Do thinner oils (SAE xW-20, xW-30) do better at high RPMs?

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Question predicated off that my Subaru is soon to have an EJ20 (JDM) in it. It MAY rev higher on prolonged highway runs; old engine turned at around 2900RPM for my preferred 75MPH on highway (I usually get passed like I am standing still) with 80 being about 3100RPM. Losing a half liter of displacement, I am thinking RPMs will rise.

I do wonder if a 0W-20, 5W-20, 0W-30, 5W-30 oil lubricates "better" than anything heavier than that at higher RPMs, they can really increase once you get flying. 90MPH yields about 4K RPM on old engine and I'm sure many engines rev higher than that.

Everyone says put 5W-30 in a Subaru engine.. even a JDM Subaru?
 
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Are you changing the transmission as well as the engine? Gearing? Tire size?
I am not understanding why the RPMs would change at all with just replacing the engine. Am I missing something here?

I would agree that higher RPMs are better with a higher viscosity oil. I don't consider 3000 to high RPM. Heck, I don't even consider 4000 to be high RPM on my FA20.
 

JT20

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4,710
Are you changing the transmission as well as the engine? Gearing? Tire size?
I am not understanding why the RPMs would change at all with just replacing the engine. Am I missing something here?

I would agree that higher RPMs are better with a higher viscosity oil. I don't consider 3000 to high RPM. Heck, I don't even consider 4000 to be high RPM on my FA20.
I mean... From all of my research, the only thing that's only actually going to have to be changed is the flywheel (use USDM one because otherwise the holes won't line up if the one video I saw is correct) HOWEVER When I used to do top speed calculations on an automatic trans, if I remember right it was engine RPM multiplied by rim size multiplied by final drive ratio or something like that... I slightly forget but

The flywheel actually is staying the same if it's replacing the older smaller one.

My question then is how can going from 2.5 L to 2 L NOT yield higher RPM?

And now I am actually rather glad that I asked this question because I was thinking of going with some kind of thinner 30 grade oil in there. As far as I know this shop likes Pennzoil Ultra and while I personally have not used Pennzoil in a very long time, as far as I know that's about pretty much the thinnest 30 you can get.
 

JT20

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4,710
Okay cool.

What I am thinking is...

I used Castrol Edge 0W-40 (BC) in my H6.
My H6 is gone.
Now I realized my EJ25 had a problem
Tough little engine, that one.
But I decided to act
And it will next see service with an EJ20 (EJ201 JDM I believe)
before that one decided to just get worse.

plus I come out of it with like a 50,000 mi used engine which is fine with me. Low miles. Low miles is good.

Replacing it BEFORE anything happened, lol.

so I'm thinking that Castrol Edge 0w40 wouldn't be the best choice for a small 2 L displacement 4 banger. For the 3.0 it seemed to do very well and I chose it over a 5W30..

so if this ej20 is going to be fine on what is probably going to be Pennzoil Ultra 5w 30 then I'll just leave it alone....

?
 

OVERKILL

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I mean... From all of my research, the only thing that's only actually going to have to be changed is the flywheel (use USDM one because otherwise the holes won't line up if the one video I saw is correct) HOWEVER When I used to do top speed calculations on an automatic trans, if I remember right it was engine RPM multiplied by rim size multiplied by final drive ratio or something like that... I slightly forget but

The flywheel actually is staying the same if it's replacing the older smaller one.

My question then is how can going from 2.5 L to 2 L NOT yield higher RPM?

And now I am actually rather glad that I asked this question because I was thinking of going with some kind of thinner 30 grade oil in there. As far as I know this shop likes Pennzoil Ultra and while I personally have not used Pennzoil in a very long time, as far as I know that's about pretty much the thinnest 30 you can get.

If you aren't changing tire size or gearing then RPM stays the same.
 
