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beatr911 · 03-07-2012, 05:52 PM

I seem to remember that some of the benefit of two intake valves weather on 3 or 4 valve heads was that they can provide for tumble as opposed to swirl.

If I recall this correctly, I think it was that at higher intake velocities say over 2500 rpm or so, swirl was detrimental as the heavier fuel droplets would centrifuge out near cylinder walls causing a lean area in the center where the sparkplug is. Tumble, with the injector putting fuel near the middle of the charge keeps the richer part of the mixture near the plug and leaner parts to the sides, aiding in more consistent combustion events. Sort of a stratified charge idea.

Didn't the VX (D15B?) motor operate with mostly one intake valve under 2500rpm and then both above 2500rpm for swirl at low speeds and tumble at high speeds?

03-07-2012, 05:52 PM	#12 (permalink)
beatr911 Master EcoModder Join Date: Feb 2008 Location: West Coast, USA Posts: 516 B2300 - '96 Mazda B2300 SE Focus - '05 Ford Focus ST The red car - '00 Honda Insight Thanks: 6 Thanked 77 Times in 56 Posts	I seem to remember that some of the benefit of two intake valves weather on 3 or 4 valve heads was that they can provide for tumble as opposed to swirl. If I recall this correctly, I think it was that at higher intake velocities say over 2500 rpm or so, swirl was detrimental as the heavier fuel droplets would centrifuge out near cylinder walls causing a lean area in the center where the sparkplug is. Tumble, with the injector putting fuel near the middle of the charge keeps the richer part of the mixture near the plug and leaner parts to the sides, aiding in more consistent combustion events. Sort of a stratified charge idea. Didn't the VX (D15B?) motor operate with mostly one intake valve under 2500rpm and then both above 2500rpm for swirl at low speeds and tumble at high speeds? __________________ Good design is simple. Getting there isn't.