Not to start a keyboard war but I’m curious as to what viscosity everyone runs in their race car and why. I’ve been involved in some discussions related to rpm, engine water temp, fuel preferences, 1/8 mile vs 1/4 mile, cold starts, outside air temp and so on. The discussion started relating to cold starts and how hard it may be on the engine with a 20/50 oil and oil system components, also gas vs alcohol related to water temp, and of course the hp differences related to viscosity…what say the masses…

10W-30 for me. I want it to flow quickly as soon as possible.
If the car has sat for a length of time, I plug in the pan heater, though the car has never seen temps under the high 40s.
I never have oil pressure or bearing problems.

[quote=RapidusMaximus]Not to start a keyboard war but I’m curious as to what viscosity everyone runs in their race car and why. I’ve been involved in some discussions related to rpm, engine water temp, fuel preferences, 1/8 mile vs 1/4 mile, cold starts, outside air temp and so on. The discussion started relating to cold starts and how hard it may be on the engine with a 20/50 oil and oil system components, also gas vs alcohol related to water temp, and of course the hp differences related to viscosity…what say the masses… [/quot

About the only thing that matters in terms of viscosity for race engines is bearing clearance. Typically race engines only operate in warmer temps and the engines are usually up to temp before max power is applied so that leaves bearing clearances as the primary issue. Modern engine design has trended towards tighter clearances and lighter oil for awhile now. Lots of "high tech" motors are using 0 weight oils. Old school guys still go with wider clearances and heavy oils.

I like and use 5w20W straight petroleum based Valvoline oil in all my street builds under 650 HP, all out drag race motors or HP street motors over 650 HP I use Valvoline VR10w30wt racing oil, I quit using 20w50 and 10w40 Wt. years ago after testing them on a series of engine dyno tests.
As AndyF mentioned oil does two things in our motors, it lubricates and cools, 5W20 weight will start doing its job a lot sooner, building and flowing under pressure, than thicker mixes will

Been running 10w30 for some time on Methanol and double entry. As stated before bearing clearance should dictate this. No reason to sling molasses when near water can do the trick.

I run gasoline. 2.200" rod .0028" clearance. 2.75" mains .0030" clearance. 5w25 JR1 synthetic. Oil temp generally stays about 150 at the end of the run. Back to back may get towards 190. My feeling is it is impossible to be to thin for cold starts.
Doug

I still go w/ the old school train of thought b/c it's served me well. I use 20w50 in my hemi b/c the clearances are on the loose side. Same w/ my 440.
My BB chevy is a little tighter, so it gets 10w30.
All using Valvoline VR1 conventional race oil.

In my drag race engine, I started using 10W-30 maybe 15 years ago. That engine had an oil temperature sensor in the pan, and it was hard to get heat in the oil. Even once the water temp was 170, the oil temp was cold. It did heat up some during the run, but never got "hot" and since it was shut off and waiting for the next round, the oil in the pan got cold again. Water temp and oil temp were very different in an engine that does not run for long. Street driven was a completely different story.

I found that 10W-30 produced less ET variation in the later rounds when there was less time between rounds. Compared to the 10W-40 I used to run.

Interesting, any concerns about methanol thinning the 10/30 too much? Do you run a vacuum pump? How much water/oil/ methanol do you get into your catch tank? Thanks

Spot on! it's hard to get the oil at a good operating temp in a drag engine application. And nearly impossible to 'overtemp' the oil unless something is going wrong.

GM recommends Mobil 1 0w-50 for their 632 crate engines. The owner is used to running 20w-50 in his race engines. I tell the guy to run what the GM engineers tell him to run but he isn't super comfortable with it.

A joke: the 1st number in a multi-viscosity, or the only number in single viscosity is the time in seconds it takes when cranking a cold engine for oil pressure to reach the last connecting rod.
20W50: 20 seconds.

That's what I have been running for a few years now. I run alky. If a lot of racers installed oil temp gauges and actually seen how hot the oil really gets they wouldn't be running syrup for oil.

I ran an oil temp sensor in my Duster. It takes a long time for oil to heat up. Usually takes about 10 miles of driving before oil is up to temp. Oil doesn't get warm in the pits or driving to the staging lanes.

What was the oil temp when it finally came up and stabilized?

Just comes down to every build is different. When I ran the cast crank/filled stock block with the diaper. It had a lot of bearing clearance (.0035 on mains), and with the filled block/diaper the oil would run hot.

After the first pass of the day it was always in the 180+ range, and that was with an oil cooler on the car.

I found when I tried thin oil the oil pressure would be uncomfortably low, so it always had thick syrup in it for those reasons.

Depends on the load and ambient. Driving around town oil temp is 150 to 180 depending on air temp. Freeway usually 180. Climbing a long hill or hammering on the engine for more than a minute spikes the oil temp pretty quickly.

Clearances weren't mentioned in the OP and that'd critical in the decision making.

Yeah, didn’t mention clearances mainly because I figured most race engine builders shoot for close to the relatively same clearances .002-.004 but I may be off base, I kinda assumed that anyway , it’s a really good point, I’m not smart enough to go down the rabbit hole of bearing clearances and viscosity relationships…lol

Thank you. One more if you don’t mind. When the temp went up with load, did it come back down to where it was or did it stay up where it was when the load was the greatest? Also, if it came down about how long did it take?

I snuck two in there.

TIA