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What factors do you use to determine oil viscosity?

Posted By: BradH

What factors do you use to determine oil viscosity? - 09/15/11 06:14 PM

What factors do you use to determine the appropriate oil viscosity to use in your race (either track-only or street/strip, etc.) engine?

- Bearing clearances?
- Engine displacement?
- RPM range?
- HP expectation?
- Valve train type (e.g. flat tappet vs. roller)?
- Oil system design / volume?
- Water and/or engine oil temperature?
- Short-duration vs. endurance-type usage?
- What the factory manual says?
- What your engine builder told you to use?
- What the guy who beat you last time uses?
- What your sponsor gave you a case of?
Posted By: Crizila

Re: What factors do you use to determine oil viscosity? - 09/15/11 06:50 PM

The last 2!
Posted By: 440Jim

Re: What factors do you use to determine oil viscosity? - 09/15/11 06:59 PM

I am not the authority on this, but my 2-cents:

- Engine oil temperature
- Bearing clearances
- Oil system design / volume
- Valve train type (e.g. flat tappet vs. roller)
- HP expectation (ie bearing load)
Posted By: AndyF

Re: What factors do you use to determine oil viscosity? - 09/15/11 08:57 PM

An engr at an oil firm told me that engines want 30 wt oil which is 210 degrees. If it is colder than that then use a lighter oil. Heavier oil is used in special circumstances.
Posted By: dOc !

Re: What factors do you use to determine oil viscosity? - 09/15/11 09:41 PM

Quote:

I am not the authority on this, but my 2-cents:

- Engine oil temperature
- Bearing clearances
- Oil system design / volume
- Valve train type (e.g. flat tappet vs. roller)
- HP expectation (ie bearing load)



....AND rod side clearance
Posted By: ahy

Re: What factors do you use to determine oil viscosity? - 09/16/11 01:17 AM

To get in the ballpark, bearing clearance and type as well as oil pump (std, high volume). Also planned use. To fine tune, I use hot oil pressure. I prefer to see at least 20 psi at idle and a steady regulated pressure over 2000 RPM.

On my stuff, I broke in with 10W30. Hot oil pressure was lower than I liked so I switched to 15W-40 and all is well.

With performance bearing clearances and full groove main bearings mine likes a little heavier oil. Also, I street drive mine and it can see extended hot weather idling in traffic from time to time... I didn't want to have to worry about the cam/lifters and top end getting enough oil in that situation. If it were race only I probably would have stayed with 10W30 for the slight performance gain.
Posted By: Blusmbl

Re: What factors do you use to determine oil viscosity? - 09/16/11 02:37 AM

Engines that have rod/crank bearings undersized for the expected load (boost on an original n/a motor is a good example of this) will require a heavier weight oil.

I'd consider expected oil temp & bearing clearance the other critical factors.
Posted By: Cab_Burge

Re: What factors do you use to determine oil viscosity? - 09/16/11 06:28 AM

MY personel N/A drag race pump gas 5W20WT Valvoline non synthetic, same on the street High output(above 800 HP) drag race motor 10W30WT or 15w40 or 25W50WT Pennzsoil racing oil ,depending on the customers desires
Posted By: Bob_Coomer

Re: What factors do you use to determine oil viscosity? - 09/16/11 07:32 AM

My
I dont consider Oil Viscosity when I set bearing clearance, so bearing clearance or any other bottom end spec shouldnt be a factor for selecting Oil.
If you have 100 PSI at idle with thick oil, its a screw up anyways, and should be addressed, about 30% more oil pressure than needed.
I run thicker oil for added protecting from "break down" I dont run the zero weight oil, and very light oil. Sorry but a 1% increase in performance isnt worth it.
I try to run 15W-50.
This oil has been around a long time, and is the best I have tried. I will run a Semi Synthetic on occasion.
Great stuff here.
Run a Accumulator, it will provide more protection than anything else.
http://www.schaefferoil.com/
.
.
Posted By: BradH

Re: What factors do you use to determine oil viscosity? - 09/16/11 04:26 PM

Quote:

I am not the authority on this, but my 2-cents:

- Engine oil temperature
- Bearing clearances
- Oil system design / volume
- Valve train type (e.g. flat tappet vs. roller)
- HP expectation (ie bearing load)


And I'll mention that I'd never really thought about how some of those factors really play into this until seeing how the Joe Gibbs racing oils are partly defined in their application specs by things like bearing clearance and oil temps.

The other thing which rarely seems to come up is what the High-Temp/High-Shear (HTHS) requirement is. There's a pretty strong correlation between higher HTHS values (e.g. > 5) and wear reduction on highly stressed/loaded components, yet it's not a commonly advertised rating. Part of that may be that the best HTHS values I've seen all come from 50-type wt oils (15w50, 20w50, straight 50 wt) and dropping down to 30 or 40 grade oils always shows a significant reduction in the HTHS ratings.

For example, I pulled these from the Brad Penn product spec sheet:

HTHS @ 150*C, cP
0w30 - 3.38
10w40 - 4.23
20w50 - 6.20
Posted By: BradH

Re: What factors do you use to determine oil viscosity? - 09/16/11 07:27 PM

Quote:

... Joe Gibbs racing oils are partly defined in their application specs by things like bearing clearance and oil temps.


Stuff from Joe Gibbs Driven web site's Products pages:

XP3 (10W-30) Synthetic
- <List of various small-block competition series & engines...>
- Engines with clearances under .0027

XP6 (15W-50) Synthetic
- <Wider variety of engines...>
- Engines designed for SAE 50 weight oils
- Engines with oil temps 240-320* F

XP7 (10W-40) Semi-synthetic
- <Crate / spec engines w/ hyd. and/or flat-tappet cams...>
- Engines with clearances under .0030

XP5 (20W-50) Semi-synthetic
- Engines designed for SAE 50 weight oils
- Engines with oil temps 220-260* F

XP8 (5W-30) Petroleum
- <"Small block / flat-tappet / N2O engines">
- Engines designed for SAE 50 weight oils
- Engines with clearances under .0027

XP4 (15W-50) Petroleum
- <"Big block / flat-tappet / N2O engines">
- Engines designed for SAE 50 weight oils
- Engines with oil temps 200-240* F


I'd be interested in knowing more of what defines "Engines designed for SAE 50 weight oils", but will assume for now it can be read as LOOSE. And going by their guidelines, I should definitely be running at least a ##w40 (or even a ##w50) in the MoPig, considering bearing clearances, expected oil temps, etc.
Posted By: Dap

Re: What factors do you use to determine oil viscosity? - 09/16/11 07:51 PM

Dwayne puts my stuff together. So it gets whatever he says to use..
Posted By: BradH

Re: What factors do you use to determine oil viscosity? - 09/16/11 08:25 PM

Quote:

Dwayne puts my stuff together. So it gets whatever he says to use..


He tells me to run 20w50... but I keep having this occasional delusion that I'm smarter than him.
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