Dry sump routing, tank to valve cover or not? Where to put the cooler?

[TurboWood]

Gents,

I'm trying to plan my dry sump system and after doing some research I see that there is some controversy over the breather lines. The base engine side appears relatively simple (tank --> oil pump --> engine --> scavenge pump --> tank...). On the breather side Caterham always connects the tank to the valve cover and to a catch can. This will surely prevent any positive pressure from building in the crankcase, but won't it also allow for the possibility of blow-by gas being recirculated?

 

If the scavenge pump is consuming more flow than the engine is producing then you will start generating a vacuum. By having the tank connected to the valve cover this never happens, but you do allow gas from the tank to be re-pumped by the scavenge pump. Wouldn't we want some vacuum in the crankcase if we can get it? From what I can tell the online opinion seems to be something like 10"Hg (~5psi) of vacuum is a good target. There are even adjustable vacuum valves on the market so this can be specified.

 

Now if there is a vacuum being created and there is a valve controlling it then that valve still needs to be connect to something. I suppose this could still be the oil tank, but why not connect it to the catch can so that it has a better chance of collecting fresh air instead of aerated oil?

 

The other question that comes to mind is the location of the oil cooler. If this is a water/oil cooler then it's relatively straight forward to integrated it with the oil filter mount (as is done on most Caterham's). With an air to oil cooler it looks like this could either be done on the scavenge pump side or the oil pump side. There appears to be arguments for both. Putting it on the scavenge pump side should maximize the delta-temperature between the oil and the air, but it's aerated. Putting in on the pump side should ensure it's all liquid, but the oil temperature should have decreased.

 

Comments?

 

Thanks,

Daniel

[bsimon]

Daniel,

 

To run a full vacuum you need to oversize the scavenge pump sections.

Most DS kits do not have enough pump to pull serious vacuum so the cambox cover is usually vented to the top of the tank with a large (AN10-12) line.

To take full advantage of vacuum in the crankcase, one needs to review what oil control rings are fitted to the pistons as well.

 

I believe in water cooling the high pressure side of the system. The cooler can be smaller (and lighter) for the application. YMMV

 

How is build coming along? Engine in chassis yet? When will we be hearing the pitter-patter of tiny little GM/Caterham tires?

[TurboWood]

Thanks Bob. I posted some pictures of the engine mounted in my thread in the members ride section. I'm hoping to get'er-done in the next 4-6mo!