0W20 load bearing capability in race block

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Belgian1979

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I'm inclined to go to a thinner oil (0W20 coming from 5W30) because of several reasons. The oil is to go into a high winding small block chevy (generation 1) with pretty standard bearing clearances (.0025-.0027 on the mains, .0023 on the rods) and with mechanical roller lifters with 570 lbs over the nose springs.

Is this oil good enough regarding load bearing capability or too thin ?
 
For 20 wt's in this engine I'd go for Mazda 0W20 (Idemitsu with a lot of Moly).

Or, I would keep it simple and go for Pennzoil Ultra 5W20 if you can get it cheap.

My third choice would be QSUD 0W20 if you can find it, if not, QSUD 5W20.
 
For racing duty I don't see why you'd run less than 30-grade. You need excellent oil temperature control to keep 20 with enough film strength under hard driving/racing conditions. You may want to read the AEHaas articles, where he explains this. Also, there is not a Chevy V8 made that I am aware of that recommends anything below 5W-30.
 
What kind of application is this for? What is the maximum expected oil temperature? My first impulse is to stick with 30-weight because that's what small block Chevies with standard bearing clearances were designed for. If you're doing drag racing with one run every two hours, and the oil temperature never gets over 150F, the 20 weight may be OK.
 
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Engine has a high volume pump that would be able to push more oil to the engine to keep a film strength. I also run a oil cooler with electric fan set at 175°F.
 
Originally Posted By: Belgian1979
Engine has a high volume pump that would be able to push more oil to the engine to keep a film strength. I also run a oil cooler with electric fan set at 175°F.


Oil pressure does not affect film strength, oil viscosity and temperature does.
Seeing that you have an oil cooler temps. should be fairly stable, however electric fan setting alone is not enough to determine what max oil temps you can see. You have to have oil temp. gauge for that.
 
Dump the HV pump; all it does is flood the top end of motor and cost you HP. You want a min 10 psi oil pressure per 1K rpm in a SBC. I have built many SBC circle track motors. I have always used a std chevy pump with a shimmed relief spring. At the end of the season, the least wear is found on motors running 10w30 race oil; the most wear has been on engines with 20w50.

FYI-a HV pump has nothing do with film strength. Keep your tolerances at the min, run a stock pump, and sleep well at night.

Dave
 
If you start out trying a light ,high VI, HTHSV 2.6cP, 0W-20 and it turns out that your hot OP is lower than you would like you can increase the oil's viscosity by adding some heavier oil such as M1 0W-40. 10% of M1 0W-40 will raise your HTHSV to 2.7cP and 20% to 2.8cP. You'll still have a 0W-20, just a heavier version.
 
The reference to oil pressure is really to the back-pressure reading on an OP gauge. OP is a convenient proxy for operational viscosity, so in effect maintaining a certain know minimum safe OP is the same as maintaining a minimum safe operational viscosity.
 
Originally Posted By: Belgian1979
Ok, so this is a definite no.

I'm not saying it's a no, but you will have to become familiar with the oil pressure characteristics of your engine to make an informed viscosity choice, regardless.
 
Originally Posted By: CATERHAM
The reference to oil pressure is really to the back-pressure reading on an OP gauge. OP is a convenient proxy for operational viscosity, so in effect maintaining a certain know minimum safe OP is the same as maintaining a minimum safe operational viscosity.


But OP doesn't run stock oil pump. He's running a high volume pump which in turn will increase the back pressure reading across the board. How is he to compare those readings to oroginal numbers published by the manufacturer that were based on stock oil pump?
 
Originally Posted By: KrisZ
Originally Posted By: CATERHAM
The reference to oil pressure is really to the back-pressure reading on an OP gauge. OP is a convenient proxy for operational viscosity, so in effect maintaining a certain know minimum safe OP is the same as maintaining a minimum safe operational viscosity.


But OP doesn't run stock oil pump. He's running a high volume pump which in turn will increase the back pressure reading across the board. How is he to compare those readings to oroginal numbers published by the manufacturer that were based on stock oil pump?

It's a good point and he will have to rely upon the builder of his Chevy engine/oil pump supplier for that answer; i.e., minimum recommended oil pressure. That said, many Chevy tuners consider 50 psi as a safe minimum at high rev's.

The OP is getting a little ahead of himself with his new engine. He needs to first become fully familiar with the oil pressure/oil temp' characteristics of his Chevy engine on the "standard 30wt oil" before fine tuning the oil viscosity choice.
 
Originally Posted By: KrisZ
Originally Posted By: Belgian1979
Engine has a high volume pump that would be able to push more oil to the engine to keep a film strength. I also run a oil cooler with electric fan set at 175°F.


Oil pressure does not affect film strength, oil viscosity and temperature does.
Seeing that you have an oil cooler temps. should be fairly stable, however electric fan setting alone is not enough to determine what max oil temps you can see. You have to have oil temp. gauge for that.


Yep, oil pressure has never lubricated an engine, it occasionally does on hydrostatic lubrication systems, but never an SBC...
 
So as long as you can keep the temperature in check and keep adequate oil pressure are you saying to use the thinnest oil you can find? Like a 0/20 in a 8500 rpm four cylinder, with a heavy 10/30 oil I get 90 psi oil pressure. It would free up some HP going to a thinner oil but I've always been to chicken to try a 0/20 in my engine.
 
Seems like he has the oil temps in check. Also, concern for the bearings? They'll be fine IMO. It's the cam lobes on those big springs that I would worry about. At least the lifters are rollers, but still.
 
Meanwhile I've been asking an engineer about this. It's not bulk oil temps that are the determining factor in this. It's the bearing exit temp which is. this is around 300°F. Viscosity is a lot lower then and too low for the 0W20 with regards to the bearing clearance. So from a technical point of view the 0W20 is a no go in a chevy with the bearing clearances involved. 30wt is about the lowest limit.

I was in search for an oil pressure problem but meanwhile I received the pump graph and everything points to a bypass being overworked. I'm going towards an external bypass exiting to the pan.
 
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Your engineer is spot on about bearing exit temperature being way higher then bulk...

Expect some heat (no pun intended) on the issue, as there are those on this board who "don't believe" such engineering realities.
 
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