Full groove, 3/4 grove, or 1/2 groove main bearings.

Hello all,

I recently bought a set of King XP main bearings for my small block stroker motor I'm building. Upon getting them I realized there not a full groove bearing. We've always run full groove bearings in our race small blocks with the theory they oiled better. What's every one running for there high horsepower, higher rpm engines? What are your guys thoughts on full groove, 3/4 groove, and 1/2 groove bearings?

Thanks, Mark

3/4 is the best if you can find them. Not a lot of choices for some of the Mopar sizes though so sometimes you just have to live with what you can find.

Any of you guys run the King XP?

If you have factory oil, I always run full groove. You can't get the oil to the rods on time. Never seen one fail because it had a full groove.

Never seen one fail because it did not have full groove--King used to make the HP series with a 3/4 groove--I always liked it but--they have dropped it and now only produce the half groove--they swear they have tested it every which way and can't see any advantage ---I have run every type in every combo you can imagine and have never been able to determine one was better than another--Full groove and loose you see it on the oil pressure gauge--other than that it is all speculation what is going on in there.
I have asked my wife that when I die and am cremated--please toss a little of me down the throat of a badd azz engine running wide open so I can finally see what is going on in there--
I do lots of other brands engines that do not offer anything other than half groove--If there is plenty of clearance and no detonation etc they all come through with flying colors. The nightmare of a "spun" rod bearing keeps many folks awake --they Fear it in some crazy way that just does not line up with the fact that very very few folks ever experience that problem--some racers go an entire career without ever hurting an engine--
Irrational fear of a problem that is very rare --

One thing a groove definitely does is reduce local pressure at the bearing/journal interface.

That's true.

The oiling system is constant flow, for the most part. Except to the rods and the rockers. They get timed oil.

If you spin the guts out of them, and don't groove the cam so some oil gets to the rockers all the time, you can blue some adjusters and things like that.

It's the same with the rods. They get timed oil. The problem is, Chrysler got the timing off. It's not usually an issue at lower RPM's. A full grooved bearing takes a timed oil system and makes it constant flow.

You may not get full pressure to the rods all the time, but you get some oil out there, all the time.

that is why I feed the rockers full time and redrill new holes in the adjuster and pushrod sides of the rocker and on thru to/into the shaft so the holes (.100") line up when the valve is closed so they get fed at that point and I solder shut the OE shaft holes on the adjuster side that are way off and also braze closed, the ones on top and the big access holes on the adjuster sides of the rockers (273 iron rockers)

I just tap a ball of lead shot into the holes that don't line up.

I'm not sure that's a Irrational Fear. IMO, that's the Most common failure, a Spun rod bearing. They spin from lack of crush/clearance or oil. My vote, Full groove for full oiling of the rod bearings. Not a Guarantee, but just extra insurance. 3/4 would be my next pick.