I changed the wastegate spring on my MTM chiptunded S4 the other day. The
new spring is a little shorter, but much stiffer. The boost is now 2,6 bar
instead of 2,3 and it comes instantly at very low revs, with an incredible
I bought the spring from Simco, a racing car tuner, who uses these springs
for his own chips. He installed it, and said that he gets a torque of 430Nm
at 2000-2500 rpm, measured on his rolling road. I could not test my car on
his dyno, as my wintertires would heat up and be damaged. After a testdrive
he said that my car probably had the same, 430Nm, which is more than the S4
4.2 and even the RS2!
The car does not get more peak power but that low end torque has made my car
very quick. The accelration is incredible, and I am really amazed how big
difference this little spring did to my car!
Increasing the boost this much is ofcourse getting close to the limit for
knocking (I'm running on 98 leadfree), and running on high boost at low revs
over a period of time may cause heat damage.
But, knowing your car and being sensible in warming up and cooling down the
engine, I consider it safe even with this boost.
92 S4 Avant
95 Yamaha 600 XTE