Heinz, does the answer from your friend also take into account that - in the TI VCT / Sigma engine - the oil has another 'job' to do in that the engine oil pressure also operates the camshaft timing through oil-fed hydraulic actuators.
I would be wary of changing any characteristics of the oil which could impact this cam timing mechanism - unless your friend has factored in this unique feature of the Sigma engine.
Yes there is an influence on the VCT action regarding the oil viscosity. With focus on the viscosity specification, the friends friend who works at Ford USA writes:
..."Too thin is a problem with VCT actuation actually. Oil too thin may not have enough pressure to allow the VCT to actuate properly when it gets hot. It thins out when it is hot and the pump can't create as much oil pressure. Too thick doesn't flow well either. Oil pressure is meaningless without flow. Too thin is a problem with VCT actuation actually. I bet it does work better with 5W40"...
He does not say that a 5W30 is a too thin oil. But you can imagine that e.g. a 5W20 if it is hot and the engine is always used hard it can crack the molecular chain which can result in a sort of "5W10" after a period of time - even faster so if the oil gets its viscosity by a heavier use of additives than a good basic oil. And that would be obviously too thin for a proper working VCT.
(BTW the fact that Ford prefers oils with lowered HTHS values regardless the general hot temp viscosity value (A5 vs. A3 in European terms) should not have any influence to the work of the actuators of the VCT because I think that at the VCT the oil is not so hot to its limits as e.g. at the piston rings).
Now regarding the engine (not only the VCT) it should not harm the Sigma engine to use a higher grade viscosity. Ford recommends normally a 5W20 or 5W30 for the 2.3 Eco boost resp. the 5.0 V8 engines you can download the 2018 service manual in pdf. Ford recommends for track use a Motorcraft (Ford) 5W50 for both of this engines and also for the Shelby Mustang (different manual). You may need slightly more fuel but the engine has a better protection. Thats why Ford recommends it to go up in viscosity when driving hard.
BTW the above mentioned engines have the same VCT mechanism as the 4/4 Sigma engine has.
I like to push my engine and I like high revving when driving the B-roads in a sporty way so I have changed my engine oil to a fully synthetic 5W40 last weekend just to test it.
My first impression is that the engine is less loud (good or bad) and above 5000 rpm the engine is a very small bit more unwillingly revving. After 500 km this unwillingness is almost gone or I am used to it now.
But the big advantage is, and this is not self fulfilling prophecy, that the engine feels much better from 2000 rpm on which I thing it could have really to do with the better working VCT mechanism due to the higher viscosity of the W40 oil. Now the engine feels more so as if there were no VCT at all but a bit more capacity, in other words much more seamless and responsive at any point of the rev band and even significantly more powerful between 3000 rpm and 5000 rpm.
My oil pressure gauge is almost meaningless and the following values cannot be right but I can see a difference. With the thinner oil it showed 1 only when cold and after one hour mostly 0 and maximum 0.5 only when revving very high. With 5W40 it shows around 1,2 when cold and 0.5 when hot and running medium revs up to 1 when revving high. At idle at a red light it goes down to 0 again when hot.
