Many experts suggest installing the EGT probe in the exhaust manifold before the turbo for three reasons:
1) The farther the EGT probe is away from the manifold, the greater the lag time response to dynamic changes in temperature.
2) Exhaust gas will cool as it travels away from the manifold which will result in lower EGT readings. EGT readings can drop over 200 degrees after the turbo.
3) Depending on the balance of your setup, the turbo itself may act as a restriction. Exhaust gas can build up excess heat before the turbo, while post-turbo Exhaust gas temperatures can be lower as a result of faster cooling due to reduced exhaust flow. This can result in higher temperatures between the motor & the turbo, yet temperature readings after the turbo will read cooler.
NOTE 1: Should there be doubt concerning specific placement of the probe, you should check with the engine manufacturer, your engine builder, or your Tuner.
NOTE 2: When installing the EGT probe BE SURE TO CLEAN ALL METAL FILINGS out of the exhaust manifold. Metal filings can cause damage to the turbo impellor if they go through a spinning turbo.