Messages
234
Location
STL, MO
I mean... From all of my research, the only thing that's only actually going to have to be changed is the flywheel (use USDM one because otherwise the holes won't line up if the one video I saw is correct) HOWEVER When I used to do top speed calculations on an automatic trans, if I remember right it was engine RPM multiplied by rim size multiplied by final drive ratio or something like that... I slightly forget but

The flywheel actually is staying the same if it's replacing the older smaller one.

My question then is how can going from 2.5 L to 2 L NOT yield higher RPM?

And now I am actually rather glad that I asked this question because I was thinking of going with some kind of thinner 30 grade oil in there. As far as I know this shop likes Pennzoil Ultra and while I personally have not used Pennzoil in a very long time, as far as I know that's about pretty much the thinnest 30 you can get.
If the engine is the only thing that is being changed, then it is physically impossible that your RPMs would change at the same speed, before and after. That is just how mechanical power transmission works.
 
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The higher the rpm, the wider the clearances need to be to account for torsional vibration, and thus a higher viscosity is needed. This also depends on the use of the engine though. A race engine will not care as much as a daily commuter trying to live for 300k miles. NHRA Pro Stock engines turn 10,500 rpm and use 0w-3/8 oil, for example, but the oil never exceeds 150°F in the entire run (except maybe when Erica is driving the thing casually around the pits). NASCAR cup engines run sustained 7000+ rpm for 500 miles straight with 280°F sump temps (~350°F bearing temps) and they use 0w-16/20, but the engine only has to last the one race or maybe 2 races at most.
 

JT20

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4,710
Okay

So. For a 2000 Subaru Legacy Outback w an EJ20... What kind of oil would you select and why?
 
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Kentucky
I owned a 2004, subaru outback. I ran everything from Idemitsu to supertech .
I settled on QSUD or Castrol Magnatec whichever was on sell,, all were 5w30.
Okay

So. For a 2000 Subaru Legacy Outback w an EJ20... What kind of oil would you select and why?
 
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Independence Ky
Are you changing the transmission as well as the engine? Gearing? Tire size?
I am not understanding why the RPMs would change at all with just replacing the engine. Am I missing something here?

I would agree that higher RPMs are better with a higher viscosity oil. I don't consider 3000 to high RPM. Heck, I don't even consider 4000 to be high RPM on my FA20.
My thoughts exactly.
 
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247
Location
Independence Ky
I mean... From all of my research, the only thing that's only actually going to have to be changed is the flywheel (use USDM one because otherwise the holes won't line up if the one video I saw is correct) HOWEVER When I used to do top speed calculations on an automatic trans, if I remember right it was engine RPM multiplied by rim size multiplied by final drive ratio or something like that... I slightly forget but

The flywheel actually is staying the same if it's replacing the older smaller one.

My question then is how can going from 2.5 L to 2 L NOT yield higher RPM?

And now I am actually rather glad that I asked this question because I was thinking of going with some kind of thinner 30 grade oil in there. As far as I know this shop likes Pennzoil Ultra and while I personally have not used Pennzoil in a very long time, as far as I know that's about pretty much the thinnest 30 you can get.
Engine size alone will NOT affect RPMS whatsoever. A smaller engine may be capable of revving higher rpms but if the engine is hooked up to the same drivetrain as your other engine was RPMS will be the same as they was before in any gear at any speed. Example if you was running 3,000 RPM in 5th gear at 75mph you will still be running 3000RPM at 75mph in 5th gear.
 
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High RPM = higher sheering on the oil. For better protection a higher HTHS rating would be better. w20 are generally around 2.7. When you factor in fuel dilution on some engines spec for w20, a regular w30 with a HTHS 3.0-3.5 I'd argue is better overall, but in reality it doesn't matter in your daily driver. For track use go thicker. A few WOT's on the street it doesnt matter, but it also depends on the engine. Try a UOA when in doubt or research other UOA's for your engine.
 

JT20

Thread starter
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4,710
Correct, displacement has zero bearing on it.
Okay, awesome.

My mechanic tells me I'm going to really enjoy the EJ20. Would you agree?

I was honestly thinking it was going to be revving higher because of smaller displacement. Never changed the type of engine before. Subaru yields a first.
 
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