0-60 WOT pull oil pressure

OVERKILL

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@ZeeOSix and I were discussing this a bit in one of the other threads so I decided to go out and do a 0-60 in the Jeep (hot) to see where that put oil pressure and whether it would overwhelm the relief on the pump and allow pressure to rise beyond the relief spec.

This is the spec viscosity for this engine, which is 0w-40. Engine has a coolant/oil heat exchanger, displaces 6.4L and makes 475HP. For the purpose of this video the vehicle was just placed in sport and floored. It went a little squirrely (did a bit of a sidestep on the squat) but came out of the hole strong with minimal tire spin and was held to the floor until 60Mph was surpassed. How far past 60Mph I went for this exercise is irrelevant, but I'll note that the video does extend beyond that rate of speed before I let off.

Important notes beforehand:
- Pump relief pressure spec is 65psi
- Idle oil pressure in gear is ~30-31psi
- Cruising oil pressure @2,100RPM is 57psi

@Quattro Pete does your ZF8 shift this quickly? I know you were complaining about the shifts being "soggy" even in Sport.

 

OVERKILL

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I don't recall mine being this quick.

I am out of town until next weekend so I won't be able to check anytime soon.

That's kind of what I suspected. This is how yours should shift, they should be very snappy in sport. Mine are even snappy in auto if I drive it a bit aggressively. They are of course soft if I drive like an elderly woman with an egg on the pedal.
 
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Looks like the oil pressure hit a max 68 PSI for a second and fluctuated around 65 PSI a few times. The pump pressure relief valve probably cracked open a few times. What would be interesting is the same kind of run with the oil a bit cooler (if you'd be comfortable), like 70-80C instead of 103C. With a bit thicker oil, the max pressure may spike up more than 68 PSI if the pressure relief valve gets more overwhelmed with more shunted volume. With cooler/thicker oil, if the max pressure doesn't go above 68 PSI then the pressure relief valve is working pretty well IMO.
 

OVERKILL

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Looks like the max oil pressure hit a max 68 PSI for a second and fluctuated around 65 PSI a few times. The pump pressure relief valve probably cracked open a few times. What would be interesting is the same kind of run with the oil a bit cooler (if you'd be comfortable), like 70-80C instead of 103C. With a bit thicker oil, the max pressure may spike up more than 68 PSI if the pressure relief valve gets more overwhelmed with more shunted volume. With cooler/thicker oil, if the max pressure doesn't go above 68 PSI then the pressure relief valve is working pretty well IMO.

I'll see what I can do. Since oil temp tracks very closely with coolant it's hard to find a stretch where I can do that without the vehicle getting up to temp in the interim.
 

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I can check in my 5.7 tomorrow if anyone is interested. FWIW, my 8HP70 shifts pretty nicely, though I don’t think as quick as yours.
Sure! The 5.7L makes peak power lower, IIRC, like 5,500 or 5,700. I know the 6.4L revs higher between shifts.

I didn't own a Charger with the 8HP, only three Grand Cherokees thus far, lol, but they all have shifted very fast. Definitely faster than the unit in my wife's truck. The "track" shifts are overly firm and not as quick as the "Sport" shifts, which are my personal favourite, it really just hammers out the gears in sport.
 
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The bypass spring on my LA-318 allows 68 psi cold but a quick rev to 2k rpm cold will briefly push 70 psi.
Mechanical gauge, not electric.

Max PSI hot is 62 psi.


Dont have an oil temp gauge. But use pressure to tell me when its at full temp.
38 to 42 psi at 65mph and -1950 rpm.
12 to 16 psi at 525 hot idle in drive foot on brake
18 to 20 psi in neutral hot, 600 rpm.

PSI was 44 to 51 at 65 mph with M1 0w-40, vs the PP 10w-30 in there now.
 
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Without the exact locations of the oil pressure sensor, as well as a schematic of the oil system, it is hard to say if the relief is cracking or not. If there is significant pressure drop through the passages between the oil pressure sensor location, and the oil pressure relief valve, it may not be cracking at all.

If it is cracking, and the two components are close together, this is called the pressure relief valve rise rate. Very common. I can post some graphs of rise rate curves.

A more interesting test would be a cold start, and slow rev from idle to high rpm. This will give you a better indication of the relief valve characteristics.
 

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Without the exact locations of the oil pressure sensor, as well as a schematic of the oil system, it is hard to say if the relief is cracking or not. If there is significant pressure drop through the passages between the oil pressure sensor location, and the oil pressure relief valve, it may not be cracking at all.

If it is cracking, and the two components are close together, this is called the pressure relief valve rise rate. Very common. I can post some graphs of rise rate curves.

A more interesting test would be a cold start, and slow rev from idle to high rpm. This will give you a better indication of the relief valve characteristics.

I posted one of those in the PCMO section.
 
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Just an example...not reflective of your HPRV

1617636646020.png
 
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Regarding the shifts, the 8HP75 in the Giulia is also very crisp like OP’s video.

Overkill, do we know for certain that the relief valve opens at 65psi or is there a degree of variance which is causing pressure to exceed that figure?
 

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Regarding the shifts, the 8HP75 in the Giulia is also very crisp like OP’s video.

Overkill, do we know for certain that the relief valve opens at 65psi or is there a degree of variance which is causing pressure to exceed that figure?

It's a standard spring-loaded relief configuration with the spring rated for 65psi, which means that's when the relief should start to open and oil begin bypassing back to the feed-side of the pump, regulating it around that pressure. I think you can see this when you see it flutter 64-65 after the 68. It might show up better on longer pulls, but I don't have anywhere I can go that I can stretch her legs beyond what was in the video.

Pressure will exceed the relief pressure if the pump is moving more oil than can be shunted through the engine and the relief at that pressure.
 
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