180-190 psi cheetah fuel question

[Alienshm]

Hi all, new to the forum. Doing a lot of searching on compression ratios and still uncertain.  Just finished a 68mm bore cheetah PV.  The Power valves are blocked off. Anyways, so did a corrected compression ratio and showing 185-190  per side. Doing the UCC  i came up with 12.57   I currently have 18cc domes with .045 of squish.  I have new domes coming from NOSS that are 20cc which will change a few  things.  I do plan on running methanol at some point but would like to stick with race gas for the moment.  I set the timing at +6 currently but wondering if 190 is too high for 110. Thanks all

[ClaudeMachining]

Hi all, new to the forum. Doing a lot of searching on compression ratios and still uncertain.  Just finished a 68mm bore cheetah PV.  The Power valves are blocked off. Anyways, so did a corrected compression ratio and showing 185-190  per side. Doing the UCC  i came up with 12.57   I currently have 18cc domes with .045 of squish.  I have new domes coming from NOSS that are 20cc which will change a few  things.  I do plan on running methanol at some point but would like to stick with race gas for the moment.  I set the timing at +6 currently but wondering if 190 is too high for 110. Thanks all

12.5 uccr and 190 psi static comp sounds weird to me.

Show me your numbers. Did you remove the cc of the spark plug from the equation???

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[Alienshm]

Sorry, just got the notice for this.  So I got my new domes and did the same calculations as before.  This time I came up with 11.5:1 and 150 psi.  The math I did was as folloWs

68mm bore

34x34x3.14x58 / 1000+20cc / 20

20cc is the amount that I injected into bore with piston at TDC set with dial indicator ,not sure if that’s correct but that’s the way I have been reading it.   

[ClaudeMachining]

Sorry, just got the notice for this.  So I got my new domes and did the same calculations as before.  This time I came up with 11.5:1 and 150 psi.  The math I did was as folloWs
68mm bore
34x34x3.14x58 / 1000+20cc / 20
20cc is the amount that I injected into bore with piston at TDC set with dial indicator ,not sure if that’s correct but that’s the way I have been reading it.   

Your math are good, but my question is did you remove the spark plug volume???

Usually, we fill it to the top, then remove 2,4cc (volume of the spark plug hole)

That make a big difference. See the pic.

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[Alienshm]

Oh ok, no I did not. I also didn’t fill it to the top just went to the first thread of the hole.   Thank you for that information.  I will redo everything before I put motor in frame.  Last question if you have a second.  Again bear with me as it has been many many years since I have done anything with a motor.  I’m going to run 110 to start with so as far as timing goes is 6-7 ok to start with or would I be better to back it down, when I do switch it methanol should I bump the compression ratio up? Current squish is .48   I have a set of 18cc that i originally spoke about but squish was like .31 to .33. And I feel that is so small. Am I incorrect or would a guy be ok

[ClaudeMachining]

Oh ok, no I did not. I also didn’t fill it to the top just went to the first thread of the hole.   Thank you for that information.  I will redo everything before I put motor in frame.  Last question if you have a second.  Again bear with me as it has been many many years since I have done anything with a motor.  I’m going to run 110 to start with so as far as timing goes is 6-7 ok to start with or would I be better to back it down, when I do switch it methanol should I bump the compression ratio up? Current squish is .48   I have a set of 18cc that i originally spoke about but squish was like .31 to .33. And I feel that is so small. Am I incorrect or would a guy be ok

With 110, you can go higher than 13:1. Start with timing at 4, .048" is ok.


I'm not familiar with the alcool setup, maybe another member can guide you with that.

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