How does chip tuning control turbo boost?

Guys, we are talking about the grand-grandfather of 1.9JTD's - the earliest 105hp version of the 1.9 JTD engine, without the variable geometry turbine. I have it on my 146, but as I know, 145/6 JTD had not been introduced to the UK, so I am posting this thread in the neighbouring 'Alfa 147, 156 & GT' section. I know for sure that it had been fitted in the early 156's.
So what I am interested in is does the remap on these engines actually rise the max boost and if it does, how does it do that? How could the ECU intervene with the boost control? AFAIK the boost control on these turbo chargers is purely mechanical
Thanks in advance.

Moved to Tuning Lounge

There is an electronic solenoid controlled by the ECU which controls the Boost level. Remapping the ECU alters the boost level by changing when this boost solenoid operates.

It basically connects the Positive pressure side of the turbo back to the wastegate. When the pressure on the positive pressure side reaches a certain point the ECU operates the solenoid allowing the wastegate to open.

The wastegate valve is mechanical, but the control of boost pressure going to the mechanical valve is electronic. In the early days of turbocharging it would have been a purely mechanical system.

Thats a basic explanation anyway.

There is a good article on Turbos on Wikipedia.

HTH Simon.

Ok. Thanks, but that goes for the engines with variable geometry of the turbos. I refer to the previous version w/o the solenoid. How is the the increase in boost achieved there? Or is there any increase after all?

Th variable geometry turbine fitted to some engines is a different setup to ordinary turbo's. Ordinary turbo's do have an electro-mechanical boost solenoid, but on variable geometry systems there is an additional solenoid to control the angle of the vanes in the turbo as well.

The reason for electro-mechanical boost control is usually to give a more progressive power delivery, insted of the all or nothing traditional turbo power delivery. It also helps incorporate safety measures, such as reducing the boost to prevent wheelspin, of to allow lower grade fuels to be used.

On most cars the wastegate is set to open at a nominal value, which is often reffered to as the base boost level. The wastegate usually opens at a pressure of around 7psi. By incorporating a valve between the inlet and the wastegate, the valve can be programmed to open at higher pressures that the base level of the wastegate hence allowing more boost than the wastegate level. When the valve is opened this allows the boost pressure to the wastegate, which casues it to open.

Its probably as simple as a spring on the wastegate which has a rating, there will be a small pipe from the boost side, as this increases boost it pushes against the spring thus opening the wastgate.
Tuning is usually done via a bleed valve, or a higher rated spring.

In other words, there is no way to increase the boost by interevening on a software level only?
The user manual for this engine says:
quote:
"...a wastegare valve is fitted which is controlled by a pneumatic actuator which makes it possible to shutter the passage of exhaust gas to the turbine depending on the engine's need of power/torque"
Unquote

Originally Posted by Trustworthy

In other words, there is no way to increase the boost by interevening on a software level only?
The user manual for this engine says:
quote:
"...a wastegare valve is fitted which is controlled by a pneumatic actuator which makes it possible to shutter the passage of exhaust gas to the turbine depending on the engine's need of power/torque"
Unquote

The wastegate is pnuematic, and it is operated whan the boost reaches a a certain level. However most modern engines have an electronic solenoid which is connected bewteen the boost source and the wastegate. The ECU controls whan this valve opens, and when it is closed the boost is prevented from reaching the wastegate. The wastegate will then stay shut even though the boost has risen.

After reprogramming the ECU it will not open the solenoid until a higher boost level has been reached.

There is a section under wastegate here that explains it a bit further..

Turbocharger - Wikipedia, the free encyclopedia