My friend called me tonight and asked what air flow I am seeing on my Apexi SAFC. Well I was hitting 68% at 9-10psi with only a complete RB exhaust on the stock turbo. (This was before I got an upgraded compressor).

Now my friend has just about the same mods as I with the exception of a complete intake system bolted right up to the turbo. He is now pushing 13psi of boost.

The wierd thing is, he is only seeing 61% airflow from his AFM on his Apexi SAFC and he said it wasnt much faster if at all from when he was boosting 10 psi before the intake which he just installed. (67% airflow on safc before intake which is wierd)

Maybe someone can tell me or him what the maximum efficient boost levels a stock tII turbo with a custom complete 3" intake and a Racingbeat complete exhaust is. Stock intercooler, intake, and stock engine.

Keep in mind I am not asking about fuel ammounts here unless its a great concern for someone to warn that fuel is the proposed lack of airflow. He has the fuel.

 

I believe one you go past about 11-12psi on the stock compressor the gains are minimal but temps become a concern. If you picture a graph of power produced and turbo outlet temperature versus boost, past that point the power line doesn’t get much higher, but the temp line starts to really climb. So you may get a little more power, but the higher inlet temps increase the risk of detonation. Also, the bearings and seals aren’t suitable for the shaft speeds you get at higher boost, so the turbo won’t last very long. An upgraded compressor wheel/housing would mean he could run lower boost (and hence lower temps and shaft speeds) and still flow much more air than stock.

 

A assume your friend has identical (i.e. exhaust) mods?


-Ted

 

Well I used to have the same mods as him with the exception of his full intake system.

You know I've got that upgraded compressor wheel on my turbo now.

OK so he is hitting 13psi of boost. What you guys are saying is that over 11-12psi the turbo is just working so hard that is fails to flow a proper ammount of air, and therefor the pressure increases do to the expansion of the air from heat????

 

That’ll make a difference; the stock intake is very restrictive. Not quite. The airflow doesn’t decrease, it just doesn’t increase as much. For example you get a bigger percentage increase in flow going from 8psi to 10 psi that you do going from 10psi to 12psi. Once a turbo is pushed past it’s peak efficiency, it has to work harder and harder to provide more boost, and that work adds more heat to the air.