oil pressure vs rpm

[aeronaut]

Anyone with actual oil gauges have oil pressure vs rpm numbers for:

Stock s50/s52.
S50/S52 with S54 dual pickup mod.

I'm trying to decide if I *need* the VAC upgraded S54 oil pump for my track car.
So far, with very little data, it seems the S54 pump/dual pickup in an S50/S52 lowers oil pressure somewhere between 5-10psi. But I'd really like to confirm that. FYI, both the S52 and S54 are limited to 58psi max, so it doesn't matter once above ~4500rpm.

[pbonsalb]

Does running 900 rpm idle instead of 600 make a difference?

[aeronaut]

I've thought about that.
It would keep the engine from seeing 7psi at idle. So it'd see something like 10psi min at 900. But at say 3500, stock vs S54 dual pickup, the S54 dual pickup version is going to be 5-10 psi lower. I think, that's kinda what I'm after. How much lower?

[AlpineM345]

How long can you wait? I got a S52 with S54 oil pan and pump in my track car but it is winterized until April or so. If you can wait, I can test it for you.

[aeronaut]

Thanks, I will have made a decision by then.

It just seems there's quite a few S52 cars out there with the S54 dual pickup and without the VAC pump, that are fine. I would have thought we'd be hearing about engines failing if the $700 VAC pump were NEEDED.

[pbonsalb]

PM Chikinhed; he runs the S54 pump in his turbo S52 and I think he data logs. He is actually in the process of changing to the equivalent of the VAC pump — putting an S52 rotor in a machined S54 pump but his car is not back on the road so no comparison data. He has posted some pressure data, I think, in the FI subforum.

[aeronaut]

Thanks, I found one of his posts. From way back in 2013. This is in an S52 with S54 pump, no VAC mods.

"54 psi at 7200 rpm and ~11 psi at idle"

That sounds perfectly fine, if a touch low at idle, but (IMO) it appears his gauge may have been reading low because at 7200 it should have been well above the check valve pressure of 58.

He wasn't happy with the above, and modded his S54 pump.

[AlpineM345]

More information from him. He shimmed the relief to get more pressure. He also has a turbo.

https://www.bimmerforums.com/forum/s...M5x-S5x-engine

I messaged him about the setup a while ago. Let me see if I can dig it out.

Here you go. This is from Chikinhed back in 10/1/2015. Hopefully he doesn't mind that I am posting this... I have more messages from him if you are interested.


Keep in mind that the 'high flow' S54 pump is just the S54 oil pump bored deeper to accept the gerotor (pump) from the M/S5x oil pump. Therefor the oil pressure at idle will be no better than the standard M/S5x oil pump.

I've used the S54 oil pump for 45,000 miles now. I am also supplying a turbo with oil from the oil system but there is an oil restrictor so it probably isn't robbing that much oil.

I have the VAC oil pump shaft upgrade but that doesn't do anything for pump output.

I would like to have the high flow upgrade but didn't feel like I've needed it so far. The shims I've added gives me 70 psi at higher rpm's.

[aeronaut]

Good stuff.
Yea, shimming increases max pressure (but doesn't get the pressure equal to S52 pump pressures between idle and max).
Lots of 4-5 post threads on this issue.

[NeilM]

Thanks, I found one of his posts. From way back in 2013. This is in an S52 with S54 pump, no VAC mods.
"54 psi at 7200 rpm and ~11 psi at idle"
That sounds perfectly fine, if a touch low at idle, but (IMO) it appears his gauge may have been reading low because at 7200 it should have been well above the check valve pressure of 58.

I'd have to disagree with that interpretation.

Mine would be that even at 7200 rpm, his S54 pump wasn't able to develop normal max oil pressure when installed in an S50/52 engine. And I have supporting evidence for my view, which is that my own S52 pump easily hit max pressure with hot oil, whereas my unmodified S54 pump did not — with the same VDO gauge.

Neil

[aeronaut]

Oh wow, that really points to needed the VAC oil pump.

