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bugguy1967 Samba Member
Joined: January 16, 2008 Posts: 4338 Location: Los Angeles, CA 90016
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Posted: Thu Jan 14, 2021 11:00 pm Post subject: Re: Compression ratio conundrum |
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Americans and their peasant petrol _________________ "A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine" |
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Ohio Tom Samba Member
Joined: February 09, 2006 Posts: 1657 Location: Marshallville Ohio
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Posted: Thu Jan 14, 2021 2:26 pm Post subject: Re: Compression ratio conundrum |
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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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Zed999 Samba Member
Joined: March 04, 2018 Posts: 1240 Location: UK
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Posted: Thu Jan 14, 2021 1:43 am Post subject: Re: Compression ratio conundrum |
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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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paul356A Samba Member
Joined: July 31, 2015 Posts: 85 Location: Brighton U.K.
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Posted: Wed Jan 13, 2021 9:58 am Post subject: Re: Compression ratio conundrum |
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Thanks guys, I'll aim for 9:1, just need to check my deck height
Paul _________________ 1956 RHD PGSG bus
1959 RHD 356A |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7178 Location: Videbaek Denmark
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sled Samba Member
Joined: February 16, 2005 Posts: 6171
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Posted: Wed Jan 13, 2021 7:32 am Post subject: Re: Compression ratio conundrum |
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.045 to .050 deck _________________ drive your split. |
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Ohio Tom Samba Member
Joined: February 09, 2006 Posts: 1657 Location: Marshallville Ohio
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Posted: Wed Jan 13, 2021 7:12 am Post subject: Re: Compression ratio conundrum |
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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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paul356A Samba Member
Joined: July 31, 2015 Posts: 85 Location: Brighton U.K.
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Posted: Wed Jan 13, 2021 3:56 am Post subject: Re: Compression ratio conundrum |
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chamber volume is 60cc, I'm just about to get on to deck height. _________________ 1956 RHD PGSG bus
1959 RHD 356A |
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UK Luke 72 Samba Member
Joined: September 07, 2011 Posts: 2867 Location: Little Britain
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paul356A Samba Member
Joined: July 31, 2015 Posts: 85 Location: Brighton U.K.
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Posted: Wed Jan 13, 2021 3:13 am Post subject: Re: Compression ratio conundrum |
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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 _________________ 1956 RHD PGSG bus
1959 RHD 356A |
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UK Luke 72 Samba Member
Joined: September 07, 2011 Posts: 2867 Location: Little Britain
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7178 Location: Videbaek Denmark
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paul356A Samba Member
Joined: July 31, 2015 Posts: 85 Location: Brighton U.K.
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Posted: Wed Jan 13, 2021 2:51 am Post subject: Compression ratio conundrum |
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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 _________________ 1956 RHD PGSG bus
1959 RHD 356A |
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