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| Ok I need the compression calculating experts https://www.slantsix.org/forum/viewtopic.php?t=41910 |
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| Author: | 1974duster kev [ Wed Sep 15, 2010 3:21 pm ] |
| Post subject: | Ok I need the compression calculating experts |
Just picked-up my block and head up from the machine shop. I cc'd the head and it is 55cc's im using the .045 over weisco piston k1 connecting rod combo. the piston is at zero deck so what ever the compression is at now, it needs to go down to 8:1 compression. how thick of a copper head gasket would i Need to obtain this?? Please help the calculations are not my strong point  If i didnt provide enough information let me know i'll answer or try to answer any other questions. Kev |
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| Author: | Doc [ Wed Sep 15, 2010 4:07 pm ] |
| Post subject: | |
Current compression is 10.36 to 1 You would need a .180 thick (yes, just under 3/16ths of an inch) to hit 8.0 to 1 (not realistic) You need to add a 28 cc dish to the top of each piston. DD |
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| Author: | 1974duster kev [ Wed Sep 15, 2010 5:48 pm ] |
| Post subject: | |
I thought copper head gaskets could be made to whatever thickness needed? 28cc dish in each piston with a regular stock thickness head gasket ? Thanks Kev |
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| Author: | Charrlie_S [ Thu Sep 16, 2010 3:37 am ] |
| Post subject: | |
Quote: I thought copper head gaskets could be made to whatever thickness needed?
Within limits. Husey copper gaskets are available from .024 to .150. I don't know for sure, about SCE gaskets, but looks like about .095 is their thickest.
Thanks Kev |
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| Author: | Doc [ Thu Sep 16, 2010 8:31 am ] |
| Post subject: | |
Quote: I thought copper head gaskets could be made to whatever thickness needed?
I based my calcs on a .045 thick gasket.28cc dish in each piston with a regular stock thickness head gasket ? Thanks Kev You could build a .180 thick "gasket" (plate?) but now everything moves higher by .180 so push rods, alturnater bracket, exhaust, throttle & kickdown linkage all need to be reviewed and "adjusted" to compensate. Trust me... money spent on the correct pistons for your application is money well spent. DD |
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| Author: | Dart270 [ Thu Sep 16, 2010 9:37 am ] |
| Post subject: | |
Kevin, To clarify: you have measured or preferably installed (test fit) the pistons/rods/crank, and now you have ZERO deck? It seems you should be around 0.010-0.040" in the hole with an uncut block and uncut pistons. If you have already bought pistons and done machining, then I would recommend flycutting pistons 0.040" and getting a 0.150" gasket. That will put you right at 8.0:1. If you flycut 0.040" and already have 0.030" deck ht before that, then you only need a 0.090" gasket for 8.4:1 or 0.120" gasket for 8.0:1. In other words, what is the meaning of "zero deck?" An exact measurement would be helpful. Thanks, Lou |
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| Author: | Shaker223 [ Thu Sep 16, 2010 10:28 am ] |
| Post subject: | |
Agree with Lou......betwenn 8 & 9 to one is fine.....depending on your cam you might have PTV issues as well. Check that measurement as well before having everything disassembled & cut (valve notches) to avoid additional issues. OR run it the way it is with 100% C16 fuel all the time. |
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| Author: | 1974duster kev [ Thu Sep 16, 2010 1:35 pm ] |
| Post subject: | |
re checked my numbers pistons are 4 thousands in the hole does that make any real difference? (hope so) the pistons already have valve notches cut in them from weisco Ya I thought this wasn't going to be such an issue i figured i would had a bigger than 55cc head considering i polished and took some bumps out of the combustion chamber and only took enough off the head just to clean it up but i guess i was wrong. So whats the concensus is a really thick copper head gasket gonna do the job? the throttle linkage is gonna be changed anyway, and if theres any other fitment problems i'd honestly rather deal with that then find ways to bring the compression down i'm much more comfortable in repositioning stuff rather than dishing pistons and such I dont know is 8:1 too low to dream for with this setup? thanks for the help guys Kev |
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| Author: | 70valiant [ Thu Sep 16, 2010 1:49 pm ] |
| Post subject: | |
Why do you want only 8:1 compression? You doing a turbo project? 9.5:1 is very streetable and can run on 87octane. |
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| Author: | Dart270 [ Thu Sep 16, 2010 2:24 pm ] |
| Post subject: | |
Yes, he is going turbo. I would think 8.5-9:1 is OK unless you want crazy boost. Lou |
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| Author: | Shaker223 [ Thu Sep 16, 2010 2:33 pm ] |
| Post subject: | |
Some here on the board found the valve reliefs to either and I'm not sure about this To be to small or not deep enough for the valve. Both Greg and Madmax had piston to valve issues. 87 octane would be for very low boost situations. |
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| Author: | Doc [ Thu Sep 16, 2010 2:54 pm ] |
| Post subject: | |
The factory valve notches on the Wiseco pistons are 6 cc's and they need to be checked for edge interference if you have an intake valve larger then 1.750 DD |
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| Author: | 1974duster kev [ Thu Sep 16, 2010 3:59 pm ] |
| Post subject: | |
Ya i've seen a post or something about that I will be checking the clearance and grinding the edges of the valve reliefs if need be i'm using the oversize valves ( those enginebuilder ones from ebay) I guess i'm in a bit of a pickle, my machine shop guy seems totally fine with the idea of a thick hunk of a copper gasket but i'm not sure how to approach this you guys obviously have tons of experience do I have to bite the bullet and dish the pistons, or can i get away with the thick hunk of copper idea.... or is there some possible ideas to remedy this situation besides dishing pistons or super thick head gasket. Would i be able to massage the piston enough around the valve reliefs to gain some cc's?? I dont mind grinding I just wouldn't want to do anything ill advised to this wallet sore of a motor. it's a street car so the race gas is out lol but, the aim is for as fast as possible on premium Guidance is very welcome and appreciated Kev |
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| Author: | 66aCUDA [ Fri Sep 17, 2010 8:06 am ] |
| Post subject: | |
Kev The copper will work for the boost. However you will need to do a couple of things first. O-ring the block (and Head). I would have a Machine Shop fly cut the piston valve clearances larger by.015 dia. Or maybe cut the entire piston face center out to help with the CR. Contact Wiseco for the amount you can safely cut out. DONT use a grinder. I dont think that will give you enough repeatability between pistons. If you are going to use copper use ARP Head studs. JMHO Frank |
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