compression on b18b forged
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compression on b18b forged
so im close to store my car for winter and i want to do a compression test on my engine...so i still got a good pull on boost but the build is close to 38 000 kilometers <<<<the engine dont take oil and coolant...no oil leaking but just to be sure..it make a sound of a cammed forged engine at cold iddle(that all mecano said)what is the compression i should read on a low compression set-up????...last time ive got 165 psi on each cylinder(hot)
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Re: compression on b18b forged
The PSI will vary with compression. What is your static compression in the engine. To some, low compression might be 7.5:1 and to others it may be 12:1...
Re: compression on b18b forged
Compression as an adjective means something is squeezed (in this case it's air and fuel)
Ratio as a noun means something is divided by something else. It is a math term meaning a quotient.
There are 2 kinds of Compression Ratios (CR):
1. Static
2. Dynamic
-------------------------------------------------------------------------------------
1. STATIC CR
1A. DEFINITION
The Static Compression RATIO is defined as the Volume of the Combustion Chamber when the piston is at the very bottom of it's travel (called "bottom dead center" or BDC) DIVIDED BY the Volume of the Combustion Chamber when the piston is at the very top of it's travel (called "top dead center" or TDC).
Static compression ratio is one factor that affects how completely the air-fuel mixture is burned, once it has been lit by the sparkplug. If you burn all of the air:fuel mixture, you make more hp. If there is some leftover unburnt air:fuel mix after the spark has been lit, you have not gotten all the power you can get out of the mix that was just added into the cylinder. This completeness of burn is called THERMODYNAMIC EFFICIENCY (measured in units of energy called joules, pronounced like "jewels").
Remember, basically, you increase horsepower by increasing 3 different types of efficiencies: thermodynamic (relates to burn), volumetric (relates air flow in and out), and mechanical (relates to weight and friction). Improving thermodynamic efficiency is one of the 3 major power-gaining methods available for engine builders.
The relationship between thermodynamic efficiency and static CR is not a simple, direct, linear, straight-forward 1:1 relationship. In plain english, if you increase the CR by 1.5 times, it does not mean the burn efficiency (or completeness of burn) will also increase by 1.5 times. It's a complex direct exponential and inverse exponential equation that relates static CR to burn efficiency.
Like anything exponential and inverse in math, there is an initial rapid increase in thermodynamic efficiency as static CR increases but at some point of CR, the efficiency levels off and plateaus. In other words, at some point, further increases in static CR no longer improves or increases the burn efficiency.
1 B. THE PROBLEMS WITH INCREASING STATIC CR
The problem is that as you increase CR, you increase cylinder pressure and temperature inside the combustion chamber. When air is squeezed hard inside a closed container like a cylinder, the pressure inside goes up the harder you squeeze. As pressure builds up, so does temperature. These 2 (high pressure and temp.) can cause the air -fuel mix to ignite on it's own without a spark from the plug....this is called detonation. So there is a CR level which will cause detonation. The value of that level varies with each engine and depends on combustion chamber's design which limit detonation risk (eg. compact combustion chambers, low surface-area-to-volume ratio combustion chambers, more quench or squish area, swirl filling of the air-fuel mix into the chamber, getting a stratified air fuel mix once the chamber is completely filled, cooling ability of the engine, etc. ... all of these other chamber design factors reduce detonation risk and speeds up the burn rate, against the effect of higher static CR ).
Secondly, as you increase static CR more and more, the cylinder pressures increase more and more. The piston must work much harder to compress the same amount of air:fuel mixture delivered into the chamber due to this higher pressure. This negative work adds more power-robbing or parasitic-losing friction and slows the piston speed momentum which affects the power you produce.
