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Compression Heigth 1.467 vs 1.456 quesiton #170013
12/18/08 01:21 PM
12/18/08 01:21 PM
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Tulsa, Ok
WadeMetzinger Offline OP
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WadeMetzinger  Offline OP
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Can you tell by the compression height which piston will be higher compared to the deck assuming the same deck height. If the 1.456 piston is at 0 deck will the 1.467 piston be out of the hole or in the hole.

4" stroke Small Block
Flat top pistons


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Re: Compression Heigth 1.467 vs 1.456 quesiton [Re: WadeMetzinger] #170014
12/18/08 01:26 PM
12/18/08 01:26 PM
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Atco NJ
DJVCuda Offline
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the 1.467 piston will be .011 taller - thus out of the hole .011

Re: Compression Heigth 1.467 vs 1.456 quesiton [Re: DJVCuda] #170015
12/18/08 02:53 PM
12/18/08 02:53 PM
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Grand Haven, MI
patrick Offline
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some simple math:

SBM blueprint deck height: 9.6"
SBM blueprint rod length: 6.123"
1/2 stroke: 2"

9.6-6.123-2= 1.477" = compression height needed for 0 deck at blueprint height. anything taller will be above deck, anything shorter, below.

the 1.467" pistons will require a .010" cut (deck height 9.59") for 0 deck, the 1.456" pistons will require a .021" cut for 0 deck (deck height 9.579")


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Re: Compression Heigth 1.467 vs 1.456 quesiton [Re: WadeMetzinger] #170016
12/18/08 04:45 PM
12/18/08 04:45 PM
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Tulsa, Ok
WadeMetzinger Offline OP
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Thank's that's exactly what I needed and I was worried these pistons were going to be taller and give me more compression which I don't need. I'll just have to leave the deck a little taller.

Re: Compression Heigth 1.467 vs 1.456 quesiton [Re: WadeMetzinger] #170017
12/19/08 01:42 PM
12/19/08 01:42 PM
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Grand Haven, MI
patrick Offline
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if you're running closed chambered heads you might want to rethink that--you might end up with more compression AND more detonation resistance with tight quench.

I have a friend who has an LT1 based 396 stroker, and his pistons are ~.015 in the hole. he was running a .04" thick gasket, and his engine was somewhat picky about which brand premium he could run (the computer would pull timing out on anything but 93 octane from the local shell station). he swapped to a .025" thick gasket, which bumped compression up ~ 1/4-1/3 point, but his engine now can run on premium from pretty much any local station without pulling timing out.


1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
Re: Compression Heigth 1.467 vs 1.456 quesiton [Re: patrick] #170018
12/19/08 02:38 PM
12/19/08 02:38 PM
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Tulsa, Ok
WadeMetzinger Offline OP
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I'll be honest I don't have much knowledge in this area but it sounds like keeping the quench to .040 or so will actually be better than .060 for detonation problem. So here is a possible configuration that I think will be pump gas safe (we only have 91 octane around here):

Cylinders - 8
Bore - 3.94 (.030 318)
Stroke - 4"
Combustion chamber cc - 65 (out of the box Edelbrocks)
Head Gasket thickness - .040
Head Gasket bore - 4.18 (Fel-pro 1008)
Piston to Deck - 0/Zero deck height
Piston cc - Flattop with valve relief of 8cc
Cubic Displacement - 390
Static compression would be 10.74

With Piston cc of 6cc compression would be 10.99

I don't think the pistons have but 5cc valve reliefs but would have them cut a little more to get 8cc.

I'm just not sure if 10.74 will run on 91 octane pump gas... the quench would be .040

What do you guys think?

I'll be running a Mopar .528 solid cam, Air Gap intake, TTI headers, MSD ignition, anyother info needed?

Re: Compression Heigth 1.467 vs 1.456 quesiton [Re: WadeMetzinger] #170019
12/19/08 02:54 PM
12/19/08 02:54 PM
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Grand Haven, MI
patrick Offline
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11:1 with a flat top and tight quench is doable with an aluminum head.

my friend's LT1 stroker is at about 11.75:1 with a [Email]230@.050[/Email] (280 adv) hydraulic roller....granted it's got reverse cooling and computerized spark control.

as long as you don't get overly aggressive with your mechanical advance & vacuum advance curve, I think you'll be OK with 11ish:1 compression

BTW the eddie heads you want are the 63cc closed chamber, not the 65cc open chamber heads. to be on the safe side you could polish the chambers and round any sharp edges in the chambers and tops of the pistons. that'll help with detonation, plus it'll increase the chamber volume a few cc's...

also, a head gasket with a smaller bore may be better, if there's an off the shelf one (say a 4.06 bore) in the proper thickness to minimize the crevice volume.

go to keith black's website (kb-silvolite.com) and play around with the dynamic compression calculator. read up on this thread:

https://board.moparts.org/ubbthreads/show...e=0#Post4885314

and play with the calculator, shooting for about 8.2-8.5DCR.

if you do run into detonation, a cam with slightly more duration will bleed more cyl. pressure out, helping things. conversely, you could also just retard your cam a couple of degrees with an offset cam key to make the intake closing point further after BDC (same thing more duration does)

Last edited by patrick; 12/19/08 03:02 PM.

1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
Re: Compression Heigth 1.467 vs 1.456 quesiton [Re: WadeMetzinger] #170020
12/19/08 09:27 PM
12/19/08 09:27 PM
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W. Kentucky
justinp61 Offline
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My 340 is 11.2-1 and runs fine on 93, I think it would run on 91 also. My Edelbrocks have been milled to 55cc and it runs Ross flat tops at 0 deck height, Fel-Pro 1008 gaskets. The cam is a Hughes 237/242 hydraulic.







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