Dry sump basics please

[millsn]

What exactly is it that a dry sump does and does anyone have any plumbing schematics they could send me?

 

How does the crank get supplied with oil if there is no reservoir for it to pass through?

 

Nigel Mills - 2.0 Zetec carbs

[greg]

From the little I know (and I could be wrong but someone like PC will correct me:)

 

Oil gets pumped into various parts of the engine by the pump. It then falls to the bottom of the engine. The crank is not splash lubircated, but fed directly to get oil to the big ends.

 

In a "wet sump" engine the oil collects in the sump where the inlet side of the pressure pump picks it up, puts it thru the filter then back through the engine. The oil here is stored in the sump (hence wet).

 

A dry sump has two "pumps" A suction or scanvenge pump that picks the oil out of the sump and puts it into a tank, where it collects. The sump is hence "dry". Another pump (pressure?) picks up from the bottom of the tank, put the oil through a filter and then into the engine. On some engines (Crossflow) these "pumps" are combined, and often have 5 ports. Other engines use two different pumps, the pressure driven in the normal fasion, and the scanvenge pump driven off a belt.

 

The wet sump is simple and hence used on nearly all road cars. The weak point is the oil "pickup" which under extreme G forces (not found on the road) will suck air. This is very bad for bearings, especially big ends that do not like even a second without oil due to the big pressures they are under.

 

In a dry sump system because the tanks tend to be big, and deep the lickely hood of the inlet sucking air is very small (there would have to be no oil in the tank or the car would have to be on its side, or a huge G force applied). The easiest way to visualise this is if you compare a pan and a glass. To expose the bottom of the pan you only have to tip it a bit, to expose the bottom of a glass you have to tip it alot (give a liquid.).

 

Dry sump systems hence are used in cars that want to reduce the chance of starving the engine of oil due to G forces.

 

There are a few side effects:

 

a) expense - Dry sump systems need a different sump, pump(s), tank, hoses ect....

b) reduced sump depth, as the sump does not need to store several litres of oil it can be alot shallover.

 

As for how oil get supplied with oil get a look of an exploded engine diagram, it will usually be fed by a gallery at one end.

 

 

Greg, Q 880 RAE (Green/Ali XF)

[stevefoster]

>>>Other engines use two different pumps, the pressure driven in the normal fasion, and the scanvenge pump driven off a belt.

 

This is how the Caterham VX solution works. At least you get the engine filling with oil and hydraulic slow down of the pistons as a warning. A 3 stage external belt driven pump and you get instant oil loss, like Neil's Zetec Westie at the Lydden meet you were at Nigel.

He had the crank re-ground after running the bearings and crank. He had the shells with him yesterday. They were completely shot.

 

The belts do throw off after a gravel trap visit or is the alternator belt comes off and takes the scavenge belt out as in Neil's case.

Reving to very high revs like R500's and 250+bhp VX's puts all these things under a lot of pressure of course.

 

If you pop down you can see how the tank supplies oil to the pump throught the front of the sump pan and how the scavenge returns it.

 

A 3 stage pump takes oil from the tank and feeds it into an oil gallery (usually near the pump / where the oil pressure sensor is).

 

All the racers say go with a 2 stage one. Reliability over out and out best possible spec on paper.....