Just fired up my friend's 396 LT1 motor a little while ago. We were running Quaker State 10W40 dino oil. We switched to 10W40 synthetic but his oil pressure dropped 5 psi.

Should he run 15W50 or 20W50 to bring it back up?

 

YES maybe 20/50.A lot of people on the board have a problem with the synthetic and for some reason don't want to go to a 50W --like it is a stigma to run a big number.

 

Synthetics tend to flow better than conventional, so that could contribute to a drop in pressure using the same weight. This actually isn't a bad thing (to a point of course)... means its flowing better. The brand of synthetic you use can matter, since some synthetics run a little thinner than others, even if they're listed as the same weight.

Oh, and the oil filter contributes to the pressure as well... so if you switched brands of filters, that can change the pressure a few psi.

Ultimately, if you're not happy with the oil pressure, you can try a thicker weight oil, or try switching brands.

 

No.

Pressure is a function of resistance to flow and the synthetic oils have less resistance, hence; all other things being equal, they will have lower oil pressure.

In fact, if that motor is built to similar or tigher tolerances as a factory LT1, then a 10w-30 or even a 5w-30 would be better. It would also cut your pumping losses, although that's not really a huge number in the first place.

People get spooked about the lower pressure you get with synthetic, but with the long chain polymers found in synthetic, you actually get better protection at lower pressures.

You should make sure that you have 10lbs at idle and another 10lbs per 1000rpm, up to at least 30lbs. If you have at least that much, you'll be fine.

 

The lower pressure will not be a problem. I have seen oil pressure rise due to (really) dirty oil filters. Even though the pressure is higher this is not the best situation.

 

It has looser clearances. He is leaning towards running Mobil 1 20W50 in hot weather and 15W50 in cooler weather just for the piece of mind but wants to make sure he doesn't hurt anything.

 

It won't hurt anything.Just gives your bearings more "cushion" when its called for.
Some of my engines run 100PSI out the back door with 20W Royal Purple but are built to do that and are trailer queens.

 

OK, how much pressure does he actually HAVE, and at what rpms?

 

I used to run 10w30 valvoline since its what my dad would stock on the shelf but decided id try that 0w40 M1 that ppl rave about. What I noticed is that my oil pressure is actually HIGHER than it was before.. about 5 psi all around and at WOT id occasionaly see the pressure gauge bounce around a little at higher RPMs where now it stays pegged on 45 or so all the way to 6k. Only downside is that I believe it might burning a little.

 

I thought the general consensus was to avoid synethic oil for the first 1,000 miles to properly break in the rotating assembly.

 

He has 20 psi at idle.

He has 500 miles on the motor right now. He wants to switch to synthetic now.

 

20 PSI at idle with another 10 psi per 1000 rpm is fine.

BTW, it IS usually suggested to use Dino oil until the engine is completely broken in.

 

IMO 20PSI is low for a built 396.
Might be OK for a stocker but will cause early wear in a performance engine.
I like to see 30@900-1000RPM's and 60+ at 6000RPM's on a built engine.