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That is all true... mostly. The bottleneck, however, is not the amount of air being pushed through, it is how fast it is being pushed through. Torque is determined by velocity. Why?
Because you can use the energy that the engine already expended to shove the last pulse of exhaust out to do more work.
If you get that pulse shooting out at a high speed, the next pulse will be pulled in really quickly. By timing the pulses with runner length in both the intake manifold and the header, you can make it so that the very next pulse gets plopped into the motor at positive pressure, since it is surrounded by vacuum. Basically, pistons goes back up with the exhaust valve open, and shoves the exhaust pulse out. At the same time, the intake valve is opening (overlap). There is a low pressure moving area that follows the exhaust pulse, which is moving on it's own momentum. This pulse moves, and leaves a vacuum in it's wake. Nature abhors a vacuum, so the intake pulse is formed. The fresh air rushes in to take the place of the vacuum. If all is timed right, you get an artificially high pressure pulse when the intake valve closes, which is why we can get over 100% VE without a turbocharger. The faster the exhaust pulse moves out, the faster the intake pulse can move in. The faster the intake pulse moves in, the more force (momentum) it has, and the higher the VE that can be obtained.
Now, back to the throttle body.
The whole motor works as one system. Meaning, that if there are any places where the air (intake or exhaust) slows down, the motor must expend a little bit more energy to speed it back up. Using a throttle body that is matched for the air requirements of a motor allows the air to be accelerated into the intake manifold from the intake tubing. The manifold can then accelerate the air towards the head. Momentum builds <suspenseful music> and the air can then positively charge the cylinder. Now, take the stock throttle body and replace it with a 60MM throttle body. The engine pushes out an exhaust pulse and pulls in a new pulse. The engine expends the energy to pull air from the plenum to the runner. The engine expends the energy to pull air from the throttle body into the plenum. But wait, the air at the throttle body is full of stagnant air. A lot of noise and activity culminating into a... whimper. With the stock throttle body, stagnant air (for all intents and purposes) hits the filter, which is exposed to vacuum. This stagnant air is pulled in, from the completely unrestricted (atmosphere) to a slightly restricted tube. This slightly restricted tube now moves into a slightly more restricted tube with a butterfly in the middle (yup, the throttle body), and guess what, speeds up! This faster moving air moves into the plenum, and is pulled into a runner, and it, yup, speeds up again. Into the head, yup, faster still! By this point, it has accelerated from stagnant to the speed of sound. By using the whole intake stream to gain more time for it to speed up, the acceleration has been more gradual. Gradual acceleration of any mass requires less work then rapid acceleration of the same mass. Case in point: A Civic DX with a motor that can do some work can accelerate to 60 in, say, 10 seconds. A Civic EX, which is capable of doing more work (has more power) can reach 60 in 8 seconds. Therefore, to get an object with all of the characteristics of a Civic to 60 MPH using the least energy, you get there slower. Both Civics were rockin' it out full tilt (yawn), and it took a lot more power to get the EX to the same velocity more quickly. Well, in a roundabout way, the same applies to the air going into your motor. You want it to take the least amount of energy to reach the velocity that it will attain, which means doing less work, and slower acceleration of the air.
That's why I recommend a longer runway, so to speak, with the stream necking down to the combustion chamber as gradually as possible.
-=B-= Dude, Boeing called. They want their wing back.
Dark0ne95: There is a butthole on that girl that his going to feel the wrath of 23 yeras of worldwide hate. Me: Can I put that in my sig? Dark0ne95: GO right fucking ahead.
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