Dry Sump question... Oil flow from catch tank to sump.

As are electrically-driven valve trains

Would only add one more factor to your list of trade-offs for dry vs wet - because a wet sump can't have a super huge depth (for the cg reason you noted), the wet sumps typically have more oil getting entrained around the rotating crankshaft/con rod assembly so that adds a small HP loss vs the dry sump (that makes no practical difference on a normal road car, but virtually forces F to accept the greater complexity of the dry sump for its models ).

 

I don't know how it could happen, as the main oil pump pulls upwards towards the oil filter: how can it happen? If it happens (i don't know why, but maybe there is a leak somewhere) it takes years and years.

correct

Correct, but not enough: it guarantees no air in the oil for the reasons I explained (no foam nor emulsions means no air in the oil, means much more reliability in a long race)

The drysump is for racing, as the 308 GTB carbed had to race, in early Ferrari plans. It just did it in Itallian rally championship, for what I know, but it's a very appreciated race design: a plus.

correct, but not for the 308 engine (drysump and wetsump are the same engine except this)

Yes and no: the more power (very low amount) loss due to the draining pump ties the lower frictions at hi G cornering with the crankshaft (in a race, the drysump is for racing)

Yes and no: the much less air in the oil helps a lot in a track day, in a race or at full speed on a (German...) motorway. But you are correct that it doesn't help much in a everyday use

The drysump is a race solution: F1 cars have it, so it's nice to have it. Ok, it's useless on a vintage car, but the vintage car itself is useless, so...

ciao

 

Gravity is what causes a Dry sump to eventually drain the tank when sitting. An oil pump is not sealed - it has required clearances in the rotors and oil will seep through those clearances - just as it leaks past a faulty gasket!

Some engines use a check valve in the feed (suction) side of the system an attempt to preclude that drainage BUT having a check valve there introduces a failure point than can destroy an engine.

 

Why are your advantages only applicable to a race car?

I'll take a dry sump any day.

Besides all the reasons mentioned, the scavenge stage(s) reduce crankcase pressure and windage which increases horsepower and helps ring seal.

 

I agree that if a wet sump system had a poorly designed pan and windage tray, the advantages you mentioned DO exist. But oil oil pan/windage tray design was pretty much established by the mid -60's so that advantage doesn't really exist in a performance-oriented modern car.

 

IMHO this thermistor is absolutely in the wrong place and the reason why we have such low oil temperature readings on our cars.
While wet sump cars measure the temperature in the sump before oil passes the cooler, dry sump cars measure after the cooler.

Regarding gravity drain I made a graph some years ago which shows the decreasing oil level in the tank over time. Will dig it out, translate and post here.

BTW. Lowering the center of gravity was also an important reason for the invention of dry-sump engines. Irrespective of how Ferrari screwed up this design principle on the 308.

Best Regards
Martin

 

I'm sorry, but you are wrong: check the 308 oil system design and you will realize that's impossible. The oil tank is filled from above, so the oil cannot come back to the sump from the oil tank. The main oil pump pumps upwards, as the oil filter is higher than the main oil pump, so the oil cannot drain into the sump through the mai oil pump as the oil pump ducts are climbing to the oil filter and then to the oil radiator (that is quite high): the oil level in the oil tank cannot go lower the oil filter and the oil radiator height even in 10 years (gravity is just towards down, not up).

This said, maybe there is something i don't know of that oil system: at present i just think it can goes down a bit but cannot be empty nor in ten years

ciao

 

I disagree. If that was the case why would any manufacturer build dry sump cars after the mid 60's? Certainly not to just spend more money.

Sure there can be great wet sump systems, they just won't work as good as a great dry sump system.

I agree they leak down when sitting but to no detriment.

Albert, you are correct the oil is returned to the top of the tank, it is not going to drain back into the scavenge stages, it will drain into the inlet port of the pressure stage of the pump.

Looking at the parts diagram, it doesn't appear there are dynamic seals on the front plate of the oil pump pressure stage so oil could (slowly) leak back from that area and also up through the pump gears into the main oil galleries/bearings.

Unless the upper oil level in the tank is lower than the crankshaft which I do not believe possible

 

Correct - it will drain into the pressure side!

List modern performance cars that have dry sump systems that can out perform modern performance cars with wet sump symptoms. You will find no performance advantage.

You will find that DS symptoms are there as much for "bragging rights" as it being a "racing system" not for any performance benefit.

I have worked extensively on both. DS systems are cool/WS systems work just as well on a NON-race car and are less complicated.

 

The only advantage is being able to lower the engine. No other as mike996 says, as a sump is just a oil tank, and can be designed just as well as a dry sump oil tank. If you can ensure the oil pressure pump always has fresh oil then the engine will not care.
Pete

 

I've worked with both extensively as well. Still, prefer dry sump.

To your question, for example the new 991 has an "integrated dry sump", which is basically a wet sump design with 4 scavenge stages. Not getting much better for a system that holds the oil in the pan.

Considering that, why do they use a dry sump on the GT3 and 911r, if it has no performance advantage over a wet sump or as they call it, integrated dry sump system of the other 911's?

