The video actually illustrates the concept. Instead of using the throttle to control the air density (power output), the throttle is left wide open and the excess air that was drawn in due to the WOT is allowed to bleed back out the intake valve before combustion. The pumping loss is overcome by allowing the piston to travel downward without the resistance created by a partially closed throttle limiting intake (imagine sucking through a straw with and without a finger/throttle partially covering the other end).quote:
Originally posted by brianl703:
Can someone explain how this works:
"Under low-load conditions on conventional engine, the throttle valve is normally partly closed to control the intake volume of the fuel-air mixture. During this time, pumping losses are incurred due to intake resistance, and this is one factor that leads to reduced engine efficiency. With the i-VTEC engine, however, intake valve closure timing is delayed to control the intake volume of the air-fuel mixture, allowing the throttle valve to remain wide open even under low-load conditions for a major reduction in pumping losses of up to 16%."
I'm having a bit of trouble visualizing how changing the intake valve timing would reduce pumping losses under low-load conditions.
neat! Delayed intake closing allows you to make the expansion stroke longer than the intake stroke, which improves thermal efficiency. Mazda did that with the Millenia's engine, but it didn't have VTEC, so they had to add a supercharger to recover the lost power. Honda seems to have theirs set up to use regular valve timing when you need power, and a delayed intake closing when you need less power.quote:
Originally posted by darryld13:
The video actually illustrates the concept. Instead of using the throttle to control the air density (power output), the throttle is left wide open and the excess air that was drawn in due to the WOT is allowed to bleed back out the intake valve before combustion. The pumping loss is overcome by allowing the piston to travel downward without the resistance created by a partially closed throttle limiting intake (imagine sucking through a straw with and without a finger/throttle partially covering the other end).quote:
Originally posted by brianl703:
Can someone explain how this works:
"Under low-load conditions on conventional engine, the throttle valve is normally partly closed to control the intake volume of the fuel-air mixture. During this time, pumping losses are incurred due to intake resistance, and this is one factor that leads to reduced engine efficiency. With the i-VTEC engine, however, intake valve closure timing is delayed to control the intake volume of the air-fuel mixture, allowing the throttle valve to remain wide open even under low-load conditions for a major reduction in pumping losses of up to 16%."
I'm having a bit of trouble visualizing how changing the intake valve timing would reduce pumping losses under low-load conditions.
Of course the engine remains somewhat low torque at 128 lb-ft at a relatively high RPM.......This is my major qualm on Honda motors.
Hence the big joke, "my lug nuts require more tourque than you Honda makesquote:
Originally posted by andyfish:
Of course the engine remains somewhat low torque at 128 lb-ft at a relatively high RPM.......This is my major qualm on Honda motors.
I didn't see the video, but it sounds like the intake valve is left open at the beginning of the compression stroke to bleed the excess air out?quote:
Originally posted by darryld13:
Instead of using the throttle to control the air density (power output), the throttle is left wide open and the excess air that was drawn in due to the WOT is allowed to bleed back out the intake valve before combustion.
The '05 Malibu is getting 35MPG. It's not a cramped econobox either, and that's with an automatic. But the Aveo does get better city fuel economy.quote:
Originally posted by Jason Troxell:
Just saw a bunch of Aveo when passing a Chevy dealer with big 34mpg printed on windshields as if that was supposed to be impressive.