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txoval
Samba Member
Joined: January 23, 2004
Posts: 3557
Location: The Woodlands, TX
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 Posted: Wed Oct 05, 2022 6:53 am Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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Geezus, I need some sleep…and should have clarified. My comment was in regards to keeping the engine narrow. You’d have cut the cylinders down if you use the C pistons
| slalombuggy wrote: |
| txoval wrote: |
Have you bought the pistons? Go with C pistons (33mm pin height) and you’ve made 2 of the 3.5mm up
Just need to do the math before ordering parts…once in hand, measure and fine tune as necessary |
He needs to move the pistons up. Not down. "A" pistons would be better suited to what he needs |
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txoval
Samba Member
Joined: January 23, 2004
Posts: 3557
Location: The Woodlands, TX
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| Posted: Wed Oct 05, 2022 7:18 am Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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Lets just do the "hypothetical" math for a +3.5mm case and 94mm cylinders
103.5mm (case centerline to case deck) + 114mm (cylinder length) = 217.5mm
41mm (half of crank stroke) + 35mm (B pin height) + 139.7mm (5.5" rods) = 215.7mm
In this scenario your pistons would be 1.8mm in the hole or a deck height of .072" (need to trim cylinders or deck case .030")
Change to 5.6" rods and the piston is sticking out of the hole .0296" (need to add .070" shim)
Change to 5.6" rods and C pistons and you have a .050" deck height
Everything needs to be measured, but this is the math if everything measured out and is useful for planning |
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jpaull
Samba Member
Joined: February 22, 2005
Posts: 3467
Location: Paradise, Ca
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| Posted: Wed Oct 05, 2022 10:14 am Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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| txoval wrote: |
Lets just do the "hypothetical" math for a +3.5mm case and 94mm cylinders
103.5mm (case centerline to case deck) + 114mm (cylinder length) = 217.5mm
41mm (half of crank stroke) + 35mm (B pin height) + 139.7mm (5.5" rods) = 215.7mm
In this scenario your pistons would be 1.8mm in the hole or a deck height of .072" (need to trim cylinders or deck case .030")
Change to 5.6" rods and the piston is sticking out of the hole .0296" (need to add .070" shim)
Change to 5.6" rods and C pistons and you have a .050" deck height
Everything needs to be measured, but this is the math if everything measured out and is useful for planning |
Great Example! |
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draksia
Samba Member
Joined: July 07, 2022
Posts: 14
Location: FL
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| Posted: Wed Oct 05, 2022 11:22 am Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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| txoval wrote: |
Lets just do the "hypothetical" math for a +3.5mm case and 94mm cylinders
103.5mm (case centerline to case deck) + 114mm (cylinder length) = 217.5mm
41mm (half of crank stroke) + 35mm (B pin height) + 139.7mm (5.5" rods) = 215.7mm
In this scenario your pistons would be 1.8mm in the hole or a deck height of .072" (need to trim cylinders or deck case .030")
Change to 5.6" rods and the piston is sticking out of the hole .0296" (need to add .070" shim)
Change to 5.6" rods and C pistons and you have a .050" deck height
Everything needs to be measured, but this is the math if everything measured out and is useful for planning |
Thanks that is extremely helpful.
I am going with 5.5" rods and the B height pistons, as I am able to get those.
My machinist buddy didn't seem to think it would be any issue taking some material off the top of the cylinders to get the compression ratio dialed in.
Thanks for all the assistance.
Next steps are cam and head choices. |
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UK Luke 72
Samba Member
Joined: September 07, 2011
Posts: 2867
Location: Little Britain
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draksia
Samba Member
Joined: July 07, 2022
Posts: 14
Location: FL
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| Posted: Wed Oct 05, 2022 12:04 pm Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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| UK Luke 72 wrote: |
| Look to trim the bottom, you won't have to trim cooling fins that way. |
Can do, thanks. |
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b-man
Samba Member
Joined: May 20, 2008
Posts: 500
Location: So Cal
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| Posted: Fri Oct 21, 2022 1:18 pm Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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| draksia wrote: |
I am a definitely newbie building engines but a scored a great deal on an 82mm crank so I was thinking about getting started. The plan is to build a very mild 2180 with AA thick wall cylinders since I am planning to add AC and I thought the extra heat load capacity would not be a bad idea. I have a Holley Sniper single barrel setup so that is likely going to be the limiting factor in performance for this build.
CB has their aluminum case in stock but only the 3.5mm raised deck version. I ran the numbers on the deck height and with Panchito heads with a 54cc chamber and that comes out to 8.1 compression. So taking a few CC's out of the heads could bump it up closer to 9.
My basic understanding though is that the deck height should be closer to .070 or so.
I am wanting to double check this before I start ordering parts.
Also since the AA thick wall 92's are available in a base of 92 or 94mm I am not sure the best option for the base either.
Thanks in advance. |
Standard deck 92 bore case is back in stock, I just bought one.
_________________
1956 Dove Blue Panel
1966 Velvet Green Single Cab
1957 L41 Black Oval Window Beetle |
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bugguy1967
Samba Member
Joined: January 16, 2008
Posts: 4343
Location: Los Angeles, CA 90016
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| Posted: Sat Oct 22, 2022 4:54 pm Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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| UK Luke 72 wrote: |
| Would there be a downside to using a +3.5mm case and trimming the cylinders to hone in on the desired deck? I like the idea of extra aluminium for support. |
Only upsides - stronget deck, more rigid top end
_________________
"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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draksia
Samba Member
Joined: July 07, 2022
Posts: 14
Location: FL
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| Posted: Mon Feb 26, 2024 4:40 pm Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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So I ended up getting some 5.6 rods and I am ordering a few more parts.
I so using the +3.5 mm deck and 5.6 rods with a roughly .070 shim puts me a total of about .208 wider.
Should I be running .25" longer head studs, I kind of think so but I am not sure? |
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fl59bug
Samba Member
Joined: November 23, 2005
Posts: 1976
Location: North Carolina
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| Posted: Thu Feb 29, 2024 12:39 pm Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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| draksia wrote: |
So I ended up getting some 5.6 rods and I am ordering a few more parts.
I so using the +3.5 mm deck and 5.6 rods with a roughly .070 shim puts me a total of about .208 wider.
Should I be running .25" longer head studs, I kind of think so but I am not sure? |
Yes better to buy longer ones. Probably 1/2" longer is easy to find, and you can cut any excess if you need to.
Ted |
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draksia
Samba Member
Joined: July 07, 2022
Posts: 14
Location: FL
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| Posted: Fri Mar 22, 2024 4:53 pm Post subject: Re: 3.5 mm Raised Deck Engine Case / 92 or 94mm base |
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Yeah went with the longer ones, of course one of them is slightly bent.
I was thinking the same thing, it is much easier to take a little off than lengthen on. |
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