OK I'm going test you then.
Calculate the et on these:

link doesn't work...

If the wheel is wider you will need a lower offset, not higher.

Check this: http://www.1010tires.com/WheelOffsetCalculator.asp

Your standard wheels have 53 offset so it will be highly improbable to be able to fit Porsche brakes with 60 offset.

No, it's the other way around. Try it with the calculator you sent me: the 8.5 inch rim "sticks out 8mm further" than the 7.5 inch rim. If the outside of the rim sticks 8mm further out, that's an extra 8mm of clearance from the caliper.

If a 7.5 inch rim clears the caliper with a 48 offset, an 8.5 inch rim will clear the caliper with a 60 offset.

:brickwall
How about this: the gap between the spokes and the caliper is NOT changing. The wheel rim is either moving inward and hitting the strut (et number to big), or outward and sticking out past the arches (et number too small).

You still disagree??

Run the numbers at the above link.

How on earth are you going to have more caliper clearance if the wheel is retracted from the outside by 1mm?!

Original wheels: 8 inches ET53
The wheels you claim will fit: 8.5 inches ET60

Inner clearance: 13mm less
Outer clearance: Retract by 1mm

Besides you will most probably hit the struts having 13mm less clearance.

No, that's not the point. Someone else on this thread has used 7.5" ET rims with the Porsche brakes. All I said is that that is equivalent to about ET60 on an 8.5 inch rim.

Everyone lets just give up, the op obviously knows better :)

7.5" what ET is equivalent to what and how did you arrive at this conclusion?

Sorry, I realize I'm being a bit slow here, just trying to get my head around this.

But my point is this: a 7.5" ET48 rim gives the same brake caliper clearance as an 8.5" ET 60 rim.

So, depending on the design of the rim, if a 7.5" ET48 rim fits over the Porsche caliper, an 8.5" ET53 rim should fit easily.

Try it and if you scratch the heck out of the calipers then you'll realize what everyone is trying to tell you is correct.

If they fit and don't damage the calipers, everyone else is wrong.

Simple

I think we're almost there. So it's an 1" wider. 8mm more rim on the outside, but 18mm more rim on the inside. It won't fit on your car the the inner wheel rim would hit the strut.

I run 8.5" rims on my car. They are ET45 and there's not much caliper clearance.
My previous rims were ET48 and were on the limit. An ET60 wouldn't work.