Thinking out loud - 1911, Found my deck height. All good? |
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Thinking out loud - 1911, Found my deck height. All good? |
jaredmcginness |
Jul 4 2020, 10:03 AM
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#1
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... Group: Members Posts: 501 Joined: 12-June 19 From: Baltimore Member No.: 23,209 Region Association: MidAtlantic Region |
See update and actual numbers on the added reply.
Sorry for the novel!! Hey guys, I'm building a 1911. I want to make sure that I have my thoughts in the right place. -96 Bore x 66 stroke. Fresh rebuilt 1.7 heads with a 105mm fly cut register. Stock valves -Running a .495 lift cam, lifters to match, HD springs + counter bore .630 (IIRC) extended. I need to CC my heads first, get the volume, then determine my deck height and compression ratio? Stock 1.7 heads are 50cc. I assume mine will end up a tad larger, maybe 52cc. (will the fly cut alter the size?) But I might be off. Is 8.5:1 a good target ratio? Ive read a few threads and this seems to be the middle ground compression. A good target DH is .045-.065? With a minimum of 0.040 to avoid contact. A few examples - per a CR calculator: 50cc, 0.065 = 8.7:1 50cc, 0.045 = 9.2:1 53cc, 0.065 = 8.4:1 53cc, 0.045 = 8.8:1 This in mind, depending on my head volume it should be easy to narrow down where I need to be. Am I on the right track? New to this and been digging into some old books. Whats a good compression ratio, that should be safe for a mild carbed (dual 36) motor and mild cam. Want this thing to last more than a summer! I dont really have a target CR, because I dont know the difference of a few decimal points! Happy 4th (IMG:style_emoticons/default/beerchug.gif) ! |
jaredmcginness |
Aug 1 2020, 11:58 AM
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#2
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... Group: Members Posts: 501 Joined: 12-June 19 From: Baltimore Member No.: 23,209 Region Association: MidAtlantic Region |
Thank you for the fantastic response @superhawk996 ! No assumption - my heads were liquid CC’d this morning at 49.5.
I did a fresh total stock head rebuild. (I probably should have done bigger valves, but I went off some good advice from Dave D of pelican parts that stock valves will be sturdy) alas, here we are. My engine guy still have my heads, so I can still have him port and polish. For clarity, if I port and polish, that will make up for the loss of CC (from fly cutting to 105mm). And... allow me to add a shim .020 or so. Thanks again for the well thought out response. |
Superhawk996 |
Aug 1 2020, 12:06 PM
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#3
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914 Guru Group: Members Posts: 5,723 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
For clarity, if I port and polish, that will make up for the loss of CC (from fly cutting to 105mm). And... allow me to add a shim .020 or so. No. Port and polish work is upstream of the valve head inside the intake and exhaust ports. It doesn't affect the CC's of the head. |
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