How so?

Originally Posted by
Coheed
Sure, you get more corrected flow with cooler air.So what's the problem?

Originally Posted by
Coheed
Cooler air is more dense. But the mach speed of the air is increased with increases in temperature. Pressure has no effect on Mach.Sure, but we only care about mass flow, am I wrong? How do you get the most air through a pipe the fastest? With cooler air.

Originally Posted by
Coheed
in order to increase speed beyond [mach 1], you must increase temperature. Increased temps cause excitation of the air molecules, which will cause them to move more quickly.Yah the molecules move more quickly, and the gas gains speed and you get more flow
volume, but you get less
mass flow. Which is what we're really interested in.

Originally Posted by
Coheed
This is why the turbo will spool faster with a manifold that is coated. But you are right about scavenging. This is a two-fold reaction. You increase scavenging, and gas speed by keeping temperatures higher.I have to concede on this point. I thought about it at dinner last night (Mexican). Even though you have less mass flow through the turbine with hotter air, you do have faster moving air, and thus more momentum to the molecules. Even though you have less molecules hitting the turbine blade they are going to hit it faster, and speed works on momentum as an exponent unlike mass which works as a coefficient.
Yah, and that's why a turbo will spool quicker with hotter air. I get it. I was a bit off there.
Still, after the turbo, or after the merge collectors in a N/A header, you want the exhaust to cool down quickly for best flow, not stay warm. Agreed?