mr2daj

iTrader: (-1)

Was in track yesterday and when i checked the logs afterwards there are big drops in oil pressure when breaking!! My pressure relief valve is set to ~4.5 Bar and stays at pretty much all the time on track but when really gard on the brakes it can get as low as 1.5 bar. The oil was filled to the F on the dipstick and it has a sump baffle fitted copied from the one maruha sell.

I was under the impression that surge was not a major problem but it obviously is. What if anything are you guys doing about it? For reference the car is getting around 1g in the brakes and 1.2g lateral but the problem seems to be mostly on the brakes.

I am considering fitting an accusump but if i am trying to mask a problem that shouldn't be there maybe i should investigate further. Dry sump would be the way to go but that's just not going to happen.

On top of this i blew up yet another 6 speed.... but that's another issue.

Savington

iTrader: (31)

Well known problem. It's not harmful to the motor as there is very little load on the bearings during hard braking. No need for an accusump or anything else.

k24madness

iTrader: (6)

I would try an accusump in this situation. While I don't doubt Sav's expertise I would evaluate the problem on a case by case basis. I have to believe some tracks are going to highlight the problem more than others. Adding slicks etc will only make the problem worse. If you got some good $$$ invested in a motor it's worth the insurance IMHO.

mr2daj

iTrader: (-1)

well that's what i was thinking. i just don't like the idea of having 1.5 bar oil pressure @ 5k revs +. i know the load at that point is low but there is still some load. its a 400whp car with a lot invested and i really don't fancy another rebuild. even if it is just for my sanity! no real downside to fitting an accusump is there? just a little more windage when there is extra oil in the sump.

Slicks, more downforce and bigger brakes are planned for the near future so the problem is only going to get worse...

bbundy

May not be much load output but rod bearings actually see the highest load with high RPM just due to accelerating the mass of the pistons back and forth not necessarily at high output torque unless you have excessive detonation. It is quite common to rev the **** out of the motor under hard braking with too soon of downshift or too much heal toe throttle application. Even really good drivers do that occasionally.

Two rebuilds for me without Accusump had rod bearing showing significant wear and overload damage. One rebuild after Accusump and the bearings looked great for me.

Same problem for me High hp car is fast as hell down the straight and only marginally faster in the corners = lots of "oh ****" brake zone where the oil sloshes out of the deep part of the pan by the pickup.

Seefo

iTrader: (5)

you might be able to "overfill" the oil some to reduce the effects there. may not be the permanent solution you want.

I have ran .5 quart over before without trouble.

bbundy

I have issues with running too much oil 1/2 qt maybe but 1 or more I've done by miss switching the valve on the accusump. combined hard driving and hard cornering I think too much of that oil ends up in the head and charges into the breather system causing issues. you will think you blew up your motor but the problem mysteriously goes away when the oil level gets back to normal.

Seefo

iTrader: (5)

yea, I agree, .5 quarts is probably close to the limit. I will take a look at my catch can, I am not turbo'd so I probably won't have it as bad as you guys.

bbundy

Turbo and ~3X the HP makes a huge differance with the breather system. stock configuration don't work so well any more when you do that.

mx5-kiwi

Is there a common or known solution to this..? I am not having any visible or obvious problems in this area but want to start improvong little things like this as I slowly get the car up to scratch with reliability...(NOT braking manifolds, downpipes etc)...

We have an "enduro" series here every year for 1, 3 and 6 hour classes. I want to start in the one hour and work my up. so looking in to things like this will be important.

Also, I see Savington says the oil surge isn't an issue but I wonder if some baffles in the sump may not be a good idea, with endurance (1 hour +) events in mind?

Savington

iTrader: (31)

Bob's empirical evidence on his rod bearings is quite interesting, and something I'd never heard before. Baffles are still horseshit, though - I've seen data from motors with and without them and they don't do anything.

Bob, 1qt accusump? Electronic or mechanical?

bbundy

Im using a 2 qt accusump it is mounted under the car near where the stock fuel filter mounts with an electric valve. I've had flaky behavior with the EPC pressure switch not clicking on for pre-oiling so I currently have the pressure switch bypassed so its just an electric on or off valve. I have a switch on the dash to override but with it on the valve opens automatically whenever the key switch is in run and you dont have to remember to open and close the valve manually.

Turn the key to run and the oil pressuer comes up to whatever it was when I last turned it off before I even hit the start button.

I still get flaky oil pressure readings associated with vibration I think under load because using the stock early miata pressure sender but it dosn't dip so much in an extended length braking zone any more.

sbiggers

Although the engine has no load when the oil level drops, would you have to worry abut temporarily low oil pressure when you roll back onto the throttle, or is the system pretty quick to build pressure back up?

bbundy

something I learned in Engineering school.

there are two soruces of load on rod bearings.
1) combustion load
2)recipricating mass acceleration load.

Not counting knock the total forces on rod bearings on typical engines with mid rpm torque peaks are higher at High Rpm red line even with no cumbustion load than they are when the engine is operating at its peak torque output.

Blipping the throttle in the braking zone to match revs or downshifting too early causing very high revs in a braking zone when the oil pressure has dropped to zero is very hard on things.

bbundy

FWIW I also bult a Baffle with hinged trap doors in my pan very simmilar to this one and I don't think it works.
http://miataroadster.com/maruha_moto.../i-412129.aspx

Leafy

iTrader: (1)

How could it not? How much pitch are you getting in hard braking and what are you pulling acceleration wise during braking? In the 1-1.2g area I'm guessing and not more than a few degrees in pitch. But I guess the bigger question is that even if the extra baffle worked properly, does it actually do anything? IE is the problem oil sloshing forward or is the problem oil not draining back into the sump? At high RPMs the oil pump is bypassing a lot of oil, does that bypass back to the oil pump inlet or back into the front of the pan? Even if it goes to the inlet more than half the oil circulating in the engine is going to be falling into the front part of the pan during hard braking and not making it back into the sump. So its not like the baffling is failing to prevent the oil from sloshing forward its the braking forces and the pitch of the car preventing the oil from flowing back into the sump. The pump's flowrate makes this seem plausible. Any merit here or am I just jerking off?

bbundy

I think it needs to seal around the edges better than it does then it might work. I experimented with water in the pan and it seemed like it slowed the slosh down but didnt stop it imperical evedence showed still got pressure drop with long braking zones. I never worked out flow rates to see if there was issues with that but there could be.

I'd like to dry sump as that would cure both oil and breather issues I think.

mr2daj

iTrader: (-1)

im getting pretty bad surge at not that much longitudinal g

Here is a screen shot from a data log comparing 2 laps. the red is a reasonably hot lap and the blue is out of pit lane taking an easy lap to warm the car. seems a lot worse when the revs have been higher for longer and obviously when the g load is higher.

bbundy

Yep braking at .8 g and you loose oil pressure. Your RPM blips arnet too bad however. I occasionally make the mistake and get crap loads of RPM while braking hard by eather too much of my foot on the throttle with the heal toe mid shift or just downshift and let out the clutch too soon. I can do it right most of the time but I cant say there will never be load on the engine in the braking zone so it is ok.

Accusump. All I can say is two rebuilds prior to accusump had damage to rod bearings. one rebuild after accusump and the rod bearings were perfect.

bbundy

Also having the engine at high revs for a period of time sends oil all over the engine and a lot of it collects on top of the head under the valve cover thus not in the pan as it doesn’t drain back quickly enough. A 300+ hp miata motor will typically have Breather issues And the breather issues make the oil not draining back into the pan even worse. Honestly I think the -10 breather hole I drilled into the side of my block improved some symptoms as well.