using thicker oil such as 20w-50

[1974dodgecharger]

Currently using rotella 15w-40 and my oil pressure reading is 55psi and at cold start she reads 60 with mechanical aftermarket guage.

I been reading about using a thicker oil to increase oil pressure and that for every 10psi you get 1k rpm shift or so.  So at 55psi I should be shifting before 5500 rpms from my understanding.  From my understanding (google) that if we can shift at a higher rpm we get more HP. 

So would using a 20w-50 oil increase my oil pressure to let me shift at a higher rpm?

I plan to use amsoil synthetic also there new line is made for flat tappet cams.

current build up on 383 engine.
KB pistons
stock 68 crank
rpm heads
509 cam
other than that stock everything else.

[myk]

I figure a thicker oil would make it more difficult (increased resistance, etc) for the rotating assembly, no?  Someone correct me if I'm wrong.  I use 10W40 in mine...

[Cooter]

55psi is plenty oil pressure. Thicker oil will only help slightly. I don't reccomend running thick oil as on start up, it can take up to 2 min. To get that 'honey' up to the top end.
Only run thicker oil if there's a problem with consumption with thinnest oil.


And yes, thicker oil does rob hp...

[Ghoste]

If the bottom end is stock I wouldn't wing that 383 much past 5500 anyway.  And I know folks will come on saying the 383 will live easily to 6500 but without knowing what you have done to the bottom end thats just my safe opinion.

[myk]

If the bottom end is stock I wouldn't wing that 383 mcuh past 5500 anyway.  And I know folks will come on saying the 383 will live easily to 6500 but without knowing what you have done to the bottom end thats just my safe opinion.

Curious: what's considered the "red line" limits for basically stock 383's, 440's? 

[Ghoste]

About 5500 for a 440, 5800 or so on a 383.

[70redbee]

I been reading about using a thicker oil to increase oil pressure and that for every 10psi you get 1k rpm shift or so.  So at 55psi I should be shifting before 5500 rpms from my understanding.  From my understanding (google) that if we can shift at a higher rpm we get more HP. 

So would using a 20w-50 oil increase my oil pressure to let me shift at a higher rpm



Does this mean with 80lbs oil pressure I can shift at 8000 rpm......BULLLPOOPY.

[Ghoste]

The oil pressure thing was never meant to be taken as a scientific formula, it's a generalization.

[myk]

About 5500 for a 440, 5800 or so on a 383.

Thank you-I will adjust my 'tach accordingly...

[1974dodgecharger]

Ill stick with my 15/40 weights, thx again folks and shift at 5k to be safe.  I think I have shifted at 5500 once, i have my light setup at that.

[BSB67]

1) If the bottom end has a performance re-built (right clearances and good rod bolts), it should be good to 7,000 to 7,500 rpm
2) That cam and those heads in a 383 should probably be shifted between 6,500 and 7,000 to utilize its full performance capability.
3) You should determine the reason why you have 55 psi.  It could simply be what the oil pump is rated for.  The standard pump will be about 55 psi. You might only need to put a higher oil pressure relief spring in the pump.
4) If you just want to shift at 6000 or 6200, I would be okay with the 55 psi that you have.
5) If you really want to push it to its full potential, I would want 65 psi.

[Ghoste]

Worth mentioning too that at the thinking was backwards at the beginning of this thread.  The 10 lbs per 1000 rpm doesn't mean with all else being equal that by merely raising the oil pressure you can now shift higher.  The inference in that general rule of thumb was that if you build to shift higher, then try and raise the oil pressure accordingly.
If that makes sense.

[Ghoste]

Oh, and can't forget about the role of volume.

[myk]

What if the gauge is off?

[Ghoste]

How true, if its a factory guage there is a good chance it can be off.