Oil Pressure Loss in Braking

[ddd4114]

After a few years of lapping and constantly seeing slightly elevated lead in my oil analysis reports, I decided to add an oil pressure transducer to my 2011 GT and start logging. I ran an event at Mid-Ohio this weekend, and I immediately found the cause. After every sustained hard braking zone, I found that oil pressure would plummet after a couple seconds, and it would stay low until I released the pedal.

Here is an example of what I experienced (Black = longitudinal acceleration, Red = oil pressure):

You can see that oil pressure normally stays around 65 psi, but in long braking zones, it drops into the 20's. The engine is entirely stock with the exception of a Boss oil heater/cooler. I started the weekend with the oil level at the top of the dipstick range, and after noticing the problem, I added ~200cc of oil each session until the pan was overfilled by about 1 qt. I didn't notice any change.

For those who have found this problem before, what do you recommend? Would an oil pan like this: http://www.americanmuscle.com/frpp-boss-r-oilpan-1114gt.html really prevent the pressure loss in long braking zones? I'm afraid that the baffling will only delay the inevitable (and not by enough). Would an Accusump be a better solution? A dry-sump system would be pretty awesome but is not going to happen.

Thanks.

 

[steveespo]

I run a Moroso aluminum road race pan. No oil pressure drop under braking or lateral g loads. Less expensive than the Ford Racing part and is also fully baffled and trap doored. Worth the investment.
Steve

 

[ddd4114]

Awesome, that pan is a lot more affordable. How high do you run your oil on the dipstick?

 

[MadBee93]

Can you overlay the engine speed (RPM) on the same plot?

If you are clutching in for an extended period and selecting the gear at the end of the brake zone and not going down through the gears during the entire brake zone, then this drop in oil pressure might NOT be a real issue. At idle oil pressure is only like 10psi.

There are cases to be made for heel toe shifting through all gears during a long brake zone, and there are cases to be made for staying on the clutch till the last part and only heel toe shifting to the final gear. It all depends on the car, the driver, etc... So, don’t feel bad if you are on the clutch till the very end of the brake zone. Just make sure you are fully in the proper gear and off the clutch before your foot comes off the brake.

 

[csamsh]

What about just doing your 5-3 shift? That would keep you off the clutch and not shifting as much

 

[SlowJim]

Awesome, that pan is a lot more affordable. How high do you run your oil on the dipstick?

The Boss 302 pan is even cheaper @139.50

 

[ddd4114]

Can you overlay the engine speed (RPM) on the same plot?

If you are clutching in for an extended period and selecting the gear at the end of the brake zone and not going down through the gears during the entire brake zone, then this drop in oil pressure might NOT be a real issue. At idle oil pressure is only like 10psi.

There are cases to be made for heel toe shifting through all gears during a long brake zone, and there are cases to be made for staying on the clutch till the last part and only heel toe shifting to the final gear. It all depends on the car, the driver, etc... So, don’t feel bad if you are on the clutch till the very end of the brake zone. Just make sure you are fully in the proper gear and off the clutch before your foot comes off the brake.

I thought the same thing at first, but I don't think it's the case.

I added engine speed (in blue) and clutch position (in green) to the graph and zoomed in on a section of the track that explains what is happening:

For those of you who are familiar with Mid-Ohio, the first braking zone visible is the left-hander leaving Thunder Valley, and the second braking zone is entering the Carousel. In the graph, you can see that I hold 4th gear for the left-hander, engine speed drops to ~4500 rpm, and oil pressure drops while trail-braking into the turn. I do a 4-3 downshift into the Carousel, and you can see the same thing happens. However, after I release the clutch, engine speed continues to drop as I scrub off speed. Even still, since I'm not decelerating much, oil pressure completely recovers. Therefore, I don't think this is related to engine speed and temperature (viscosity); I think it's simply caused by hard braking. Also, by looking at the graph, the oil pressure trend more closely resembles the acceleration trace than it does engine speed (except of course for the time shift).

Thanks for the suggestion.

What about just doing your 5-3 shift? That would keep you off the clutch and not shifting as much

That is exactly what I do.

Here is a video showing my braking and shifting:

 

[ddd4114]

Apparently I don't understand how to make Youtube links...

