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  #31 (permalink)  
Old 01-21-2013, 06:40 PM
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.. Round off any razor sharp edges in the combustion space to prevent detonation such as on pistons, valve seats, etc...

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  #32 (permalink)  
Old 01-21-2013, 06:43 PM
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Originally Posted by BuzzLOL View Post
.. Round off any razor sharp edges in the combustion space to prevent detonation such as on pistons, valve seats, etc...
am i too close to the line? should i find a different kit? They say the kit it designed for pump gas and i know you can go that high with pump but im a little nervous..
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Old 01-21-2013, 08:03 PM
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am i too close to the line? should i find a different kit? They say the kit it designed for pump gas and i know you can go that high with pump but im a little nervous..
I'm running the exact same kit from skip white and I am using a comp 12-433-8 HR cam and my dynamic is around 8.6...my piston was about six thousandths of an inch from the top of the deck at TDC and I used a FelPro 1034 head gasket....041 compressed thickness so my squish is .047...I currently have no detonation issues...I have blueprint aluminum heads, 64cc comb. chambers...aluminum heads cool faster than cast iron heads thus helping prevent detonation a little bit
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Old 01-21-2013, 10:51 PM
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You are very close with your static compression ratio estimate. I came out with 10.35:1 using your supplied info. Aluminum heads require an additional point of compression over iron heads because of their ability to suck heat out of the combustion chamber so you are completely safe. An 800 DP is way too much carburetor, and no reason for a double pumper on a street vehicle. Holley backs this up on their website recommendations stating that a double pumper needs a light vehicle, loose torque converter, and lower gears. It's not sexy, but a 750cfm carb with vacuum secondaries will be much more efficient on a 406. That translates to more power and much better gas mileage. I would also come down a notch on the cam choice. The 230/236 duration @ .050" is a little rowdy for a 406 in a heavy vehicle. You should also have a higher stall converter over stock, and vacuum for your power brakes will be marginal. While the cam would work, I'd just go somewhat smaller for a heavy vehicle.
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Old 01-22-2013, 04:27 AM
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You are very close with your static compression ratio estimate. I came out with 10.35:1 using your supplied info. Aluminum heads require an additional point of compression over iron heads because of their ability to suck heat out of the combustion chamber so you are completely safe. An 800 DP is way too much carburetor, and no reason for a double pumper on a street vehicle. Holley backs this up on their website recommendations stating that a double pumper needs a light vehicle, loose torque converter, and lower gears. It's not sexy, but a 750cfm carb with vacuum secondaries will be much more efficient on a 406. That translates to more power and much better gas mileage. I would also come down a notch on the cam choice. The 230/236 duration @ .050" is a little rowdy for a 406 in a heavy vehicle. You should also have a higher stall converter over stock, and vacuum for your power brakes will be marginal. While the cam would work, I'd just go somewhat smaller for a heavy vehicle.

yea i get what you are saying, ive changed most of the things i said in that first post already. But yea, i will probably end up with a 750 holley. But you are saying that i should be okay because i have a aluminum heads? ive heard that but never knew why, so since its taking heat away its essentially lowering the compression in the cylinder?
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Old 01-22-2013, 11:22 AM
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Compression remains the same. A better (but not perfect) definition is that there is an ideal combustion pressure to force the piston down. Iron heads retain the heat, so say this ideal is reached at 9.3:1 compression on my theoretical example. Any less and you loose power, any more and you detonate. The aluminum heads bleed much more heat out of the chamber, so another full point of compression is required to maintain the same amount of heat in the combustion process. So the process sees the same amount of heat with 9.3 iron heads and 10.3 in aluminum heads. Over simplified, but it gets us close to what is going on.

There are also limitations in stock cast iron heads that limit the amount of porting that can be accomplished. Since the aluminum heads are designed from the beginning as a performance head, there is more meat designed in around the port area so a better port can be designed, and better flow is the result. Aluminum heads save weight, and they weigh half of an iron head. Aluminum heads are cheaper and easier to produce than iron, and are also much easier to machine and port. Because of this more companies make aluminum heads - and that competition brings a better product to the market, and keeps the prices down for us.
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