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Re: Compression question
[Re: GTS440]
#993633
05/16/11 03:36 PM
05/16/11 03:36 PM
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Joined: Jan 2003
Posts: 75,020
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,020
U.S.S.A.
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Quote:
I have a .030 over 440 with flat top pistons .065 in the hole. I can run a set of
915 ( 78cc combustion chamber I think ) with a .019 compressed head gasket
& have a static compression ratio of 10.27. Is this to much compression for 92
Octane fuel? I also could use my MP " 452 " aluminum heads ( 84cc ) with a
.039 compressed head gasket but my compression would drop to 9.35. Engine
Is for a 65 satellite @ 3700 pounds with max wedge manifolds & 2.5 inch exhaust.
Is 10.27 to much compression for 92 octane with cast iron heads? Or will I make
More power with the better flowing aluminum heads with less compression? Any comments or suggestions appreciated. Thanks, GTS
You have no Quench , try to keep your compression 9.5.
I think some of your numbers are off , the std for steel shim gaskets are .021 and Are you sure of the CC of that head ? I just CC'd a pair of 915's , approximately .025 decked and they measure ~81cc.
I just plugged in numbers , .021 gasket and your 78 cc I get 10.1, if you go to a composite , like the felpro 8519 which is .041 you'll have 9.5 , since you don't have quench anyway that would be the way to go given the parts you have.
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Re: Compression question
[Re: GTS440]
#993634
05/16/11 03:39 PM
05/16/11 03:39 PM
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Joined: Aug 2003
Posts: 43,202
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,202
Bend,OR USA
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Quote:
The .039 gasket drops compression to 9.83 is this suitable for 92 octane with 3.55 gears? I don't know enough about cams to make a good call. Where is the best place to educate myself on cams?
If I was you I would shoot for 9.5 to 1 max on a iron headed pump gas motor  The heat and humidity can raise hail with the tune up from spring, summer and fall in most places in Texas  Way better to be safe than sorry If you switch to a aluminum head then raise the compression up to 10.0 to 1 to 10.7 to 1 with a big cam, 250 + degrees at .050 valve lift  Go to KB pistons web site and use thier dynamic and mechanical on line compression calculator to see the effects of the cam on the dynamic compresson ration, put in a small cam, a meduim cam and then a big cam. You will need the intake valve closing degrees after bottom dead center plus so many degrees( I can't remember exactly how many now  ) they ask you to add onto that event. Bigger (more degrees at .050) lower the dynamic compression ratio Is there ethanol in your gas now? If not can you be sure that it will not be added to your pump gas later? I've made 500 + HP on CA pump gas with 10% ethanol in a 440 bored .060 with 906 heads a bunch of times with less than 9.5 to 1 mechanical compression ratio, you can too 
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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