the 3.6 turbo head I have are a completely different casting than the N/A heads. The heads are designed taller with an extra fin, the cylinders are also approx 3-4 mm shorter. This moves the sealing surface farther away from the combustion process. Notice the extra fin and "deep" relief. The piston deck height is approx 3-4mm positive... meaning the piston protrudes out of the cylinder.

Here are some pics of one that failed. 3.8 turbo with, when set to the performance setting, required 98 octane. This one was ran with 91.

http://forums.pelicanparts.com/uploa...1290357058.jpg
http://forums.pelicanparts.com/uploa...1290357080.jpg