Volumetric efficiency explanation
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Opinions wanted on this - found on another forum:
This is a basic mechanical explanation of what you can achieve with your engine.
It's all about volumetric efficiency as this is what defines how much power an engine is capable of producing. It's a measure of the efficiency of the power cycle - that is induction, ignition, and the exhaust process. Typical modern engines (in particular the latest german ones) will have a volumetric efficency rating of about 85-90+, with older engines like the mk1 & mk2 maybe at something like 80-85, whilst my old mgb falls at around 65-70 This means the tuning potential is a lot greater in my mgb with bigger gains to be achieved quite cheaply. The Japs managed to tune the mr2 engines to quite a high state of efficiency so if your mk1 is running at a healthy say 82% efficiency @ 122bhp, you could probably hit 150bhp @ 100% efficiency, whilst a mk2 rev 3 running at 85% efficiency @ 178bhp could theoretically attain 210bhp @ 100% efficiency.
Whilst this sounds tempting, please be aware that it is theoretically impossible to attain 100% volumetric efficiency, and getting up to the high 90's is gonna cost megabucks. So that's it i hear you cry? All is lost?
Nope. To increase the volumetric efficiency quite cheaply (well at least on my 'B) you can simply increase the volume of the engine. A bigger engine allows for wilder cams without losing grunt. The other way is to increase the amount of air that flows through the engine - in otherwords forced induction such as turbo or supercharging.
So throughout the whole cycle, a less restrictive air filter will flow air more freely into the engine. An induction pipe that holds more air than the volume of the engine will ensure you are not spending power from the engine having to draw air in throughout it's cycle. A port and polish will flow more air more freely into the cylinders. Better ignition such as more powerful coils, electronic timing, better HT leads and a spot on dizzy will provide peak ignition performance. Wilder cams will allow the valve timing to achieve optimium flow. A large bore exhaust system will then ensure the air gets out the back the quickest and a little louder
Finally, stroking the engine will allow more air to flow, and so will forced induction, making the effects of each of the above improvements more pronounced.
Just depends on how much cash you have!!!!
This is a basic mechanical explanation of what you can achieve with your engine.
It's all about volumetric efficiency as this is what defines how much power an engine is capable of producing. It's a measure of the efficiency of the power cycle - that is induction, ignition, and the exhaust process. Typical modern engines (in particular the latest german ones) will have a volumetric efficency rating of about 85-90+, with older engines like the mk1 & mk2 maybe at something like 80-85, whilst my old mgb falls at around 65-70 This means the tuning potential is a lot greater in my mgb with bigger gains to be achieved quite cheaply. The Japs managed to tune the mr2 engines to quite a high state of efficiency so if your mk1 is running at a healthy say 82% efficiency @ 122bhp, you could probably hit 150bhp @ 100% efficiency, whilst a mk2 rev 3 running at 85% efficiency @ 178bhp could theoretically attain 210bhp @ 100% efficiency.
Whilst this sounds tempting, please be aware that it is theoretically impossible to attain 100% volumetric efficiency, and getting up to the high 90's is gonna cost megabucks. So that's it i hear you cry? All is lost?
Nope. To increase the volumetric efficiency quite cheaply (well at least on my 'B) you can simply increase the volume of the engine. A bigger engine allows for wilder cams without losing grunt. The other way is to increase the amount of air that flows through the engine - in otherwords forced induction such as turbo or supercharging.
So throughout the whole cycle, a less restrictive air filter will flow air more freely into the engine. An induction pipe that holds more air than the volume of the engine will ensure you are not spending power from the engine having to draw air in throughout it's cycle. A port and polish will flow more air more freely into the cylinders. Better ignition such as more powerful coils, electronic timing, better HT leads and a spot on dizzy will provide peak ignition performance. Wilder cams will allow the valve timing to achieve optimium flow. A large bore exhaust system will then ensure the air gets out the back the quickest and a little louder
Finally, stroking the engine will allow more air to flow, and so will forced induction, making the effects of each of the above improvements more pronounced.
Just depends on how much cash you have!!!!
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Whilst this sounds tempting, please be aware that it is theoretically impossible to attain 100% volumetric efficiency
To increase the volumetric efficiency quite cheaply (well at least on my 'B) you can simply increase the volume of the engine
#7
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Total horse shit
VE can only be quoted for a fixed Rpm
It varies at different rpm and peak VE usually happens at the same RPM as peak torque
In a four-stroke naturally aspirated engine, the theoretical maximum amount of air that each cylinder can ingest during the intake cycle is equal to the swept volume of that cylinder (0.7854 x bore x bore x stroke).