So you can make more power by improving burn efficiency via increasing the static CR up to a point. For street engines, the maximum static CR on pump gas is around 12.5:1 CR if you know how to tune. If you do not, the maximum is around 11.5:1 CR. For a race engine, the point at which cranking pressure causes negative work or parasitic friction and affects power output is around 14:1 CR. Alcohol-fueled race engines can afford to run 15-17:1 CR, since the alcohol cools the chamber and lowers both the cylinder temperature and detonation risk. Methanol race engines run much richer air-fuel ratios (around 5-6:1) than gasoline engines, as well.
In simple terms: for static CR, the first number is the chamber volume at BDC, second number is chamber volume at TDC...the higher the first number is, the more squeeze you have. More squeeze improves burn up to a certain point. This point varies for each engine design.
2. Dynamic CR
The piston is always moving up and down but the intake valve opens and closes during this time as well.
As the piston is beginning to squeeze at BDC, the intake valve is beginning to close. The intake valve is not completely shut until the piston is near TDC. There is a connection between the cylinder combustion chamber and the intake port/intake manifold runner, when the intake valve is still partially open. As the piston is squeezing and approaching TDC, some cylinder pressure can bleed up in the intake port which reduces overall cylinder pressure.
If you use your adjustable intake cam gear to close the intake valve earlier (advancing the cam gear), the amount of cylinder pressure bleeding up the intake port is reduced. The cylinder pressure builds up faster and you get a better burn.
If you let the intake valve close later (retard the intake cam gear or use a longer duration intake cam), more cylinder pressure will bleed out or be reduced and the burn will be less complete.
This is why it is important to increase your static CR when you get extremely longer duration cams.
Ratio as a noun means something is divided by something else. It is a math term meaning a quotient.
There are 2 kinds of Compression Ratios (CR):
1. Static
2. Dynamic
-------------------------------------------------------------------------------------
1. STATIC CR
1A. DEFINITION
The Static Compression RATIO is defined as the Volume of the Combustion Chamber when the piston is at the very bottom of it's travel (called "bottom dead center" or BDC) DIVIDED BY the Volume of the Combustion Chamber when the piston is at the very top of it's travel (called "top dead center" or TDC).
Static compression ratio is one factor that affects how completely the air-fuel mixture is burned, once it has been lit by the sparkplug. If you burn all of the air:fuel mixture, you make more hp. If there is some leftover unburnt air:fuel mix after the spark has been lit, you have not gotten all the power you can get out of the mix that was just added into the cylinder. This completeness of burn is called THERMODYNAMIC EFFICIENCY (measured in units of energy called joules, pronounced like "jewels").
Remember, basically, you increase horsepower by increasing 3 different types of efficiencies: thermodynamic (relates to burn), volumetric (relates air flow in and out), and mechanical (relates to weight and friction). Improving thermodynamic efficiency is one of the 3 major power-gaining methods available for engine builders.
The relationship between thermodynamic efficiency and static CR is not a simple, direct, linear, straight-forward 1:1 relationship. In plain english, if you increase the CR by 1.5 times, it does not mean the burn efficiency (or completeness of burn) will also increase by 1.5 times. It's a complex direct exponential and inverse exponential equation that relates static CR to burn efficiency.
Like anything exponential and inverse in math, there is an initial rapid increase in thermodynamic efficiency as static CR increases but at some point of CR, the efficiency levels off and plateaus. In other words, at some point, further increases in static CR no longer improves or increases the burn efficiency.
1 B. THE PROBLEMS WITH INCREASING STATIC CR
The problem is that as you increase CR, you increase cylinder pressure and temperature inside the combustion chamber. When air is squeezed hard inside a closed container like a cylinder, the pressure inside goes up the harder you squeeze. As pressure builds up, so does temperature. These 2 (high pressure and temp.) can cause the air -fuel mix to ignite on it's own without a spark from the plug....this is called detonation. So there is a CR level which will cause detonation. The value of that level varies with each engine and depends on combustion chamber's design which limit detonation risk (eg. compact combustion chambers, low surface-area-to-volume ratio combustion chambers, more quench or squish area, swirl filling of the air-fuel mix into the chamber, getting a stratified air fuel mix once the chamber is completely filled, cooling ability of the engine, etc. ... all of these other chamber design factors reduce detonation risk and speeds up the burn rate, against the effect of higher static CR ).
