Oil weight based on bearing clearance

[swordfish]

Any suggestions as to what weight synthetic would be best suited to these bearing clearances in a stressed daily driven turbo engine? The bore is also set up pretty loose as this is a high boost, high compression (10.0:1) and nitrous application.

Main Bearing Clearances: Listed 1-5
.0015 - .0015 - .0013 - .0015 - .0014

Rod Bearing Clearances: Listed 1-4
.0012 - .00125 - .0013 - .0012

Bore Clearance: IE bore size minus piston size.
.004 every cylinder 1-4

I am asking because my first 3000 mile change (Amsoil 10-40) is coming up and will be sending off for my first UOA, but I would like to try something else for the next change and to also have it UOA'd. Thanks for any suggestions.

jeff
www.swordfishGSX.8m.com

 

[Al]

Well..I think that may not be realistic. In general the viscosity, load and speed of a bearing are related. Classical bearing equations use the form Viscosity X Speed/Load= Coefficient of Friction. Bearing Design is a function of these specific parameters (which includes bearing clearances). So really clearances are just a small piece of the puzzle. It makes more sense to get clearances within the tolerances of a specific engine/machine and then go by the manufacture's recommendation for that engine.

 

[sprintman]

Tyrolkid uses Redline 5W40 in his turbo engine running high boost and he has multiple UOA's here that are exceptional by any standard. Do a search and you should be able to find them.

 

[benjamming]

If you're trying to determine which oil is best by UOA, you'll need to do more than 1 OCI with a particular oil. Terry would be great to consult for your application & fine tune your oil selection.

 

[ebaker]

For the bearing clearances I'd use a 10w30. The .004 piston skirt clearance seems loose, so consider something heavier.

 

[swordfish]

The bore clearance is a bit loose in order to get this thing to live. Thanks for the suggestions and information. I'll spend more time searching around the site.

jeff

 

[Steve S]

How can a high compression, nitrous,turbo charged engine run?

 

[Dr. T]

Viscosity is temperature based, not clearance based because the viscosity changes dramatically with temperature changes compared to the little clearance changes that occur within the same temperature range.

Such analysis may be suited for racing teams, but not for the general public or your daily driver.

 

[mechtech]

Bear in mind that even though that .004" bore clearance is pretty loose, it is a COLD measurement, and there IS a turbo. That clearance will tighten up a lot with those hot combustion temps ensuing.
I'd get an oil that is the right visc. when at your elevated oil temps., since turbos under load make any engine real hot [esp. with 10-1 comp!].

 

[LarryL]

Differences in viscosity for the same engine and internal specs are now being studied by racing teams that use a specific oil for racing and a different oil for qualifying. The only problem is that this kind of info is difficult to translate into useful data for street applications. We are involved in such a racing program and there is one real big problem. The thin qualifying oil airates and causes real problems with efforts to keep a vacuum in the crankcase. Expected gains, do to less oil pumping and friction drag are lost when the spray inside the crankcase collects too much oil spray and associated drag. We have one engine that acually looses power on the dyno with lighter oil and the problem might be worse when the engine is moving around. Also the requirement for ring changes to compensate for the higher crankcase pressures with lighter oil has made us very careful about new super light oils. There are no secret bullets, here.

 

[oil pan 4]

How could a 10:1 c/r turbo nitrous engine run?
Lets see...
A 10:1 engine with a V.E. of 80%.
You could run 7 psi to with 100 octaine gas.
10psi would give you a stadic compression ratio of 11.7:1 and you would need 105 octaine gas.
Those are hot air numbers.
With the cooling effects of nitrous then you could easly run more boost.
Plus they did it in the movies

.
Now it looks like he will have nirtous also so I bet he ain't running pump gas.
If you have Magnesium alloy forged pistons then .004'' is perfect.
If you have cast hypereutectic pistons then

. I just hope there not cast hypereutectic pistons.