Static vs Dynamic Compression???
Re: Static vs Dynamic Compression??? http://www.hotrod.com/tipstricks/34219/index5.html
http://www.hotrod.com/tipstricks/34219/index.html
http://www.schube.com/notes.htm
Some quick information I found..
http://www.hotrod.com/tipstricks/34219/index.html
http://www.schube.com/notes.htm
Some quick information I found..
Re: Static vs Dynamic Compression??? 
TECH Addict
Joined: Nov 2001
Posts: 2,207
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From: College Station, Tx
Re: Static vs Dynamic Compression??? Basically you get to a point where the longer your intake valve stays open the more
DCR = 1 + (((Stroke - ( Stroke * (1/2 - 1/2*(cos(IVC * pi / 180))))) * 2.54^3 * Bore ^2 * pi / 4) + CompressedVolume) / CompressedVolume
will give you your DCR, it is set up for units of " with bore and stroke, and CC's for compressed volume (basically head+quench+valvereliefs/dishes, etc.). Valve events are for seat timing. This is a basic forumla as it doesn't compensate for air density differences, etc. - but it will give you an idea of the factors and magnitudes involved. For a FI enging I haven't seen any good calculators yet - at a minimum they would need to take into account discharge density - and I haven't seen any that do that. For NA applications there are some decent ones out there - like
the rbracing one listed above.
Essentially you are calculating the actual compression that the motor observes vs. just the ration of compressed/uncompressed volumes. Your intake valve isn't going to close until the piston has moved a good bit up in the bore on the compression stroke (around an inch or so probably, though it depends on the cam and r/s ratio). As your valve closes later you can get to a situation where you are actually pushing intake charge back into the intake - not compressing, but forcing it out.
So the longer your intake valve stays open (IVC closing evens) the lower your dynamic compression ratio will be. The sooner it closes the larger it will be.
DCR = 1 + (((Stroke - ( Stroke * (1/2 - 1/2*(cos(IVC * pi / 180))))) * 2.54^3 * Bore ^2 * pi / 4) + CompressedVolume) / CompressedVolume
will give you your DCR, it is set up for units of " with bore and stroke, and CC's for compressed volume (basically head+quench+valvereliefs/dishes, etc.). Valve events are for seat timing. This is a basic forumla as it doesn't compensate for air density differences, etc. - but it will give you an idea of the factors and magnitudes involved. For a FI enging I haven't seen any good calculators yet - at a minimum they would need to take into account discharge density - and I haven't seen any that do that. For NA applications there are some decent ones out there - like
the rbracing one listed above.
Essentially you are calculating the actual compression that the motor observes vs. just the ration of compressed/uncompressed volumes. Your intake valve isn't going to close until the piston has moved a good bit up in the bore on the compression stroke (around an inch or so probably, though it depends on the cam and r/s ratio). As your valve closes later you can get to a situation where you are actually pushing intake charge back into the intake - not compressing, but forcing it out.
So the longer your intake valve stays open (IVC closing evens) the lower your dynamic compression ratio will be. The sooner it closes the larger it will be.
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Joined: Nov 2001
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From: Chi-Town
Re: Static vs Dynamic Compression??? 
