| paul356A |
Wed Jan 13, 2021 2:51 am |
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I am building a 2180cc motor for my split bus and need to decide on what compression ratio to use. Looking through many post it's seems people are using 8 - 8.5 to 1 for my set up, which to me being in the U.K. sounds quite low. Is this because people are building to suit U.S. pump gas which looks to be 87 octane? Regular petrol here in the U.K. is 95.
My spec is :
2180 (82 x 92)
Scat C35 with 1:1.25 rockers
Tims stage one plus heads (42 x 37)
Twin Dellorto DRLA 40
What do people think?
Cheers
Paul |
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| Alstrup |
Wed Jan 13, 2021 3:03 am |
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| 9-1. |
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| UK Luke 72 |
Wed Jan 13, 2021 3:07 am |
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Do you have the parts already?
Our fuel isn't directly comparable to theirs.
Our 95 is their 91 |
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| paul356A |
Wed Jan 13, 2021 3:13 am |
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Yes I have the parts, I am in the mock up stage of the build. I have been reading more about fuel and it seems UK 95 is like US 91 because of different use of RON MON and PON
Paul |
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| UK Luke 72 |
Wed Jan 13, 2021 3:32 am |
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Yeah it can be a nightmare.
Reason I ask is, what chamber cc and deck height is it coming in at? |
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| paul356A |
Wed Jan 13, 2021 3:56 am |
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| chamber volume is 60cc, I'm just about to get on to deck height. |
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| Ohio Tom |
Wed Jan 13, 2021 7:12 am |
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CB Performance has a nice "engine calculator" you can punch in your info and it spits out the CR.
I like to play with different scenarios just to get an idea of where I need to land.
I do calcs for deck heights:
.040"
.050"
.060"
.070"
.080"
If I do my math right. I can flycut the heads and land in the normal deckheight range with some room to go up/down if needed. |
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| sled |
Wed Jan 13, 2021 7:32 am |
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| .045 to .050 deck |
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| Alstrup |
Wed Jan 13, 2021 8:14 am |
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| Yes. at 1,2 mm deck youre right at 9-1 |
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| paul356A |
Wed Jan 13, 2021 9:58 am |
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Thanks guys, I'll aim for 9:1, just need to check my deck height
Paul |
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| Zed999 |
Thu Jan 14, 2021 1:43 am |
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| just for a UK comparison for you I run a stock cam at 8:6:1 (not my doing) and it's fine. |
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| Ohio Tom |
Thu Jan 14, 2021 2:26 pm |
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It's also typically cooler in the UK than parts of the USA.
outside temps have alot to do with it... |
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| bugguy1967 |
Thu Jan 14, 2021 11:00 pm |
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| Americans and their peasant petrol :lol: :lol: :lol: :lol: |
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