DEAL! Pig or cow?
The only difference between how I did the math and how you did it is which number gets divided by the other.
Using your method, a 177 intake to 147 exhaust is 0.83, but it's not a percentage yet, just a number. The way it would be written is intake : exhaust = 1.0 : 0.83 If you want a percentage, multipy it times 100, for a result of 83%
Again, using that method, the closer the exhaust number gets to 1, the better the turbo will like it. So you would want a bigger result from your math. Your first example of 0.62 is worse than the second result of 0.82. Keep in mind, though, there are practical limitations as to how close that number can get to 1, but they relate to the physical limitations of the valve sizes and exhuast passages. Lets face it, it would be tough to find or modify ANY head to have an exhaust valve/port that is just as big and flows as well as the intake.
I guess what I need to say is that the exhaust needs to flow better for a turbo installation than for an aspirated motor. If you want to start out with an unmodified head, and the intake is flowing OK, then figure out how, and put your money into making the exhaust flow better.
The low static compression on a turbo motor cannot push the spent gasses out of the cylinder as well as a high-compression aspirated engine. There is also a larger volume of "dead" gasses in the combustion chamber that has to be cleared by fresh intake charge during valve overlap. To get a turbo to work at maximum efficiency, you have to get the maximum amount of spent, heated gasses to it with the least amount of resistance.
Hope this helps, and if anybody else has a question or two that I haven't touched on, jump in and ask!
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David
newbie #4153