Since each cylinder has one intake stroke every two revolutions of the crankshaft, then the theoretical maximum volume of air it can ingest during each rotation of the crankshaft is equal to one-half its displacement. The actual amount of air the engine ingests compared to the theoretical maximum is called volumetric efficiency (VE). An engine operating at 100% VE is ingesting its' total displacement every two crankshaft revolutions.
Forced induction can give way way over 100% VE
VE can only be quoted for a fixed Rpm
It varies at different rpm and peak VE usually happens at the same RPM as peak torque
In a four-stroke naturally aspirated engine, the theoretical maximum amount of air that each cylinder can ingest during the intake cycle is equal to the swept volume of that cylinder (0.7854 x bore x bore x stroke).
Since each cylinder has one intake stroke every two revolutions of the crankshaft, then the theoretical maximum volume of air it can ingest during each rotation of the crankshaft is equal to one-half its displacement. The actual amount of air the engine ingests compared to the theoretical maximum is called volumetric efficiency (VE). An engine operating at 100% VE is ingesting its' total displacement every two crankshaft revolutions.
Forced induction can give way way over 100% VE
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#9
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Originally Posted by MattRS1600i
It varies at different rpm and peak VE usually happens at the same RPM as peak torque
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
peak torque occurs at that rpm precisely because it is peak VE
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
#10
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Originally Posted by foreigneRS
Originally Posted by MattRS1600i
It varies at different rpm and peak VE usually happens at the same RPM as peak torque
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
peak torque occurs at that rpm precisely because it is peak VE
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
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I didn't write it for god's sake Matt, you pleb!
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
#13
............
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Originally Posted by RichardPON
I didn't write it for god's sake Matt, you pleb!
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
I can read
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
#14
Testing the future
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Originally Posted by MattRS1600i
Mapping - which I suppose can be described as magic ![Top](https://passionford.com/forum/images/smilies/smile011.gif)
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
the highest VE will always give you the highest possible torque available (as it's when the most air and fuel are in the cylinders). whether the mapping takes advantage of it is another thing
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
#15
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Originally Posted by foreigneRS
Originally Posted by MattRS1600i
Mapping - which I suppose can be described as magic ![Top](https://passionford.com/forum/images/smilies/smile011.gif)
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
the highest VE will always give you the highest possible torque available (as it's when the most air and fuel are in the cylinders). whether the mapping takes advantage of it is another thing
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
You the man
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
#17
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Originally Posted by foreigneRS
Originally Posted by MattRS1600i
Mapping - which I suppose can be described as magic ![Top](https://passionford.com/forum/images/smilies/smile011.gif)
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
the highest VE will always give you the highest possible torque available (as it's when the most air and fuel are in the cylinders). whether the mapping takes advantage of it is another thing
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
Its still not actually 100% accurate though.
As if you have 0.1% higher VE at 5000rpm than at 2000rpm, or vice versa, where do you think will make the most torque in each case, would it change with the change in VE? Or would it be at the same point in both despite the different peak VE points?
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
(not a trick, question, think about things like heat relative to rpm, and piston speed and its effect on resistance, and also think about the flame front speed versus the speed of the engine and the effect that has on peak cylinder pressure and hence Det, then you need to consider the different amount of time for air to leak past the valves and rings.
When you have done all that answer these questions:
5000rpm 78.1% / 2000rpm 78% = which is going to give better torque
5000rpm 78% / 2000rpm 78.1% = which is going to give better torque
If you dont answer:
5000
2000
Then you have just given yourself a
![007](https://passionford.com/forum/images/smilies/bond.gif)
#18
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haven't fully read all that yet chip, but how can 78% be peak VE when you have 78.1% somewhere else?
gotta go and do a test now. will come back to it later
![Confused](https://passionford.com/forum/images/smilies/icon_confused.gif)
gotta go and do a test now. will come back to it later
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
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Originally Posted by MattRS1600i
Originally Posted by RichardPON
I didn't write it for god's sake Matt, you pleb!
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
I can read
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
#21
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Originally Posted by RichardPON
Originally Posted by MattRS1600i
Originally Posted by RichardPON
I didn't write it for god's sake Matt, you pleb!
