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Positive vs. negative piston deck height #173181
12/23/08 12:07 AM
12/23/08 12:07 AM
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Central Coast
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Plumcrazyracing Offline OP
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Just got a call from my machine shop and learned that i needed take more off the block than anticipated. Pistons are now going to be about .008 out of the hole. I figure i will run a cometic compressed at about .051 to give a quench of .043. Any opinions as to having a positive deck hieght like this?

Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173182
12/23/08 12:45 AM
12/23/08 12:45 AM
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Canada
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Quote:

Just got a call from my machine shop and learned that i needed take more off the block than anticipated. Pistons are now going to be about .008 out of the hole. I figure i will run a cometic compressed at about .051 to give a quench of .043. Any opinions as to having a positive deck hieght like this?




Depends on the heads etc, but many 383s were positive deck height stock I believe...?


CrAzYMoPaRGuY
Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173183
12/23/08 01:40 AM
12/23/08 01:40 AM
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Bend,OR USA
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Cab_Burge Offline
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all domes are usually above the top of the deck, the 1970 440 6 paks where .005 above and the early HP 340 (Pre 1972) called for a positive deck hieght also. The last legal 340 stocker I built had the pistons around .030 above, if I'm remembering the blueprint spec on the piston deck hieghts correctly

Last edited by Cab_Burge; 12/23/08 02:07 AM.

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Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173184
12/23/08 01:49 AM
12/23/08 01:49 AM
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Canton, Ohio
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Sport440 Offline
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Quote:

Just got a call from my machine shop and learned that i needed take more off the block than anticipated. Pistons are now going to be about .008 out of the hole. I figure i will run a cometic compressed at about .051 to give a quench of .043. Any opinions as to having a positive deck hieght like this?





At that positive deck height .008 I wouldnt be concerned about a thing/nothing mike

Re: Positive vs. negative piston deck height [Re: Sport440] #173185
12/23/08 01:56 AM
12/23/08 01:56 AM
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Plumcrazyracing Offline OP
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Thank you. Makes me feel better.

Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173186
12/23/08 02:20 AM
12/23/08 02:20 AM
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Manitoba, Canada
DaytonaTurbo Offline
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That deck height sounds very reasonable to me. 008 above is nothing to worry about.

Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173187
12/23/08 02:55 AM
12/23/08 02:55 AM
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Owego, NY
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JBurch Offline
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I'm currently running my 360 with the pistons .008 out of the hole, .039 gasket, no worries.

Re: Positive vs. negative piston deck height [Re: JBurch] #173188
12/23/08 07:16 PM
12/23/08 07:16 PM
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Alberta, Can
JUST_N_TIME Offline
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would that be with open chamber or closed chamber heads?

Quote:

I'm currently running my 360 with the pistons .008 out of the hole, .039 gasket, no worries.



Re: Positive vs. negative piston deck height [Re: JUST_N_TIME] #173189
12/23/08 09:20 PM
12/23/08 09:20 PM
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houston texas
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gremlinsteve Offline
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heck..late model 6.1 3g hemis are 15 out of the hole new. the 5.7 is less...like 5


steve


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Re: Positive vs. negative piston deck height [Re: JUST_N_TIME] #173190
12/23/08 09:55 PM
12/23/08 09:55 PM
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Central Coast
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Plumcrazyracing Offline OP
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Closed chamber Indy's. .620 lift solid roller on my 493 stroked 440

Last edited by Plumcrazyracing; 12/23/08 10:00 PM.
Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173191
12/23/08 10:07 PM
12/23/08 10:07 PM
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Canton, Ohio
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Sport440 Offline
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Quote:

Closed chamber Indy's. .620 lift solid roller on my 493 stroked 440




In that case that with that .008 positive piston deck height will cause you a whole heap of trouble.

Plum I , think that open vs closed question was directed a jburch. Plum you will be fine with a closed chamber, jburchs head if its closed is on the tight side. mike

Re: Positive vs. negative piston deck height [Re: Sport440] #173192
12/23/08 10:18 PM
12/23/08 10:18 PM
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Central Coast
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Plumcrazyracing Offline OP
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oops, you're right. Thanks for the info.

Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173193
12/23/08 11:20 PM
12/23/08 11:20 PM
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Johnstown
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A safe way to make sure it'll have proper head clearance is to bolt the head on without the gasket and make sure the engine will turn over by hand. Then once you add the head gasket you'll have at least the .039. The pistons on my 451 stick up a little bit. I went with open chambered Edelbrocks and all worked out perfect.


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Re: Positive vs. negative piston deck height [Re: 69dart] #173194
12/24/08 12:43 AM
12/24/08 12:43 AM
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Glendale Az
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Darryls-Demon Offline
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I have a .030 over 440 with Indy SRs. My pistons are 5 out of the hole using a Felpro .039 head gasket. But I will only run it to 6500. The engine builder did spin it to 6900 on the dyno on one of the break in pulls.

Re: Positive vs. negative piston deck height [Re: JUST_N_TIME] #173195
12/24/08 02:47 AM
12/24/08 02:47 AM
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Owego, NY
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JBurch Offline
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It's a closed chamber head

Re: Positive vs. negative piston deck height [Re: JBurch] #173196
12/24/08 04:24 PM
12/24/08 04:24 PM
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Left Coast
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You also need to check your piston to valve clearance. -Bob

Re: Positive vs. negative piston deck height [Re: BobR] #173197
12/25/08 10:27 AM
12/25/08 10:27 AM
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Toronto Ontario, Can
Glen440 Offline
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My 511 was originally .023 above deck. My 400 block was not close to square. Every piston was a different height till I had the machine shop square it. I fixed it with a .062 head gasket.

