F4r geometry is that of a pimped up 1800, that's the problem. The Williams engine was a case of trying to cram extra capacity into an 1800 block in the first place then the f4r just copied it. Leaves very little room for an aftermarket builder to manoeuvre.
Xe can go to 88mm easily which means much better valve area than you can ever get in an f4r, and you can go up or down in stroke to then end up either with a mega revvy 300bhp or so 2.0 or a mega torquey 2.5 or anything in between. There is also a taller GM block you can use to get a longer stroke and still have a decent rod ratio.
For a basic competion build of off the shelf forged internals, hot cams etc and 230-240bhp the two are much of a muchness but going further the XE starts to shine.
Xe can go to 88mm easily which means much better valve area than you can ever get in an f4r, and you can go up or down in stroke to then end up either with a mega revvy 300bhp or so 2.0 or a mega torquey 2.5 or anything in between. There is also a taller GM block you can use to get a longer stroke and still have a decent rod ratio.
For a basic competion build of off the shelf forged internals, hot cams etc and 230-240bhp the two are much of a muchness but going further the XE starts to shine.