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Most turbocharged street cars (aka: daily drivers) have the turbo interrupting the primary exhaust flow. Using the
wastegate flow direction as the primary flow would keep the turbine cooler and aid flow for the exhaust when off
boost - the vast majority of the time spent driving a turbo engine is
in the off boost condition. This would increase
fuel efficiency.
This would have a couple of easily foreseeable positive and negative side effects:
Positives:
1. The turbo would remain cooler and "unspun" (reducing bearing wear and keeping oil and coolant at lower temps)
during the vast majority driving.
2. Exhaust flow would be unrestricted by turbine impeller impedance - hence the increase in fuel efficiency.
Negatives:
1. The cooling of the impeller after a boosted period (with low temp exhaust gas) would be a technical hurtle.
Without the cooling effect from exhaust gas the turbo would remain much hotter much longer after boost is no longer
needed.
2. Lag would increase as exhaust manifold temps would have to ramp up before turbine spin would be effective - a
reflective insulating rap may help.
3. The currently available external wastegates are designed for on boost flow regulation and have apertures that are
too small for use in the primary flow direction. A second wastegate (suitable for primary flow) might be needed.
This might be in the form of a non-off-the-shelf design. Perhaps a "slapping shut" solenoid type of valve could be
used.
4. The turbo would need to be moved out of the current conventional primary flow direction. Again; no of the shelf
designs exist.
[link]
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[longbowgun], you got your account in '04, posted two annos in '05 and are now getting around to your first idea? |
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This does not resemble turbo-like behavior, but you get extra points for dwell time. And the category choice is appropriate as well. |
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Back in the previous century I used to assist a 1/4 mile funny car race guy turbo motorhomes for gentlemen with more money than patience. It was all custom then, no turbo cars in the marketplace yet. |
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Fun to watch a motorhome smoke the front tires from a standing start. |
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Using this idea, can we construct a transmission that will not only
supply inverse reactive current for use in unilateral phase detractors,
but will also be capable of automatically synchronizing cardinal
grammeters? |
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//Most turbocharged street cars (aka: daily drivers) have
the turbo interrupting the primary exhaust flow. Using
the wastegate flow direction as the primary flow would
keep the turbine cooler and aid flow for the exhaust
when off boost - the vast majority of the time spent
driving a turbo engine is in the off boost condition.// |
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Firstly, a turbo isn't that restrictive. If it's designed to
flow a 2.0l engine at 7000 rpm, then it's going to be
providing an awful lot less while tooling around at 1300
rpm, the relationship isn't linear either, especially when
you add temperature in, definitely less than 10 fold. Also,
there are factory fit wastegates built into the manifold
structure that offer equal paths, think Y-pipe, turbo one
way, exit the other. |
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Next, does removing airflow restriction improve
efficiency? No, probably not. On the exhaust side, the
biggest restrictions are the catalytic converter and
silencer/muffler arrangements. Turbos have a silencing
effect, you'd likely have to add in more restrictive
muffler to compensate if you bypassed the turbo. |
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If you bypass the turbo's turbine, it isn't going to be
spinning. Even at idle they can sit at 10,000-20,000 rpm.
That's 10-20% more spinning up you have to do to get
boost, but it also means the compressor isn't spinning. So
bypassing the exhaust turbine now means the compressor
is a restriction, or is being spun by the intake airflow. |
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Does this matter? No. At least in a spark ignition engine.
It's a common misconception that when your right foot
goes down, some extra fuel is squirted into the engine
and exciting times begin. What actually happens, in a
modern engine, is that your right foot controls the
THROTTLE* a butterfly valve usually, that deliberately
restricts the engines airflow. Airflow restriction is the
way a spark ignition engine is controlled. |
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In the same engine, to decrease fuel use, just restrict the
airflow, either end is OK, but intake is much easier to
work with. The engine management system just changes
the fuel flow to maintain a roughly stoichiometric 14.7:1
Air-fuel ratio. |
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//This might be in the form of a non-off-the-shelf design.
Perhaps a "slapping shut" solenoid type of valve could be
used.// |
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Putting valves in the exhaust stream leads to valves that
don't work anymore. You may have an EGR valve in your
car, it's probably seized. Take a look at the materials
used on exhaust manifolds and turbine housings, cast iron
mostly. It's a minor miracle the turbine itself doesn't
incinerate. The current system of a passive spring is still
notoriously tricky to get working. |
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//The turbo would need to be moved out of the current
conventional primary flow direction. Again; no of the
shelf designs exist.// |
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Remote turbos exist. Kelly Johnson was a fan, he put a
pair in the tail booms of the second-best aircraft to be
named "lightning". You can get some packaging
advantages, but in general, you worsen the lag
dramatically and gain numerous opportunities for exhaust
and boost leak. Overall, you're making the on-boost
performance worse for a 0 to marginal off boost
efficiency gain. That's a difficult sell on the sales floor,
"sure it's laggy as hell and there's pipes everywhere, but
look at the off-boost BSFC map!" |
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If you want efficiency, take the turbo and give it away,
it'll break at a measly 100,000 and the bolts are a
nightmare. Design your engine slightly larger, put a very
clever valving and engine management system on it and
very carefully look at sliding friction and reciprocating
mass. Turbos are only there because governments are
morons who legislate on engine capacity because they
don't understand air-fuel ratios. |
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// I wish we had italic // |
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You can't mean that. Their economy's nearly as bad as Greece, their politics are a corrupt shambles, the drains stink, the whole place reeks of garlic, petrol fumes and cigarettes, and it's earthquake-prone and dotted with active volcanos. |
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You'd be better off with Turkey ... not too bad if roasted properly, and the feathers are good insulation. |
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I dunno, [8th]. When I retire, I'm planning to move to one of the italic islands, maybe San Serif. |
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We understand that the cathedral there has a very fine medaeval
font .... |
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That pun was unjustified. |
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True, it's obviously left-aligned. |
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I thought it was rather bold. |
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You have to, if they're running... |
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Is all this really justified ? |
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