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
I just knew something was wrong wtih what was written, but just wanted confirmation from far more knowledgeable people than me!
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
I can read
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
![Pthbbbb](https://passionford.com/forum/images/smilies/smile045.gif)
i was just making reference to your sig pic that i saw for the first time, thats all
![](https://passionford.com/forum/images/smilies/smile16.gif)
you pleb
![007](https://passionford.com/forum/images/smilies/bond.gif)
#25
Testing the future
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Originally Posted by chip-3door
Careful bit of rewording to now say "available"
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
Originally Posted by chip-3door
Its still not actually 100% accurate though.
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
Originally Posted by chip-3door
As if you have 0.1% higher VE at 5000rpm than at 2000rpm, or vice versa,
![](http://www.team-integra.net/images/BAEC1978-D3A7-4405-AB2D-2761DC15A96D/articles/tuan/peakVEpeaktorque.gif)
i can imagine the same being true of an engine. how are you going to have 2 places so far apart in the rev range that have a similar peak VE?
you can have 2 places that have similar VE either side of peak, in which case we can start looking at all the other points that you have made below that I still haven't properly read.
![Red Faced](https://passionford.com/forum/images/smilies/icon_redface.gif)
Originally Posted by chip-3door
where do you think will make the most torque in each case, would it change with the change in VE? Or would it be at the same point in both despite the different peak VE points? ![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
(not a trick, question, think about things like heat relative to rpm, and piston speed and its effect on resistance, and also think about the flame front speed versus the speed of the engine and the effect that has on peak cylinder pressure and hence Det, then you need to consider the different amount of time for air to leak past the valves and rings.
When you have done all that answer these questions:
5000rpm 78.1% / 2000rpm 78% = which is going to give better torque
5000rpm 78% / 2000rpm 78.1% = which is going to give better torque
If you dont answer:
5000
2000
Then you have just given yourself a![007](https://passionford.com/forum/images/smilies/bond.gif)
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
(not a trick, question, think about things like heat relative to rpm, and piston speed and its effect on resistance, and also think about the flame front speed versus the speed of the engine and the effect that has on peak cylinder pressure and hence Det, then you need to consider the different amount of time for air to leak past the valves and rings.
When you have done all that answer these questions:
5000rpm 78.1% / 2000rpm 78% = which is going to give better torque
5000rpm 78% / 2000rpm 78.1% = which is going to give better torque
If you dont answer:
5000
2000
Then you have just given yourself a
![007](https://passionford.com/forum/images/smilies/bond.gif)
#26
Testing the future
![Default](https://passionford.com/forum/images/icons/icon1.gif)
Originally Posted by chip-3door
where do you think will make the most torque in each case, would it change with the change in VE? Or would it be at the same point in both despite the different peak VE points? ![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
(not a trick, question, think about things like heat relative to rpm, and piston speed and its effect on resistance, and also think about the flame front speed versus the speed of the engine and the effect that has on peak cylinder pressure and hence Det, then you need to consider the different amount of time for air to leak past the valves and rings.
When you have done all that answer these questions:
5000rpm 78.1% / 2000rpm 78% = which is going to give better torque
5000rpm 78% / 2000rpm 78.1% = which is going to give better torque
If you dont answer:
5000
2000
Then you have just given yourself a![007](https://passionford.com/forum/images/smilies/bond.gif)
![Wink](https://passionford.com/forum/images/smilies/icon_wink.gif)
(not a trick, question, think about things like heat relative to rpm, and piston speed and its effect on resistance, and also think about the flame front speed versus the speed of the engine and the effect that has on peak cylinder pressure and hence Det, then you need to consider the different amount of time for air to leak past the valves and rings.
When you have done all that answer these questions:
5000rpm 78.1% / 2000rpm 78% = which is going to give better torque
5000rpm 78% / 2000rpm 78.1% = which is going to give better torque
If you dont answer:
5000
2000
Then you have just given yourself a
![007](https://passionford.com/forum/images/smilies/bond.gif)
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
the truth is, i don't know the answer to that one. i think that there's too many unkowns.
#27
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Originally Posted by foreigneRS
have read it now.
the truth is, i don't know the answer to that one. i think that there's too many unkowns.
![Top](https://passionford.com/forum/images/smilies/smile011.gif)
the truth is, i don't know the answer to that one. i think that there's too many unkowns.
![Surprised](https://passionford.com/forum/images/smilies/bigcry.gif)
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