I don't believe that the hole diameter would have any effect whatsoever as long as the spray pattern was not affected. since it apparently is not with the smaller hole, then there should be no change with the larger hole. It's not like a depth change either, as the outer ring is the same thickness and is the ultimate travel stop. What I was getting at is the quality of seal on the injector face I have had a few seal failures even though they were properly torqued. That seemed to disappear after I lapped the nozzle faces so the slightest amount of irregularity seems to be enough to cause failure. I was wondering if the larger diameter hole somehow provided a better seal and if so, why not use them instead? I don't have a picture to post but they look even larger than the "ford" ones shown.
I find it astounding that anything has to be lapped as there should be no movement after the initial torque. I could see some smearing form assembly but the marking looks more like erosion related. Nonetheless, it happens and apparently the trick set-up is to get them spiffy smooth so that there is an almost molecular bond between the parts. (see wringing in a machinist book). I have always heard that it was a felony to re-use the seals. I thought that like head bolts, that once used, that was it. I didn't think that there was any spring back and regardless, how would you know? If you ran them & checked again, you would know if they had worked or not but would you re-re-use them again? They're only a buck apiece. There's a point where you can be too cheap. As for annular contact pressure, your first picture shows different contact points so it seems that there is variation between "identical" parts. I agree about the actual psi at the contact point and a smaller hole would have a higher pressure and therefore a better seal. So why does Mercedes use the bigger one. If the V-dub ones are better for the aforementioned reasons, then why not standardize? Now there's a question about heat shielding. (Is it a shield or a seal?) There is an obvious dead air space but how much temperature differential is there? How much change is there between big hole and little hole nozzles? None of the nozzles get high enough to effect any metallurgical changes so is this a detriment? I'd opt for the hotter one myself. Hotter fuel has better atomization and better burning. I run my SVO at 170* and there's no difference in performance but anything below 140* ran like crap. This may all be invalid if there's an appreciable difference between the two pre-chambers. I don't have that information. Maybe next time I'll just do it and see what happens.