Turbo efficiency question...

[dsm john]

I'm kind of a newb at reading compressor maps and all of that jazz. Would running 10psi on a turbo thats rated to be efficient at higher boost make it not pull as hard as a turbo thats efficient at lower boost and also on 10psi ?

Not sure if I could word that any more clearly. :\

 

[Dragon Talon]

depending on spool up. it might.. w/ the 14b turbo has fast spool cause it is small... my homey got a 57trim big turbo and at the same boost i spool and launch faster....

 

[dsm john]

I know the spool up differences and stuff like that , but if both cars are in boost is what I'm talking about.

Would the turbo with an efficiency raiting be flowing better than a turbo with a higher efficiency rating at 10psi ?

 

[Dragon Talon]

It would be flowing more but it would have spool lag.. so i dont think it would be effeiciant.. What are you trying to do anyway? what turbo do you have????

 

[95blackGsTurbo]

10 psi is 10 psi. You have to go by how much CFM they move.

 

[Carter97GSX]

I'll try and explain to you what the efficiency of a compressor means.

Because of some law of thermodynamics, if you increase the pressure of a gas this naturally will increase the temperature a given amount. This is basically represented as a pressure ratio and a temperature ratio multiplied by a constant. If a compressor is 100% efficient then the equasion will look like the one below.

New pressure/old pressure = constant * new temperature/old temperature

If the compressor is 90% efficient then it will look like this one below.

0.90 * New pressure/old pressure = constant * new temperature/old temperature

As you can see, to get the same amount of pressure increase the less efficient compressor will have a greater increase in temperature due to inefficiencies.

The final answer to your question is that the less efficient compressor at a given pressure ratio and flow rate will definately be spitting out warmer air and thus produce less power. This is independant of the spool up. Hope this helps.

 

[RED_AWD_BLUR]

This is a great guide and it is FREE!!!!
Basics:
http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html
http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech102.html

this next on tells more about the efficiency stuff.

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html

"Efficiency Islands are concentric regions on the maps that represent the compressor efficiency at any point on the map. The smallest island near the center of the map is the highest or peak efficiency island. As the rings move out from there, the efficiency drops by the indicated amount until the surge and choke limits are reached. " - http://www.turbobygarrett.com/ website

An overly large turbo for the car would be running less efficient than a smaller turbo assuming it is in the lower part of the compressor efficiency map on the big turbo instead of the small turbo.

Anyway just size your turbo so it is close to the efficiency range you want but if not the percentages don't drop off that drastically you just need a little bit bigger intercooler.

It is cool to know this stuff but The simplest thing to do is to just buy what already works too.

 

[dsm john]

As you can see, to get the same amount of pressure increase the less efficient compressor will have a greater increase in temperature due to inefficiencies.

Let me see if I'm comprehending this correctly.

Let's say you've got a car with a 14b , and one with a 20g. Both cars are set at 10psi. Both cars have the same exact mods and are running properly , let's assume that both cars are the exact same, except for the turbos, for the sake of the conversation.

Will the 14b be flowing better cfm than the 20g because it's closer to it's efficiency range and the 20g is at the bottom of it's map ?

Now if we take the situation and turn the boost up to like 18psi , the 20g should be flowing much better cfm than the 14b because it is getting closer to it's desired application , and the 14b is peaking out of what it is made for , right ?

 

[RED_AWD_BLUR]

Yes and no, you need to understand what you are talking about. when you say "better CFM" that is incorrect. at 10psi both turbos will flow the same CFM. the thing is like Carter97GSX said. it obeys thermodynamics, the Ideal gas law. P*v=m*R*T
“m” = mass of a gas/molar mass of gas, R = Ideal Gas Constant, p=press, v=volume, T=temp. Any way what this means even though the volume flow rate and pressure are the same the Mass flow rate is different. since we assume the 20G is in a less efficient region it has converted more mechanical energy into heat than the 14B has. Thus there is less actual mass of air entering the motor. By the way this is how your car knows how to run. It has a mass air flow sensor, that has a know crosssectional area and the computer knows the air out side because the car has a barometric (ambient pressure) , R is a constant the computer knows, and from the specific heat of air (another constant the computer knows) it figures velocity and converts this to a mass air flow signal.

bottom line the mass air meter will be reading more air entering the motor with the 14B than the 20G

this is true