Effect of viscosity, speed and load on bearings

[buster]

LINK

Quote:
For example an NHRA Pro Stock engine makes over 1,400 HP and uses a 0W-5 weight engine oil. A NASCAR Nextel Cup Engine only makes 850 hp but uses a 5W-20 weight oil. How can a more powerful drag motor use a lighter weight oil? The NHRA Pro Stock motor runs at a cool 100 degrees F. A NASCAR Nextel Cup engine runs around 220 degrees F. Our Joe Gibbs Driven XP0 racing oil is 11.5 Centistokes at 100 degrees F, and the XP0 oil is popular with the NHRA drag racers. Joe Gibbs Racing uses the XP1 in our un-restricted NASCAR Nextel Cup engines, and the XP1 is 9.5 Centistokes at 212 degrees F. As you can see, the operating viscosity of the 5W-20 XP1 oil is lighter than the operating viscosity of the 0W-5 XP0 oil due to the difference in operating temperature.

All material referenced from Lubrication Fundamentals, Second Edition, By D.M. Pirro and A.A. Wessol, Published By Marcel Dekker, Inc., Copyright 2001 Exxon Mobil Corporation

 

[JAG]

Interesting. Why would the NHRA Pro Stock engine have cool 100 F oil? I don't watch that kind of car racing so don't know their driving routine.

 

[BuickGN]

Originally Posted By: JAG
Interesting. Why would the NHRA Pro Stock engine have cool 100 F oil? I don't watch that kind of car racing so don't know their driving routine.


More power.

 

[XS650]

Originally Posted By: JAG
Interesting. Why would the NHRA Pro Stock engine have cool 100 F oil? I don't watch that kind of car racing so don't know their driving routine.


They only run under load for 6 or 7 seconds at a time. If you assume 7000 rpm, that's only 700 crank revolutions under full load before they are shut down.

You can do some wild things with an engine with that short a duty cycle.

 

[MGregoir]

Engine runtimes under a minute.

The engine spends very little time operating so although it is of an "extreme" performance level, the oil never comes up to operating tempurature. This allows them to run a thin viscosity rating, but although it is thinly rated, at that temperature it is thick enough. a 5W-20 in that engine would be 40-ish cSt at operating temperature instead of 11.5.

The oil at operating temperature in that engine is no thinner than the 10W-30 many of us use in our street cars, once the engines in those are fully up to temperature and the oil temperature rises.

Conversely, a top fuel engine uses straight 70 weight oil.

 

[mkIIIman089]

I IMAGINE it has something to do with how much fuel they drown their engines in as they run. They certainly run long enough to build more then 100F in a "normal" automotive engine.

 

[BarkerMan]

These drag engines have very little in common with any other type of engine. There are a lot of other things done to make power for under 10 seconds. These things are learned the old fashioned way. Try it and if it does not produce power or goes bang you now know one more thing not to do. We do a lot of dyno runs trying stuff out. The window into the cell is very thick bullet resistant glass mounted in a heavy duty frame. Some of these new ideas have tested the glass. But you have the right idea. Worry about the viscosity inside the bearing, not the viscosity on the label. We are doing some engine development with a 0w-2 oil, but inside the bearings it does just fine and is the equal to 0w-20 oil if not for the special circumstances we have developed for testing. We did have a crankshaft let go and the bearings squeezed out like peanut butter. We now know one more thing not to do in the future.

 

[SubLGT]

Originally Posted By: BarkerMan
........ The window into the cell is very thick bullet resistant glass mounted in a heavy duty frame. Some of these new ideas have tested the glass.......


Flying conrods?

 

[mkIIIman089]

Or just shrapnel...

 

[Shannow]

When I was doing my automotive maintenance TAFE course (ages ago, pre-driving licence), there was a speedway racer in town who did a lot of his own development work.

Was test running a high horse alky injected small block on a stand in his shed/workshop.

Winging the throttle, and it ended up at stuck at full noise. He grabbed the throttle linkages, jammed them shut, and the flywheel bolts sheared off...killing him.

Bomb proof enclosures are a great idea.

 

[mechtech2]

buster - That makes sense.
Also, large sumps help with heat build up.

 

[BarkerMan]

Years ago an auto mechanic was killed by a fan blade while timing an engine, bent over the front of the engine watching the timing marks. Ever since hearing that I stay away from the line of fire with anything rotating. Same with my R/C airplanes.

 

[Lazy JW]

Originally Posted By: BarkerMan
...We are doing some engine development with a 0w-2 oil, but inside the bearings it does just fine ...


Seems to me that a crankshaft spinning at high speed will act somewhat like an oil pump in itself. It receives oil from the mains, then sends it to the rods. The rotary forces would then tend to throw the oil toward the rod journal, thereby increasing effective delivery pressure at the rod. The higher the speed, the more effect this would have.
Just guessing though...
Joe

 

[BuickGN]

I've had a flywheel come through the floor and exit the car through the dash.

On the dyno I always stand way back from the car/engine. When my dad's GN which makes more power and spins an extra 2,000rpm than mine was on the dyno the WOT timing had to be checked due to a computer problem. That's the most nervous I've been bending over a new motor spinning 7,500rpm shining a timing light on the crank pulley.

 

[Shannow]

Originally Posted By: Lazy JW
The rotary forces would then tend to throw the oil toward the rod journal, thereby increasing effective delivery pressure at the rod. The higher the speed, the more effect this would have.
Just guessing though...
Joe


It has to get from the journal to the main bearing centreline first, which is going against the direction of developed head.

 

[Lazy JW]

Originally Posted By: Shannow
Originally Posted By: Lazy JW
The rotary forces would then tend to throw the oil toward the rod journal, thereby increasing effective delivery pressure at the rod. The higher the speed, the more effect this would have.
Just guessing though...
Joe


It has to get from the journal to the main bearing centreline first, which is going against the direction of developed head.


True. But the much larger radius of the rod would largely overcome that with force to spare.

A normal oil pump has to overcome some force to lift oil out of the pan, which it does with force to spare as well.
Joe

 

[Gary Allan]

I imagine, that at a certain point, injecting oil into the journal is like loading a hopper. The lateral (albeit rotational) action should "draw away" oil enabling easier injection.