[aeronaut]

I'm only reading 29PSI oil pressure at 4000 rpm.
Could be a number of things, obviously the sensor, etc.
But crap.

[fbirch]

I'm only reading 29PSI oil pressure at 4000 rpm.
Could be a number of things, obviously the sensor, etc.
But crap.

On what setup - S52 pump?

[aeronaut]

On what setup - S52 pump?

Nope. S50 with S54 VAC modified pump.

[fbirch]

Thanks. How is your cold start pressure? Bimmerworld sells an S54 oil-pan-plus-modified-S54-pump for the S52/S50 that they claim will produce higher pressure than the S52/S50 pump itself. I wonder if they are just selling the same VAC mod'ed pump as part of that kit.

My Accusump LED normally blinks (indicates oil is being supplied to the engine) briefly in about half the turns on my home track. At the last event I noticed it was coming on with solid illumination, in more places n track and for longer time periods than normal. I then noticed that the hot oil pressure was lower than normal (Accusump turned off, car stationary), when rev'ing the engine in the paddock. Cold start pressure is normal. Reading some threads here, it seems the S52/S50 is prone to cracking pickup tubes on tracked cars. That will be my first path of investigation. Just when I thought I had this car whipped into shape......

[aeronaut]

Cold first start idle pressure is low 20's. Once warm, idle pressure is around 10-11. Note, only 3 starts on the current setup (new pump, headgasket, etc).

I'm using an AiM 0-5bar (0-72psi) sensor, which they say is good for fuel and water, but not oil pressure. They sell a 10bar sensor specific for oil. I'm not sure why the 0-5 bar sensor wouldn't work for pressures below 5bar, but hopefully that's the issue. Or something else cheap and not time consuming. I'll pick up a cheap mechanical oil pressure test gauge and see what that says.

[aeronaut]

Ok, I just found actual AiM documentation on the sensor I'm using. It's fine for oil, but there's a 50/50 chance I have it wired backwards, or am using the wrong connector (it needs a pull-up resistance). We'll see. I'll report back tomorrow.

[aeronaut]

Update, bought a cheap ass harbor freight mechanical oil pressure gauge. All is good. Start /idle pressure from cold is ~35psi. Settling down to around 25psi at idle and 60psi around 3000 rpm. These are all measured well below operating temps. Whew.

[olemiss540]

That makes much more sense......

[aeronaut]

Yea, I was going to be really pissed if I had to call VAC. Again. LOL.

[NeilM]

Update, bought a cheap ass harbor freight mechanical oil pressure gauge. All is good. Start /idle pressure from cold is ~35psi. Settling down to around 25psi at idle and 60psi around 3000 rpm. These are all measured well below operating temps. Whew.

Excellent! Just what you should be seeing.

Also a good demonstration of what can sometimes happen when you change more than one thing at the same time and then don't get the result expected. Ask me how I know! Not that it's stopped me much. ;-)

Neil

[aeronaut]

Exactly. That exact issue (changing multiple things) was in the back of my mind the whole time.
Cams, lifters, oil pump, head gasket, tune, injector rate, and instrumentation. YIKES. lol. Oh, and clutch and PP. What could go wrong?

[AlpineM345]

Just a data point. I drove my E36 M3 track car for the first time this year just a few minutes ago. It has an S54 oil pan and an unmodified S54 oil pump. Cold startup pressure is ~63 psi. At approximately 195 deg. F, I see just below 50 psi at 3,000 rpm. It idles at ~11 psi at that temperature.

These pressures were measured with an Autometer 0-100 psi analog gauge.

[aeronaut]

That's a good data point, and fairs well for the stock S54 pump. 195deg oil or water temp?

[AlpineM345]

That's a good data point, and fairs well for the stock S54 pump. 195deg oil or water temp?

195 oil temperature. Water was around 180. I couldn't get it any higher than 195 on freeway since I got an oil cooler and it wasn't too hot outside.