I understand that you like wet sump systems but just can't agree that a dry sump system has no advantages unless it's a race car.

I mean, we are talking about sports cars here correct? That may occasionally see track use even though they aren't "race" cars?

 

Incorrect.

An oil pan being as flat as it needs to be ends up being a rather large dimensional area to have enough oil capacity. This is a tougher job for the inlet side of your oil pump as the oil could end up at any corner of the pan no matter how many baffles and trap doors there are.

Dry sump tanks being tall/narrow and more oil capacity are inherently better at doing their job as the returned oil has one place to go, straight down.

Just no way around it. (unless you can show me a modern sports car with an oil pan 2 feet deep)

 

Like promised attached my graph I made some years ago and shows the oil lever decrease over time. Taken oil temperatur into account after engine shut off.

Best Regards
Martin
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Martin, the oil level in the tank can go down just until it reaches the oil filter level, no lower. That's the lowest point after the oil pump: the pump sends the oil to the oil filter first, and just after that to the crankshaft (see the color drawing some posts above), so it cannot go down by gravity below the level of the oil filter base. Unless there is an hole directly into the sump after the oil pump (impossible). It could have a leak from the relief valve after the oil pump (the relief valve opens to the sump), but no more, so it would take many years to drain and just if there is a leak from the relief valve.

ciao

 

I could talk for hours about the NPSH (net positive suction head), emulsions in the oil, cavitation, gas separation from liquids, blow-by in the sump, hydraulic design and so on, but I will resume it all in very simple few words: the 308 GTB drysump lubrication system is VERY well designed and there is no doubt that the drysump system is much better than any wetsump system if you want the top performances from your engine.

The higher is the liquid column above the inlet port of the oil pump and the better is the air separator from the oil, the better is your oil system: The wetsump hasn't any air separation system and the oil column over the inlet oil pump is the lowest possible (if there is, as sometimes it can even happen there isn't at all or at least there is more air than oil).

The drysusmp system has just one problem: it costs much more than the wetsump and requires (more often than the wetsump) an oil radiator, as there isn't the cooling given from the oil pan. Except this, it has only advantages: race engines are drysump


ciao

 

Not incorrect at all. I was being theoretical, so yes imagine an oil pan 2 feet deep if you like.

Again the first reason for a dry sump system is to ensure oil is always there for the engine at all times. In racing with high cornering forces, the oil used to run away from the oil pump introducing air and causing crankshaft bearing failure. This is solved by a dry sump system AND sure then you can design the oil tank to improve the quality of the oil, etc. but the first reason is as I have stated. But it is possible to design a wet sump system so the oil pump always has oil too.
Pete

 

If this is the case, then why is my tank completely empty? It didn't take many years for the tank to empty.

 

I sincerely have no idea. Maybe there are some parts that I don't know of that system: I'm thinking if there is some draining hole somewhere, for example something that allows you to drain all the oil when you change the oil. Did it become completely empty or just goes down a lot?

ciao

 

In the sump, at WOT and at full RPM, there is a big storm: pressure waves from the pistons, a lot of blow by compustion gases from the liners (and from the turbocharger, if you have one...) that is trying to pressurize the sump. If you add the high speed cornering and braking on a track, you can imagine how big is the oil pump difficulty to pump oil, that is a foam and no more an oil: the dry sump design solves all those problems.

ciao

 

Ok, I was being realistic, meaning there is no way in any vehicle that I know of to build/shape an oil pan like a dry sump tank and have it still fit in the car without being a jackstand.

 

Why could oil not leak from the shaft that drives the pump and goes through the front cover plate of the pressure stage?

 

+1 -- thru the clearances in the high pressure pump, thru the clearances in the crankshaft, and drips back into the sump. Note in that lubrication figure that the main high pressure galley coming off the high pressure pump that feeds the crankshaft is below the bottom of the oil tank.

 

It's completely empty, it's obviously finding its way to the sump in some way.

 

If all of the oil is sitting in the sump, how long would it take to re-pressurize the system after startup. Quick enough that there shouldn't be a concern I assume.

 

What I know (this seen with my eyes) is that after a cold start pressure gauge goes up quicker on the drysump than with the wetsump (two 308-328, same engine, of course). In the westsump there is a second during which the oil pressure is at zero and the engine rattles a bit. With the drysump this there isn't.

In the wetsump the oil pump is higher than the oil level in the sump, so it drains (100%) just in some minutes or even less. So every time you start the car, the oil pump works empty for a second:with the drysump this only can happen for a VERY LONG rest (if it happens). I think the main drain (in the drysump) is around the part 15 (piston of the oil pressure relief valve).

Yes, there aren't seals around the oil pump drive shaft nor around the reliev valve piston: it can drain from there, you are correct, but 10 liters (or what they are) requires a long time before draining through those passages: much more (one million times) than from the intake suction in the wetsump that immediately drains all the oil from the oil pump in the wetsump. Just this is enough (in my opinion) to show how better the drysump system is: you don'y have your crankshaft bearings nor camshafts work without oil pressure for a second after each engine start (and this is why I recomend a 5W or a 0W oil...)

ciao
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