Let’s say for instance - you have a t-28.
We are running it at … oh… 22PSI
Now, we take a 50 trim t3/t4 and slap it on the same exact motor.
and run it at 22PSI
Would the air post turbo actually be cooler on the larger turbo than the smaller?
My train of thought : As the turbo exceeds its efficiency range, the air it compresses gets much warmer.
But : if we were to be running, say, 15psi, would it be safe to say that the air temp difference would be negligible?
when you’re talking about the compressor…more efficient = cooler air
bigger isn’t always better
I know you know that…but I don’t want others to be confused. Also we’re really simplifying things here, but yes as you push a turbo out of it’s efficiency range it will run hotter. A turbo running in a more efficient zone will run considerably cooler than one at a higher one.
On a turbine housing for instance a bigger housing will lower temps if you’re pushing enough air that a smaller one has increased backpressure. The design of the housing and wheel is very important too though, so just because one turbo is bigger than another doesn’t mean it’s more efficient. If it’s a poor housing and wheel design it may be bigger and less efficient.
damnit i keep editting to add more and more…i’ll just stop with this… 
-Mike
But what if we are going to say…
like, 40% efficiency and 50%?
I know how “simplified” this situation is.
i just editted and added more crap including your answer
If you’re compressor efficiency is down to 40 or 50 get ready for your pistons to melt like butter over a flame. Seriously though try to stay above 60%
A larger compressor wheel will have an easier time keeping air compressed at higher pressure than a smaller one. The smaller compressor has to rev. a lot higher to achieve the same pressure that a larger one does. That over-revving will produce more heat, etc…
it will be less air and will be hotter air out of the smaller turbo.
nope.
whichever one is more efficient on the compressor side and is operating in a more efficient zone will create the lesser amount of heat.
If you run two turbos, let’s say a T25 and a T66 at 25psi, which one do you think is going to produce more heat?
Read Howie’s example.
exactly, its not just the physical size that matters in regards to efficiency, and different turbos are efficient in different areas in regards to airflow and pressure, you guys really need to start looking at compressor maps before you start sticking T88s on your moms 1.8T
I somewhat doubt it… reason being that compressing air to 22 psi, thru a small compressor or a larger one is still going to produce the same amount of heat… as long as one of the said turbos wasnt getting overworked (obviously over spinning it would generate some heat)
^
you’re missing the point of the question. no one is putting a t90billion on a 1.2l anything.
2 turbos with the same wheel design. the larger one will always move more air, and not heat it up as much. no one is asking about turbo size vs. engine size.