Heavy braking and my engine sucks air???
 

Anyone else see this? Repeatably? Oil is at full mark on dip stick (if not a little higher). This is one of the next items on my list of 'to dos' this year. Want the car to be sound for some track use next year. Running Amsoil 0w-30 signature series oil and my engine details are in link below. Thoughts on causes, possible fixes?

wtf are you smoking?

i think he's saying he's getting oil starvation when braking. i don't know the answer, maybe better baffling or a dry sump

Yes, perhaps not clear in my post. Oil pressure gauge drops to zero. Looking to see if it is common and what solutions there may be.

Accusump is one but looks like a major under taking? Anyone installed similar? What would it involve?

I get pretty low oil pressure after a full track session ~10PSI or so. Never seen 0 PSI, never want too either..

Corvette people run a quart over full to prevent starvation. Any reason not to do this in our engines?

Just fill it up until it wont take anymore, problem solved

Do you have an oil cooler? If the fittings are facing down, you'll read full when you check it, but while it's running it'll actually run [insert oil cooler capacity here] quarts low.

So do turbo Subaru guys.

Excellent way to lose a ton of power from additional drag.

just fill some oil, then fill the rest of it with water till it start flowing out the cap. That will make sure your oil system still stays pressurised :P haha

love that dumbass that ran water through the engine to get rid of the dirty oil :D

But save your motor. I'd rather drive the car onto the trailer at the end of the day and make 5hp less throughout the day.

I don't think a quart over would be enough to cause problems. When the engine is running, most of it is in circulation, which is why it is so easy to suck air in some engines. An extra quart would be fine I would think.

This may be the problem. I have an FM twincooler though - both in and out fittings are at the top (see here about 3/4 of the way down).

I suspect that the cooler itself wouldn't drain - but the lines might? The fittings and line are -8AN, ID 12.7mm and about 0.85m long in all, I make that about 340cc? I'll go 0.5L over the full mark on the dip stick and see what happens.

I keep my oil level just over the top of the "F" on the dipstick, run r-comps with lots of sustained corners and never see oil starvation. If I did, accusump is the way. Its probably not a bad idea right now, but I know several peeps who've been tracking miatas hard, for a long time, that don't have this issue.

however if you add oil the pressure will drop, so by adding oil it will show that your pressure is lower with regular driving/street driving, but will prob get rid of you sucking air in hard braking and cornering

And possibly, with a high enough level, see all sorts of frothing due to crankshaft/oil interaction. I don't know how high oil would have to be in a Miata to lead to this, and I'd rather not find out.

If it's the stock gauge dropping to 0, it's worth checking the connection on the sender. If it's actually dropping to 0, an Accusump is the cheap/effective solution.

Wat?

How will adding the oil (reasonable amount) reduce the oil pressure?

adding oil maybe 2 qt or even 1 qt will cause the pump to work harder to push the same amount of oil through the system.

The pump flows just as much oil with normal or slightly higher oil levels. More oil will actually result in a larger positive suction head due to higher oil level in the pan since. The rest of the oiling system only holds so much oil and will not work any different with more oil in the sump. Thats why adding the oil helps with startvation since the oil level overall will be higher even with shloshing in the pan.

My car used to hit 0 psi under heavy braking, but since the turbo install it doesn't do it anymore. Adding more oil will give you more oil pressure, until you burn it up lol.

O rly?

:noob:

No, it won't.

Some other options
 

Thicker oil - try Mobil1 15w50. Sure, it will reduce power a tad, but it's better than a nuked engine.

Crank scraper and windage tray - requires dropping the subframe(or pulling the motor) to get to the oil pan, but crank scrapers are proven to increase power and reduce oil starvation by minimizing oil movement in the pan.

I had a crank scraper, windage tray and a modified oil pickup(1.8L pickup modified to fit my 1.6L pan) as the 1.6L pickup was not very low in the pan. I never saw low oil pressure on high speed sweepers(yes, on R compounds). I plan to rebuild the motor again(I nuked the #4 rings last year) and knife edge the crank and get a teflon scraper.

Probably the first thing I would do is as TheMan mentioned - make sure the electrical connections @ the sender are clean, but IMO if this is ONLY happening on high G sustained turns it most likely is oil starvation.

If dropping the pan is not your cup of tea I would first try some thicker oil and adding 1/2 to 1 quart additional oil. If that is no workie then an accusump would be the least painful option.

At high sustained RPMs more oil is being pumped everywhere in your engine. The oil that is pumped out under pressure relies on gravity and passages to allow it to return to the pan. The oil that is pumped into your valve covers is designed to return primarily through the rearmost section of the head. With sustained high RPMs, prolonged extreme braking enhanced by upgraded brakes and tires, oil that is pumped into the cam and valve cover area could conceivably exceed two or three quarts in volume. Think of your engine sanding on it's nose with the valve cover area half full of oil. At 1+ g-forces the oil won't make it to the drain holes as quickly as it is pumped, and held, up there.

And for those who are not familiar, racers often run an extra quart (or two) if they are limited to a stock oil pan by rules. As long as you are not interfering with the rotational mass of the crank assembly, you are just fine.

There is much misinformation in this thread from people who really don't understand their engine's oiling system and shouldn't be commenting.

Thanks all. The pressure drop is real, not only on the stock gauge (now installed in a sandwich plate port), but also on my SPA gauge whose sensor is in the stock position in the block. First thing to try is to see if I can stop it by adding 1/2 litre of oil above the full dip stick mark. As has been mentioned here it maybe that I am getting 1/3 litre drain into the pan from the cooler lines anyway. If not then it looks like an accusump - but goodness knows where I'd mount it!

Shit, my bad. It might help if I didn't read like a dyslexic. I misinterpreted his issue as oil sloshing in the pan in sustained high G turns. Six-shooter is SPOT on: since this is happening only during prolonged hard braking the problem is a lack of oil @ the pickup, which is @ the rear of the pan. Whatever oil is in the pan is pulled to the front, away from the pickup. Come to think of it I remember seeing my oil pressure drop to zero a few times under prolonged braking, but since this was PRE-engine build + turbo install I didn't care since my engine was beat to crap.

Prior to the engine rebuild I used to do an oil change before every event and always overfilled by 1 quart(was running 15w50 on a very tired 1.6(150K miles) at the time. I found that I would burn off the entire quart during the event so I then tried only adding 1/2 quart and found that I still burned off the excess, but I still had ~ the same amount of oil at the end of the day(@ the full mark). Why did I burn more oil when I added more?

My theory is that if you overfill the crankcase you will end up increasing the air pressure in the crankcase which leads to oil getting past the rings and seals. I am not sure if that is bad, but it sure seemed like a waste of oil to me and I never saw a huge oil pressure drop at any time when I only added 1/2 quart, even under hard braking such as entering turn-2 and turn-11 @ Laguna.

I still think a crank scraper would help and I never saw zero pressure after the new engine was installed(maybe the crank scraper and modified oil pickup was enough?), but an accusump is probably the best way to avoid oil pressure loss when flogging on the track.

good luck,
Mike

perhaps can you weld a piece horizontally that is open at the back to prevent the oil from sloshing too far forward

Do you see the red piece of steel? When you slow down, the oil will be stuck there creating a nice cup.

Attachment 203410

My Moroso eight quart pan is designed just like that.

Tomei has a fix for this problem for RB Nissan engines by designing little "reducers" (so to speak), which go into the oil galleries to reduce the flow.
There are quite a few sump baffles out there that are bolt-in. Doesn't Racing Beat sell one?