Hi Guys:
I'm breaking in my 400 SBC; it has 400 size mains and 350 size crankpins. Bearing clearances on both rods/mains are between .0026 and .0029, and piston to wall is .006 at the center of the skirts. It's a bracket motor.
With 10-30 Comp Cams "break-in" oil, it has excellent oil pressure, even when hot. So this begs the question: Should I consider just racing it with 10-30 in the motor, or revert it to the 20-50 I've run forever? What do you guys think?
Thanks.

with your description, in my experience, the 10/30 will be a good choice

10w-30

Used to run 10w/30

Went to 20w/50 3 years ago last year for refresh motor never looked so good. I feel oil is more stable and takes more of a beating than thinner stuff...

Is all good... Really based on clearences and preferences. I change mine every 20-30 runs. 9 qrts with accumulator.

Bought 140 some quarts at advanced auto for 50cents each... Just by asking nice! Actually just joking with the guy and he said sure it's not a big mover with today's cars. Loaded up every quart he had in the store.

Based on you guess of clearances, I would say 10-30w

I use Mobil 1 10-30. I really thought that 50 stuff was over in the 70s--old school

I always prefer the heavier viscosity.Like 15w40.
Not knocking the 10w30. I don't care for the thin pour rate.. Etc. Mine at .0025 and .0027 works just fine. The 20/50 you ran for ever with no ado issues? All preference.

Depends on how tight the clearances are. Looser clearances you run a heavier oil but a heavier oil takes more power to pump. On one of my motors I picked up around .05 IIRC by going from 20-50 to 10-30 oil. A thinner oil also drains back into the oil pan faster, on one of my motors by the end of the run much of the oil was up top at end of run and if I stood on the brakes the oil pressure would drop big time with the heavy oil. Thinner oil no problem so I recommend the lighter oil if possible. I would not feel comfortable using any lighter oil than 10-30 though.

By the way I think the oiling system on most motors could be improved for the oil to drain back better. But that is a different issue.

10-30

quote:

Originally posted by Curly1:
Depends on how tight the clearances are. Looser clearances you run a heavier oil but a heavier oil takes more power to pump. On one of my motors I picked up around .05 IIRC by going from 20-50 to 10-30 oil. A thinner oil also drains back into the oil pan faster, on one of my motors by the end of the run much of the oil was up top at end of run and if I stood on the brakes the oil pressure would drop big time with the heavy oil. Thinner oil no problem so I recommend the lighter oil if possible. I would not feel comfortable using any lighter oil than 10-30 though.

By the way I think the oiling system on most motors could be improved for the oil to drain back better. But that is a different issue.

I had the same top end issue on the brakes. I used to click the engine off and restart on the return road. For a bracket car that is stupid. Went from 15W/50 to 10W/30, both Mobil 1, no more issues on the brakes, engine still looked perfect at 400-500 passes (1/4 mile). Engine builder said keep using what I am using, everything was perfect.

PS: I am doubled-entered every time I race, and some classes are back to back with less than 10 minutes between runs, no issues with the 10W/30.

Thick oils are gone with the 60's....
I've run 10-30 or 5-30 oils for many years now.
In naturally aspirated non-endurance applications easy flow is more important than viscosity.
The oil is the coolant for your rotating assembly and valvetrain, thin oil exchanges heat better and flows more easily.
Thick oil is hard on your oil pump drive / camshaft / distributor gear for no benefit.

In extreme applications clearances are wider and the resistance to shock loads is necessary, so thick oil is good.

To the OP, at your clearances 10w30 is an excellent choice, not knowing what, if any, oil control efforts you've done. (windage trays, baffles, trap doors, which style pickup, crank wiper,etc., etc......

Well, with both oils my bearings always looked perfect for what that is worth but it did bother me seeing oil pressure take a dump when I hit the brakes.

Thicker oils are not gone. There is just a proper function for them. But and engine with less than .003 clearances is not a place for them. The 10-30 is proper.

I only put 20W-50 in things that knock or smoke. Take care. Tom Worthington

50w for me

Ever since I went from a sbc to a BBC in my present car back in 2001, I've used 25-50 pennzoil racing oil. So far not one problem with the 461,468, or a 540 with just a hv77 pump, still maintains 45 psi at 180 degs at idle in shutdown. They say racing oil has the additives that regular oil doesn't or was taken out.

Great topic that requires some thought.

Therefore my following comments/ opinions are for gas engines, Alky and nitro engines require heavier oils due in part to load rates and fuel contamination of the oil.

It takes more power to pump heavier oil. Give some thought to what is required to move that heavier oil through the small oil gallies and bearing clearances in the engine. You can certainly load up a lot of oil in the valve cover and lifter galley area which reduces/lowers the amount of oil around the oil pump pick-up, the recovery rate at higher RPM is slower.

Heavier oil creates thicker windage in the oil pan, that also creates a power loss. Think about like this, you are standing next to a bathtub filled with water and you are trying to swing a broom through the water, now think about this process but the tub is now filled with oil. That “broom” in this case would be the crank and rods.

Thinner oil can penetrate small areas faster like roller lifters and roller rockers, it also can evacuate debris faster. If you have experienced a lifter failure perhaps you might consider running a lighter weight oil.

Heavier oil “loads” light weight piston ring packages. Late model and many foreign cars specifically recommend using lighter weight oil because it leads to premature ring failure and engine smoking. If you are using a .043/.043- 3mm oil ring package stay with the lighter weight oil. It may be OK with a 1/16- 1/16 (or heavier ring sets) but not so well with the lighter sets.

The quality and composition of the oil is more important, that discounted “deal” at your local Parts Store may not be your best option. Look at what is in that oil.

Just trying to give people some things to consider, not wanting to start a war of words.

Bob

The boiling point of Methanol is 148 degrees. It certainly was not doing you any good. As the temperature goes up the fuel expands. So you will have fewer BTU's ( energy contained) per volume. It's best to keep it as cool as reasonably possible.

Go on rehermorrison website and read the info there , it speaks for itself