Hello! Log in or Register   |  Help  |  Donate  |  Buy Shirts New!  See all banner ads | Advertise on TheSamba.com  
TheSamba.com
 
Compression ratio conundrum
Forum Index -> Performance/Engines/Transmissions Share: Facebook Twitter
Reply to topic
Print View
Quick sort: Show newest posts on top | Show oldest posts on top View previous topic :: View next topic  
Author Message
paul356A
Samba Member


Joined: July 31, 2015
Posts: 18
Location: Brighton U.K.
paul356A is offline 

PostPosted: Wed Jan 13, 2021 2:51 am    Post subject: Compression ratio conundrum Reply with quote

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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Alstrup
Samba Member


Joined: July 12, 2007
Posts: 5068
Location: Videbaek Denmark
Alstrup is offline 

PostPosted: Wed Jan 13, 2021 3:03 am    Post subject: Re: Compression ratio conundrum Reply with quote

9-1.
_________________
https://www.thesamba.com/vw/forum/viewtopic.php?t=435993
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
UK Luke 72
Samba Member


Joined: September 07, 2011
Posts: 2172
Location: Little Britain
UK Luke 72 is offline 

PostPosted: Wed Jan 13, 2021 3:07 am    Post subject: Re: Compression ratio conundrum Reply with quote

Do you have the parts already?

Our fuel isn't directly comparable to theirs.
Our 95 is their 91
_________________
2276 Beetle build https://www.thesamba.com/vw/forum/viewtopic.php?t=670744&highlight=2276+beetle+daily
2276 EFI Conversion https://www.thesamba.com/vw/forum/viewtopic.php?t=689172
1835 Camper build https://www.thesamba.com/vw/forum/viewtopic.php?t=670745&highlight=1835+camper
Back to top
View user's profile Send private message Gallery Classifieds Feedback
paul356A
Samba Member


Joined: July 31, 2015
Posts: 18
Location: Brighton U.K.
paul356A is offline 

PostPosted: Wed Jan 13, 2021 3:13 am    Post subject: Re: Compression ratio conundrum Reply with quote

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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
UK Luke 72
Samba Member


Joined: September 07, 2011
Posts: 2172
Location: Little Britain
UK Luke 72 is offline 

PostPosted: Wed Jan 13, 2021 3:32 am    Post subject: Re: Compression ratio conundrum Reply with quote

Yeah it can be a nightmare.
Reason I ask is, what chamber cc and deck height is it coming in at?
_________________
2276 Beetle build https://www.thesamba.com/vw/forum/viewtopic.php?t=670744&highlight=2276+beetle+daily
2276 EFI Conversion https://www.thesamba.com/vw/forum/viewtopic.php?t=689172
1835 Camper build https://www.thesamba.com/vw/forum/viewtopic.php?t=670745&highlight=1835+camper
Back to top
View user's profile Send private message Gallery Classifieds Feedback
paul356A
Samba Member


Joined: July 31, 2015
Posts: 18
Location: Brighton U.K.
paul356A is offline 

PostPosted: Wed Jan 13, 2021 3:56 am    Post subject: Re: Compression ratio conundrum Reply with quote

chamber volume is 60cc, I'm just about to get on to deck height.
_________________
1956 RHD PGSG bus
1959 RHD 356A
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Ohio Tom
Samba Member


Joined: February 09, 2006
Posts: 1023
Location: Marshallville Ohio
Ohio Tom is offline 

PostPosted: Wed Jan 13, 2021 7:12 am    Post subject: Re: Compression ratio conundrum Reply with quote

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.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
sled
Samba Member


Joined: February 16, 2005
Posts: 5611

sled is offline 

PostPosted: Wed Jan 13, 2021 7:32 am    Post subject: Re: Compression ratio conundrum Reply with quote

.045 to .050 deck
_________________
drive your split.
Back to top
View user's profile Send private message Instagram Gallery Classifieds Feedback
Alstrup
Samba Member


Joined: July 12, 2007
Posts: 5068
Location: Videbaek Denmark
Alstrup is offline 

PostPosted: Wed Jan 13, 2021 8:14 am    Post subject: Re: Compression ratio conundrum Reply with quote

Yes. at 1,2 mm deck youre right at 9-1
_________________
https://www.thesamba.com/vw/forum/viewtopic.php?t=435993
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
paul356A
Samba Member


Joined: July 31, 2015
Posts: 18
Location: Brighton U.K.
paul356A is offline 

PostPosted: Wed Jan 13, 2021 9:58 am    Post subject: Re: Compression ratio conundrum Reply with quote

Thanks guys, I'll aim for 9:1, just need to check my deck height


Paul
_________________
1956 RHD PGSG bus
1959 RHD 356A
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Zed999
Samba Member


Joined: March 04, 2018
Posts: 1019
Location: UK
Zed999 is offline 

PostPosted: Thu Jan 14, 2021 1:43 am    Post subject: Re: Compression ratio conundrum Reply with quote

just for a UK comparison for you I run a stock cam at 8:6:1 (not my doing) and it's fine.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Ohio Tom
Samba Member


Joined: February 09, 2006
Posts: 1023
Location: Marshallville Ohio
Ohio Tom is offline 

PostPosted: Thu Jan 14, 2021 2:26 pm    Post subject: Re: Compression ratio conundrum Reply with quote

It's also typically cooler in the UK than parts of the USA.

outside temps have alot to do with it...
Back to top
View user's profile Send private message Gallery Classifieds Feedback
bugguy1967
Samba Member


Joined: January 16, 2008
Posts: 4002
Location: Los Angeles, CA 90016
bugguy1967 is offline 

PostPosted: Thu Jan 14, 2021 11:00 pm    Post subject: Re: Compression ratio conundrum Reply with quote

Americans and their peasant petrol Laughing Laughing Laughing Laughing
_________________
"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"
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
Display posts from previous:   
Reply to topic    Forum Index -> Performance/Engines/Transmissions All times are Mountain Standard Time/Pacific Daylight Savings Time
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

About | Help! | Advertise | Donate | Premium Membership | Privacy/Terms of Use | Contact Us | Site Map
Copyright © 1996-2020, Everett Barnes. All Rights Reserved.
Not affiliated with or sponsored by Volkswagen of America | Forum powered by phpBB