Is turbo charge heat a function of the amount of boost pressure, or the amount of air flow?

For example, Say I bolted a non-intercooled turbo kit to my dead stock truck today and was able to make 7psi before my AIT goes crazy. Later I decide I'm not happy with the power output, but instead of buying an intercooler and upping the pressure I want to increase flow with a cam and/or head work. Will I still be able to run that turbo at 7psi without increasing intake temps? Or does the fact that the turbo must spin faster mean that I might only get away with 6psi?

 

Now Im going to go out on a limb here on what I think your getting at.

Turbo X, with a waste gate set to 7psi, will always operate at 7 psi. If you do heat/cam mods and reduce the restrictions (increase flow) you will still see 7 psi of boost (provided turbo X can keep up with it) because because pressure is what will open up the waste gate to limit boost. Now, that being said the more air your turbo moves the more heat it will make. So with your better flowing heads and more efficent cam your packing more air and fuel in the cylinder your also now making more heat.

 

Its not the flow of more air that makes more heat, its the potential drop in efficiency when air flow demand is increased. Compressing the air is what heats it.

 

Totally agree with post above.

I'll also add, that it depends on if efficiency is increasing or decreasing with flow.
The center "circle" is highest efficiency. If you increase flow, you increase efficiency to point, then further increases at the same pressure ratio, decrease efficiency.

 

I get that compressing the air is what makes more heat, but if he goes from moving 50 pounds of air per minute to 60 without increasing his pressure hes not getting any extra heat from compressing the air because hes isnt compressing it any more. It is from the added friction, making up for any additonal pumping loses, and more exhaust heat transfer within the turbo itself.

 

Additional pumping losses in the engine or friction would result in an increase in boost. Since the cam profile doesn't change, this isn't possible. The compressor map Coban posted is a volumetric efficiency map. While it is an accepted comparison, the efficiency I am talking about is adiabatic efficiency. As this adiabatic efficiency falls with an increase in air flow, compressor pressure must also increase in order to increase the air flow. Hence with the necessary increase in compressor pressure, the heat output also rises. When adiabatic efficiency falls while maintaining the increase in air flow, work input to the system must increase as well. That extra energy has to go somewhere...so it exits the compressor as heat.

That looks like a rambling paragraph to me, but I hope it makes sense

 

Heat comes mainly from boost.

 

Thanks for the responses guys. I'm gathering that the short answer to my question is "yes you will be able to continue to run the same psi withought significant temp increases in most cases".

I get what has been said here about adiabatic efficiency, but the initial question was about what happens if you increase adiabatic efficiency.

Air is such a good insulator that I find is hard to believe that increased air speed outside of the turbo will cause a significant temp increase due to friction, and since the air would be traveling fast it would spend less time picking up heat from exhaust transfer in the turbo.

Makes sense that the biggest factor would be turbo efficiency at the before/after pressure and lbs/min.

This has been really helpful! I didn't have the first clue about turbo surface maps before and now I'm starting to get it.

 

Good question, and I think smokey the bear answered it.
I think a simple way to think of it is that a compressor is designed to have a effective/efficient range based on a predetermined flow value at a specific shaft rpm (notice boost #'s are irrelevant). If you stray from either of those two set points you will walk out of that compressor's efficiency range.
So if you make your engine breath easier, the turbo will have to spin a bit faster to provide the additional cfm's necessary to keep up with the pre-determined boost threshold. The type of turbo you have will determine whether it can or can't handle the change.