Secondly, as you increase static CR more and more, the cylinder pressures increase more and more. The piston must work much harder to compress the same amount of air:fuel mixture delivered into the chamber due to this higher pressure. This negative work adds more power-robbing or parasitic-losing friction and slows the piston speed momentum which affects the power you produce.
So you can make more power by improving burn efficiency via increasing the static CR up to a point. For street engines, the maximum static CR on pump gas is around 12.5:1 CR if you know how to tune. If you do not, the maximum is around 11.5:1 CR. For a race engine, the point at which cranking pressure causes negative work or parasitic friction and affects power output is around 14:1 CR. Alcohol-fueled race engines can afford to run 15-17:1 CR, since the alcohol cools the chamber and lowers both the cylinder temperature and detonation risk. Methanol race engines run much richer air-fuel ratios (around 5-6:1) than gasoline engines, as well.
In simple terms: for static CR, the first number is the chamber volume at BDC, second number is chamber volume at TDC...the higher the first number is, the more squeeze you have. More squeeze improves burn up to a certain point. This point varies for each engine design.
2. Dynamic CR
The piston is always moving up and down but the intake valve opens and closes during this time as well.
As the piston is beginning to squeeze at BDC, the intake valve is beginning to close. The intake valve is not completely shut until the piston is near TDC. There is a connection between the cylinder combustion chamber and the intake port/intake manifold runner, when the intake valve is still partially open. As the piston is squeezing and approaching TDC, some cylinder pressure can bleed up in the intake port which reduces overall cylinder pressure.
If you use your adjustable intake cam gear to close the intake valve earlier (advancing the cam gear), the amount of cylinder pressure bleeding up the intake port is reduced. The cylinder pressure builds up faster and you get a better burn.
If you let the intake valve close later (retard the intake cam gear or use a longer duration intake cam), more cylinder pressure will bleed out or be reduced and the burn will be less complete.
This is why it is important to increase your static CR when you get extremely longer duration cams.
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Honda-Tech Member
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Re: compression on b18b forged
Compression as an adjective means something is squeezed (in this case it's air and fuel)
Ratio as a noun means something is divided by something else. It is a math term meaning a quotient.
There are 2 kinds of Compression Ratios (CR):
1. Static
2. Dynamic
-------------------------------------------------------------------------------------
1. STATIC CR
1A. DEFINITION
The Static Compression RATIO is defined as the Volume of the Combustion Chamber when the piston is at the very bottom of it's travel (called "bottom dead center" or BDC) DIVIDED BY the Volume of the Combustion Chamber when the piston is at the very top of it's travel (called "top dead center" or TDC).
Static compression ratio is one factor that affects how completely the air-fuel mixture is burned, once it has been lit by the sparkplug. If you burn all of the air:fuel mixture, you make more hp. If there is some leftover unburnt air:fuel mix after the spark has been lit, you have not gotten all the power you can get out of the mix that was just added into the cylinder. This completeness of burn is called THERMODYNAMIC EFFICIENCY (measured in units of energy called joules, pronounced like "jewels").
Remember, basically, you increase horsepower by increasing 3 different types of efficiencies: thermodynamic (relates to burn), volumetric (relates air flow in and out), and mechanical (relates to weight and friction). Improving thermodynamic efficiency is one of the 3 major power-gaining methods available for engine builders.
The relationship between thermodynamic efficiency and static CR is not a simple, direct, linear, straight-forward 1:1 relationship. In plain english, if you increase the CR by 1.5 times, it does not mean the burn efficiency (or completeness of burn) will also increase by 1.5 times. It's a complex direct exponential and inverse exponential equation that relates static CR to burn efficiency.
Like anything exponential and inverse in math, there is an initial rapid increase in thermodynamic efficiency as static CR increases but at some point of CR, the efficiency levels off and plateaus. In other words, at some point, further increases in static CR no longer improves or increases the burn efficiency.
