at the same time. they are separate events.

 

[ZeeOSix]

Originally Posted By: 29662
A "cycle" is a 180 deg rotation of the CRankshaft. An Otto cycle is 720 deg of crankshaft rotation. I think youre the one who is not using correct terminology. That's why it's called a 4 cycle engine.


Nope ... it's called a "4-stroke" or "4-cycle" engine. The "Otto Cycle" is a "4-stroke".
4-Stroke Engine

When I say a "complete cycle" I mean all 4 stokes of the cycle have been completed. And in a 4-stroke engine that takes 2 crank revolutions, or 720 degrees.

Originally Posted By: 29662
A v4's pistons don't line up like an L4's pistons do. you're forgetting the separation in piston plane alignment due to the V.


Not sure what you're trying to say here, but in any typical V4 engine, 2 of the pistons will be at TDC when the other 2 are at BDC. And in a V8, 4 of the pistons will be at TDC when the other 4 are at BDC.

 

[29662]

[censored] I can't believe I'm having an online debate at 3:30 A.M.. Boy am I glad I don't work tomorrow; or is that today.

Z, if you're ever in my part of the world I would be more than happy to show you around the shop. Got everything from 2 cylinder twins to H4's, H6's, v8's, L8's, and even some diesel 3 cylinders that we do from time to time.

 

[ZeeOSix]

Originally Posted By: 29662
[censored] I can't believe I'm having an online debate at 3:30 A.M.. Boy am I glad I don't work tomorrow; or is that today.

Z, if you're ever in my part of the world I would be more than happy to show you around the shop. Got everything from 2 cylinder twins to H4's, H6's, v8's, L8's, and even some diesel 3 cylinders that we do from time to time.

Maybe you are rummy, being so late and all.

Just read what I said and I think it's just terminology here. I've been around engines forever. It's not rocket science.

 

[Merkava_4]

The Walking 'W'
Intake Stroke = piston going down - intake valve open
Compression Stroke = piston going up - both valves closed
Power Stroke = piston going down - exhaust valve starting to open
Exhaust Stroke = piston going up - exhaust valve open

 

[ZeeOSix]

Originally Posted By: 29662
A BIG BANG does not fire multiple cylinders at the same time. they are separate events.


Sometimes ... "Big Bang" Engines

 

[29662]

Originally Posted By: ZeeOSix
Originally Posted By: 29662
A "cycle" is a 180 deg rotation of the CRankshaft. An Otto cycle is 720 deg of crankshaft rotation. I think youre the one who is not using correct terminology. That's why it's called a 4 cycle engine.


Nope ... it's called a "4-stroke" or "4-cycle" engine. The "Otto Cycle" is a "4-stroke".
4-Stroke Engine

When I say a "complete cycle" I mean all 4 stokes of the cycle have been completed. And in a 4-stroke engine that takes 2 crank revolutions, or 720 degrees.

Originally Posted By: 29662
A v4's pistons don't line up like an L4's pistons do. you're forgetting the separation in piston plane alignment due to the V.


Not sure what you're trying to say here, but in any V4 engine, 2 of the pistons will be at TDC when the other 2 are at BDC. And in a V8, 4 of the pistons will be at TDC when the other 4 are at BDC.


Sorry to tell you but you're way off. A 4 stroke/4cycle/Otto cycle is all the same thing, with different monikers.

With regard to 4 of 8 pistons being at TDC or BDC, that is incorrect in a regular production v8 with a crossplane(the most common type) crankshaft. Each crank throw is separated by 90 deg. and each carrying two cylinders, separated by a 90 deg V(typically). If you're talking about a an all out race engine with a Flatplane (180 deg) crankshaft. That is still not correct because of the included 90 deg angle of the V configuration. What you're describing Only applies to "L" (inline) motors with a flatplane crankshaft.

 

[29662]

Originally Posted By: ZeeOSix
Originally Posted By: 29662
A BIG BANG does not fire multiple cylinders at the same time. they are separate events.


Sometimes ... "Big Bang" Engines


Never. They never fire multiple cylinders simultaneously.

 

[ZeeOSix]

Originally Posted By: 29662
Sorry to tell you but you're way off. A 4 stroke/4cycle/Otto cycle is all the same thing, with different monikers.


Originally Posted By: ZeeOSix

... it's called a "4-stroke" or "4-cycle" engine. The "Otto Cycle" is a "4-stroke".
4-Stroke Engine

Go to bed, really ... that's what I said above.

Originally Posted By: 29662
With regard to 4 of 8 pistons being at TDC or BDC, that is incorrect in a regular production v8 with a crossplane(the most common type) crankshaft. Each crank throw is separated by 90 deg. and each carrying two cylinders, separated by a 90 deg V(typically).


You are obviously not understanding what I'm saying. I was giving an "odd-ball" example with that V8 example. Go re-read my posts, carefully.

 

[Merkava_4]

Nobody's corrected me yet so maybe I got it right.

 

[ZeeOSix]

Originally Posted By: 29662
Originally Posted By: ZeeOSix
Originally Posted By: 29662
A BIG BANG does not fire multiple cylinders at the same time. they are separate events.


Sometimes ... "Big Bang" Engines


Never. They never fire multiple cylinders simultaneously.


In the article it said:
"The Honda NSR500 began and ended its life as a screamer. However in 1990 Honda connected both of the pistons in one bank to the same crankpin and both of the other pistons to a crankpin offset 180°. This NSR500 was called a 'big bang'."

In that V4 engine, two of the four pistons fired at the same time. It was essentially like a big V-twin in terms of power pulses from the pistons firing (two at the same time in the same bank).

 

[29662]

You said
"Not sure what you're trying to say here, but in any typical V4 engine, 2 of the pistons will be at TDC when the other 2 are at BDC. And in a V8, 4 of the pistons will be at TDC when the other 4 are at BDC"

Please give me an example of a V8 where 4 of the pistons are at TDC and 4 are at BDC.

 

[ZeeOSix]

Originally Posted By: 29662
You said
"Not sure what you're trying to say here, but in any typical V4 engine, 2 of the pistons will be at TDC when the other 2 are at BDC. And in a V8, 4 of the pistons will be at TDC when the other 4 are at BDC"

Please give me an example of a V8 where 4 of the pistons are at TDC and 4 are at BDC.


Yes, my bad. In a typical V8 the pistons will be 90 degrees apart, as I've said many times already. So no, what I said there is not correct for the V8, BUT is correct for a typical V4 which will have pistons 180 degrees apart.