GT Motorsports: 370Z Supercharger system development

G37Sam · 02-17-2010, 07:20 PM

Quote:

Originally Posted by RCZ

It just might be. Could you explain how 5psi manifold pressure aka cyl pressure is different whether its a turbo creating the pressure or a sc creating the pressure?

I am a little confused as to how the same amount of PSI makes more power depending on what is creating that pressure. I always knew that bigger turbos had to work less because they flow more, therefore they can force MORE air into the same space more easily. Thats why a bigger turbo will have a much easier time making 40psi than a tiny one which would have to spin itself into kingdom come to generate 40psi.

However, that hardly explains anything. So please someone explain to me how "boost isnt boost".

You could have two compressors blowing air at the same pressure but one could be flowing twice as much air as the other.. the one flowing more air will obviously see higher hp numbers.

BalanBro · 02-17-2010, 08:00 PM

Turbo's don't make pressure, they just blow air. The pressure that we see on our boost gage is a direct result of this blown air "building up" between the compressor outlet and the intake manifold. While different turbos have different flow capability and efficiencies, two identical engines with the same manifold pressure will have the same net flow rate into each cylinder regardless of the turbo that's being used.

When you hear about a smaller turbo falling on it's face, it typically means that it has reached or exceeded it's optimum efficiency, and you would see a decrease in the manifold pressure when this happens. A large turbo will make more power here simply because it can provide the necessary cfm to maintain the predetermined pressure level as set by the wastegate.

Keep in mind that high cfm almost always means turbo lag. Therefore the ideal setup would be the smallest turbo that would efficiently provide the necessary cfm for your target HP level. Any bigger would just increase lag with a marginal at best increase in peak power.

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02-17-2010, 08:00 PM	#2 (permalink)
BalanBro Enthusiast Member Join Date: Apr 2009 Location: NJ Posts: 318 Drives: 40th Anniv. 370Z Rep Power: 1113	Turbo's don't make pressure, they just blow air. The pressure that we see on our boost gage is a direct result of this blown air "building up" between the compressor outlet and the intake manifold. While different turbos have different flow capability and efficiencies, two identical engines with the same manifold pressure will have the same net flow rate into each cylinder regardless of the turbo that's being used. When you hear about a smaller turbo falling on it's face, it typically means that it has reached or exceeded it's optimum efficiency, and you would see a decrease in the manifold pressure when this happens. A large turbo will make more power here simply because it can provide the necessary cfm to maintain the predetermined pressure level as set by the wastegate. Keep in mind that high cfm almost always means turbo lag. Therefore the ideal setup would be the smallest turbo that would efficiently provide the necessary cfm for your target HP level. Any bigger would just increase lag with a marginal at best increase in peak power.