High flow oil pump? Thinner oil?

[SnowDrifter]

Just thinking. Vehicles spec'd for Xw30 are a result of bearing tolerances, no? Newer vehicles can use Xw20 due to tighter internal tolerances

Race and higher performance vehicles use a higher flow oil pump on account of larger bearing tolerances.

So, would it not then serve to reason that one could take a stock vehicle and use a high flow oil pump, then step down in viscosity to reap the benefits associated with it?

Aside from the conceptual, has anyone actually tried it?

 

[spasm3]

I don't think bearing clearances are any tighter than they used to be. Now piston ringlands are higher on the pistons than in the past, but i don't see how that affects oil viscosity choice.

An 8th generation honda accord main bearing clearance is .0007 to .0016 inch. A b18 engine which was spec'd for 5w 30 oil , main bearing clearance is ( guess what!!!) .0007-.0016

http://www.haccord.org/crankshaft_main_bearing_replacement-798.html

http://mywikimotors.com/honda-b18c-b18b/

 

[ka9mnx]

I think a high flow oil pump would negate the benefits of the thinner oil?

 

[ka9mnx]

Moving the top ring closer to the top of the piston reduces the area where air/fuel mixture can accumulate and not combust. Thus reducing ring land and piston carbon and better fuel efficiency. Nothing to do with viscosity as you stated.

 

[ZeeOSix]

As long as you have adequate oil flow supply to all engjne components, having a higher output oil pump doesn't gain you much except slightly more journal bearing cooling due to more forced flow (above the journal bearing's natural oil flow due to rotation) through the bearings.

This is one reason why engine designers are using variable output oil pumps to cut back on oil flow to save oil pump HP loss and gain a hair of fuel mileage.

 

[Shannow]

Bearing operating point, which comprises load, speed, diameter, length, and clearances define the amount of oil that needs to be supplied to the engine, and thus the sizing of the oil pump.

Flow doesn't make lubrication. In bearings, it's the hydrodynamic process...you don't get that by jamming oil into it.

Some charts...
first is the design chart. In designing from scratch, you pick the Minimum oil film thickness, and start there.
Second you go to the flow chart, which helps you calculate the amount of oil that you need to supply the bearing with.
Third is from a Mahle presentation on why variable displacement oil pumps are common, note the rough shape of the demand curve with chart two.
Last is a practical, calculated demonstration of MOFT, flow, and wasted power.

So you can see that with thinner oil you NEED more flow, but it doesn't compensate and get your film thicknesses back.

 

[Linctex]

Originally Posted by Shannow

Flow doesn't make lubrication. In bearings, it's the hydrodynamic process...you don't get that by jamming oil into it.


Yes, Which is why replacement main bearing sets for some engines that were originally 360* grooved are often supplied replacements with only the top 180* bearing shell grooved (to supply the connecting rod oil channel)

Rod bearings are NEVER grooved. Yeah, so the 1928-1931 Ford model A did - - but nobody uses that design anymore.

 

[Chris142]

Originally Posted by spasm3
I don't think bearing clearances are any tighter than they used to be. Now piston ringlands are higher on the pistons than in the past, but i don't see how that affects oil viscosity choice.

An 8th generation honda accord main bearing clearance is .0007 to .0016 inch. A b18 engine which was spec'd for 5w 30 oil , main bearing clearance is ( guess what!!!) .0007-.0016

http://www.haccord.org/crankshaft_main_bearing_replacement-798.html

http://mywikimotors.com/honda-b18c-b18b/

You are correct. Clearances have not changed since the 1940's or so.

 

[CR94]

Originally Posted by SnowDrifter
... Race and higher performance vehicles use a higher flow oil pump on account of larger bearing tolerances.
... Aside from the conceptual, has anyone actually tried it?
You're confusing tolerances with clearances (which isn't unusual). They're not the same.

Manufacturers have obviously considered what you're proposing and adopted it, to the extent it makes sense.

 

[OilUzer]

Originally Posted by SnowDrifter
Just thinking. Vehicles spec'd for Xw30 are a result of bearing tolerances, no? Newer vehicles can use Xw20 due to tighter internal tolerances ...


Same "Newer vehicles" with same design, clearance ... and tolerance (limits of variation) in different countries (with similar temp range) have different oil spec. Typically lower viscosity in U.S. ... and I always wondered why until I read about CAFE on bitog.

Whatever the reason (cafe or not), the different spec never made sense to me! So without researching too much or trying to get a PhD on this subject, till further notice, the cafe thing makes a logical sense! At least for me.