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matthew henricks Samba Member
Joined: January 02, 2002 Posts: 1219 Location: So. Cal
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Posted: Mon Nov 22, 2021 9:17 pm Post subject: Big Bore Build. Deck Height and Compression guidance please |
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Have not build a motor in 20 years. This is my first time actually measuring anything. I have read many Big Bore threads. Seems like most are going to power and using mild cams & higher compression. My is just basic stock.
Using 83's because they came new with the motor. I am also trying to learn and go through the motions of a nice build.
My question is what compression for low grade fuel should i shoot for? 7:1, 7.9:1, 8.5:1??? I figure it is the mid to high 7's but not sure.
This is what i have.
- CC each head.
1=42.4cc 2=43.5cc 3=44.7cc 4=43.8cc
- Deck height checked with cylinder clamped Using depth mic.
1=.041" 2=.032" 3=.023" 4=.050"
- Stock crank so using 64mm as stroke.
- Big Bore P&C so using 83mm for bore.
I looked at this swapping heads from L/R to see what combination is best. Seems like i need .010" shims in either 1-3 for one .02" set-up or #3 alone for the other if i shoot for just below 8:1 but is that the right target CR?
My spread sheet based on Glenn's. (Red means above 8:1 CR)
My home made deck height gauge. Using tool plate so i know it is flat and parallel. I also know that if i were doing this alot the aluminum would wear.
My homemade CC system
I will be making my cylinder shims in the next few days since you cannot buy them for 83's.
My project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=702135&highlight=
Can i get some guidance? _________________ 1964 Original Owner build Thread. https://www.thesamba.com/vw/forum/viewtopic.php?t=702135&highlight=
Ambulance Fan's. https://www.thesamba.com/vw/forum/viewtopic.php?t=627707&highlight=
Parts i am looking for:
64 bug nice used front/rear Black LHD floor mat. |
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matthew henricks Samba Member
Joined: January 02, 2002 Posts: 1219 Location: So. Cal
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Posted: Tue Nov 23, 2021 1:07 pm Post subject: Re: Big Bore Build. Deck Height and Compression guidance please |
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Did more digging and found some good stuff on the performance side that pertain to 40HP. Wish you could link particular users to a thread to give them
credit.
Found alot of good BB 40HP info by Glutamodo pertaining to CR and lower octane fuel.
Looks like I want to be closer to 7.5:1. That means .040" for #1-3 and .020 for #4 using the first option for head cc.
Also found that:
1. Do not use paper washers under the cylinders. Use RTV
2. Do not use crush gasket under head. Use RTV
I know what i am making tonight. _________________ 1964 Original Owner build Thread. https://www.thesamba.com/vw/forum/viewtopic.php?t=702135&highlight=
Ambulance Fan's. https://www.thesamba.com/vw/forum/viewtopic.php?t=627707&highlight=
Parts i am looking for:
64 bug nice used front/rear Black LHD floor mat. |
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glutamodo The Android
Joined: July 13, 2004 Posts: 26306 Location: Douglas, WY
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Posted: Tue Nov 23, 2021 2:58 pm Post subject: Re: Big Bore Build. Deck Height and Compression guidance please |
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The crush seal between the head and cylinder is only for "stale air" application. This is a very high temperature location well beyond the limits of silicone (RTV) so don't even bother with it there. You just need good clean flat contact surfaces... to this end, one c an use valve grinding compound to "lap" the cylinders to the head openings. But don't bother with RTV there. At the cylinder base, yes that's fine, but be frugal in its application. _________________ Andy T.
IMAGE NOTE: It has been noted that Chrome based browsers may have issues in displaying my vast image library, which use non-secure links and are on an FTP server. Images should still be viewable if the link is clicked though.
I do not know how to fix this. All I can say is it all works fine for me with what I use, Firefox. |
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matthew henricks Samba Member
Joined: January 02, 2002 Posts: 1219 Location: So. Cal
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esde Samba Member
Joined: October 20, 2007 Posts: 5965 Location: central rust belt
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Posted: Tue Nov 23, 2021 7:34 pm Post subject: Re: Big Bore Build. Deck Height and Compression guidance please |
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glutamodo wrote: |
The crush seal between the head and cylinder is only for "stale air" application. This is a very high temperature location well beyond the limits of silicone (RTV) so don't even bother with it there. You just need good clean flat contact surfaces... to this end, one c an use valve grinding compound to "lap" the cylinders to the head openings. But don't bother with RTV there. At the cylinder base, yes that's fine, but be frugal in its application. |
Yes, that gasket between the cylinder and head is to make sure that there is never a compression leak into the cooling air stream. If there was, it would pump carbon monoxide right into the cabin. This was the reason for the upgrade to a "fresh air" system where cooling air was taken from the fan before and the engine cooling system. _________________ modok wrote:
Bent cranks are silent but gather no moss. I mean, ah, something like that. |
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matthew henricks Samba Member
Joined: January 02, 2002 Posts: 1219 Location: So. Cal
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Chickensoup Samba Member
Joined: January 06, 2018 Posts: 5368 Location: Good Hope, GA
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Posted: Wed Nov 24, 2021 12:56 pm Post subject: Re: Big Bore Build. Deck Height and Compression guidance please |
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what cam? How much duration at 50? LSA? _________________ -'85 c10 5.3 LS, 222 cam, long tubes, x pipe, 3 inch spin tech's
-'05 B5.5 TDI Wagon 17in sport rims ;EGR + BSM + ASV Delete, Stage-2 Tune, straight pipe
'65 Tourist Delivery Build
'66 RIP
'69 RIP
Hosea 4:6 "My people are destroyed for lack of knowledge" |
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matthew henricks Samba Member
Joined: January 02, 2002 Posts: 1219 Location: So. Cal
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Teeroy Samba Member
Joined: April 20, 2003 Posts: 3685 Location: Eastern WA
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Posted: Thu Nov 25, 2021 10:52 am Post subject: Re: Big Bore Build. Deck Height and Compression guidance please |
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You cant use different size shims on cylinder pairs, bead wont sit flat. Try moving rods to different journals to lessen variation. Once you get it as close as you are able to or willing to spend on new parts or labor, set your tightest cylinder to your desired deck/compression and let the others be a bit lower _________________ Pres. Rivercity VW Club www.rcvwclub.org
Founder Derr Wheat Panzers (DWP)
ARR #3
www.autosportsnorthwest.org |
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