1 B. THE PROBLEMS WITH INCREASING STATIC CR
The problem is that as you increase CR, you increase cylinder pressure and temperature inside the combustion chamber. When air is squeezed hard inside a closed container like a cylinder, the pressure inside goes up the harder you squeeze. As pressure builds up, so does temperature. These 2 (high pressure and temp.) can cause the air -fuel mix to ignite on it's own without a spark from the plug....this is called detonation. So there is a CR level which will cause detonation. The value of that level varies with each engine and depends on combustion chamber's design which limit detonation risk (eg. compact combustion chambers, low surface-area-to-volume ratio combustion chambers, more quench or squish area, swirl filling of the air-fuel mix into the chamber, getting a stratified air fuel mix once the chamber is completely filled, cooling ability of the engine, etc. ... all of these other chamber design factors reduce detonation risk and speeds up the burn rate, against the effect of higher static CR ).
Secondly, as you increase static CR more and more, the cylinder pressures increase more and more. The piston must work much harder to compress the same amount of air:fuel mixture delivered into the chamber due to this higher pressure. This negative work adds more power-robbing or parasitic-losing friction and slows the piston speed momentum which affects the power you produce.
So you can make more power by improving burn efficiency via increasing the static CR up to a point. For street engines, the maximum static CR on pump gas is around 12.5:1 CR if you know how to tune. If you do not, the maximum is around 11.5:1 CR. For a race engine, the point at which cranking pressure causes negative work or parasitic friction and affects power output is around 14:1 CR. Alcohol-fueled race engines can afford to run 15-17:1 CR, since the alcohol cools the chamber and lowers both the cylinder temperature and detonation risk. Methanol race engines run much richer air-fuel ratios (around 5-6:1) than gasoline engines, as well.
In simple terms: for static CR, the first number is the chamber volume at BDC, second number is chamber volume at TDC...the higher the first number is, the more squeeze you have. More squeeze improves burn up to a certain point. This point varies for each engine design.
2. Dynamic CR
The piston is always moving up and down but the intake valve opens and closes during this time as well.
As the piston is beginning to squeeze at BDC, the intake valve is beginning to close. The intake valve is not completely shut until the piston is near TDC. There is a connection between the cylinder combustion chamber and the intake port/intake manifold runner, when the intake valve is still partially open. As the piston is squeezing and approaching TDC, some cylinder pressure can bleed up in the intake port which reduces overall cylinder pressure.
If you use your adjustable intake cam gear to close the intake valve earlier (advancing the cam gear), the amount of cylinder pressure bleeding up the intake port is reduced. The cylinder pressure builds up faster and you get a better burn.
If you let the intake valve close later (retard the intake cam gear or use a longer duration intake cam), more cylinder pressure will bleed out or be reduced and the burn will be less complete.
This is why it is important to increase your static CR when you get extremely longer duration cams.
Ratio as a noun means something is divided by something else. It is a math term meaning a quotient.
There are 2 kinds of Compression Ratios (CR):
1. Static
2. Dynamic
-------------------------------------------------------------------------------------
1. STATIC CR
1A. DEFINITION
The Static Compression RATIO is defined as the Volume of the Combustion Chamber when the piston is at the very bottom of it's travel (called "bottom dead center" or BDC) DIVIDED BY the Volume of the Combustion Chamber when the piston is at the very top of it's travel (called "top dead center" or TDC).
Static compression ratio is one factor that affects how completely the air-fuel mixture is burned, once it has been lit by the sparkplug. If you burn all of the air:fuel mixture, you make more hp. If there is some leftover unburnt air:fuel mix after the spark has been lit, you have not gotten all the power you can get out of the mix that was just added into the cylinder. This completeness of burn is called THERMODYNAMIC EFFICIENCY (measured in units of energy called joules, pronounced like "jewels").
