I've always been under the impression that one should not switch from head bolts to head studs without a proper bore using a deck plate.
Looking around the internet, either this has been lost from time itself or it was never really an issue. Has anybody removed their head bolts, installed head studs over a plate, and measured the roundness of the cylinder bores to confirm it is or is not necessary?
Furthermore, I know most of you run iron block v8 engines. what about an all aluminum 4-cyclinder? I would think there would be more of a chance for distortion(despite iron sleeves...), and given the tight tolerances they require compared to a v8, even more important for a proper deck plate / bore before switching from bolts to studs.
And last, I am fairly certain one should never go from main bolts to studs. But just throwing that out there for confirmation as its been 10 years since I built a v8.
I've decided there will be a difference. Of course there is a difference. the real question is, how much of a difference will it make? Maybe leakdown/blowby would be 5% or 0.5% different or maybe skirt wear is 5% different or 0.5% or 0.005% along an axis. And these values would be application specific of course, all engine designs would tolerate differently- and nobody checks the difference, usually we just want to get it spinning.
My prescribed moral would be, do it right if the opportunity is available obviously. But, if you are going to truly require the additional clamping ability that studs provide, use as necessary.