327 SBC cranking cylinder pressure - Team Camaro Tech
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post #1 of 10 (permalink) Old Mar 30th, 05, 07:44 PM Thread Starter
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327 SBC cranking cylinder pressure

Does anyone know what is the limit on cylinder cranking pressure in a 327.

Would 220psi be too high? What is limit?
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post #2 of 10 (permalink) Old Mar 30th, 05, 08:08 PM
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Re: 327 SBC cranking cylinder pressure

220 psi cranking must mean that you are up around 11:1 I would think. It might not like pump gas too much.

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post #3 of 10 (permalink) Old Mar 30th, 05, 08:49 PM Thread Starter
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Re: 327 SBC cranking cylinder pressure

I am running some numbers through a program that gives me 10.27 to 1 cr and a 8.25:1 dcr and it also comes up with 214psi cranking pressure.

The heads are alumminum edelbrock performer RPM heads with 64cc chambers but I am getting them milled down so that the compression ratio is around 10.3 to 1 and DCR is around 8.2 to 1.

I need the heads around 60cc chambers.
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post #4 of 10 (permalink) Old Mar 30th, 05, 09:18 PM
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Re: 327 SBC cranking cylinder pressure

The guidelines I always hear is that you can run 8.5:1 DCR with aluminum heads and 8:1 for iron heads. You need to target a .040 quench. Is the 220psi a measured number or a calc? What cam are you running? The other alternative to lowering the static compression is to run a cam with a later intake closing event.
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post #5 of 10 (permalink) Old Mar 30th, 05, 10:13 PM Thread Starter
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Re: 327 SBC cranking cylinder pressure

I will be running a XS274S solid camshaft. I know that the cylinder pressure I am asking about is a calculated pressure.

The camshaft has a 63 degree closing at .015" tappet lift.
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post #6 of 10 (permalink) Old Mar 31st, 05, 06:30 AM
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Re: 327 SBC cranking cylinder pressure

EA3.0 comes up with 7.47:1 DCR and 155# of cranking compression.
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post #7 of 10 (permalink) Old Mar 31st, 05, 07:22 AM Thread Starter
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Re: 327 SBC cranking cylinder pressure

onovakind67,

My deck ht clearance is going to be pretty much 0 to -.003".

With a .039" head gasket.

How are you getting 7.47 to 1 DCR?

I have done the calculation on two different programs and am getting over 8.1 to 1 DCR.

Did you have the heads at 64cc or 60cc.

Thanks for the replys.
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post #8 of 10 (permalink) Old Mar 31st, 05, 08:52 AM
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Re: 327 SBC cranking cylinder pressure

You've specified your compression ratio as 10.27:1, and it doesn't really matter how you arrive at it. Small chambers, dished pisons, special gasket, etc., 10.27:1 is 10.27:1. I enter this in EA3.0 as the specified compression, along with the cam installed at 106 ICL and lashed at .015".

I have a 331" SBC with 10.8:1 compression and a TMR-50-4040-10A4 cam ( 269 @ .020", 240 @ .050" ) and it has 195# cranking compression.
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post #9 of 10 (permalink) Old Mar 31st, 05, 09:45 AM Thread Starter
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Re: 327 SBC cranking cylinder pressure

Thanks onovakind67,

What is your DCR?

I need to get between 8.2 : 1 and 8.5:1 DCR to be optimum for aluminum heads.

Are you running aluminum heads?

With EA3.0 what kind of compression ratio would I need to get 8.2:1 DCR?

Thanks for your help.
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post #10 of 10 (permalink) Old Mar 31st, 05, 08:06 PM
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Re: 327 SBC cranking cylinder pressure

EA3.0 figures my DCR at about 7.8. It's an aluminum headed engine. I wouldn't put too much emphasis on exact DCR unless you know exactly when the intake valve closes fully. Using advertised duration can be a little misleading, since many modern cams are lashed less than the tappet lift at the advertised duration.
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