Anyone bored enough to want to try and explain exactly what compression ratio is??
#1
Heh, you'd probably have to either be a postwhore, REALLY bored, or actually want to help out. I understand if no-one wants to explain it. How does it affect everything? In what circumstances would one want to lower it? Thanks. Just trying to expand my knowlege.
#2
Originally posted by Keh mon
Heh, you'd probably have to either be a postwhore, REALLY bored, or actually want to help out. I understand if no-one wants to explain it. How does it affect everything? In what circumstances would one want to lower it? Thanks. Just trying to expand my knowlege.
Heh, you'd probably have to either be a postwhore, REALLY bored, or actually want to help out. I understand if no-one wants to explain it. How does it affect everything? In what circumstances would one want to lower it? Thanks. Just trying to expand my knowlege.
Vh = volume displaced by piston moving between TDC and BDC
Vc = compression space, the space left at the top of the cylinder above the piston at TDC
I think one may want to lower the compression ratio if the engine has high boost, to avoid detonation of the air/fuel mixture when it is compressed.
#3
You can probably find out here: http://www.howstuffworks.com/category.htm?cat=Auto
#6
That basic equation accounts for most of it. But but the "area above the piston" is made up of a few things other than just the combustion chamber of the head. It includes dish/dome of the actual piston, the thickness of the headgasket and the area between the cylinder wall and piston, above the last piston ring.
Originally posted by ru4real
Compression Ratio (epsilon) = (Vh + Vc) / Vc (those should be subscripts)
Vh = volume displaced by piston moving between TDC and BDC
Vc = compression space, the space left at the top of the cylinder above the piston at TDC
I think one may want to lower the compression ratio if the engine has high boost, to avoid detonation of the air/fuel mixture when it is compressed.
Compression Ratio (epsilon) = (Vh + Vc) / Vc (those should be subscripts)
Vh = volume displaced by piston moving between TDC and BDC
Vc = compression space, the space left at the top of the cylinder above the piston at TDC
I think one may want to lower the compression ratio if the engine has high boost, to avoid detonation of the air/fuel mixture when it is compressed.
#8
Originally posted by Jeff92se
That basic equation accounts for most of it. But but the "area above the piston" is made up of a few things other than just the combustion chamber of the head. It includes dish/dome of the actual piston, the thickness of the headgasket and the area between the cylinder wall and piston, above the last piston ring.
That basic equation accounts for most of it. But but the "area above the piston" is made up of a few things other than just the combustion chamber of the head. It includes dish/dome of the actual piston, the thickness of the headgasket and the area between the cylinder wall and piston, above the last piston ring.
I think stock compression is like 11:1 ??
#9
Originally posted by Jeff92se
That basic equation accounts for most of it. But but the "area above the piston" is made up of a few things other than just the combustion chamber of the head. It includes dish/dome of the actual piston, the thickness of the headgasket and the area between the cylinder wall and piston, above the last piston ring.
That basic equation accounts for most of it. But but the "area above the piston" is made up of a few things other than just the combustion chamber of the head. It includes dish/dome of the actual piston, the thickness of the headgasket and the area between the cylinder wall and piston, above the last piston ring.
#10
it's simple
really!!!
10:1 ratio means that the volume of Air/Fuel mixture when the piston is at it's lowest position (BDC) will be compressed TEN TIMES smaller it's volume when the piston goes up to it's highest position (TDC).
and of course when air is compressed it heats up, so when ever you increase the compression it heats up more, thus couasing Pre-Ignition (Detonation, ping, knock ect...)of the air/fuel mixture. and vise-versa.
so if you add forced induction (already compressed and hot air) it will amplify the "pre-ignition" symptoms of an engine, so tuners like to lower the compression to help that side effect.
see simple huh?
10:1 ratio means that the volume of Air/Fuel mixture when the piston is at it's lowest position (BDC) will be compressed TEN TIMES smaller it's volume when the piston goes up to it's highest position (TDC).
and of course when air is compressed it heats up, so when ever you increase the compression it heats up more, thus couasing Pre-Ignition (Detonation, ping, knock ect...)of the air/fuel mixture. and vise-versa.
so if you add forced induction (already compressed and hot air) it will amplify the "pre-ignition" symptoms of an engine, so tuners like to lower the compression to help that side effect.
see simple huh?
#11
Originally posted by ru4real
Compression Ratio (epsilon) = (Vh + Vc) / Vc (those should be subscripts)
Vh = volume displaced by piston moving between TDC and BDC
Vc = compression space, the space left at the top of the cylinder above the piston at TDC
I think one may want to lower the compression ratio if the engine has high boost, to avoid detonation of the air/fuel mixture when it is compressed.
