was over at JP's today, he was cleaning up a bunch of core heads to be redone, took the opportunity to look at one that was an R1/late V-8 casting number. I'd always wondered why the same casting number was used for an R1 and a regular V-8, yet different reach spark plugs were spec'd for both. I happened to have been helping JP change plugs on his '52 hardtop earlier so there were a handful of spark plugs laying around. I had both J12Ys and H14Ys handy.
First thing I noticed was that the spark plug holes were not at a 90 degree angle to the combustion chamber, so no matter what you do, there's going to be some kind of exposed threads. I'm not sure if it would be better to work this out if you were porting/grinding on the heads or if that would lower compression so much that it would be a net loss.
Secondly, the H14Ys seemed to be a much better fit - darn near perfect toward the outside of the chamber with a little bit of exposed head threads toward the valves. The J12Ys were recessed slightly all around.
What I didn't do, and now wish I did, was lay a steel rule across the gasket surface to see if it hit the electrode on the H14Y or not.
So it seems to me that Studebaker spec'd the J12Ys for one of two reasons with the R-engines... either a) they thought the colder heat range was desirable and they didn't have the option of using a H12Y which as far as I know never existed or b) the flat top piston would have been too close to the ground electrode of the H14Y for comfort. I believe the latter is not the case however as I seem to recall that my R1 engine has some Bosch WR9FC plugs in them, which are roughly equivalent to a H14Y. I used those simply because they were in my old engine, I didn't have any fresh plugs on hand when I went to fire up the new one, and they seem to work OK although I am not sure if I will require a colder plug or not when I actually start driving it.
My suspicion is that if I could find a colder plug with a 7/16" reach (Bosch WR8FC? if it exists?) that would be the "best of both worlds" if in truth the colder heat range is required with the R-motor and might provide a slight advantage in staving off detonation as there wouldn't be the "hot spots" of the exposed head threads that there are with the factory recommended plugs, and it would also push the spark farther into the chamber.
thoughts? Anyone have any evidence one way or another as to whether my reasoning is correct?
nate