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Join Date: Jul 2009
Location: Sharon Springs NY
Posts: 350
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Deck Height
So I measure the deck height on my 3.0 with JE 10.5:1 pistons, and the flat surface around the edge of the piston measures 1.3mm below the top surface of the cylinder head. When I do the method with solder on the piston, and with the head bolted down per the book instructions, the solder compresses and gives me a 2.02mm height. All of this with one base gasket installed. So now I'm totally confused as to what is correct (and seems to me that ~2mm is way to much
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06-14-2012, 09:24 AM
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Join Date: Oct 2003
Location: Central Fla
Posts: 1,864
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deck
You are dealing with two different dimensions, the deck height as you have posted is neg. 1.3mm, the other is piston to head clearance and that is not deck hgt. what you should do is pour the chamber, figure out what the dome vol. is and then we can figure out what you have for CR
Mike Bruns
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The two most useless things to a driver are the braking distance behind you and nine-tenths of a second ago. |
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06-14-2012, 10:10 AM
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Location: Sharon Springs NY
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ok then i must have miss read Wayne's book on deck height checking. I'll go back and re-read that section
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06-14-2012, 10:43 AM
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Location: Central Fla
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Deck
The deck is the dimension from the top of the cyl./block to the top edge of the piston before the dome begins at TDC, down in the bore is neg. deck and above the surface is positive deck.
Mike Bruns
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The two most useless things to a driver are the braking distance behind you and nine-tenths of a second ago. |
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06-14-2012, 10:57 AM
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ok.. i see in the book, that it says technically its not measuring deck height, but piston to head clearance. However, the book also says that 1.5 to 1.25mm of deck height is recommended (but one can run 1mm for higher compression). If the solder method measures piston to head clearance, what is an acceptable (the book seems to indicate that anything less than 0.050 inch (why we insist on mixing measurement standards) is not good. at 2mm piston to head clearance thats about 0.078 inch. which in my reading should be good.. but i'm not sure.
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06-14-2012, 11:04 AM
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Registered
Join Date: Oct 2003
Location: Central Fla
Posts: 1,864
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Deck
When we design a piston we shoot for 1 mm neg. deck, I have seen factory setups at .035 in (.88mm) to .040 (1mm) plus, I have seen piston to head as tight as .030 in. and not have a problem, On hemi heads its tough getting all the CR you want sometimes so you have to work at it. At the end of the day you have to check everything to see what you really have, just because the shelf pistons say they are 10.5 to 1 that is based on a certain chamber vol. and deck hgt. etc... you may have 11 to 1 or 9 to 1
Mike Bruns
__________________
The two most useless things to a driver are the braking distance behind you and nine-tenths of a second ago. |
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06-14-2012, 11:24 AM
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Registered User
Join Date: Jun 2012
Posts: 144
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It sounds like youve answered your own question. 1.25 recommended and you have 1.3 while maintaining a good safe piston to head clearance.
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06-14-2012, 11:26 AM
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911 2.2 T targa
Join Date: Jun 2012
Location: Netherlands
Posts: 89
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I just finished the same chapter and had similar doubts. After talking to my local specialist an doing some extra measurement I got the concept.
To answer you question: I think your save to go ahead with this set-up. De dome shape (radius) of the head is different then the piston dome, so if the solder is not completely on the edge of the piston (touching the cylinder), the measurement will increase quite a bit. |
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06-18-2012, 11:21 PM
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