Well, I've got my motor back in the boat.  Set the timing and ran in the cam.  All this was done with 20w50 Valvoline oil.  Now I am wondering, is this heavy weight oil really necessary on a pleasure jet boat?  I'm not going to be out racing WOT.  Yes, I might jump on it once in a while for very short spurts but, wouldn't something like 10w40 or even 10w30 work just fine?  This is a 460 BBF that's .30 over and nothing more than a mid-grade gas motor.

Thanks,
Greg

Did I really just cook up a batch of popcorn for nothing?

the weight of oil will be determined by your bearing clearances, so what you are asking there is not enough info about your build. if you did not build it ask your builder

Ralph,  What numbers should I be looking for?  I think he said something about .060?  Does that sound about right?

you should be looking for his phone # if your bearing clearances are 0.60

I'd hope .060 is in reference to a piston bore size, bearing clearances should be in the .002 to .003 range.  I ran 10-30 Mobil 1 in my jet (SBC, I know, but the boat came with it) for the better part of 15 years.  I ran 15-50 when I first went to synthetic, but switched to the thinner oil after a couple years.  The bottom end was stock GM, every time I had the pan off, which was only a few times, I took the liberty of checking a couple bearings and they always looked mint, and in fact that engine was still running strong when I pulled it over the winter and replaced it with stroker small block, which will get 10-30 synthetic after I get some hours breakng it in. I had no difference in oil pressure between the 2 weights.  I have a FE powered Mustang with some pretty loose bearing clearances and if I run 10-30 in that I lose about 10 psi of pressure and it's noisy, so I have to stick with 15-40 dino oil.  Me personally, I'd give the thinner oil a shot and if your happy with the pressure on a long run when it's hot use it, else go back the the thicker stuff. 

If your operating your mild engine build in typical jet boat fashion and have 80 psi with 20w-50 pertroleum based motor oil, then i would say that you can try some 10w-40 and see what that does for your oil pressure.  80 psi is acceptable oil pressure and most people might tell you to stick with it.  No argument there; frankly 70 psi is perfectly fine too in a mild build and this is why you might try the 10w-40.

Also, things may change in a few months...beware that during hot peak summer days you just might find that twenty-hour-old 10w-40 petroleum based motor oil just isn't cutting it anymore and your oil pressure is lower than you may like to see.  Adjust accordingly...be it stepping back up to  20w-50 or maybe synthetic 10w-40 (after a thorough break-in), etc.

In short, for a mild rebuilder 460 with carb, intake, small cam, etc, I wouldn't want to see anything over the 80 psi that you have.

LO

Thanks all for the input.  After reading everything several times.  I'm headed out to get me a case of 10W-40 fossil oil and see what happens.  I think I'll do several oil changes over this summer just to keep everything clean while breaking in.  I've got a big az magnet stuck to the oil pan and another on the oil filter.  When I pull the motor to do the hull restoration, I'll drop the pan and see if I've collected anything.

Thanks again,
Greg