International Lancia Forums

i have a thema turbo 92, my boost does not come in till 3500-4000rpm. is this normal? every other turbo car i have been in it comes in at 2500rpm.

Yes , and it has a two stage boost system which operates dependant on speed and revs.

T o provide an increase in torque under particular operating conditions in turbo charged engines a overboost solenoid is used. When energised this overboost solenoid discharges some of the pressure on the turbos waste gate valve, this greatly increases the engines performance by raising the turbo pressure.
The thema s2 has two overboost solenoids, the first solenoid is not controlled by the ecu but directly suppied by microswitch fitted to the throttle body when the inlet flap is opened to 60 deg. When the first overboost solenoid valve is opened the reduction in pressure on the wastegate valve causes an increase in rpm of the turbo, thus increasing the engines turbocharging pressure. This is maintained throughout the acceleration period.
The second solenoid is energised by the ignition ecu via a second microswitches again mounted on the throttle body when the flap is at 77deg. this second overboost valve is only temporary and is limited to a max time of 30 secs down 2 secs and dependant on turbo pressure below 0.39 bar and speed of 2500 to 5000 rpm. With the second valve open with the first there is a further discharge of pressure on the wastegate which causes a sudden temperary increase of turbo pressure.

So check both thottle switches are working and the turbo dump valve is not leaking and potential switch block on the back of the thottle is ok as well

paul.o.....

can i modify this system to obtain an extra power. i have seen some valvles wich putting them here you can increase the turbo pressure manually.

cam you tell me something in this way.....i want more hp at highs rev.

thanks

You can allways install a bleeder valve. This valve will cheat the Wastegate to find the pressure lower than it actually is so higher turbo pressure will be needed to actuate the wastegate thus the turbo pressure will become higher. A bleder valve is inexpensive and works on the S2. I will cost you around 2$ to 300 $ depending on where you buy. I have used it myself without any problems. Increasing the turbo pressure will probably shorten the life of the motor some. And you always have the risk of something in the motor breaking but i think that up to 220 hk you shuld be fine if the motor is in good condition. And i would recoment you to install a turbo pressure meter before experimenting. When the rest of the motor is standard, the motor will cut the fuel when the presssure gets to high. I think you will get around 220 hk before fuel cut. I you use google you can find plenty about buying, instaling and using the bleeder valve. Good luck.
Villads

PS if you have the money i would suggest a unichip instead for custom fit and smother drive.