penberth3
Well-known member
Shaped pistons, yes? The "flat head" bit might confuse things.
Running engine (diesel) with the ignition turned off
- Thread starter Robert Wilson
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Shaped pistons, yes? The "flat head" bit might confuse things.
JumbleDuck
Well-known member
RichardS
N/A
Indeed .... any digression into side-valve engines is going to throw another spanner into the works.
Richard
black mercury
Active member
Dare anyone to bring up two strokes?Indeed .... any digression into side-valve engines is going to throw another spanner into the works.
Richard
JumbleDuck
Well-known member
convey
N/A
The answers would be the same for an IOE engine as any other (Wankels irrelevent in this discussion)
The statement was
I can think of 3 things affecting the (static) compression ratio. Indeed, determining it.
So what's the third?
It's pretty damned elementary (and I'm not talking leaks etc). I'll give you a clue, it's adjustable, hence affecting the compression ratio.
The statement was
I can think of 3 things affecting the (static) compression ratio. Indeed, determining it.
The first, is shape of the piston crown.
The second, is the shape of the cylinder head's combustion chamber.
So what's the third?
It's pretty damned elementary (and I'm not talking leaks etc). I'll give you a clue, it's adjustable, hence affecting the compression ratio.
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RichardS
N/A
How many times do so many of us have to keep telling you that the shape of the piston crown or cylinder head does not affect the compression ratio.
The compression ratio is a mathematical derivation and when it is determined the shape of the piston crown or cylinder head does not feature in this derivation at all.
Some low compression engines have flat and some have shaped pistons and some high compression engines have flat and some have shaped pistons, thus proving Paul correct beyond doubt.
For a given engine, altering the shape of the pistons will affect the compression ratio, but no-one is arguing the contrary.
Richard
VicS
Well-known member
The shape of the piston crown or the combustion chamber only affect the compression ratio if they change the value of Vc in the equation Roger quoted
convey
N/A
And it's completely wrong.
It's actually the opposite to the truth.
I'm trying to politely and humbly correct you.
VicS corrects you, Rogershaw having given you the better equation.
The shape of the piston crown and cylinder head's combustion chamber DETERMINES the compression ratio ... but there's a third element, what is it?
Strikes me, you don't even know that you don't even know, or perhaps just can't admit it for egotistical reasons.
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JumbleDuck
Well-known member
rogerthebodger
Well-known member
The Vc is constant for a particular engine and does not change under normal conditions.
It can be changed by modifying the engine by skimming the head or polishing the combustion chamber as I have done many times. Machining out the cylinder and fitting new bigger pistons can also affect the CR but there are all due to a dismantle and engineering modifications
Stemar
Well-known member
A diesel one of those could be interesting. It'd need some serious edge seals, thoughOr ...
VicS
Well-known member
I thought so ... arguing at crossed purposes ........... load of rotary engines the lot of you
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rogerthebodger
Well-known member
Ah my name sake except is was an Irish Shaw where I am from the Scottish Shaw's
Richard and convey are talking at cross purposes.
Richard IMHO is saying that in running conditions you cannot change the CR but what convey is if you change the piston for one with a bigger or smaller indent you will change the CR all other parameters being equal.
This applied to all parameters inside the cylinder/head. As is said skimming the head reduces the volume in the cylinder head thus increased the compression ratio.
convey
N/A
Sorry, I was writing the below as you posted a second time. Possibly cross purposes ... I don't know yet. Richard might, but not sure about the beta dogs in his attack pack though. What he said though was,
Nothing about changing while operating.
Polishing won't but, obviously grinding will, we could summarise the latter as modifying the capacity (shape) of the cylinder head's combustion chamber, which could also include welding it up.
Skimming won't always, in the case of a flat cylinder head. It won't change it all.
But that's changing it, not the 3rd design factor that determines the compression ratio.
It's funny when people don't know the answer and can't admit it, how they've got to throw up a load of distractions and insults to hide it.
Nothing about changing while operating.
Polishing won't but, obviously grinding will, we could summarise the latter as modifying the capacity (shape) of the cylinder head's combustion chamber, which could also include welding it up.
Skimming won't always, in the case of a flat cylinder head. It won't change it all.
But that's changing it, not the 3rd design factor that determines the compression ratio.
It's funny when people don't know the answer and can't admit it, how they've got to throw up a load of distractions and insults to hide it.
Sorry Jumbleduck, very drole but you were the guy telling us diesel ignites as flash point just a few posts ago.
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Gixer
Well-known member
As this thread seems to have gone askew I'm going to ask a question.
Ever since I've owned a 1GM10 engine, 15 odd years, I've switch the ignition on, counted to ten and then it the starter. I've no idea why as I don't think the 1GM10 has a glow plug.
I've never pushed the button without counting to ten....
I feel like that bloke in the bunker in that TV series LOST....
Ever since I've owned a 1GM10 engine, 15 odd years, I've switch the ignition on, counted to ten and then it the starter. I've no idea why as I don't think the 1GM10 has a glow plug.
I've never pushed the button without counting to ten....
I feel like that bloke in the bunker in that TV series LOST....
penberth3
Well-known member
Not sure if you can do that half way through the compression stroke!
penberth3
Well-known member
What happens if you count to eight? Have you tried?
VicS
Well-known member
What is your question ?
rogerthebodger
Well-known member
You were assuming that he did not mean that through
Just polishing will as all polishing involved removing material to get a smooth/polished surface. The amount will be small it it will change the volume.
Of cause reshaping the cylinder head combustion chamber will change the volume thus the compression ratio. And while you are at it balancing the volume of the cylinder head combustion chamber on a multi cylinder engine will also change the volume by definition
Of cause with a totally flat cylinder head CR will not change by skimming. List the normal marine/vehicle engines that have a flat head.
The third design factor that determines the compression ratio is the volume of the cylinder. If you increase the volume of the cylinder without changing the volume of the head and the volume in the piston crown. If you seperate the cylinder diameter and the cylinder stroke the are 3rd and 4th design factor.
Yes if you look at the Kruger Dunning Syndrome that exactly what that says but most "well known members" have more than enough knowledge to fall into that syndrome as the know enough to understand how much they don't know.
I have a pretty good idea of JD's knowledge and experience that he knows what he is talking about and like I scottish farther is a straight talker hence and his hole digging post.
Richard, JD and myself are into rebuilding classic cars and I us to tune BMC A series engines when I lived near Longbridge in the UK.
It would be interesting to know where you are located
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