gruntguru wrote:Tommy Cookers wrote:wastegating to so-called zero (or partial reduction of) so-called backpressure is interesting
the turbine is at max rpm and will try to evacuate the exhaust manifold ??
the mu-h motoring power lost by driving the turbine will be how much ? ..... and how/why ??
we might want to throttle the turbine but cannot ?
I think a radial inflow turbine will actually backflow (pressurise the exh manifold) rather than evacuate it due to centrifugal force. This may be an advantage for axial or mixed flow turbines in this scenario.
I tend to think they must be relying on blowdown energy to overcome turbine windage (and backflow) without pressurising the exhaust during the exhaust stroke.
to reduce to nominal 'zero backpressure' ie close to ambient .....
the exhaust proportion that must exit via the wastegate is about 50% or 60%
ie as the blowdown 'AC component' exhaust gas is not seperable from the default 'DC component' exhaust gas
(without some high-speed dedicated porting/valving device that is not permitted ?)
the blowdown energy available in the turbine region is only 40 or 50% of the normal level
constant AFR above 10500 rpm (ie reducing MAP and exhaust pressure) has good points (and bad)
as hollus has reminded me, shifting up gives a rev drop of about 20% in the middle gears and 13% in the highest gears