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Chamber porting for dropping compression

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Chamber porting for dropping compression

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Old 01-13-2019, 04:26 PM
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Default Chamber porting for dropping compression

Jim V is going to be porting my combustion chambers to help reduce the compression on my Promaxx heads in preparation for boost. They start at 119cc, does anyone have any experience on how many ccs can be removed on a head like this?
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Old 01-13-2019, 05:04 PM
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When I was done cleaning up the Edelbrock chambers it removed 10cc by the time I was done and good for .68 of a compression point.
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Old 01-13-2019, 05:46 PM
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Originally Posted by rob vanharten View Post
Jim V is going to be porting my combustion chambers to help reduce the compression on my Promaxx heads in preparation for boost. They start at 119cc, does anyone have any experience on how many cc’s can be removed on a head like this?
Rob, When Valako chamber ported my heads he got me to 129cc on Darts combustion chambers. Did you tell Jim where you wanted to be at? He didn't just do a fluff and buff on my chambers. It was strategic to optimize flow and ward off detonation. I'll assume he'll do the same for you. I run 87 octane in my engines. I actually gained RPM after I removed 0.70 of compression.
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Old 01-13-2019, 07:40 PM
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Jason, I spoke with Jim on Saturday regarding my project. I am sitting around 9.8 right now and would like to get down in the 8.5-8.75 range. I understand this will not be doable with the porting alone but am hoping he can remove as much as possible while helping flow. I will still have to run thicker head gaskets but I am trying to run the thinnest gasket possible after the porting to get me to my desired compression ratio. Jim was thinking he could get them into the upper 120s while increasing flow. I would be very happy with 10ccs but a little more would be even better!!
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Old 01-13-2019, 07:48 PM
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Originally Posted by rob vanharten View Post
Jason, I spoke with Jim on Saturday regarding my project. I am sitting around 9.8 right now and would like to get down in the 8.5-8.75 range. I understand this will not be doable with the porting alone but am hoping he can remove as much as possible while helping flow. I will still have to run thicker head gaskets but I am trying to run the thinnest gasket possible after the porting to get me to my desired compression ratio. Jim was thinking he could get them into the upper 120s while increasing flow. I would be very happy with 10ccs but a little more would be even better!!
Whats your current bore stroke and head gasket?
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Old 01-13-2019, 07:52 PM
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Originally Posted by hogie roll View Post




Whats your current bore stroke and head gasket?
4.560 bore, 4.375 stroke, .027 gasket, piston is about .025 in the hole.
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Old 01-13-2019, 08:45 PM
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Does the quench become an issue at some point?
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Old 01-13-2019, 09:11 PM
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Originally Posted by Baja Rooster View Post
Does the quench become an issue at some point?
Research has shown that in blown applications quench can be basically disregarded. Merc 1075 has a .051 head gasket with the piston being .098 in the hole. It uses a flattop piston as well.
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Old 01-13-2019, 09:57 PM
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Originally Posted by rob vanharten View Post

4.560 bore, 4.375 stroke, .027 gasket, piston is about .025 in the hole.
Piston cc?
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Old 01-13-2019, 10:10 PM
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Originally Posted by hogie roll View Post

Piston cc?
flat top with 3cc valve pocket.
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