The Combustion Chamber Is Too Wide Part 2
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An object lesson in why a larger bore is better....
Think about it. You've got a 4" bore, looks like. Those valves are 2.02" and 1.6", or larger, for a total of 3.62" or more, and they're off to one side of the cyl besides, where there's not the full 4.0x" available for them to be in. How could they fail to be close to the cyl wall?
It has nothing to do with what kind of heads they are, as such. Wouldn't make the least bit of difference what brand of heads; if the valves are that big, and the bore that small, then they're going to be that close.
This is one of the reasons why putting larger valves in a set of heads can actually HURT performance, by actually REDUCING flow. Doesn't hardly matter how big the valve is, if all the material coming through it has to squeeze through that little crack around the edge, to get into or out of the cyl. Why, for example, it's not good to run 2.02" intakes in a 305, even if they don't outright hit the deck.
Think about it. You've got a 4" bore, looks like. Those valves are 2.02" and 1.6", or larger, for a total of 3.62" or more, and they're off to one side of the cyl besides, where there's not the full 4.0x" available for them to be in. How could they fail to be close to the cyl wall?
It has nothing to do with what kind of heads they are, as such. Wouldn't make the least bit of difference what brand of heads; if the valves are that big, and the bore that small, then they're going to be that close.
This is one of the reasons why putting larger valves in a set of heads can actually HURT performance, by actually REDUCING flow. Doesn't hardly matter how big the valve is, if all the material coming through it has to squeeze through that little crack around the edge, to get into or out of the cyl. Why, for example, it's not good to run 2.02" intakes in a 305, even if they don't outright hit the deck.
EXCELLENT ANSWER!!!!! THE VALVES ARE 2.08 AND 1.60
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A well designed head directs the flow across the back of the valve toward the center of the cylinder, as the long port does on a big block. This is also why a lot of folks notch the tops of the bores on big blocks, just as GM did to the 396 and 4-bolt 454's.
It's also why my big block is 4.600 bore
It's also why my big block is 4.600 bore
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551 Posts
this is the very reason i stayed with a 2.02 valve in my 383. Dave
2.06 is the largest valve i have ever used in a 4.030" bore engine making great power
Why the heck do you need a valve over 50-51% of the bore size? With a 4.030" bore at 50% you would need a 2.015" so you see why you can make good HP with a 2.02 as sheetmetal says he uses
The Dart '220' heads that are cnc ported for the 4.030" bore come with 2.055" valves and make some good HP too
Why the heck do you need a valve over 50-51% of the bore size? With a 4.030" bore at 50% you would need a 2.015" so you see why you can make good HP with a 2.02 as sheetmetal says he uses
The Dart '220' heads that are cnc ported for the 4.030" bore come with 2.055" valves and make some good HP too
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