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The Terminator
Engine/Tuning
Cast iron block vs. Aluminum block
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<blockquote data-quote="tjvineyard" data-source="post: 1755470" data-attributes="member: 22289"><p>In most situations, you can design any part of aluminum (including a block) and make it as strong or stronger than an iron piece. Generally, you have to use more material (hence a larger aluminum connecting rod as compared to its steel counterpart) to get the same performance, but the final product is generally still lighter despite the larger size.</p><p></p><p>It is also imporant to note that "stiffer" and "stronger" do not always go together. Going back to the connecting rod example, aluminum rods are preferred in many engines because they actually "give" a little bit. The designed stretch and compression of rod actually absorbs stress.</p><p></p><p></p><p></p><p></p><p>I have never heard of a "coefficient rate" so I am not sure exactly what you are referring to. However, because engines operate in a fairly limited temperature range (compared to the range you are likely referring to for metallurgic properties), thermal expansion can be compensated for fairly readily. Sure, forged pistons make some noise warming up, but once in range they function effectively. The same holds true for a block.</p><p></p><p>Now, I also assume, that in this theoretical engine that we are each choosing, that you are going to put iron heads on your iron block. If you are concerned about thermal expansion rates, this is where it would be most obvious. You do not want your heads and block expanding at different rates, do you? Or is the expansion negligible and controlled enough that you can compensate for it?</p><p></p><p></p><p></p><p>This is the one that forced me to respond. </p><p></p><p>How would it have superior heat rejection if it is a poor conductor? Heat is rejected from the surface based on the temperature differential from the interior (chamber) to the exterior (engine compartment). The differential is substantial. A better conductor would move heat away faster (higher heat rejection) and a poor conductor would move it away slower (lower heat rejection).</p><p></p><p>Further, you want to KEEP heat in the chamber on the block side. This is the beauty of a "reverse" cooling system. Ask Smokey Yunick - cold heads and warm block make power. You WANT relatively low heat rejection in the block. You actually had an argument for your iron block there and undermined it.</p><p></p><p>Finally, you seemed to be back on the right track when you said that aluminum would have more localized heating and cooling (I think you were now associating higher heat rejection with an aluminum block) and indicated that this would be uneven. Since the aluminum block is a better conductor, the law of thermodynamics indicated that it is LESS likely to have regional temperature differentials. Heat stabilizes itself and does so more quickly and efficiently in better conductors.</p><p></p><p>TJ</p></blockquote><p></p>
[QUOTE="tjvineyard, post: 1755470, member: 22289"] In most situations, you can design any part of aluminum (including a block) and make it as strong or stronger than an iron piece. Generally, you have to use more material (hence a larger aluminum connecting rod as compared to its steel counterpart) to get the same performance, but the final product is generally still lighter despite the larger size. It is also imporant to note that "stiffer" and "stronger" do not always go together. Going back to the connecting rod example, aluminum rods are preferred in many engines because they actually "give" a little bit. The designed stretch and compression of rod actually absorbs stress. I have never heard of a "coefficient rate" so I am not sure exactly what you are referring to. However, because engines operate in a fairly limited temperature range (compared to the range you are likely referring to for metallurgic properties), thermal expansion can be compensated for fairly readily. Sure, forged pistons make some noise warming up, but once in range they function effectively. The same holds true for a block. Now, I also assume, that in this theoretical engine that we are each choosing, that you are going to put iron heads on your iron block. If you are concerned about thermal expansion rates, this is where it would be most obvious. You do not want your heads and block expanding at different rates, do you? Or is the expansion negligible and controlled enough that you can compensate for it? This is the one that forced me to respond. How would it have superior heat rejection if it is a poor conductor? Heat is rejected from the surface based on the temperature differential from the interior (chamber) to the exterior (engine compartment). The differential is substantial. A better conductor would move heat away faster (higher heat rejection) and a poor conductor would move it away slower (lower heat rejection). Further, you want to KEEP heat in the chamber on the block side. This is the beauty of a "reverse" cooling system. Ask Smokey Yunick - cold heads and warm block make power. You WANT relatively low heat rejection in the block. You actually had an argument for your iron block there and undermined it. Finally, you seemed to be back on the right track when you said that aluminum would have more localized heating and cooling (I think you were now associating higher heat rejection with an aluminum block) and indicated that this would be uneven. Since the aluminum block is a better conductor, the law of thermodynamics indicated that it is LESS likely to have regional temperature differentials. Heat stabilizes itself and does so more quickly and efficiently in better conductors. TJ [/QUOTE]
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Cast iron block vs. Aluminum block
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