For the supercharged models, what was the difference between these years when the 4.2 eventually was marketed as 400hp? Smaller pulley?

Interested in 'making' my 2005 an iteration with 400hp if it's wholly reasonable and unlikely to break anything. Already eyeing a Mina Gallery exhaust setup (and maybe high-flow catalytic converters if they exist for the X350) in the next couple years regardless, but which might achieve this alone without messing with pulleys and ugly cold air induction kits.

 

Different engine management system and variable engine timing

 

VVT or variable valve timing. There may be small differences in other details on the engine.
The 2006 and 2007 MY are actually x356 models. The big difference is the car system management. The buss and protocols changed. Little more up to date.

 

I'm glad my 05 doesn't have VVT, for 10 hp that's a fair trade. I say this due to frequently having trouble with high mileage VVT equipped cars. I've seen it enough to just as soon not have it in the first place. I attribute this to fairly close tolerances to make it work. The only thing that cured my sons 5.4 Triton was a new oil pump. He went for high volume just to put it to bed for once and for all. This was after he changed all the chains, idlers, and control valves, and it didn't help at all.

 

there are no vvt problems on these cars. 230k on an 06 zero noise

 

The VVT offers gain in power from low end to redline. Non VVT have the cams dialed for some rpm range. VVT allows for optimizing a broader rpm range.
I would think the NA engines show the added power more than the supercharged engines. That blower can mask snn my all changes.
And 230k is great. Most modern cars should last this long. My son sold a 2005 Ford Focus with 235k year. Leaked in a few places but did not burn oil. Lasted 100k more than I expected.

 

Also a 420HP rating for the 4.2L SC V-8 in the later XK's. Was told it was due to twin air boxes instead of the earlier single air box set up.
The addition of VVT was not for power but emissions.
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