Hi guys, just wondering if anyone can give me a idea on how to CC the head, if thats what its called and work out the compression ratio of an engine, Pistons stick out above the top of the block and It uses a copper head gasket.
Cheers
Les
How to check compression ratio
Started by
mrlctorana
, Aug 08 2006 04:45 PM
14 replies to this topic
#1
mrlctorana
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Posted 08 August 2006 - 04:45 PM
#2
originalglenn
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Posted 08 August 2006 - 08:23 PM
Hi Les,
Head down to your friendly chemist and ask them for a syringe with 1/2 ml graduations( 1 ml = 1cc)
take the head off turn it upside down, get it level, and fill the chamber with a light oil( i used transmission fluid)
do it a couple of times and average the results
Head down to your friendly chemist and ask them for a syringe with 1/2 ml graduations( 1 ml = 1cc)
take the head off turn it upside down, get it level, and fill the chamber with a light oil( i used transmission fluid)
do it a couple of times and average the results
#3
_finer70_
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#4
_jklumpp_
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Posted 09 August 2006 - 01:52 PM
thanks for that site finer70, should make it a bit easier, as I'm about to do the whole compression ratio check too.
MrLC, here's what I've been told (haven't done it yet);
Get a piece of perspex to cover the combustion chamber, with a 1/4" hole drilled in it (the diameter of the hole is apparently important to overcome serface tension)
Put a smear of moly grease on the deck around the chamber, put perspex over, and fill the chamber with light oil (atf) or kero - the coloured liquid makes it easier to see.
Using the syringe, measure the amount of liquid in each chamber - a larger
syringe is better here, as the lesser number of 'full' syringes you have to use, the more accurate your measurement will be.
Once you've got the capacity of the combustion chamber, use the we-site Finer70 has given us to get the compression ratio.
Hope this helps.....Let me know how you go, and if you have any tips for me!!
MrLC, here's what I've been told (haven't done it yet);
Get a piece of perspex to cover the combustion chamber, with a 1/4" hole drilled in it (the diameter of the hole is apparently important to overcome serface tension)
Put a smear of moly grease on the deck around the chamber, put perspex over, and fill the chamber with light oil (atf) or kero - the coloured liquid makes it easier to see.
Using the syringe, measure the amount of liquid in each chamber - a larger
syringe is better here, as the lesser number of 'full' syringes you have to use, the more accurate your measurement will be.
Once you've got the capacity of the combustion chamber, use the we-site Finer70 has given us to get the compression ratio.
Hope this helps.....Let me know how you go, and if you have any tips for me!!
#5
_LX8VD69_
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Posted 09 August 2006 - 02:47 PM
just out of curiousity what is the CC size of stock red V8 heads?
#6
Tiny
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Posted 09 August 2006 - 07:08 PM
Jklumpp: THe method you have mentioned is the best by far! Appart from using a syringe if you;ve got access to a burette then your home and hosed!
We use Kero when we CC heads at the engine shop as its easy to see and works well!
Dont forget you'll need to measure any depressions in the piston top too! you can use the same method with a piston in the bore and some vaseline to seal around the top edge and also the rings to kelp stop any kero from going past the rings.
LX8VD69: Hard to say, i dont know what they were made with but if they've ever been shaved or reconditioned that will affect the CC!
We use Kero when we CC heads at the engine shop as its easy to see and works well!
Dont forget you'll need to measure any depressions in the piston top too! you can use the same method with a piston in the bore and some vaseline to seal around the top edge and also the rings to kelp stop any kero from going past the rings.
LX8VD69: Hard to say, i dont know what they were made with but if they've ever been shaved or reconditioned that will affect the CC!
#7
_JNR_ATE_
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Posted 12 August 2006 - 10:47 AM
LX8, i have blue heads and i think they are 55 CC
Cheers
JNR_ATE
Cheers
JNR_ATE
#8
_LX8VD69_
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Posted 12 August 2006 - 12:41 PM
i thought they were 56cc but it seems too small for some reason, and when i use those figures i come out with nearly 12 to 1 comp ratio. which im pretty sure it aintLX8, i have blue heads and i think they are 55 CC
Cheers
JNR_ATE
#9
_jklumpp_
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Posted 13 August 2006 - 08:24 AM
Measured the combustion chambers on my new head yesterday using the above method - i got around 52cc.
How accurate do you need to be? I found that drawing the liquid out, I would always end up with a bit left in the bottom of the chamber....then I'd have a second go at sucking that out with the syringe, and add it to the first amoun.....but 52 total seemed to be about right.
