SocialSecurity wrote:[rant]
its a misconception that turbos produce heat purely because they are attached to a turbine, but because compressing air with a centrifugal compressor causes lotsa heat & friction. sure theres gonna be some heat comming from the turbine, but centrifugal blowers would make it just the same! maybe a TINY bit less heat, but not gonna let you reach crazy boost levels without an intercooler. most vortech kits (for cars) that run more than 8psi need an intercooler. twin-screw blowers dont need a cooler quite as badly cause they are a lot more efficient (and a lot more expencive, if your thinking of cheap blowers then its probably a rootes blower)... centrifugal superchargers (ie, a pully driven turbo compressor) certainly dont produce boost from idle, if anything they take more RPM's to make the same boost as a turbine driven compressor, depending how you gear ...snip
[/rant]
guys some info...based on experience...
back to basics.....
a turbocharger is subject to heat...coz its zorst driven...
the 2 impellers are only a short distance apart
so the one compressing air...is hot MAINLY because of zorst heat
mind you...
anything compressing air..will get warm.. and the outgoing air is therefore
warmer than the air going in..(this applies to turbochargers and any belt driven supercharger..be it Rootes or whipple or whatever...)
but
because superchargers are usually fairly close to the inlet port....
the density of the inlet charge is not affected very much (warm air reduces the density of the inlet charge) and so ppl put Rootes or screw type superchargers in the Vee on V8's or they are the inlet for things like 6 cylinder engines (think norman superchargers)
but turbochargers???
they are a long way from the inlet port so we do need to reduce the temperature of the air...and also because the compressed air from a turbocharger is very hot (as I said, because of the exhaust heat)
so we need to cool it down...hence the intercooler..
you also need to cool the turbo itself....
the better systems (think porsche and SAAB) use oil to lubricate and cool the turbo and they also watercool the turbo... a SAAB for example has an oil lubed and cooled and watercooled turbo (and the water line goes to a separate radiator and the engine has an oil cooler) and an intercooler for the inlet charge...(and the plumbing is amazing!)
a turbocharger is also known as a 'free' compressor as it takes no horsepower to drive, unlike a supercharger(which does require hp to drive it...)
but a turbo also needs a large volume exhaust (with no back pressure)
for maximum effeciency....
it is interesting to note the different applications....
when it comes to forced induction...
aircraft (think Spitfire or Mustang) tend to use Superchargers
diesel trucks and railway locomotives use turbos
cars with Vee engines tend to use superchargers
and cars with inline engines (or flat or boxer engines)
tend to end up with turbos.....
all interesting stuff....
hth
cheers