Compression Ratio (epsilon) = (Vh + Vc) / Vc (those should be subscripts)
Vh = volume displaced by piston moving between TDC and BDC
Vc = compression space, the space left at the top of the cylinder above the piston at TDC
I think one may want to lower the compression ratio if the engine has high boost, to avoid detonation of the air/fuel mixture when it is compressed.
Originally posted by Maxx-s-ter
really!!!
10:1 ratio means that the volume of Air/Fuel mixture when the piston is at it's lowest position (BDC) will be compressed TEN TIMES smaller it's volume when the piston goes up to it's highest position (TDC).
and of course when air is compressed it heats up, so when ever you increase the compression it heats up more, thus couasing Pre-Ignition (Detonation, ping, knock ect...)of the air/fuel mixture. and vise-versa.
so if you add forced induction (already compressed and hot air) it will amplify the "pre-ignition" symptoms of an engine, so tuners like to lower the compression to help that side effect.
see simple huh?
really!!!
10:1 ratio means that the volume of Air/Fuel mixture when the piston is at it's lowest position (BDC) will be compressed TEN TIMES smaller it's volume when the piston goes up to it's highest position (TDC).
and of course when air is compressed it heats up, so when ever you increase the compression it heats up more, thus couasing Pre-Ignition (Detonation, ping, knock ect...)of the air/fuel mixture. and vise-versa.
so if you add forced induction (already compressed and hot air) it will amplify the "pre-ignition" symptoms of an engine, so tuners like to lower the compression to help that side effect.
see simple huh?
and I'm getting impatient. This thing won't send.
#12
Originally posted by Keh mon
TDC = Top D(?) Cylinder ? what does the D stand for? Thanks for the info I understand it completely Are you going to the dragway next wed? I'm going again and my friend in the SI is going also.
Ok I definately understand all of what you guys were saying. Woo hoo. :
and I'm getting impatient. This thing won't send.
TDC = Top D(?) Cylinder ? what does the D stand for? Thanks for the info I understand it completely Are you going to the dragway next wed? I'm going again and my friend in the SI is going also.
Ok I definately understand all of what you guys were saying. Woo hoo. :
and I'm getting impatient. This thing won't send.
I probably won't be going this Wednesday. The next time will be when my friend finishes some work on his Eclipse, in a week or two. Have fun!
#13
Re: it's simple
Originally posted by Maxx-s-ter
really!!!
10:1 ratio means that the volume of Air/Fuel mixture when the piston is at it's lowest position (BDC) will be compressed TEN TIMES smaller it's volume when the piston goes up to it's highest position (TDC).
and of course when air is compressed it heats up, so when ever you increase the compression it heats up more, thus couasing Pre-Ignition (Detonation, ping, knock ect...)of the air/fuel mixture. and vise-versa.
so if you add forced induction (already compressed and hot air) it will amplify the "pre-ignition" symptoms of an engine, so tuners like to lower the compression to help that side effect.
see simple huh?
really!!!
10:1 ratio means that the volume of Air/Fuel mixture when the piston is at it's lowest position (BDC) will be compressed TEN TIMES smaller it's volume when the piston goes up to it's highest position (TDC).
and of course when air is compressed it heats up, so when ever you increase the compression it heats up more, thus couasing Pre-Ignition (Detonation, ping, knock ect...)of the air/fuel mixture. and vise-versa.
so if you add forced induction (already compressed and hot air) it will amplify the "pre-ignition" symptoms of an engine, so tuners like to lower the compression to help that side effect.
see simple huh?
#15
Re: Re: it's simple
Originally posted by paxus
Ok, so does forced induction include CAIs? No one wants to have this pre-ignition problem, so what does one do to lessen the compression ratio to something like 8:1? For example, if one got an Injen CAI installed (assuming this falls under the forced induction category) would this screw with the ignition timing of your engine? If so, how is this fixed?
Ok, so does forced induction include CAIs? No one wants to have this pre-ignition problem, so what does one do to lessen the compression ratio to something like 8:1? For example, if one got an Injen CAI installed (assuming this falls under the forced induction category) would this screw with the ignition timing of your engine? If so, how is this fixed?
#16
Re: Re: Re: it's simple
Originally posted by maximaman777
CAI's or HAI's do not fall in the forced induction category. Forced induction is the use of supercharges or turbos where the air charge is pressurized prior to entering the intake manifold. That increase of pressure also increases the temp. of the air and possibly causing pre-ignition. That is when you would want to look at lowering your compression ratio.
CAI's or HAI's do not fall in the forced induction category. Forced induction is the use of supercharges or turbos where the air charge is pressurized prior to entering the intake manifold. That increase of pressure also increases the temp. of the air and possibly causing pre-ignition. That is when you would want to look at lowering your compression ratio.
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