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| Compression ratio https://ausmini.com/forums/viewtopic.php?f=5&t=37996 |
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| Author: | mini-dunger [ Tue Nov 20, 2007 8:50 pm ] |
| Post subject: | Compression ratio |
Hi guys I am having trouble finding in the yellow book what the chamber size (only) needs to be on a 1098+.60 to give an approx ratio of 10.5 - 1 I have done some looking on line and from what i can gather I need a 14 cc chamber volume. That sounds pretty small..... any ideas? thanks 
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| Author: | sgc [ Tue Nov 20, 2007 9:01 pm ] |
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14cc may sound small, but that's only in the chamber. How much extra will you get in the gasket and piston dish? 6cc? 8cc? Does that add up to something approaching the right number.. ? |
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| Author: | mini-dunger [ Tue Nov 20, 2007 9:08 pm ] |
| Post subject: | |
yeah it looks better, the gasket etc etc accounts for about 15cc. Will keep digging thanks mate |
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| Author: | drmini in aust [ Tue Nov 20, 2007 9:36 pm ] |
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PM sent. |
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| Author: | TheMiniMan [ Tue Nov 20, 2007 9:42 pm ] |
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a 14cc cyl head is REALLY dam small & no matter what mini engine i`d "guess" that`s way too small |
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| Author: | mini-dunger [ Wed Nov 21, 2007 7:03 am ] |
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OK this is what I think I know..... my total capacity for 1 cylinder is 288cc so i devided that by 10.5 and I got 27.4 SO I am guessing 27.4 is my total chamber volume(ring land,gasket,piston to deck clearance) so, using your numbers as a guide, - 3cc gasket - 8cc for piston dish (I am using hypertecs too) -1 cc for the piston to dec clearance so therefore my chamber volume in the head alone should be 27.4cc - 12cc = 15.4 cc?? Unless of course I am an idiot and its all wrong 
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| Author: | ken@miniauto [ Wed Nov 21, 2007 7:30 am ] |
| Post subject: | Compression ratio |
To work out the total combustion chamber volume divide the cylinder capacity by ONE LESS than the desired CR So for 10.5:1 divide 288 by 9.5 equals 30.3 total chamber volume Hope this helps |
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| Author: | mini-dunger [ Wed Nov 21, 2007 5:33 pm ] |
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yes it does mate, thanks 18 cc sounds doable, maybe. with all the deshrouding I have done the chambers are farily big. still bloody small tho |
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| Author: | titi de lille [ Wed Nov 21, 2007 6:29 pm ] |
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14cc it's strange, because the nominal volume is 24.3cc as the 998 and 21.4cc for a 12g940. which cylinder head have you got? because with 14cc, you should have a cr of 14 not less. if you buy your piston from the minisport shop send a mail to andrew. for me these piston should give 9.6 or 9.75. a 998 with flat piston gives 10.3. |
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| Author: | mini-dunger [ Wed Nov 21, 2007 8:46 pm ] |
| Post subject: | |
its a 12g202 How much has anyone been able to mill off these things? OR should I get the pistons squared off and have the block decked? |
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| Author: | mini-dunger [ Wed Nov 21, 2007 8:51 pm ] |
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actually I think I might go and drink some paint 
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| Author: | drmini in aust [ Wed Nov 21, 2007 8:56 pm ] |
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mini-dunger wrote: its a 12g202
How much has anyone been able to mill off these things? The more you take off the more gasket probs you can have. Having said that, Gafmo's has has about .090" off I think... :shock:  OR should I get the pistons squared off and have the block decked? Yes that's a possibility but talk to GR.  |
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| Author: | gafmo [ Wed Nov 21, 2007 10:01 pm ] |
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| havent had a gasket for some time now
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| Author: | mini-dunger [ Thu Nov 22, 2007 6:51 am ] |
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what do you mean by havent had a gasket?? I should have picked up a 1275 head in the first place. I have spent $300 so far on this piece of crap,plus about 3 weekends. And now I am left with something that more or less makes the whole motor worth no more than a piece of crap. Mr V said getting compression up after all this deshrouding and such would be no problem.... well it bloody is. I have 2 options as far as I can see, well 3 kinda... 1Flat top pistons (if they fit,cause its bored .60 for my hypertecs) 2get 3mm or so milled off my hypertecs to reduce the dish cc, then get the block decked to suit. or get about 4mm milled of the head
If the piston dish cc was out of the equation I wouldnt have to skim the head to death and it "should" survive. Im am so close to having this built yet so far... end rant 
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| Author: | 1018cc [ Thu Nov 22, 2007 8:47 am ] |
| Post subject: | |
mini-dunger wrote: what do you mean by havent had a gasket??
I think gaf means that he hasn't blown a head gasket recently. Correct me if I'm wrong gaf 
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