Mistakes were made, my R34 Story

[Kinkstaah]

Went over my datalogs on a whim and noticed a worrying combination of events.

High RPM
High Temperature
Low Oil Pressure
Knock Retard

I bought some 10w-60 because I actually think this will be better going forward given track temp is 125C and 10-40 will actually be thinner in those environments. I know I had a leak but it's not entirely sure how much pressure loss can be attributed to that.

The knock retard does correlate with all of the above. When it's not present oil pressure is higher. And by 'low' I mean at 6800 RPM the oil pressure was recorded as low as ~35psi pretty constantly. Which is obviously very not good. I'm hoping that thicker oil that ISNT LEAKING will result in a bit more pressure when I need it.

Also in the last session I got a very spongy break pedal. I bled the lines as the car is on jack stand right now with the wheels off and I noticed... no air in the lines? Maybe the tiniest bit of tiny frothy bubbles for the first 0.1 seconds of bleeding the whole car?

The breaks did come back to me after I backed off (and felt fine driving normally). Doesn't appear to be any leaks anywhere that I can see. Any thoughts on that?

[Duncan]

I don't know what you should expect with an LS, but the oil pressure sounds terrible, sorry.

As for the brakes, you can get fade from the pads not just the fluid, although generally that feels like a wooden block not doing anything while fluid feels like an oh shit there is no pedal so you can generally tell. What pads are you running front and rear?

[Kinkstaah]

Yeah the rule of thumb with an LS is 7psi per 1000rpm. That is decidedly not enough at 6800rpm. I mainly looked for the scenarios where knock started to be picked up and it was later in the session when things were hotter, and oil was thinner, and the pressure was lower than it should be.

(i.e very horrible).

I am hoping with thicker oil (I was running Penrite ten tenths 10-40, the manual specifies 10-30) that does not leak that it's much improved at that time!!!

I am using Project Mu Club Racer CR pads. I'm also using the Project Mu 335C fluid. The symptoms imply that it was fluid that boiled, but no bubbles seemed pretty weird to me when I bled it today. I want to try Castrol SRF as it has a much higher wet temp but, well, I have new Project Mu fluid lol... so I should at least use that.

The pedal on track was really noticable. It went from basically normal feeling to instantly near-floor. The car did pull up as before, it was just very much nearly at the floor before the brakes engaged. At that point I pretty much decided the day was very done, it did *kinda* come back during that very slow cooldown lap into the pits. Felt perfectly fine driving home.

[The Bogan]

Would a Mellings oil pump be a viable option 

From my time with a LS, and talking to tuners and LS specialists, the "weak" OEM oil pump is one of the first things they recommend to swap out if I was going to give the engine any high RPM

I opted for a Mellings high volume, with the high pressure springs and I never had a issue with it

Cost wise they are not expensive in the scheme of things 

[Kinkstaah]

(it is a brand new ported mellings pump)

I suspect the lack of pressure is due to the leak. It was *not* that low in other logs of oil pressure in the past. It wasn't that hot either, but not far off.

[GTSBoy]

I take it that the knock retard is from bearings tapping a little tune?

Thicker oil is a fragile bandaid. You need a much bigger oil cooler and probably the bigger pump being discussed.

[Kinkstaah]

1 hour ago, GTSBoy said:

I take it that the knock retard is from bearings tapping a little tune?

Thicker oil is a fragile bandaid. You need a much bigger oil cooler and probably the bigger pump being discussed.

I don't know it is due to that. It could just be due to load on track being more than a dyno. But it would be nice to rule it out. We're talking a fraction of a second of pulling ~1 degree of timing. So it's not a lot, but I'd rather it be 0...

Thicker oil isn't really a "bandaid" if it's oil that is going to run at 125C, is it? It will be thicker at 100 and thus at 125, where the 40 weight may not be as thick as one may like for that use. I already have a big pump that has been ported. They (They in this instance being the guy that built my heads) port them so they flow more at lower RPM but have a bypass spring that I believe is ~70psi.

I have seen 70psi of oil pressure up top in the past, before I knew I had this leak.

I have a 25 row oil cooler that takes up all the space in the driver side guard. It is interesting that GM themselves recommend 0-30 oil for their Vette applications. Unless you take it to the track where the official word is to put 20-50w oil in there, then take that back out after your track day is done and return to 0-30.

[MBS206]

The oil pressure sensor for logging, does it happen to be the one that was slowly breaking out of the oil block?

If it is,I would be ignoring your logs. You had a leak at the sensor which would mean it can't read accurately.

It's a small hole at the sensor, and you had a small hole just before it, meaning you could have lost significant pressure reading.

 

As for brakes, if it's just fluid getting old, you won't necessarily end up with air sitting in the line. Bleed a shit tonne of fluid through so you effectively replace it and go again.

Oh and, pay close attention to the pressure gauge while on track!

[GTSBoy]

9 hours ago, Kinkstaah said:

I don't know it is due to that. It could just be due to load on track being more than a dyno. But it would be nice to rule it out. We're talking a fraction of a second of pulling ~1 degree of timing. So it's not a lot, but I'd rather it be 0...

I myself AM TOTALLY UNPREPARED TO BELIEVE that the load is higher on the track than on the dyno. If it is not happening on the dyno, I cannot see it happening on the track.

