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post #1 of (permalink) Old 11-22-2002, 07:39 PM Thread Starter
 
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compression ratio w/ iron heads.

What is the max compression ratio with iron heads you can run a 400 on with high test gas. i am aiming for a 9.75:1 comp ratio, im pretty sure ill be fine with 93 octane , but i want your opinion too.
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post #2 of (permalink) Old 11-22-2002, 08:12 PM
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Re: compression ratio w/ iron heads.

My rule of thumb on iron head compression ratio is the divide by 10 rule. If your using using 87 octane gas, divide 87 by 10 which equals 8.7:1 as the safe compression ratio for 87 octane gas. My divide by 10 rule would allow for 93 octane gas to run 9.3:1 compression. I changed my intake manifold to the Edelbrock Performer Air Gap and I'm now able to use 87 octane gas with a 9:1 compression 350 using iron heads. I had problems with 87 octane gas on hot summer days before I switched to the Performer Air Gap. I think it might be a good idea to lower your engine compression to about 9.5:1 using a .051" thick head gasket. I really recommend using the Air Gap intake manifold!
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post #3 of (permalink) Old 11-23-2002, 03:38 PM Thread Starter
 
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Re: compression ratio w/ iron heads.

well, ill leave it down to 9.5 or so then, i already have 3 edelbrock performer q/jets for small blocks so im gonna use one of them, no point buying a new one. I havent ordered any parts yet, but i *may* need a crank because i just noticed a pretty deep nick on the 5-6 rod journal, hopefully it can be turned out, cause its a steel crank.
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post #4 of (permalink) Old 11-23-2002, 06:02 PM
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Re: compression ratio w/ iron heads.

[img]images/graemlins/confused.gif[/img] To the best of my knowledge, the factory 400 crank was always a nodular iron crank. Factory steel cranks after 1968 became rare. [img]images/graemlins/frown.gif[/img]
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post #5 of (permalink) Old 11-23-2002, 06:31 PM Thread Starter
 
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Re: compression ratio w/ iron heads.

Its not a factory crank, according to the guy who i got it from its a callies(sp?) crank. he was gonna build it to something serious for racing but never did, so i bought it so hed have money for x mas.
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post #6 of (permalink) Old 11-23-2002, 08:59 PM
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Re: compression ratio w/ iron heads.

I've been thinking, I have some SBC 400 parts I'd like to sell. Maybe someone here would be interested. Send me a private email for more details.

1. 6" connecting rods.
2. Factory SBC 400 crank, reground -.010" with bearings.
3. Special pistons + .030" 7cc dish and rings for SBC 400 using 6" connecting rods.
4. SBC 400 4 bolt main block +.030", aligned honed mains.

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post #7 of (permalink) Old 11-24-2002, 07:49 AM
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Re: compression ratio w/ iron heads.

What about those q-jet. what cfm are they and are you willing to sell one?
post #8 of (permalink) Old 11-24-2002, 02:52 PM
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Re: compression ratio w/ iron heads.

I have several quadrajet carburetors. I seem to remember the quadrajet CFM for a SBC was something like 735. [img]images/graemlins/confused.gif[/img] I've been working with TBI's and TPI for the last few years, so please forgive me if I've forgotten a few details on quadrajets. I'll need to know which choke style and linkage (throttle, transmission, curise) your looking for before I could quote a price.
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post #9 of (permalink) Old 11-24-2002, 05:28 PM
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Re: compression ratio w/ iron heads.

edlebrock makes a heat insulator gasket for their intakes runs about $12.00 works great a buddy uses it on his performer RPM and i use it on my performer RPM AIR-GAP call summit raceing they have the part#
post #10 of (permalink) Old 11-25-2002, 08:15 AM
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Re: compression ratio w/ iron heads.

Matters what kind of cam you want to runn too. What is this going in? If ita a stick nova with a vic jr that your planning on running to 7 grand you can get by with more compression because of the cam. Also you can run a bit more if you are paying very close to things when building like your quench. And also making sure that your compression is what you think it is.

a general 1/2 assed guess would be around 9 maybe a bit higher to be safe.
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