Posted By: Plumcrazyracing
Positive vs. negative piston deck height - 12/23/08 04:07 AM
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?
Posted By: Cab_Burge
Re: Positive vs. negative piston deck height - 12/23/08 05:40 AM
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
Posted By: Plumcrazyracing
Re: Positive vs. negative piston deck height - 12/23/08 05:56 AM
Thank you. Makes me feel better.
Posted By: DaytonaTurbo
Re: Positive vs. negative piston deck height - 12/23/08 06:20 AM
That deck height sounds very reasonable to me. 008 above is nothing to worry about.
Posted By: JBurch
Re: Positive vs. negative piston deck height - 12/23/08 06:55 AM
I'm currently running my 360 with the pistons .008 out of the hole, .039 gasket, no worries.
Posted By: JUST_N_TIME
Re: Positive vs. negative piston deck height - 12/23/08 11:16 PM
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.
Posted By: gremlinsteve
Re: Positive vs. negative piston deck height - 12/24/08 01:20 AM
heck..late model 6.1 3g hemis are 15 out of the hole new. the 5.7 is less...like 5
steve
Posted By: Plumcrazyracing
Re: Positive vs. negative piston deck height - 12/24/08 01:55 AM
Closed chamber Indy's. .620 lift solid roller on my 493 stroked 440
Posted By: Plumcrazyracing
Re: Positive vs. negative piston deck height - 12/24/08 02:18 AM
oops, you're right. Thanks for the info.
Posted By: 69dart
Re: Positive vs. negative piston deck height - 12/24/08 03:20 AM
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.
Posted By: Darryls-Demon
Re: Positive vs. negative piston deck height - 12/24/08 04:43 AM
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.
Posted By: JBurch
Re: Positive vs. negative piston deck height - 12/24/08 06:47 AM
It's a closed chamber head
Posted By: BobR
Re: Positive vs. negative piston deck height - 12/24/08 08:24 PM
You also need to check your piston to valve clearance. -Bob
Posted By: Glen440
Re: Positive vs. negative piston deck height - 12/25/08 02:27 PM
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.
Posted By: mopacltd
Re: Positive vs. negative piston deck height - 12/25/08 02:50 PM
I have read that a .055 piston to head clearance is the minimum you should have. Is this not true?
Posted By: JBurch
Re: Positive vs. negative piston deck height - 12/25/08 05:31 PM
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.
Posted By: JBurch
Re: Positive vs. negative piston deck height - 12/25/08 05:34 PM
As I remember, .030 to .060 is the range of ideal quench. More you lose benifit, less you go clank!
Posted By: 360view
Re: Positive vs. negative piston deck height - 12/26/08 02:02 PM
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"
Posted By: goldmember
Re: Positive vs. negative piston deck height - 12/28/08 04:29 AM
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.
Posted By: 360view
Re: Positive vs. negative piston deck height - 12/30/08 04:23 PM
mike
