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Discussion Starter · #1 ·
Wanted to get some thoughts on what oil to use for this application. For the past 20 years I've used nothing but Valvoline 10W30 conventional in all my SBC motors. It's worked just fine.

Now I've got this SBC 383 motor in a road race car. It's a fresh build with stock bearing clearances. Rev limiter is set to 6600 RPM but I expect to shift at 6200. So not a super high revving motor. Forged pistons, roller cam, aluminum heads. No oil cooler (yet). Very big radiator and Stewart Stage 2 pump.

I've got about 35 miles (10 laps) on the motor so far and need to do an oil change after replacing the timing cover due to a leak. My next event is at COTA on July 25th. It'll be very hot that day (over 100 degrees) and I'll have about 5 sessions of 30 minutes each.

I was thinking of switching to synthetic to better handle the heat. But then I've read that I should wait longer on the fresh build before switching to synthetic. I've also been reading that race motors can use something like 20W50. This is not a street car so I have plenty of time to let it warm up before ripping on it.

Thoughts?
 

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Race it, Don't rice it!
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The 9000 is Full Syn and the 7000 is Partial Syn.
You don't need anything more than 10/40 in a SBC, Ever.

Valvoline VR1 Racing and Penn Grade are also good.

I have no idea where the idea of Full Syn is not to be used in a fresh engine came from but it's internet garbage.
Way back in the day, when Synthetics were relatively new, leaks would sometimes show up because the molcules are smaller and would weep out seals and gaskets. Also, 5/64 cast ring packs and bad hone jobs are pretty much gone in favor for better rings and better hone patterns and so the issues with Synthetics are pretty much all gone to the bayou. The internet loves to hang onto old technology so perhaps the regurgitation of half wrong information is where it started I don't know.
 

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Do you have an oil cooler?
Do you have an oil temp gage?
Long pulls in hot weather for a significant duration might require something like 20/50 oil. That used to be the norm in short track late models running a few hundred laps at a time, especially when everyone was wet sump and no cooler.
 

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Well, with no oil cooler you're going to get into trouble quickly. A synthetic for sure and you may want to go with a heavy weight just to try and starve off some of the heat thinning you will get. Honestly I would take an oil change with you and then see what it looks like after each run - if the oil starts to get dark on you that's a sure sign that it's losing the battle against heat and you should change it out. Another indicator will be oil pressure. I can tell in my dragster that I need to change the oil when I drop 5 pounds at warm idle. It's normally 65 psi on fresh oil but as soon as I start seeing 60 psi, I replace it.
 

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Discussion Starter · #5 ·
I have an oil temp gauge so I can keep an eye on it while running the car.

On the subject of synthetic oil and a good cylinder hone... This was a garage rebuild on a block that was in pretty good shape where all it got was a dingle ball hone and a fresh set of rings in the new pistons. Not sure if that makes a huge difference in the choice between conventional and synthetic oil.
 

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I’d recommend a full synthetic the molecules tolerate more heat for longer periods of time.

Viscosity is something of an experiment, to some extent it is sensitive to crankshaft bearing clearances and pump volume, wide clearances bleed more oil than tight, a high volume pump pushes more oil through the system so even with high side bearing clearances it keeps them lubricated. A high volume pump on normal clearances will unless yo run a high pressure spring on the bypass will with normal bypass will be constantly looping oil back to the inlet side. This heats the oil unnecessarily which isn’t good for the oil and wastes power on the pump moving more oil than is needed. These things said because pump flow is related to pump speed not engine need you can’t optimize this to the best practice for all possible conditions.

My major concern is wrong gear cornering where the gear is too high and engine speed to low for the crankshaft loading. In this case the loading on the bearings is high but pump output is low. So for road course in particular and circle track racing in general I tend to size oil viscosity and pump volume around this contingency which speaks to a higher viscosity oil with a high volume pump. Which usually means like a 15-40, 20-40 or a 20-50 the latter for maxed out bering clearances and a bulky shifting transmission. For tight clearances and a fast, smooth and predictable transmission I think 10-30 is fine.

A part of this is that the oil is cooling the bearings and the underside of the pistons so moving a lot of oil is important in getting the heat out.

Bogie
 

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Discussion Starter · #7 · (Edited)
Thanks Bogie!

I'm running a standard Melling M155 oil pump. Bearing clearances should be "standard". I didn't set the motor up loose or anything like that. On the transmission, I'm running a 4 speed dog ring that I'm just learning how to shift. I expect to not be downshifting enough and end up coming out of the corner at low RPM (~2500) while I'm figuring out how to drive this thing.
 

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How many quarts is the pan? Most defiantly put a cooler on the engine. I ran a Boss 302 in SCCA many years ago. Seven quart pan, oil cooler and after 3 - 4 laps on a nine turn 1.9 mile course the oil temp was up in the 250 range running in the 5500 - 7500 RPM range. It held steady during the many 50 lap competitions. That was back in the day before synthetics were widely known. I ran Valvoline 20W50 racing oil.

With respect to the synthetic I would start with 10W40 and look closely at temps and pressure during a run. Don't worry about burning oil as you will be running in the 100 - 200 mile range and I'm sure all the systems and fluids will be checked after each run. I did oil changes along with filter after each weekend. The base I was at had an oil chemistry lab for the aircraft engines so the guys there did the oil annalists on my drain oil to make sure the internals were still behaving.
 

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As far as viscosity is concerned, it needs to match pressures as a rough guide. Too thin and it will squeeze out of the bearing spaces too easily. Too thick and it will have trouble getting in there and pressures will be so high that it just opens the bypass. I would think 10w30 should be fine.
 

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Get some real racing oil, the stuff that says it's not for highway use, it has better chemistry for the abuse you are going to throw at it. Mobil 1 Racing, Penngrade and Schaffer are the ones I use. With wet sump I am always concerned with oil control---sucking air into the oil pump is what causes the rods to exit the block.
 

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I pretty much run Delo 20-50 or 15-40 in everything that doesn’t require 2 cycle or bar oil. There are excursions to Rotella and Delvac. I haven’t used Valvoline or any other fancy brand of race oil in 50-60 years I guess.

Bogie
 
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