JGTurbo
Well-known member
And the next one:
Don't turbos have to be really hot to work properly?
Putting a torch to your turbo and getting it hot doesn't produce boost. What
produces boost is airflow across the turbine which causes the turbine to
spin. If turbochargers required very high temperatures to produce boost,
Diesel trucks and Methanol Race cars wouldn't be able to run turbos.
However, each of these "Low Exhaust Temperature" vehicles work very
well with turbochargers when, like any turbo application, the turbocharger
is sized correctly.
In a conventional, exhaust manifold mounted turbocharger system, the
extra heat causes the air molecules to separate and the gas becomes
"thinner" because of the extra space between the molecules. This extra
space increases the volume of air but doesn't increase the mass of the air.
Because the volume is higher, the velocity of the gas has to be higher to
get it out in the same amount of time.
By mounting the turbo further downstream, the gasses do lose heat
energy and velocity, however, there is just as much mass (the amount of
air) coming out of the tailpipe as there is coming out of the heads. So you
are driving the turbine with a "denser" gas charge. The same number of
molecules per second are striking the turbine and flowing across the
turbine at 1200F as there is at 1700F.
Front mounted turbos typically run an A/R ratio turbine housing about 2
sizes larger because the velocity is already in the gasses and the volume
is so big that the turbine housing must be larger to not cause a major
restriction in the exhaust system which would cause more backpressure.
With the remote mounted turbo, the gasses have condensed and the
volume is less, so a smaller A/R ratio turbine housing can be used which
increases the velocity of the gasses while not causing any extra
backpressure because the gas volume is smaller and denser.
Sizing is everything with turbos. There is more to sizing a turbo for an
application than cubic inches, Volumetric Efficiency, and RPM ranges. A
turbo must also be sized for the exhaust temperatures. A turbine housing
sized for 1700F gasses would have lag if the gasses were 1200F. This is
why turbo cars have lag when they are cold and not warmed up yet. Both
systems work well if sized correctly.
Don't turbos have to be really hot to work properly?
Putting a torch to your turbo and getting it hot doesn't produce boost. What
produces boost is airflow across the turbine which causes the turbine to
spin. If turbochargers required very high temperatures to produce boost,
Diesel trucks and Methanol Race cars wouldn't be able to run turbos.
However, each of these "Low Exhaust Temperature" vehicles work very
well with turbochargers when, like any turbo application, the turbocharger
is sized correctly.
In a conventional, exhaust manifold mounted turbocharger system, the
extra heat causes the air molecules to separate and the gas becomes
"thinner" because of the extra space between the molecules. This extra
space increases the volume of air but doesn't increase the mass of the air.
Because the volume is higher, the velocity of the gas has to be higher to
get it out in the same amount of time.
By mounting the turbo further downstream, the gasses do lose heat
energy and velocity, however, there is just as much mass (the amount of
air) coming out of the tailpipe as there is coming out of the heads. So you
are driving the turbine with a "denser" gas charge. The same number of
molecules per second are striking the turbine and flowing across the
turbine at 1200F as there is at 1700F.
Front mounted turbos typically run an A/R ratio turbine housing about 2
sizes larger because the velocity is already in the gasses and the volume
is so big that the turbine housing must be larger to not cause a major
restriction in the exhaust system which would cause more backpressure.
With the remote mounted turbo, the gasses have condensed and the
volume is less, so a smaller A/R ratio turbine housing can be used which
increases the velocity of the gasses while not causing any extra
backpressure because the gas volume is smaller and denser.
Sizing is everything with turbos. There is more to sizing a turbo for an
application than cubic inches, Volumetric Efficiency, and RPM ranges. A
turbo must also be sized for the exhaust temperatures. A turbine housing
sized for 1700F gasses would have lag if the gasses were 1200F. This is
why turbo cars have lag when they are cold and not warmed up yet. Both
systems work well if sized correctly.