I agree with Mpampis, when running high power, the hot gas need to get out of the engine as well. With a small turbo meaning turbo with small turbine wheel or too small exhaust, some gas can be trapped in the combustion chamber. This can cause detonation. And it will show in the EGT.
And now I have to be careful as this was the most successful turbo car up to the VW GTI. I have not tried to push the max on my Q4 yet, so I don't have an opinion about the engine's reaction. On the turbo TS 262/7 whp came at 0.75/0.8 bar boost and with 800C EGT. This was with standard NA cams Intake locked.
In this regard I question the "small" exhaust cam in the Q4s. It should be fine for the "normal" power up to 250hp. But even then I am for Steve Webb's suggestion to use the intake cam on the exhaust side and a NA Lancia cam on the intake. This will make the same power at lower boost and improve the gasflow out of the engine, be more safe with an good exhaust.
I have seen pistons from a turbo car with a few spots that show melting on top of the piston. The rest of the piston looked fine, but the shape of the piston changed and it was loose in the sleeve. Unfortunately the car did not have a EGT gauge on.
I am waiting for Guy Croft's book as he has a defnite oppinion about the ratio between intake and exhaust cams on turbo cars. Until then I stand by my opinion.
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