My custom pistons that are in it now have .025 less pin height to put them -.002.


87 dakota 6.1 hemi
Re: Positive vs. negative piston deck height [Re: Darryls-Demon] #173198
12/25/08 10:50 AM
12/25/08 10:50 AM
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yarnell,az
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I have read that a .055 piston to head clearance is the minimum you should have. Is this not true?

Re: Positive vs. negative piston deck height [Re: BobR] #173199
12/25/08 01:31 PM
12/25/08 01:31 PM
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Owego, NY
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JBurch Offline
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I checked piston to valve clearance, as well as piston to head clearance before lighting the fires. P to V ( as foggy memory allowes me to remember ) was .070+, .090+ intake and exhaust, P to H was .031. The pistons are KB 107's, not lots of clearance, they don't rock much. I'm not worried.

Re: Positive vs. negative piston deck height [Re: mopacltd] #173200
12/25/08 01:34 PM
12/25/08 01:34 PM
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As I remember, .030 to .060 is the range of ideal quench. More you lose benifit, less you go clank!

Re: Positive vs. negative piston deck height [Re: Plumcrazyracing] #173201
12/26/08 10:02 AM
12/26/08 10:02 AM
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USA
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it is worth pondering the
"crevice volume"
effect

crevice volume is generally thought to be a bad thing
because it 'quenches' the flame and creates unburned hydrocarbons ... which reduces both power and fuel economy

there is crevice volume in the little gaps of the head gasket joint

there is crevice volume in the 'ring land' from the top of the first ring to the piston crown

could the undesired two crevice volumes
be combined
to eliminate a bit of both?

some engine builders try to do this
by having the piston come above the deck
enough to cover the head gasket joint
during the peak of the combustion event

it is an approach that might gain a bit of
power and fuel economy

in one of the last 'Engine Masters' competitions one of the top engines had a very large value for positive deck and this may have been one of his strategies

there is also a small effect in being able to use a tiny bit longer connecting rod

it is worth thinking about

another small detail

"The Devil is in the Details"

Re: Positive vs. negative piston deck height [Re: mopacltd] #173202
12/27/08 11:00 PM
12/27/08 11:00 PM
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Grand Haven, MI
patrick Offline
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Quote:

I have read that a .055 piston to head clearance is the minimum you should have. Is this not true?




maybe with aluminum rods...but with tradtional rods, ~.040 is ideal, if you're very precise on measurements and keep the RPM's down you may be able to go as tight at .030"


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Re: Positive vs. negative piston deck height [Re: patrick] #173203
12/28/08 12:29 AM
12/28/08 12:29 AM
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Gainesville,FL
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Alot of good points,most don't add up to 2 hp,but good points. Most post what they read or internet info.Keep it safe and don't try to get it too tight.

Last edited by goldmember; 12/28/08 12:30 AM.
Re: Positive vs. negative piston deck height [Re: 360view] #173204
12/28/08 01:39 AM
12/28/08 01:39 AM
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Canton, Ohio
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Sport440 Offline
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Quote:

it is worth pondering the
"crevice volume"
effect

crevice volume is generally thought to be a bad thing
because it 'quenches' the flame and creates unburned hydrocarbons ... which reduces both power and fuel economy

there is crevice volume in the little gaps of the head gasket joint

there is crevice volume in the 'ring land' from the top of the first ring to the piston crown

could the undesired two crevice volumes
be combined
to eliminate a bit of both?

some engine builders try to do this
by having the piston come above the deck
enough to cover the head gasket joint
during the peak of the combustion event

it is an approach that might gain a bit of
power and fuel economy

in one of the last 'Engine Masters' competitions one of the top engines had a very large value for positive deck and this may have been one of his strategies

there is also a small effect in being able to use a tiny bit longer connecting rod

it is worth thinking about

another small detail

"The Devil is in the Details"




I like that idea as you described it.mike

Re: Positive vs. negative piston deck height [Re: Sport440] #173205
12/30/08 12:23 PM
12/30/08 12:23 PM
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USA
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an article on crevice volume

http://www.gofastnews.com/board/technica...ower-thief.html

for the hard core engine nuts

Re: Positive vs. negative piston deck height [Re: 360view] #173206
12/30/08 01:26 PM
12/30/08 01:26 PM
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organ
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Quote:

an article on crevice volume

http://www.gofastnews.com/board/technica...ower-thief.html

for the hard core engine nuts


good article-thanks!


for what is the good life if not doing things thoughtfully?
Re: Positive vs. negative piston deck height [Re: 360view] #173207
12/30/08 11:12 PM
12/30/08 11:12 PM
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Canton, Ohio
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Sport440 Offline
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Quote:

an article on crevice volume

http://www.gofastnews.com/board/technica...ower-thief.html

for the hard core engine nuts





Thanks, Ive never seen a article from David Vizard that I couldnt make good logical sense out of.
mike

Last edited by Sport440; 12/30/08 11:16 PM.
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