Oil weight

I noticed alot of peps use 20w50. Why not 10w30 or 5w30?
thanks

tconnection wrote:I noticed alot of peps use 20w50. Why not 10w30 or 5w30?
thanks

I use straight 30.... just makeing sure its warmed before runnin, I would think the hotter you run on temp the higher the viscocity for less oil breakdown, I spun a oil pump rod by useing straight raceing 50 not warmed enough..........

Depends on the motor.

I typical run 10-30, 10-40 or 30 & 40

With .003 on the mains and .0025 on the rods. What weight should be ran?
Thanks

you should never need anything over a 10-30 if you do you are wasting HP

the Coug wrote:you should never need anything over a 10-30 if you do you are wasting HP

Yep. I broke my motor in on the dyno with 20w50 because i didn't know any better. On the 3rd pass we drained it and put in some 10w30 "green oil" and it picked up hp. To this date, I've always run it with 10w30 and never looked back. On winter tear down, the bearings have looked great with no signs of wear going on the 3rd year.

If I may present an opinion?

If an engine's crankshaft bearing oil clearance is "large", that engine may benefit from thick oil.
If an engine's crankshaft bearing oil clearance is "normal to small", that engine may benefit from thin oil.

The above ideas are based on a theory of 0.001" of oil clearance per 1.0" of crankshaft journal diameter. There are many variables. Synthetic oil, petroleum oil, application and so on! Everyone has their preferences, practices that have worked time after time. IMO, if you have success with your current assembly dimensions, continue those practices.

Dave.

On another note, Lake Speed Jr. mentioned at the 2012 WTS that "heavy oil" used in conjunction with OEM oil clearances will create more oil temperature than "lighter oil".

tconnection wrote:I noticed a lot of peps use 20w50. Why not 10w30 or 5w30?
thanks

Because a lot of people on this forum like to run a lot of bearing clearance and doing that is not conducive to using lighter weight oils.

Lighter oils are recommended when tighter clearances are to be used.

Good info. Thanks!

The posting indicating that large oil clearances run with heavier oils is correct:

Not only does the orifice size (restriction) through the engine change significantly, the heavier oil's film thickness has influence on shear thickness which interaction is a constituent of the hydrostatic bearing model (bearing/crank geometric relationship is the other). It's the latter mentioned that pounds out bearings with light oil in a high clearance motor.

Pro Stockers run light oil to gain the performance advantage of reduced pumping losses, but these guys are looking for every conceivable Hp gain and put bearings in regularly. That's not to say that everyone should run out and switch to 20-50wt, just that the 0w, 5w, 10w oils are an expensive option for someone without full time sponsorship. They come at a cost.

Most spun bearings with heavier oils are a result of cold oil and/or too tight oil clearances. Both flow and pressure are important. If you address these two, you'll have no problems.

Mike