.100 cut wouldn't bother me a bit.
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| Decking, part two https://www.slantsix.org/forum/viewtopic.php?t=24524 |
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| Author: | polara pat [ Sat Aug 18, 2007 7:42 pm ] |
| Post subject: | Decking, part two |
This is kind of a follow up post from my "Decking Advantages" post. I've gone ahead and mocked up my rotating assembly and my average measurement from piston to deck is .155, over an eighth of an inch!!! So I brought my block back to the machine shop and I think I will go ahead and take .100 off the top. Do you old pros think this is too excessive for a stock build? Any and all advice is appreciated. Now without doing all the number crunching could someone give me a ballpark CR and possible HP output from such an engine. The quick rundown is as follows: Re-ring standard bore '80s 225 super six(Carter BBD), new bearings, turned crank, (hypathtically) decked .100, new stock solid lifter cam, stock valves and seats ground and lapped new timing set. All through a 904. Let me know if I left anything out. Thanks, Pat. |
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| Author: | slantzilla [ Sat Aug 18, 2007 10:08 pm ] |
| Post subject: | |
.100 cut wouldn't bother me a bit.
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| Author: | BigBlockBanjo [ Sat Aug 18, 2007 10:38 pm ] |
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Do it....I did mine, and it runs great. I believe that alone puts the compression up to around 9-1??? I used a re-ground cam, and the pushrods fit like a glove. |
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| Author: | dakight [ Sun Aug 19, 2007 6:02 am ] |
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I'm going to tell you what most evyone will tell you. Without measuring it's impossible to know what your CR will be. The problem is that casting tolerances in the early 60s were very wide for both the block and the head. You best bet is to measure the chamber CC then calculate your CR at your desired deck height. You may find that you'll need to tweak the head a bit to even up the combustion chambers then, and ony then, you will know how much to take off your deck. Taking .100 off will certainly raise your CR from where it currently is but you have no way to know with any reasonable certainty what it actually is, nor will you have any confidence that it is even from cylinder to cylinder. It's a lot like laying the foundation for a house; if you don't start with a square foundation then everything you build on will be askew. |
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| Author: | slantzilla [ Sun Aug 19, 2007 8:11 am ] |
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Yes, a true deck job is measured from the centerline of the main bores, not just skimming a number off the top. Figure out what you want for actual deck height and cut it that way. You also have to make sure your machinist is competent. I have seen Slant blocks off .030" from front to back because the block was not mounted in the cutter correctly. 
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| Author: | polara pat [ Sun Aug 19, 2007 9:00 am ] |
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Alright, alright, I was only looking for ballpark. So given my current measurements my "average" deck height will be .055" I'm not shooting for .000" just a good all-round performance bump over the factory spec. And my machinist is verging on genius for a guy pushing 80. 9:1 CR would be ideal I think for my set up. Maybe if I phrase my question differently you guys could help out. What is a realistic HP from a re-ringed 80s Super Six? And what sort of over all gains could be made from .055" head space, sorry I don't know my combustion chamber cc at this point. Are the cc variances that big in the eighties? By the way thanks for everyones advice, this board is great for bouncing around ideas that may otherwise never materialize. |
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| Author: | slantzilla [ Sun Aug 19, 2007 9:37 am ] |
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My feeling is that just decking the block will not do a whole lot in and of itself, but it will allow other mods to work better if you add them down the road. Realistically, upping the compression in an otherwise stock motor will give you maybe 10 horse. That is a decent gain on a motor that makes 110 or so to start. |
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| Author: | polara pat [ Sun Aug 19, 2007 10:02 am ] |
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Quote: My feeling is that just decking the block will not do a whole lot in and of itself, but it will allow other mods to work better if you add them down the road. Realistically, upping the compression in an otherwise stock motor will give you maybe 10 horse. That is a decent gain on a motor that makes 110 or so to start. See that wasn't so hard. Thanks Slantzilla. You think I'll be pushing a whopping 120 HP. All other input is still welcome. |
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