On a small block the difference is about .0003-.0015 depending on the position you measure when you check the finished bore diameter near the head bolt holes without a head in place. The problem with not using the plate is the top of the bore where the rings are sealing has the highest pressures. That change in bore wall shape in that area can make it impossible for the rings to properly seal near the bolts. The distortion can also be simulated using some spacers and the same fasteners you're using for the heads, plus the same type of gasket. The load of the fastener will deform the iron around it. Remember the block is not a solid casting. It's hollow. So as you pull or distort one spot, the adjacent areas deform as well. The amount of deformation depends on the material, the fastener, and the load. Big blocks don't deform as much because they have 5 head bolts per hole and are torqued at 10 foot pounds less. So the load is more evenly distributed around the bore. Small blocks move a lot IMO.
hi, the only drawback, is you have to select the head gasket and it's the one you will use always. also, the mains have to be torqued with hone plate for correct results!! usually small blocks pull .001 -.003 depending on casting. another thing, don't torque at 95 #, use 85 # with moly lube, has less distortion and same clamping power. after the plate is torqued, the block needs to set for 12-24 hours to settle at final shape, then hone it. just food for thought. just bolting them on then hone right away gives very poor results.
Yup. This is why just the honing costs me "so much". The only way to get quality is know what it is and use a shop that cares enough to produce it. Interestingly, just by changing the wall finish the shop I use has found 40+hp on an engine that used to make 455hp with a Nascar 2bbl. The honing is that important.