Remember, basically, you increase horsepower by increasing 3 different types of efficiencies: thermodynamic (relates to burn), volumetric (relates air flow in and out), and mechanical (relates to weight and friction). Improving thermodynamic efficiency is one of the 3 major power-gaining methods available for engine builders.
The relationship between thermodynamic efficiency and static CR is not a simple, direct, linear, straight-forward 1:1 relationship. In plain english, if you increase the CR by 1.5 times, it does not mean the burn efficiency (or completeness of burn) will also increase by 1.5 times. It's a complex direct exponential and inverse exponential equation that relates static CR to burn efficiency.
Like anything exponential and inverse in math, there is an initial rapid increase in thermodynamic efficiency as static CR increases but at some point of CR, the efficiency levels off and plateaus. In other words, at some point, further increases in static CR no longer improves or increases the burn efficiency.
1 B. THE PROBLEMS WITH INCREASING STATIC CR
The problem is that as you increase CR, you increase cylinder pressure and temperature inside the combustion chamber. When air is squeezed hard inside a closed container like a cylinder, the pressure inside goes up the harder you squeeze. As pressure builds up, so does temperature. These 2 (high pressure and temp.) can cause the air -fuel mix to ignite on it's own without a spark from the plug....this is called detonation. So there is a CR level which will cause detonation. The value of that level varies with each engine and depends on combustion chamber's design which limit detonation risk (eg. compact combustion chambers, low surface-area-to-volume ratio combustion chambers, more quench or squish area, swirl filling of the air-fuel mix into the chamber, getting a stratified air fuel mix once the chamber is completely filled, cooling ability of the engine, etc. ... all of these other chamber design factors reduce detonation risk and speeds up the burn rate, against the effect of higher static CR ).
Secondly, as you increase static CR more and more, the cylinder pressures increase more and more. The piston must work much harder to compress the same amount of air:fuel mixture delivered into the chamber due to this higher pressure. This negative work adds more power-robbing or parasitic-losing friction and slows the piston speed momentum which affects the power you produce.
So you can make more power by improving burn efficiency via increasing the static CR up to a point. For street engines, the maximum static CR on pump gas is around 12.5:1 CR if you know how to tune. If you do not, the maximum is around 11.5:1 CR. For a race engine, the point at which cranking pressure causes negative work or parasitic friction and affects power output is around 14:1 CR. Alcohol-fueled race engines can afford to run 15-17:1 CR, since the alcohol cools the chamber and lowers both the cylinder temperature and detonation risk. Methanol race engines run much richer air-fuel ratios (around 5-6:1) than gasoline engines, as well.
In simple terms: for static CR, the first number is the chamber volume at BDC, second number is chamber volume at TDC...the higher the first number is, the more squeeze you have. More squeeze improves burn up to a certain point. This point varies for each engine design.
2. Dynamic CR
The piston is always moving up and down but the intake valve opens and closes during this time as well.
As the piston is beginning to squeeze at BDC, the intake valve is beginning to close. The intake valve is not completely shut until the piston is near TDC. There is a connection between the cylinder combustion chamber and the intake port/intake manifold runner, when the intake valve is still partially open. As the piston is squeezing and approaching TDC, some cylinder pressure can bleed up in the intake port which reduces overall cylinder pressure.
If you use your adjustable intake cam gear to close the intake valve earlier (advancing the cam gear), the amount of cylinder pressure bleeding up the intake port is reduced. The cylinder pressure builds up faster and you get a better burn.
If you let the intake valve close later (retard the intake cam gear or use a longer duration intake cam), more cylinder pressure will bleed out or be reduced and the burn will be less complete.
This is why it is important to increase your static CR when you get extremely longer duration cams.
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Re: compression on b18b forged
so ive got the same numbers !!! 165 psi on each cylinders (hot)...so i figure that my engine is in great shape..and ive got the comp ratio.. 8.3:1
Last edited by duf2570; Oct 17, 2012 at 03:53 PM.
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