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128vw
Samba Member
Joined: April 05, 2006
Posts: 222
Location: Western Massachusetts
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 Posted: Sat Dec 29, 2007 11:49 am Post subject: deck height |
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I'm building a 1914 and when checking the deck I find the deck on the 1/2 side to be .123/ .125 but the deck on the 3/4 side is .148/.135.
I want all the decks to be about .090 to get the 8.5 comp that I want.
I am going to cut the cyl bottoms on 1/2 side .030 but the 3/4 side can I cut the piston top on #3 .013 then cut the cyls .040 ? I must have a long rod on #3 as I have swapped pistons all around to get the best combo.
They are stock rods that are a balanced and rebuilt set.
Cut the piston top OK??? |
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Nater
Samba Member
Joined: June 19, 2006
Posts: 493
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| Posted: Sat Dec 29, 2007 12:07 pm Post subject: |
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I have never had a problem cutting more than that off the tops of pistons.
So, I say yea go ahead. |
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128vw
Samba Member
Joined: April 05, 2006
Posts: 222
Location: Western Massachusetts
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| Posted: Sat Dec 29, 2007 1:02 pm Post subject: |
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Is .099 to much deck? I have heard that .090 should be the max deck.
But .099 gives me a comp of 8.3 and I don't want to go much more. |
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Nater
Samba Member
Joined: June 19, 2006
Posts: 493
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| Posted: Sat Dec 29, 2007 1:11 pm Post subject: |
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| Eaallred wrote: |
I personally would never go any tighter than .040". The gains after that point taper off pretty quick, and you really risk having the piston slap the head. People have gone tighter than .040" before, but not worth the risk IMHO vs. the minimal gain.
On the other side of it, I try not to go wider than .060" because then you do start to loose the 'squish' effect that really helps mix the air/fuel better. Once you get close to .100" the effect of squish is essentially gone.
So for me, .040" to .060" is where its at. With good components I go closer to .040, with stock components I go closer to .060".
I would rather CC my heads to get the compression ratio I need than run a lot of deck. A bigger chamber and tighter deck will make more power than a smaller chamber and looser deck. |
I think Eric about summed it up there  |
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128vw
Samba Member
Joined: April 05, 2006
Posts: 222
Location: Western Massachusetts
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| Posted: Sat Dec 29, 2007 2:26 pm Post subject: |
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Can I cut a dish in the piston to lower the comp and get a better deck?
I can do the lathe work but would need a way to figure the comp with the
dish cut. |
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grimace007
Samba Member
Joined: August 30, 2006
Posts: 2673
Location: swampville, florida
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| Posted: Sat Dec 29, 2007 4:59 pm Post subject: |
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you can cc the piston dish just as you would a combustion chamber, i would assume anyway
_________________
Brian
68 sedan
Dallas Air Coolers
| perrib wrote: |
Hey It is The Samba where well thought out rational answers can take a while and getting side tracked is normal. I was just lucky this time.  |
| cr@M wrote: |
No one has any personal responsibility these days. This country is sue happy. Intelligence is no longer a requirement, just an accessory. |
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Eaallred
Samba Member
Joined: May 18, 2003
Posts: 5756
Location: West Valley City, Utah
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| Posted: Sat Dec 29, 2007 5:50 pm Post subject: Re: deck height |
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| 128vw wrote: |
I'm building a 1914 and when checking the deck I find the deck on the 1/2 side to be .123/ .125 but the deck on the 3/4 side is .148/.135.
I want all the decks to be about .090 to get the 8.5 comp that I want.
I am going to cut the cyl bottoms on 1/2 side .030 but the 3/4 side can I cut the piston top on #3 .013 then cut the cyls .040 ? I must have a long rod on #3 as I have swapped pistons all around to get the best combo.
They are stock rods that are a balanced and rebuilt set.
Cut the piston top OK??? |
With that much deckheight I wouldn't worry about machining pistons to even them all out. It won't make a huge difference. Unless you have the time and you can do it for free that is. If you were building a blueprinted HP motor that would be another story.
_________________
Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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Max Welton
Samba Member
Joined: May 19, 2003
Posts: 10697
Location: Black Forest, CO
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