how do ya measure compresion ratio !!!!!
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From: Im behind you
how do ya measure compresion ratio !!!!!
as in whats the correct way, ive heard people mention fluid inn the head bowl but can someone tell me what the whole procedure is from start to finish please 
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basically, you need to know:
Swept Volume.
This is the volume your piston travels from top to bottom. This is found by doing the calulation: bore area x bore area x 3.14159 x stroke
Clearance volume:
This is teh volume above the piston at TDC. This is best found by filling it with a fluid.
You then do the calculation:
CR = Swept volume + Clearance volume / Clearance volume.
I have pics somewhere to show using a burette i expect if you need to see one.
Swept Volume.
This is the volume your piston travels from top to bottom. This is found by doing the calulation: bore area x bore area x 3.14159 x stroke
Clearance volume:
This is teh volume above the piston at TDC. This is best found by filling it with a fluid.
You then do the calculation:
CR = Swept volume + Clearance volume / Clearance volume.
I have pics somewhere to show using a burette i expect if you need to see one.
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just finding my feet
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stu can ya do it with the head on the car 
hey im not that bad, just im gonna be doing a few engine builds to practice before i start on the cossie and wanna learn all of it
hey im not that bad, just im gonna be doing a few engine builds to practice before i start on the cossie and wanna learn all of it
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Stu, do you actually measure the CR with the burette whilst the head is on/
I can't work out how you can do it propperly that way, on a CVH head anyway.
If it was a Cossie or Zetec, yes, fill to the base of the spark plug thread and thats about right (but not perfect, due to the plug not being there).
But on a CVH head, where the sparkplug is mounted off centre, and not at the top of the combustion chamber, I don't see how you can CC it that way? As if you fill the combsution space with water (or whatever fluid your using), it will not propperly fill upto the roof of the combustion chamber? It would spill out of the plug whole long before then?
I can't work out how you can do it propperly that way, on a CVH head anyway.
If it was a Cossie or Zetec, yes, fill to the base of the spark plug thread and thats about right (but not perfect, due to the plug not being there).
But on a CVH head, where the sparkplug is mounted off centre, and not at the top of the combustion chamber, I don't see how you can CC it that way? As if you fill the combsution space with water (or whatever fluid your using), it will not propperly fill upto the roof of the combustion chamber? It would spill out of the plug whole long before then?
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There are various ways to do it that ive no time to explain, but to tackle purely the issue you have raised, its simple, all engine stands i own "ROTATE" 
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1. Head should be removed to do properly .. and supported level.
2. http://www.beecroft-science.co.uk/20...roductList=328
Dont think you will buy a lot cheaper. Last one I used was a 200Ml, but was plenty big enough, reckon a 100 would be OK.
3. Stuff I do ...
Grease the bores a little to seal ring gaps, etc.
Perspex plate greased onto the head surface (to seal off) with a small filling
hole in the centre.
Make sure valves aren't leaking (or seal/wipe off with grease)
Use Paraffin to measure up, not water. You want something like this with low
surface tension!
2. http://www.beecroft-science.co.uk/20...roductList=328
Dont think you will buy a lot cheaper. Last one I used was a 200Ml, but was plenty big enough, reckon a 100 would be OK.
3. Stuff I do ...
Grease the bores a little to seal ring gaps, etc.
Perspex plate greased onto the head surface (to seal off) with a small filling
hole in the centre.
Make sure valves aren't leaking (or seal/wipe off with grease)
Use Paraffin to measure up, not water. You want something like this with low
surface tension!
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How do you calculate/allow for the headgasket thickness when calculating the CR with the head off the engine, or is this why you measure the CR with the engine assembled?
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From: In my GTR Skyline as often as poss ; )
You gat a thickness figure .. or estimate a compressed depth of the gasket ..
The you use the volume of a cylinder rule using pi = 3.142 to give you the volume of the gasket area when fitted.
eg .. gasket bore 85mm
fitted (compressed depth) 1mm
Volume occupied will be pi x r squared x h
The you use the volume of a cylinder rule using pi = 3.142 to give you the volume of the gasket area when fitted.
eg .. gasket bore 85mm
fitted (compressed depth) 1mm
Volume occupied will be pi x r squared x h
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