there is an small electro mechanical controlled valve on turbo loader . this valve control    pressure in turbo ... when engine rotate in small rpm valve is closed , and when engine reach mid state rpm valve is opening more and more , and pressure in turbo stay constant value .... all about tunning is the time when the open this valve a how wide or narrow ... other important thing is the amount of fuel that can be injected in cylinder ... if pressure is higher then we have more air or oxygen and we can burn more fuel ... pressure of fuel is not changeable  value ...high pressure pump works with about 1500 to 2000 bar or KPa .....diesel engine intake fuel and air separately ...air must be first cooled and pressured and after that injected in cylinder .....
what we have after tunning ... turbo pressure goes high , torque goes high , pollution goes high and  lifetime of your engine goes DOWN ... remember , turbo rotate about 100.000 rpm to max 200.000 rpm and he is max temperature sensitive ....

my friends in Serbia work with german made ABT tunning chip and I try to drive VW and AUDI cars with this modification made .... result is magnificent but for very short time , and I saw how turbo die .... diesel engine is a very very vulnerable machine and you MUST be very careful with them ....

http://www.abt-sportsline.de/

first you must respect engine  temperature , no hard acceleration with cold engine , and second if you push engine hard wait about 1 minute before you stop the engine
always bay only clean diesel fuel , this is most important for long life for injection valve ....imagine how send destroy injectors on 2000 Bar pressure ....

and if you love torque by large petrol engine , this is love without fear .... :)
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