suspendedHatch
Legalize Illegal Aliens
In extreme laymans terms:
At low RPM, you want small air openings so that the air speed is faster. At high RPMs, you want big air openings because the engine is pulling it much harder. You can observe this principle by putting your thumb over the end of the garden hose. The water squirts out much faster. Now crank the water up. Your thumb is in the way and you get more water by removing it. (By "air openings" I'm referring to valves, throttle bodies, and intake runners. The valve size doesn't change, but the amount they open, how long they stay open, and how much they overlap with the exhaust valves opening all control the amount of air that passes by them.)
This contradiction of low RPM vs high RPM leads to extreme compromises. Historically, an engine builder had to decide where to make power. For a daily driver, you'd have low to mid power within the driving RPM range. Small air openings... and power would completely choke off by 6000 RPM, but that's where they'd put the redline anyway. For a race car, you'd use big air openings. The engine would have no power until it climbed up past 5000 RPM and redline would be shifted to 10k or higher. You launch the car hard and keep the RPMs high for the whole race.
Honda didn't invent variable valve timing, but they were the first to put it into production. The non-VTEC cam lobes cause the valves to open less than a normal car. So you're able to make good power down low with a smaller engine. Then, to prevent the engine from completely choking off, the cams switch to a much more aggressive profile around 5k. The valves open sooner, stay open longer, and open higher with more overlap with the exhaust. Honda pushed the redline up higher to make use of this high end power. All this so they could advertise a higher hp output but keep the engines small.
On a GSR, this principle is extended to the intake manifold as well. Normally, the air goes through the smaller runners on the intake manifold. This increases your low to mid RPM power. Then right around 5k, the intake manifold runners open up allowing a larger volume of air to pass.
At low RPM, you want small air openings so that the air speed is faster. At high RPMs, you want big air openings because the engine is pulling it much harder. You can observe this principle by putting your thumb over the end of the garden hose. The water squirts out much faster. Now crank the water up. Your thumb is in the way and you get more water by removing it. (By "air openings" I'm referring to valves, throttle bodies, and intake runners. The valve size doesn't change, but the amount they open, how long they stay open, and how much they overlap with the exhaust valves opening all control the amount of air that passes by them.)
This contradiction of low RPM vs high RPM leads to extreme compromises. Historically, an engine builder had to decide where to make power. For a daily driver, you'd have low to mid power within the driving RPM range. Small air openings... and power would completely choke off by 6000 RPM, but that's where they'd put the redline anyway. For a race car, you'd use big air openings. The engine would have no power until it climbed up past 5000 RPM and redline would be shifted to 10k or higher. You launch the car hard and keep the RPMs high for the whole race.
Honda didn't invent variable valve timing, but they were the first to put it into production. The non-VTEC cam lobes cause the valves to open less than a normal car. So you're able to make good power down low with a smaller engine. Then, to prevent the engine from completely choking off, the cams switch to a much more aggressive profile around 5k. The valves open sooner, stay open longer, and open higher with more overlap with the exhaust. Honda pushed the redline up higher to make use of this high end power. All this so they could advertise a higher hp output but keep the engines small.
On a GSR, this principle is extended to the intake manifold as well. Normally, the air goes through the smaller runners on the intake manifold. This increases your low to mid RPM power. Then right around 5k, the intake manifold runners open up allowing a larger volume of air to pass.