 

[csamsh]

Apparently I don't understand how to make Youtube links...

It's not obvious. Just copy the bold part and put it in

 

[mpm_1]

nice use of data and share your concern

I usually associate lead with getting past the overlay and down to the base metal on a bearing... never good

 

[ddd4114]

It's not obvious. Just copy the bold part and put it in

 

[MadBee93]

yup, looks like it's not from engine speed. If you get an aftermarket pan do an update and let us know how it works on fixing this drop in oil pressure!

I'm currently installing a DAQ system in my car also. I will see if I have the same issue at the next track event.

 

[ArizonaGT]

Get the Moroso 10-quart pan. The B302 pan will not be enough.

I had low oil pressure (10-15 psi) under heavy braking that was completely eliminated with the Moroso pan (50-70psi). These figures are from AIM.

Fill 12 quarts total during change including filter and about 5' of oil line to Setrab 925 cooler.

 

[Nutter281]

Would definitely be interesting to see the same graph on a deep-sump oil pan. Transducer + DAQ is pretty sensitive. Just throwing useless crap at the wall, but I wonder how much impact vacuum is having during braking. I don't even know our generation of braking well enough to state whether they are vacuum assist, but assuming they are, an increase in vacuum during braking may increase pull from the PCV into the intake right? Sounds like the issue is the pan but given the vacuum system and crankcase pressure are coupled through the PCV, it would be interesting to know how much periodic vacuum changes impact the pressure observed on the high side of the oil pump....

food for thought

Austin

 

[steveespo]

I run just above the full line on the dipstick. about 1/16". I made it a point to observe my Autometer elite gauge under full braking and cornering at the Glen last week end and under -1.15 and lateral 1.2 g the needle did not waver below 70 psi. A dedicated road race pan is a valuable mod. My engine now has over 12000 track miles (375 last weekend) and is as strong as ever. I run either Motul 300V 15W50 or Lubri Moly 10W60 oil and Ford Racing 820S filter on my stock longblock '11 GT motor.
Steve

 

[ddd4114]

I just installed the Moroso oil pan, and it was a bit more of a pain in the ass than I was hoping (since I'm doing it on jack stands in my garage). Unfortunately, I also found that my clutch was making noise, so I decided to replace that too. It turns out that one of the inner springs on the disk broke in half, so the whole thing was basically a time bomb. I also found that the factory driveshaft boot was torn and had puked grease all over the frame, so I have to replace that too. I think I need a new hobby...

I'm planning to run Mid-Ohio again in June, so I'll report back after that weekend. Based on what you guys have said, this should fix the problem.

Thanks everyone for your input.

 

[SlowJim]

I'll be at MO June 6-7 as well in HPDE3. Look forward to seeing you there

 

[ddd4114]

I'll be at MO June 6-7 as well in HPDE3. Look forward to seeing you there

Cool. I'm a red 2011, #411. If you see me there, feel free to drop by to chat!

 

[ArizonaGT]

I just installed the Moroso oil pan, and it was a bit more of a pain in the ass than I was hoping (since I'm doing it on jack stands in my garage). Unfortunately, I also found that my clutch was making noise, so I decided to replace that too. It turns out that one of the inner springs on the disk broke in half, so the whole thing was basically a time bomb. I also found that the factory driveshaft boot was torn and had puked grease all over the frame, so I have to replace that too. I think I need a new hobby...

I'm planning to run Mid-Ohio again in June, so I'll report back after that weekend. Based on what you guys have said, this should fix the problem.

Thanks everyone for your input.

That is a very common failure mode for the OEM clutches on these cars, and I've blown up two factory two-piece DSes like that.

Got a McLeod RXT now and a Dynotech DS and all is right with the world.

 

[ddd4114]

Yeah, the driveshaft failure doesn't surprise me. I bought an aluminum one-piece to replace it, so hopefully that does the trick. I am surprised that the clutch disk failed after only 39k miles, but I guess since ~5k of them are track miles, I can't expect too much. I'm replacing it with a Spec clutch, so hopefully that holds up better. The friction pads on the OEM disk were hardly worn, and the friction surfaces on the flywheel and pressure plate looked pristine.