Design of a custom wet sump from scratch for VQ37

Background / Problem:

I'm swapping a Nissan VQ37 into an E46 BMW and its looking hopeful bar the sump layout. The engine only came in a front sump model and of course it sits directly over the rack and cross member. A dry sump solves my problem (there are two options available) but is super pricey for what is supposed to be a fun road car build. I need all the height reduction I can get to be able to close a factory bonnet as its a very tall motor with intake and VVEL steppers on the rear.

Aftermarket wet sumps are non-existent for the engine unfortunately also, so the mid-position between a dry sump setup and completely changing platform is to look at making a custom wet sump to suit my needs.

The Questions:

1. Are there any rules / guidelines or theories when designing a sump from scratch ? I'm not concerned about trap doors / baffles etc at this point but more a confirmation that 'it simply needs to hold x litres of oil and have a pickup y mm below the high tide mark' sort of thing ... or there is complicated science to it and its sure to doom the engine ? ie: its function seems basic, are there gotchas ... what are they ?

2. How shallow can the pan be at the end where I need maximum clearance ? Just enough to cover the windage tray and allow for the pickup plumbing and no more ? As shallow as I like but must run downhill to the 'big end' at some minimum gradient ?

3. Keen to hear any comments and ideas :) FYI I'm unable to modify the stock 'pan' as its a massive casting with a pressed steel bowl at the front for the oil.

hello there is no hard and fast rule on this as long as it holds the required amount of oil and doesn't allow the oil to hit the rotating parts the pick up needs to be at least 8mm off the bottom of the pan and the piping to the engine can go in the shortest possible route but doesn't matter what direction angle etc it heads in. keep in mind the g forces on the oil in the pan when building it as the oil when hot moves fast like water around and can easily push up to the crank when windage is added

Regards Ross

That's great advice thanks Ross ... so the shallow end of the pan can be just clear of the windage tray keeping things really slim ? I'll have to route connections to / from the remote filter out the side of the shallow end of the pan also which I assume will be no drama but will somewhat dictate the depth in order to get an appropriate sized fitting in.

Looks like my Christmas leave plans have been set !!

Something that is likely to be a problem, when welding, is the assembly distorting and it's pretty much impossible to seal a warped sump.

What I'd suggest is picking up a steel plate, big enough to drill and bolt the sump flange to, to hold the sump rigid as it's welded. 20mm should be fine and I'd be looking at cutting out the inner part for access to weld inside.

For the drain bung position, while the bottom may be best fro drainage, consider ground clearance (you said you're dropping the engine as far as practical) and whether it's preferable to put it on the side, close to the lowermost part of the sump - don't forget to allow for access as things like exhausts can make it difficult. I'd look to see what magnetic plugs are available and use that thread size, and pitch, for the drain fitting.

I assume you've some experience with fabrication, so don't need to point out that you're best to weld short sections, alternating sides and positions to minimise heat input?

Oh, almost forgot, the shape of the pickup can be important to ensure oil pickup and avoid cavitation - you may be able to cut off the OEM one and use it.

Dave, i have had hem built to be about 8mm off the windage tray i would like to have seen more if yu can on your project

Regards Ross

Thanks for the comments Ross and Gord. I'll get the stock pan removed in the coming weeks and then start to form a picture of what sort of dimensional freedom we have to play with.

Gord, I'll hopefully not have to do any welding ... will look to machine from ~50mm-70mm plate or similar for the most part and see if I can find an OEM pressed steel 'bowel' to fix at the big end for the oil. I'll investigate casting it as well as this sounds like a lot of fun and satisfaction but not an easy shape to get dimensionaly stable etc I imagine.

I'm a little envious of your resources, there. If you're happy with a separate, bolt on, sump it opens up quite a few options, as there are quite a few engines from different manufacturers you could use one off. Heck, there'll be local chaps who've swapped to dry sumps that should have the 'bowls' lying around surplus to requirements, that may save you some fabrication costs - however, if you' re planning on using it on the twisty stuff, a chance to fit a big wing design may be better?