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| lowering compression by shimming? https://www.slantsix.org/forum/viewtopic.php?t=20241 |
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| Author: | Bren67Cuda904 [ Sun Oct 15, 2006 10:17 am ] |
| Post subject: | lowering compression by shimming? |
I am having lots of head work done to my 68-75 cylinder head and would hate to have to do other head later. Right now are target CR is 10.5:1. In the future I may (30% chance and at least 2.5 years away) put on a supercharger. This CR is to high for this however and I don't what to give up CR for plans that are way down the road and may not happen. Is there a way to low CR in the future by added a steel plate with two head gaskets on either side? New target CR would be around 8.5:1 Or is my only option to rework a new head and mill it for the lower CR? |
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| Author: | Rust collector [ Sun Oct 15, 2006 10:42 am ] |
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Anyone tried a steel shim gasket between 2 of the new style ones? |
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| Author: | Charrlie_S [ Sun Oct 15, 2006 12:21 pm ] |
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You would have to "run" the numbers, but might be able to run a thick solid copper gasket. They are availble from Cox Bros. I think they can be had up to about .100 thick. |
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| Author: | Slant Cecil [ Sun Oct 15, 2006 2:18 pm ] |
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MP used to offer a shim plate the sandwiched between two gaskets to lower the compression of a Street Hemi. CJ Yother may be able to make one for a slant six. It would take a plate thickness of .90 plus an extra .040 gasket, +.130 total, to drop the squeeze 2 points. |
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| Author: | Ron Parker [ Sun Oct 15, 2006 5:31 pm ] |
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Build your 10.5 head now a lot of things can happen in 2 and a half years. You could become a milloinare i asume you are not one now or this would not be a issue. You can always save pocket change for 2 and half years and build a supercharger head or turbo head witch is what i would like to have. I doint think rednecking a 10.5 head for a supercharger would be a good idea and may cost more than a new head. Thanks Ron Parker  It Aint Over Until I Win |
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| Author: | sandy in BC [ Sun Oct 15, 2006 6:11 pm ] |
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How bout decking the block for 10.5 compression leaving the head with enough chamber to bolt to a stock deck block and get 8.5? It has to be cheaper to move the rotating assembly to a fresh block than to build a new head. Nothing is more expensive than blowing a crazy expensive ,fat ,head gasket and having to go back to square one. Third idea....a cheap one at that. Just build one motor the way you want it the first time. Focus on one thing at a time and get that done. |
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| Author: | Bren67Cuda904 [ Sun Oct 15, 2006 6:41 pm ] |
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Milloinare or not Planning ahead seems logical. Shimming a head is concidard rednecking it? Its got to be cheaper than redoing a head with porting and new oversized valves. New block sonic ck and > .100 over bore with gound block to fit my 4.5 stroke seem pricey too. Is shimming the head an unreliable practice? |
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| Author: | Ron Parker [ Sun Oct 15, 2006 7:24 pm ] |
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For a supercharged engine i would think so . You can ask my racing friend Dale Rose about high compression engines and superchargers. He has blown two no shims or stunts. If one wants to build a engine build it right for the appacation doint try to do two defferent engines. Also Sandy reply is right on the mark your good Sandy. Thanks Ron Parker It Aint Over Until I Win |
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| Author: | slantzilla [ Sun Oct 15, 2006 9:10 pm ] |
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That's pretty bad when Possum calls something redneck. 
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| Author: | sick6 [ Mon Oct 16, 2006 12:05 pm ] |
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so what is the max compression for a supercharger then? I can't find that info anyplace on this site. (yes, I realize there are many variables......I am trying to make a point) I can't imagine a head gasket costs as much as a custom head rework and a balanced and blueprinted engine. does anyone have an idea of how much a custom thicker gasket would run? ron, do you know off hand how to contact that friend of yours? I have a higher comp slant too (10.5 to 1) and I have heard multiple ways to get around that for a supercharger, and I am wondering what your friend did. |
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| Author: | Bren67Cuda904 [ Mon Oct 16, 2006 2:29 pm ] |
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Was told today that there is no max CR in regards to using a power adder. You will just need a timing "computer" to retard timing based on boost. MSD make one that plugs into the MSD 6A ,AL boxes. The more boost the more retard. |
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| Author: | Ron Parker [ Mon Oct 16, 2006 3:49 pm ] |
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First i was not calling Brennan a redneck i was refering to that sounds like something i would try. I have talked to two supercharger suppliers and one turbo supplier about buliding a engine. Also a couple that race with us that run power enhancer. All three told me the same thing for a supercharger or turbocharger to work well c.r. should be about no higher than 9 to 1 to 9.50 to one My current engine is running about 11 to 1 . They said yes you can run c.r. that high problems could come up. My friends engine is a 12.50 cr engine and issues have come up. All three suppliers said a 9.50 cr would work fine. I would shoot for a 9 to 9.5 engine and run it now and be set for the future. This is my opinion and research may leed you to a different answer. Thanks Ron Parker It Aint Over Until I Win |
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| Author: | sick6 [ Tue Oct 17, 2006 5:44 am ] |
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bren, thats what I have heard also, I have seen those before when I was looking into a retard computer for nitrous. ron: ooooohhhh......okay, I get it now. thanks for answering my questions. |
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| Author: | rosspulliam [ Tue Oct 17, 2006 8:21 am ] |
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I'm not an expert on building heads by any means, but I've always been told around the machine shop that when building a head to be natural aspirated it, the goal is a balance between high flow and a high velocity input charge. Whereas for a turbo or supercharger applications its more of a high volume deal because all the velocity you need will be provided by the power adder. I'm with Ron on this one entirely, build it for what you want, or scale it back to fit the power adder in the future. You can't always have your cake and eat it to. |
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| Author: | LUCKY13 [ Tue Oct 17, 2006 12:22 pm ] |
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The CR that one can get away with is a big vairable that is hard to anwser. There are some people running 11:1 and higher on turbo apps. But I am going to guess they are just smarter than the most of use and the average person is not going to get away with this. To stack head gaskets probabbly would be a bad idea (prone to hot spots & blowing). But the thick copper head gasket could be a good option if the right precausions are used to get it to seal the water jackets good. If nothing in this line worked then changing or milling the pistons could be the cheapest route if changing the engine config is what it came down to. And you will need a way to retard the timing even if you had 7:1 CR. All this is something you will have to anwser when you put the Suppercharger on. Pump it up & retard the timing and if you dont det or ping you have gotten away with the CR you are running with the boost you are using. You can also inject water/meth to help this. Edging the pistons & combustion chamber can help this ( smooth any rough or sharp edges on the piston top & CC) dont polish, just radius the edges. Also the special ceramic coatings that are out can help this alot, coat the piston tops & the combustion chamber & also the exhaust valve face and even the exhaust port. Ofcourse this takes money and is something you would have to deside on yourself but the results have been very good with these coatings, both in det & ping control & producing horse power buy keeping the heat in the chamber & not in the componets themself which would promote pinging. Jess |
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