Dry Sump / Wet (semi wet) sump

[911teo]

Anybody here can give me good explanation of the differences?

Why and how does a wet sump set up suffer from oil starvation on the track?

[Tim Walsh]

a wet sump is where the oil drains back to a pan in the bottom of the engine before getting picked up by the oil pump and back to the oil passeges

a dry sump is one where there is a middle step. It goes from the oil passages, to the bottom of the engine, pumped to a seperate tank, then pumped from there into the oil passages. This prevents windage losses by removing the oil from the engine, and starvation because of oil sloshing away from the oil pickup. that's why our tanks our so narrow.

[Wil Ferch]

In theory, this is correct...the "dry" sump doesn't suffer windage losses ( by the crank whipping in-and-out of a large volume of oil)...the crank centerline can theoretically be placed lower ( since the dry "pan" is shallower)...and the separate sump tank can be configured never to "lose prime" in high-g loadings. A wet-sump..in contrast...can easily start sucking up "air" as the volume of oil gets pushed "way" over to one side on a high-g maneuver.

However, our 911's suffer too...in "real-world" actuality.

The "s" shape hose coming off of the sump tank...notice..is located at the rear of the tank. Under high "g" braking....the oil in the rear of the tank moves forward and we suffer the same kind of maladies as the classsical wet sump. Some people ( here on this board) have gone to cutting open and baffling the tank to avoid this. SmartRacing Products does something similar ( at higher $) and also extends the bottom of the tank for two extra quarts of capacity....to avoid this. I would think a mod that puts the oil pickup in the "front" of the tank should be do-able and even cheaper......our cars can't accelerate at the same high g's as they can brake...so I propose this is a better approach than factory.

Wil

[addictionMS]

true dry sumps have the oil pump external to the motor, most non "porsche" race motors are that way. On these there is no oil collecting in the motor at all, unlike our motors where the oil does collect in the bottom some.

At least that is my understanding

jim

[doozer]

Minimum of two stages on an true dry sump, one sucking hot oil out of the engine into the tank, and another sucking oil out of the tank and squirting it in the engine

[911teo]

Originally posted by addictionMS
true dry sumps have the oil pump external to the motor, most non "porsche" race motors are that way. On these there is no oil collecting in the motor at all, unlike our motors where the oil does collect in the bottom some.

At least that is my understanding

jim

Jim

so you are saying that in true "dry sump" engine there is no oil lubricating the crankshaft? Sorry if this is really dumb... I am just to understand properly.

[randywebb]

No, the oil for the crank is pumped in -- then it is pumped out.

BTW, this is just like the circulatory system of a bird or mammal - the system is closed. In invertebrates, the blood just sloshes around in a body sump and is not under high pressure. Maybe Porsche can use that in it s adrvertising for the next car they come out with -- the sea slug or something...

[911teo]

Originally posted by randywebb
Maybe Porsche can use that in it s adrvertising for the next car they come out with -- the sea slug or something...

LOL

[Tspringer]

Some dry sumps also give you external oil pressure regulation. On my Daytona, you can turn the oil pressure up or down with a simple nut located on a fitting at the oil tank. Dry sump definitely gives you more consistent and constant oil pressure including providing full oil pressure on engine startup much faster.

[Wil Ferch]

We're getting off base.... I think my original post came close...here's yet more from a google search--->

http://auto.howstuffworks.com/question331.htm

- Wil

[911teo]

Wil
great link, thanks for all the replies.

[jluetjen]

Originally posted by addictionMS
[B]true dry sumps have the oil pump external to the motor, most non "porsche" race motors are that way.

The only reason for this is because Porsche's 911 motor was designed from the get-go as a large scale production motor with dry sump. Most stock-block race motors (read Le Mans and Nascar) were designed as wet-sump motors and the dry sump system was an after thought. F1 engines I believe are designed that way because mounting the oil-pump next to the block is the best packaging and servicing solution. Doing that on a commercial production motor would increase the part count which is generally not the preferred solution from a Design For Manufacturability perspective.

On these there is no oil collecting in the motor at all, unlike our motors where the oil does collect in the bottom some.

At least that is my understanding

Much of that has to do with the design of the pan. But a dry sump is a dry sump, the bulk of the oil is kept in the tank, not in the sump.