Wastegate Chatter Myth
There is confusion in the automotive world about so called "wastegate chatter" or "turbo flutter". A noise created on lifting off the throttle in a turbocharged car, commonly described as a chipmunk or a rattlesnake, is often stated incorrectly as being a result of the turbo's wastegate closing.
The noise is in fact the air compressed by the turbo passing back through the compressor wheel of the turbo after the airflow is abruptly halted by the throttle plate closing, called compressor surge. However, in some cases, i.e. where the throttle plate doesn't open fast enough or is set up to only react to high boost, some chatter will remain. Surge can occur on diesels when the turbo is attempting to pressurize the air at a higher pressure ratio than the compressor wheel can flow at a given speed. Most Diesel engines have no use for a blow off valve as they do not have a throttle plate.
The chatter noise is very noticeable on World Rally Cars, where anti-lag is used.
A compressor stall like this can cause excess stress and wear on the turbo's shaft or bearings under higher load applications of the turbo (around 15 psi (1.00 bar) and greater depending on the trim and flow rate of the compressor side).
Actual wastegate flutter occurs instead under partial boost conditions such as partial throttle near the boost threshold. It sounds like FftFftFftFft not ShuShuShushu and is caused by the rapid opening and closing of the wastegate at boost levels near the spring pressure. It is commonly heard more clearly and may be more prominent on cars with modified intake silencers, up-pipes, downpipes, or an oversized wastegate incorrectly matched to that specific engine. Also, vehicles using on/off solenoids to control boost can do this under certain conditions. It is not harmful to the engine. Some may claim that it can damage the wastegate, which may be possible under some circumstances, however some vehicles flutter regularly inherently from the factory without any consequence.
Read more about this topic: Wastegate
Famous quotes containing the words chatter and/or myth:
“One has but to observe a community of beavers at work in a stream to understand the loss in his sagacity, balance, co-operation, competence, and purpose which Man has suffered since he rose up on his hind legs.... He began to chatter and he developed Reason, Thought, and Imagination, qualities which would get the smartest group of rabbits or orioles in the world into inextricable trouble overnight.”
—James Thurber (1894–1961)
“Two myths must be shattered: that of the evil stepparent . . . and the myth of instant love, which places unrealistic demands on all members of the blended family. . . . Between the two opposing myths lies reality. The recognition of reality is, I believe, the most important step toward the building of a successful second family.”
—Claire Berman (20th century)