Captain Tom

I've got a Maggie S/C and I'm using Mobile 1 20w/50w oil. I've been told thats too heavy. Any thoughts????

jbsblownc5

By Who?? I run Torco 20w/50, and it works great!

robert miller

More info on your motor spec,s please to give you a correct answer. I mean is it stock or build motor really set up for the maggie or blower set up. But if you have a stock bottom end motor that is to heavy oil. Robert

LedfootLarry

If stock bottom end, stick with a 30wt oil, 5w or 10w in warmer weather.
If you have a built engine, better ask buider if loose or tight !!

BLOWNBLUEZ06

Oil pressure, just like boost is a measurement based on of the resistance to forward flow. The key to selecting proper viscosity oil is to select it based on things like internal clearances, load, type of use and temperature range of use.
If you have tight clearances, you need thinner oil. Looser bearing clearances need thicker oil. This is in an attempt to maintain what Joe Gibbs calls the "Hydrodynamic Oil Wedge" or protective boundary layer of oil.

Here's a video you can watch that may help.

Captain Tom

Bought it used and don't know much about the build. Writing in engine compartment says to use 20-50 so I guess I'll continue to use it. thanks for the useful info....

robert miller

If the person you got it from had a motor build for it. and it was put together to use 20w 50. Then by all means use it.

PEETYZ

How about Rotella T6 5w-40 on a well broken in 69k 01 LS6?

I've had pretty good luck with Mobil 1 HM 5w-30 but always looking to switch it up.

LTstewy8

For a good idea of the variables involved with selecting the correct weight: http://en.wikipedia.org/wiki/Sommerfeld_number
For a more advanced explanation: http://www.eng.auburn.edu/~marghitu/...II_5_Lubri.pdf

directnosfogger

blownblue is right, there is no recommending the appropriate oil for your application. you go by the pressure seem by the oil pressure guage at rpm. it's better than any advice anyone can give you. sending away your oil to have analyzed by companies such as blackstone will also give you insight to how long you can run the oil in your motor before changing. motor oil is trial and error. start thick and drop down. my only advice is that i always run 0w anything. better viscosity in whatever grade you use for startup which is the hardest on the motor. gone are the days of winter/summer oils.

Milan

I'm guessing you are still on the stock motor since not to many people build a motor for that blower. If so, yes, that's too heavy.

LTstewy8

Um, maybe not... If I'm not mistaken that gauge isn't telling you anything useful about the bearing's hydrodynamic wedge. Correct me if I'm wrong, because I'm not going to do the research since I'm studying/procrastinating for the most important exams of my life right now and my brain is fried. Try reading the second link I posted, maybe.

-calculate your sommerfeld # and there's a chart somewhere you use to determine the weight of oil you need. It's been a long time since I've done it, sorry.

directnosfogger

so a rule of thumb is for example 4000 rpm's should be 40 psi, 5000 50 psi, 6000 60psi. i have no idea what hydrodynamic wedge means. pressure relates to flow. if you have too much pressure, you are essentially killing and overworking your oil pump to reach a certain flow at operating temperature. if you have too little pressure, you have no flow thus not lubricating moving parts. it's an easy medium where you want to end up to ensure you have appropriate flow compared to pressure. so yes, your pressure gauge is the determining factor to what oil you should be using. there are obviously other factors, such as what you consider your normal operating temperature which you need to use an SAE index for a base oil weight. for the sake of this discussion no one should be running over 240-280 degrees though unless they are tracking their car which would put them in the neighborhood of 300 degrees. this would bump you up to a higher weight, which is why racers use thicker oil, thus changing the flow characteristics and viscosity at operating temperature.

LTstewy8

So what you're saying is that you didn't read the second link I provided, which discredits everything you just said in the first sentence of the section on Petroff's equation. It states, "Hydrodynamic lubrication is defined when the surfaces of the bearing are separated by a film of lubricant and does not depend upon the introduction of the lubricant under pressure." fyi, the main bearings are hydrodynamic. Here's another useful link that nobody will read because it's not as fun as sifting through bs on a forum: http://www.brighthubengineering.com/...c-lubrication/

You can lead a horse to water...