How accurate do you need to be? I found that drawing the liquid out, I would always end up with a bit left in the bottom of the chamber....then I'd have a second go at sucking that out with the syringe, and add it to the first amoun.....but 52 total seemed to be about right.
#10
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Posted 13 August 2006 - 10:34 AM
are these stock heads as going by those figures my comp ratio is 12.3 to 1. it seems a bit high, almost too high for pump fuel. if thats right then i can forget about trying to squeeze some low bost through itMeasured the combustion chambers on my new head yesterday using the above method - i got around 52cc.
How accurate do you need to be? I found that drawing the liquid out, I would always end up with a bit left in the bottom of the chamber....then I'd have a second go at sucking that out with the syringe, and add it to the first amoun.....but 52 total seemed to be about right.
#11
_LHoon_
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Posted 13 August 2006 - 12:43 PM
Shouldn't your measurement be made from the amount of liquid you can add to the empty chamber using the syringe? It sounds like you are filling the chamber up and then drawing it out with the syringe.How accurate do you need to be? I found that drawing the liquid out, I would always end up with a bit left in the bottom of the chamber....then I'd have a second go at sucking that out with the syringe, and add it to the first amoun.....but 52 total seemed to be about right.
#12
_devilsadvocate_
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Posted 13 August 2006 - 02:20 PM
Interested in the calcs here:
Compression ratio = volume of chamber when piston at bottom of stroke/vol at top
for a 5L vehicle- volume of chamber = swept volume + vol in bore above piston+head gasket + area enclosed by head = 5000/8 +? + ~55(from measurements taken by a few here)
=625 + 55 = 680 if the pistons are flat and go to the top of the block and no gasket.
If this fig is used 680/55 = 12.36....as some have been suggesting. But that would mean no head gasket and pistons going right to the top of the bore?
Suggest that the distance between top of block and head gasket width is critical....a 2mm head gasket(how thick are they) is goint to add about 14ml by itself
(680+14)/(55+14)=10.1, which leads to a more realistic value?
For domed top 90mm diameter pistons, assuming perfectly uniform spherical tops add/subtract 3.1cc for every mm the dome is above/below the piston edges. (if anyone wants the mathematical proof pm me!)
If the dome is non uniform, best to measure its vol by pressing the piston into a clay mould etc and measuring the vol of that.
Compression ratio = volume of chamber when piston at bottom of stroke/vol at top
for a 5L vehicle- volume of chamber = swept volume + vol in bore above piston+head gasket + area enclosed by head = 5000/8 +? + ~55(from measurements taken by a few here)
=625 + 55 = 680 if the pistons are flat and go to the top of the block and no gasket.
If this fig is used 680/55 = 12.36....as some have been suggesting. But that would mean no head gasket and pistons going right to the top of the bore?
Suggest that the distance between top of block and head gasket width is critical....a 2mm head gasket(how thick are they) is goint to add about 14ml by itself
(680+14)/(55+14)=10.1, which leads to a more realistic value?
For domed top 90mm diameter pistons, assuming perfectly uniform spherical tops add/subtract 3.1cc for every mm the dome is above/below the piston edges. (if anyone wants the mathematical proof pm me!)
If the dome is non uniform, best to measure its vol by pressing the piston into a clay mould etc and measuring the vol of that.
#13
Tiny
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Posted 13 August 2006 - 10:52 PM
LH Hoon is right.. you should squirt the liquid INTO the chamber through the hole in the acrylic... you'll see the air bubble come out ( if you positioned the hole at the edgle like i just remebered you need to...) and you'll have your CC!
Defintiely add TO the chamber not suck OUT of!
Defintiely add TO the chamber not suck OUT of!
#14
TerrA LX
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Posted 14 August 2006 - 12:27 AM
^^ a 40 tho gasket is roughly 12cc
#15
_jklumpp_
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Posted 14 August 2006 - 06:29 PM
Yeah, I did think of that, & tried it....problem was when the bubble went elsewhere, and kero came out the hole!!!....Might try it again with a slight angle on the head, and the hole at the edge as you suggest....LH Hoon is right.. you should squirt the liquid INTO the chamber through the hole in the acrylic... you'll see the air bubble come out ( if you positioned the hole at the edgle like i just remebered you need to...) and you'll have your CC!
Defintiely add TO the chamber not suck OUT of!
Having said that, I the one I tried that way, I measured 52cc and squirted it in, and it still seemed to be about right...
No, these are not stock heads. It is originally a 186 head, but has had quite a bit of work done....are these stock heads as going by those figures my comp ratio is 12.3 to 1. it seems a bit high, almost too high for pump fuel. if thats right then i can forget about trying to squeeze some low bost through it
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