Engine Clearances

[dodj]

Another thread made me wonder about this. 
I asked @Brads70 why run 20/50 and the answer was it was clearanced for it.  Ok,  fair enough,  running the recommended oil. But I run lighter oil than that in my 930 ft/pd  cummins diesel.
My question is this
Why intentionally open up the clearances on your ebody engine?  What does this get you in an engine build?

[Cuda Cody]

I once heard that looser tolerances equal more horse power because things can move as easy as possible.  In racing where every single fraction of an HP matters I think it would be more important.

[dodj]

Hmmmm. I was thinking the thicker oil might rob horsepower.

[DeathProofCuda]

Hmmmm. I was thinking the thicker oil might rob horsepower.

Yeah, that's what I would think .  Large clearances with thicker oil vs. tighter tolerances with lighter oil.  Seems like it would be a wash to me.

[YellowThumper]

Yes a free're spinning motor.
Thermal expansion is another reason.
Diesels run from 0 (lol) to only a couple grand rpm.
Now take a motor and spin it much higher for long durations. Added clearancing is a must.

[tparker]

Doesn't looser tolerances or wider gaps essentially mean there is more lateral motion? or motion in unwanted directions? Seems like that would cause some extra shock and wear on the system. So are we talking high perf race engines or even mild street engines? If looser was better, wouldn't they come that way from the factory? Seems like there are trade offs.

[rikkitik]

There absolutely are tradeoffs.
Many things come into play in the design of an oiling system. Part of the reason the Cummins can run lighter weight oil has to improved production processes (the engine can be held to closer tolerances than 50 years ago). Part of it also has to do with higher efficiency requirements. It takes more HP to pump heavier oil, fuel is wasted, and the energy is dissipated into in the form of heat (higher oil temperature due to the increased fluid friction).
Improved oils (synthetics) have helped as well. With improved film strength, plus higher inherent stability.
So, for some of the reasons listed above, most modern designs have been designed to run lighter weight oils.
Hellcat > 0W40, ZR1/LS7 5W30
The stupid Orange thing in my avatar, spins 13,000 rpm, and makes slightly less than 3 horsepower per cu. in. Allowable main bearing clearance range is .0007-.0012 thousandths of an inch. Yes, that's 7 to 12 ten thousandths of an inch. Changing from 10W30 to 0W20, dropped sump temperature 12 degrees, and freed up slightly less than 4 horsepower.
Most people don't completely understand oiling system functions. They're not quite as simple as a lot of people think.
If you don't already know the term, look up hydrodynamic wedge, it might give some insight into "how does it work?"

[Chryco Psycho]

Oil has a # of functions not only does it lubricate & keep the parts from actually touching , hyd wedge as mentioned by Rikkitik but it does a great deal of the cooling  .
Using minimal clearance the oil flow is restricted so it moves slower but increases pressure , open the clearances & more oil is moved through the engine which may require a high flow pump & larger capacity to keep the needed oil pressure but this can take away a lot of the heat produced as well .
So with a tight engine & thicker oil you now have reduced the flow more than normal , open up the clearances & oil flow returns to normal but with thicker oil to retain the needed pressure .
SO try this take a coat hanger & bend the wire constantly for a minute or so , increase speed also , that wire gets very hot & quick , imagine a valve spring , at Only 600 RPM the piston is at top dead center 10 times / second & the valve is open 5 times a second , How are you making out with the coat hanger wire ? Now at 6000 RPM the piston is at top dead center 100 times / second & the valve is being opened 50 times / second , how much heat is the valve spring making now ?? , you need a good volume of oil  moving through the engine all the time ,

[rikkitik]

 And, to underscore some of CP's point, Manley Performance once built a roller cam small block. They set it up to be spun externally via electric motor. IIRC, it was spun at 6000rpm. The oil reached 225 degrees in 6 minutes without any combustion taking place. They attributed the majority of oil temperature gain to valve springs.
If interested, a bit of reading insight into bearing clearances
https://blog.k1technologies.com/bearing-clearance-and-oil-viscosity-explained

[jimynick]

"They attributed the majority of oil temperature gain to valve springs." and that boys and girls, is the reason NASCAR engines, for example, run valve spring oilers AND piston oilers, as well as big a$$ oil coolers. The Jammies got it right- keep it cool mon! 

[dodj]

It comes down to intended use then. If you are expecting long run time of high rpm, a little more clearance and higher oil flow helps parts longevity and engine cooling? 

[Chryco Psycho]

For sure , , everything is a balance you need enough pressure to get enough oil to all areas but higher clearance  allows more flow reducing pressure & heat so a thicker oil will help maintain the pressure , pushing thicker oil such as 20-50w through an engine with stock clearances can actually starve the the engine / valve springs reducing the amount of oil reaching the springs & rockers .
Our engines are dinosaurs , there is no readily available oils for them , you need SJ which can be found in agricultural stores as it still is the best oil & allowed for "offroad". All oils since SJ are garbage without additives SL , SM  SN will not keep flat tappet cams alive . Roller cams are an option & then SN oils are fine but too much low RPM / Idling can cause the roller lifters to fail as they are not oil fed all they get is the run off from the heads so now you need more flow to the springs & rockers again !
Most of this is on the extreme side , will a valve spring fail running 20-50w in a stock engine likely not because the engine is not pushed hard enough or long enough to fail but yes it could happen or at least shorten the life .
Personally I tend to run my engines Hard so I build for that or use compatable oils , I ran my 440 Duster for 9 seasons + many street miles ,drag racing most weekends & shifting at 7200 rpm , nothing failed  no , brg wear , broken valve springs , Nothing ! I did make my own oil pan holding 12 qts with baffles to keep the oil in place even when wheelstanding !

Bottom line is I would use a 10-30 or 10-40 oil with additives in a stock build over using 20-50 racing oils .

[MoparLeo]

It boils down to application. A NASCAR engine only has to last 500 miles max. A drag car a 1/4 mile at a time under full load.
Now a street car must last over 100k under various conditions and be reliable with only fluid and filter changes
Modern engines use very light weight oils based on low friction ( fuel economy) and modern materials and manufacturing tolerances which
are much different then the old complete cast iron engines of old.
Using thick oils for street use is because of using old tech in your engine build or maybe not the ideal engine for street use.
Street/strip is a compromise. It is either street or strip. 2 different applications and builds.

[7212Mopar]

I use Turbo Maxx additives with 10w30 Mobil 1 full synthetic motor oil. Silky smooth.