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| Peanut head chamber volume question https://slantsix.org/forum/viewtopic.php?t=53365 |
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| Author: | hideogumperjr [ Wed Sep 18, 2013 8:01 am ] |
| Post subject: | Peanut head chamber volume question |
Hi folks, hope everyone has been having a wonderful summer, Weather is changing here in Seattle area and I am getting ready to hopefully paint this week. Those who have read my thread on the machine shop that did my engine work may understand my dilemma now. I had my 81 head rebuilt locally here and it came back nice but after the head was rebuilt I asked them to cut it .060". I was told that was done and got the head home but when I cc'd the chamber it came out to 54cc where I was expecting to be closer to 45-45cc. From what I have gathered the 54cc is closer to stock so it does not appear that the head had been cut as requested. Now I have .2" deck height but I have assembled the bottom end and its a pain to get the engine to the machine shop, Nope I didn't check the height before disassembly, my bad. So the easiest thing would be for me to take the head back in for milling. Can yall tell if it appears that the head has been milled the .060" or if the head has such a variance as to have been 62+cc before the machine work? Thanks all. John |
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| Author: | Fopar [ Wed Sep 18, 2013 8:41 am ] |
| Post subject: | |
Measure from head gasket surface to valve cover gasket surface. I just measured 2 heads and got 3.600" on one and 3.610" on the other. Richard |
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| Author: | Charrlie_S [ Wed Sep 18, 2013 8:57 am ] |
| Post subject: | |
Quote: Measure from head gasket surface to valve cover gasket surface. I just measured 2 heads and got 3.600" on one and 3.100" on the other.
Richard  Are you sure? That would mean the second head was milled 1/2 inch. I have measured several heads and the "nominal" dimension for an unmilled head is 3.600. I have found most are between 3.590 to 3.610 |
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| Author: | Fopar [ Wed Sep 18, 2013 10:05 am ] |
| Post subject: | |
I miss wrote diamentions look again.  Richard |
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| Author: | DusterIdiot [ Wed Sep 18, 2013 10:37 am ] |
| Post subject: | Did? |
The 54cc is correct for a stokc head, remember that if the head had valve seat work done there might be a a little more or less combustion chamber volume. So if the head had a valve job and started at 54 cc, it could feasibly end up at 58 cc or so before you had it milled. -D.Idiot |
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| Author: | Charrlie_S [ Wed Sep 18, 2013 12:11 pm ] |
| Post subject: | |
Quote: I miss wrote diamentions look again.
That's more better Richard 
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| Author: | kesteb [ Wed Sep 18, 2013 6:23 pm ] |
| Post subject: | |
I CCed a stock '80 head and it was at 60cc's. So your '81 was probably around the same size. Also a stock '78 block had the deck high at -.184. Not much compression in the later engines. There were reasons the hp ratings were around 90hp towards the end. After milling a combined .120, I ended up with 8.75 static compression ratio. |
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| Author: | Rug_Trucker [ Wed Sep 18, 2013 6:31 pm ] |
| Post subject: | |
I would unshroud the valves. (even stock sized ones) Then re-CC it. Did you do any chamber polishing? That can add volume. |
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| Author: | hideogumperjr [ Wed Sep 18, 2013 7:49 pm ] |
| Post subject: | |
Thanks guys. I get so dang paranoid since it has been so long since I rebuilt an engine. I have not done any work on the head other than taking it and getting it rebuilt. I have the body I am working on (VERY SLOWLY!!) so putting a lot of energy into engine work is a bit too ambitious for this old cuss! Ill measure the head and post back. Thanks for all the great info guys. John |
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| Author: | hideogumperjr [ Thu Sep 19, 2013 2:34 pm ] |
| Post subject: | |
I measured my head and it is right around 3.60" so it would appear that the head had not been milled it seems? If it had been milled the .060" I should be around 3.540". Looks like a trip back to the machine shop and discussing the .060" removal again. It would make my life a lot easier than disassembling the bottom end and then taking the block back to them. Such a pain for not getting it done in the first place... POOH! John |
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| Author: | Reed [ Thu Sep 19, 2013 2:36 pm ] |
| Post subject: | |
Bummer! |
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| Author: | DadTruck [ Thu Sep 19, 2013 6:02 pm ] |
| Post subject: | |
the stock 83 head with the stock valves was 58 to 59 cc's after the os valves were installed, the chambers measured at 56 to 57 after doing some minor valve de shrouding, with the os valves the chambers were back at 58 to 59 cc's to get to my target of 53 cc's I had the machine shop cut the head .040 |
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| Author: | hideogumperjr [ Sun Sep 22, 2013 9:34 pm ] |
| Post subject: | |
so using the following dimensions I end up with SCR 7.98/1 Bore 3.46" Stroke 4.125" cc vol. 54cc HG thick .039" HG bore 3.54" deck .2" flat pistons Using my Inlet Valve Closes ABDC of 52° I get dynamic compression ratio is 6.87:1. I believe I read DCR target is around 8:1 is that correct? Changing my SCR to 9.35:1 should make my DCR 8.03:1. If I keep the combustion volume at 54cc and get the block milled .100" I then hit my SCR target of ~9.4:1. Does this sound right? My brain is so fried from all this, I envy all yall being so into this stuff and wish you were closer! Thanks John |
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| Author: | DadTruck [ Mon Sep 23, 2013 9:27 am ] |
| Post subject: | |
Quote: deck .2"
what is that number? are you saying the piston recession is .200 at TDC ? if so that is more than mostand what calculator are you using for static and dynamic ? I found the one at RB Racing to be accurate and ez to use. http://www.rbracing-rsr.com/compression.htm |
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| Author: | hideogumperjr [ Mon Sep 23, 2013 4:19 pm ] |
| Post subject: | |
yep .200" at TDC. I used both the downloaded calculator from Pat Kelly and the one here https://www.uempistons.com/index.php?ma ... fe07f707da Thanks John |
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