MVP'S ZO6

Rule of thumb and I believe that rule of thumb don't necessarily apply to a race spec engine. As bbzo6 said, bearing clearances ect. Play a vital role in viscosity selection.

I can tell you for sure that if my car only had 60Lbs of oil pressure at 6K engine rpms. Id be very concerned. Just me though.

PEETYZ

I think I see about 65 or so at 6k stock bottom stock ls6 pump with 5w-30.

How relevant is mileage for oil weight on say a stock bottom? I mean the motor will be looser with miles and rings will be more worn etc.

Not the worst thing as most all the LS's ive seen with same mods dyno higher after about 40k than new ones. My 123k mile stock bottom ls1 GTO usually dynos higher than very similar combos on same dyno that have lower miles. I do use HM 5w-30 which is a bit thicker than standard 5w-30 from what i'm told.

directnosfogger

You tend to forget that without pressure you wouldn't have any continual lubrication in your engine. One of the main factors of a rotating centrifuge is that it pushes oil out, so without pressure you wouldn't continually fill the space necessary to suck the oil and create a film, which is what your whitepapers are essentially getting at. That movement (based on clearances) is called flow and it directly relates to pressure. If pressure wasn't a pivot point on the data, or you don't believe me test it out on your own vehicle. You have a platform keeping all variables the same since you won't be modifying your bearing clearances. Try different weight oils and see if your pressure doesn't change.

How much pressure do you see in your motor? Just curious because extremely high pressure is a sign of a problem. As in 100-120lbs..

MVP'S ZO6

about 75-80 psi at full tilt.

LTstewy8

No, I'm not forgetting that. The concepts which you clearly have limited understanding of, but are hinting at, are related to boundary lubrication, which is also covered in one of the links that I provided you. I would suggest less typing and more reading. Start with looking up what a centrifuge is, unless you just want to talk about purifiers and clarifiers instead of tribology.

Btw, I'm not discounting what you say about oil pressure's importance. It certainly is, but there is much more to it.

BLOWNBLUEZ06

Adding to my previous post and repeating some of what I said for possible better clarification:
Too much or low of a pressure being a problem depends on how your oiling is set up and where it's measured from relative to the supply and load. More pressure (supply) at the pump and less at the load (galleys) can be bad and indicative of a restriction in the filter or something on the way to feeding the galleys, such as an external cooler or the "dumbell" being improperly installed, improperly installed bearings blocking the feed, lifters (only certain ones) installed backwards). Too low of a pressure can indicate stuck pressure relief circuit, the suction side sucking air due to the O-ring being pinched, cracked pickup tube, restricted pickup tube an internal oil leak on the load side. I've seen shifted cam bearings, galley plugs come out, or the "barbell" missing or installed improperly and solid roller lifters among many other things cause low pressure.
The law in fluid dynamics that all series pressure drops must add up to the source pressure and if you have a RHS or LSX with priority mains then the oil pressure sending unit is at the very end of the circuit with it having passed the mains before getting to the lifter galley.You may be getting 80psi at the mains and 50 at the lifter galley for this reason. With the stock LS engine, it's only passed through the filter prior to getting to the sending unit and all the bearings are fed from the same galley, so what you see at the sending unit is what the entire galley that feeds both lifters and mains is getting.
Yes the pressure will change with increasing weight due pressure being based on the resistance to flow.
Increase weight and your pressure goes up and the flow goes down, so the ability to get into the bearing spaces and maintain the protective layer can suffer. Thicker oil also affects the speed at which it will flow back to the pan to keep your oil pickup submerged in the sump.
Decrease the weight and the pressure drops, but it gets to/through the bearings more easily and is able to return to the pan more quickly too. Too low of a weight and you will, at some point lose your "hydrodynamic wedge", protective layer of oil that works to cool and prevent the parts from touching. It's important to find that balance between flow and pressure.
The well respected Erik Koenig of HKE has stated on more than one occasion that the rule of 10psi per 1kRPM isn't the rule for the LS engines and running 6800RPM and 55psi isn't an issue.

stock LS engine oiling


Priority main oiling


Hope this is all legible because I've been up WAY too long to read it over for errors.