The difference you are seeing is because it is hot on the track, and I am pretty sure your tuner is not belting the crap out of it on teh dyno when it starts to get hot.

The only way that being hot on the track can lead to real ping, that I can think of, is if you are getting more oil (from mist in the inlet tract, or going up past the oil control rings) reducing the effective octane rating of the fuel and causing ping that way.

9 hours ago, Kinkstaah said:

Thicker oil isn't really a "bandaid" if it's oil that is going to run at 125C, is it? It will be thicker at 100 and thus at 125, where the 40 weight may not be as thick as one may like for that use.

Yeah, nah. Look at this graph

which I will helpfully show you zoomed back in.

As an engineer, I look at the difference in viscocity at (in your case, 125°C) and say "they're all the same number". Even though those lines are not completely collapsed down onto each other, the oil grades you are talking about (40, 50 and 60) are teh top three lines (150, 220 and 320) and as far as I am concerned, there is not enough difference between them at that temperature to be meaningful. The viscosity of 60 at 125°C is teh same as 40 at 100°C.

You should not operate it under high load at high temperature.

9 hours ago, Kinkstaah said:

It is interesting that GM themselves recommend 0-30 oil for their Vette applications. Unless you take it to the track where the official word is to put 20-50w oil in there, then take that back out after your track day is done and return to 0-30.

That is purely because the only way they can achieve their emissions numbers is with thin-arse oil in it, so they have to tell you to put thin oil in it for the street. They know that no-one can drive the car & engine hard enough on the street to reach the operating regime that demands the actual correct oil that the engine needs on the track. And so they tell you to put that oil in for the track.

9 hours ago, Kinkstaah said:

I have a 25 row oil cooler that takes up all the space in the driver side guard.

Find a way to get more air into it, or, more likely, out of it. Or add a water spray for when it's hot. Or something.

 

As to the leak --- a small leak that cannot cause near catastrophic volume loss in a few seconds cannot cause a low pressure condition in the engine. If the leak is large enough to drop oil pressure, then you will only get one or two shots at it before the sump is drained.

[MBS206]

59 minutes ago, GTSBoy said:

As to the leak --- a small leak that cannot cause near catastrophic volume loss in a few seconds cannot cause a low pressure condition in the engine. If the leak is large enough to drop oil pressure, then you will only get one or two shots at it before the sump is drained.

I agree with everything else, except (and I'm rethinking this as it wasn't setup how my brain first though) if the sensor is at the end of a hose which is how it has been recommended to isolate it from vibrations, then if that line had a small hole in, I could foresee potentially (not a fluid dynamic specialist) the ability for it to see a lower pressure at the sensor.

But thinking through, said sensor was in the actual block, HOWEVER it was also the sensor itself that broke, so oil pressure may not have been fully reaching the sensor still. So I'm still in my same theory.

 

However, I 100% would be saying COOL THE OIL DOWN if it's at 125c. That would be an epic concern of mine.

 

Im now thinking as you did Brad that the knock detection is likely due to the bearings giving a bit more noise as pressure dropped away.

Kinkstah, drop your oil, and get a sample of it (as you're draining it) and send it off for analysis.

[GTSBoy]

11 hours ago, Kinkstaah said:

I have seen 70psi of oil pressure up top in the past, before I knew I had this leak.

I neglected to respond to this previously.

Get it up to 100 psi, and then you'll be OK.

[Kinkstaah]

1 hour ago, GTSBoy said:

The viscosity of 60 at 125°C is the same as 40 at 100°C.

But.... the reason I want to run a 60 weight is so at 125C it has the same viscosity as a 40 weight at 100C. That's the whole reason.

If the viscosity changes that much to drop oil pressure from 73psi to 36psi then that's another reason I should be running an oil that mimics the 40 weight at 100C.

I have datalogs from the dyno with the oil pressure hitting 73psi at full throttle/high RPM. At the dyno the oil temp was around 100-105C. The pump has a 70psi internal relief spring. It will never go/can't go above 70psi. The GM recommendation of 6psi per 1000rpm is well under that...

The oil sensor for logging in LS's is at the valley plate at the back of  the block/rear of where the heads are near the firewall. It's also where the knock sensors are which are notable for 'false knock'. I'm hoping I just didn't have enough oil up top causing some chatter instead of rods being sad (big hopium/copium I know)

LS's definitely heat up the oil more than RB's do, the stock vettes for example will hit 300F(150C) in a lap or two and happily track for years and years. This is the same oil cooler that I had when I was in RB land, being the Setrab 25 row oil cooler HEL thing.

I did think about putting a fan in there to pull air out more, though I don't know if that will actually help in huge load situations with lots of speed. I think when I had the auto cooler.

The leak is where the block runs to the oil cooler lines, the OEM/Dash oil pressure sender is connected at that junction and is what broke.

I'm actually quite curious to see how much oil in total capacity is actually left in the engine. As it currently stands I'm waiting on that bush to adapt the sender to it. The sump is still full (?) of oil and the lines and accusump have been drained, but the filter and block are off. I suspect there's maybe less than 1/2 the total capacity there should be in there. I have noticed in the past that topping up oil has improved oil pressure, as reported by the dash sensor.

This is all extremely sketchy hence wanting to get it sorted out lol.