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Old 01-17-2012, 07:42 PM
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Cast iron heads

I have heard a few people say not to exceed 9:1 with cast iron heads but im thinking about 10:1 dr with stock heads, any thoughts?

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Old 01-17-2012, 07:50 PM
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Quote:
Originally Posted by birkey
I have heard a few people say not to exceed 9:1 with cast iron heads but im thinking about 10:1 dr with stock heads, any thoughts?
it depends too with cylinder pressure, ignition timing, octane, and chamber style. I run just a little over 10.25:1 on my 355 with iron heads and no problems. I run 89 or 91 octane and run around 34-36* total timing with closed chamber heads and no signs of detonation on the plugs. Like I said it really depends.
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Old 01-17-2012, 07:52 PM
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another big factor is load and engine temp.
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Old 01-17-2012, 08:04 PM
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If im not worried about detonation, heat transfer, and weight what is the disadvantage with cast heads?
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Old 01-17-2012, 08:38 PM
How fast is fast enough?
 
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They cost more to weld or port. Iron makes more power than aluminum but its harder to work with and weighs more.
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Old 01-17-2012, 09:11 PM
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Another question about heads. im building a 360 mopar, the cylinder .060" overbore and i have some room to make the valves bigger. 1.880 intake 1.600 exhaust are stock, i don't know the valve spacing off the top of my head but for a motor that is expected to pull around 7000 rpm and will be driven on the street, would you recommend going bigger with both valves or mainly the exhaust? 10:1 cr

Last edited by birkey; 01-17-2012 at 09:17 PM.
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Old 01-17-2012, 11:17 PM
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you can run up to 10.5:1 SCR with iron heads on 93 octain I know I tune on a guys S10 with a 360sbc with no issuse of detonation.. The biggest thing is to make sure for one that your dynamic compression of the engine with a piticular cam does not exceed 8.5:1. His was right at 8.5:1 DCR running 93 with 38 deg totall timing, engine temp at 180.. Keep in mind to, keeping your quench area which is deck clearence to head surface, thickness of head gasket and keep it tight as possible between at least 35-45 thou will help minimize detonation...also run a step or two colder plug as well.. you can use this calculator to help with some figures. http://www.kb-silvolite.com/calc.php?action=comp2

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Old 01-18-2012, 09:43 AM
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i didnt know that you could lose that much just between static and dynamic.
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Old 01-18-2012, 10:26 AM
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I guess Chevy, Ford and Mopar were all wrong back in the 60's when they were selling Corvettes, Thunderbolts, and 426 Max Wedge cars off the show room floor with cast iron heads and compression ratios form 11:1 - 13:1. Yes I know they used leaded gas but there are additives we can use now days to make up for that. Cast iron heads are as strong or stronger than aluminum heads... its all about weight, porting, and improved chamber design that make aluminum heads a good bang for the buck now days.

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Old 01-18-2012, 10:44 AM
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centerline: you do have a point
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Old 01-18-2012, 10:54 AM
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Quote:
Originally Posted by birkey
i didnt know that you could lose that much just between static and dynamic.
dynamic will ALWAYS BE LOWER than static, reason is dynamic adds in your rod length and the intake valve closing point from your camshaft in crankshaft degrees which is the most critical number.. the intake valve closing point ABDC { After Bottom Dead Center} this determines your DCR how much the cylinder will start to fill up.. A cyclinder will not build compression untill the intake valve is completly closed at that point is where you build dynamic compression. A DCR 7.5-8.5 is best with pump gas with out addititives on cast heads, alumium im sure a guy can get by with a higher DCR due to aluminum disapating the heat more preventing detonation..
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Old 01-18-2012, 10:54 AM
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Quote:
Originally Posted by Centerline
I guess Chevy, Ford and Mopar were all wrong back in the 60's when they were selling Corvettes, Thunderbolts, and 426 Max Wedge cars off the show room floor with cast iron heads and compression ratios form 11:1 - 13:1. Yes I know they used leaded gas but there are additives we can use now days to make up for that. Cast iron heads are as strong or stronger than aluminum heads... its all about weight, porting, and improved chamber design that make aluminum heads a good bang for the buck now days.

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So I can go get lead additive and 87 octane and run 13:1 compression?
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Old 01-18-2012, 01:29 PM
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you will need to run a much higher octane fuel, and probably aluminum heads.
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Old 01-18-2012, 04:43 PM
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Quote:
Originally Posted by zildjian4life218
So I can go get lead additive and 87 octane and run 13:1 compression?
If you're going to run that much compression you'll need to add an octane booster. Back when the factories were turning out Max Wedges and the like you could purchase Sunoco 260 for $.29 a gallon with an octane rating of 102. I ran that in my '66 L-72 427 Corvette and that had 11:1 compression from the factory.

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Last edited by Centerline; 01-18-2012 at 04:48 PM.
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Old 01-21-2012, 07:54 PM
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I have an old compression tester, don't know how accurate it actually is, but, if it shows 200psi I can run 87 octane and when it shows 220psi I run 93.
I do spend a lot of time getting squish (quench) around 0.040", removing all edges that could cause a hot spot and machining blocks, head and/or combustion chambers.
I've never really been interested in 'theoretical' CR, only used dynamic for at least last 30 yrs (I guess it makes a difference if your bench racing?)
You can run 18~20:1 'static' if you have enough cam to lower cylinder cranking pressure to 220psi
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