Compression ratio
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2nd Gear
Joined: Jul 2015
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From: KC
Compression ratio
I am currently in the process of putting in a 95" big bore kit. I am using the SE 95" cast piston at 9.4-1. I am porting the heads he is decking the heads 10 thousands to return to stock chamber size as he says porting the heads will make the chamber a little bigger. If I use a .030 head gasket what will that make my compression be?
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2nd Gear
Joined: Jul 2015
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From: KC
I was just trying to get a ballpark ratio. The machinist thought around 9.5-1 with the .030 head gasket. The cams S&S 510s work best 9.7-1 or less just wanting to make sure I'm around there. Thanks
Road Warrior
Joined: Aug 2007
Posts: 1,558
Likes: 66
From: Oakdale Ca.
Get a syring 50 or 60 cc . Fill up the chamber level. ( Not easy) then pull out the fluid . Should be between 83cc and 90 cc then plug all your numbers into big boys calculator that will give you ballpark.
Sponsor
Joined: Dec 2007
Posts: 12,084
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100 ml graduated burrette, filled with dyed alcohol is HOW to measure the cc's of a combustion chamber, along with other dedicated fixturing.
Just arbitrarily removing material, does not insure equal volume front to rear, nor does it allow anyone to actually know the actual compression ratio.
Scott
Just arbitrarily removing material, does not insure equal volume front to rear, nor does it allow anyone to actually know the actual compression ratio.
Scott
Banned
Joined: Sep 2009
Posts: 3,569
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From: deland,florida
if whoever is doing your heads cant cc the chambers to determine a accurate compression ratio its time to see this as a major red flag.we get calls to "fix" heads done by shops who shouldn't be doing headwork all the time
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2nd Gear
Joined: Jul 2015
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From: KC
He can cc heads. He is a very reputable machinist and mechanic in the KC area. I was wanting to order all my gaskets and I wanted to make sure I wasn't going over compression for the cams. He put it in the 9.5-1 just getting others opinions.
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Road Warrior
Joined: May 2011
Posts: 1,956
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From: florida
If you're guy cannot give you an exact number of what the chamber volume is then you're just guessing. You also need to know deck height, piston volume and which gasket you're going to use to find compression.
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Cruiser
Joined: May 2016
Posts: 227
Likes: 45
From: Santa Maria
This is a key part of the build. Ball park figures wont work here. If your trying to decide between a .040 and .030 head gasket wait for the CC numbers. The difference between 85cc and 86cc could be 9.6:1 and 9.5:1 which you can fix with the proper gasket.
I.E. heads CC @ 85cc and you got the .030 gasket which gives 9.6:1. If you had went with .040 gasket you would have been right at your 9.5:1 ratio. (100% made up numbers, just proving a point)
HDF Community Team
Joined: Jun 2006
Posts: 12,763
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From: san antonio
If the OP is hand porting the heads, it is not likely that the chamber volumes will be equal. JMHO but seems to me the OP sends his ported heads to the machinist and the machinist will have to equalize the chamber volume, and deck heads as required to produce the target CR with a .030" head gasket. I don't know what the OPs head porting bona fides are, no disrespect intended, but he might be better off just sending his heads to a competent porter with instructions.