This one isn't really about EFI at all, but it's a subject close to my heart...Preamble :
I don't know how many of you will appreciate/use this information, but in the event that someone is building a car for the track/fast road rather than tracking/thrashing an existing car, or has an oil surge problem on an existing car that they are willing to put some effort into fixing then this information could come in quite handy.Applicability :
Firstly, the problem of "oil surge" (low pressure due to sucking up air instead of oil) is MUCH more applicable to inline engines that are mounted longitudinally. Straight 6 and inline 4 rwd being worst affected. fwd engines are rarely affected and flat/V engines are also less affected.The issue :
Obviously a good supply of clean, cool/warm, high-pressure, non-aerated oil is essential for good bearing and engine life. Depending on your OEMs care in this area it *may* be a non-issue for you. If you have ever taken the opportunity to watch your dash while braking on the limit from 100mph down to 30mph for a tight one you may have had the displeasure of seeing your oil pressure warning light on. For me the light was on from around 80mph all the way down to the turn in point with both an open sump 4 pot and an open sump 6 pot (both inline). Fortunately because during braking the forces on the crankshaft and conrods is minimal the residual oil will probably see you through and it will be OK. On the other hand if you are like me, seeing that light makes you cringe inside :-)Effect of configuration :
Solutions from worst to best :
- If your pickup is at the rear of the sump you will be likely to have issues under brakes and extremely unlikely to have issues under hard acceleration. Cornering will be average and depend on the level of trail braking and/or rolling into the throttle across the corner.
- If your pickup is at the front of the sump your braking will almost certainly be fine, however you may experience surge under hard throttle off the line (this is VERY bad for the bearings)
- If your pickup is in the middle you are best set for a well balanced package.
- If your pickup is considerably up off the bottom you are much more likely to have issues with oil surge.
Opponents to the flat top say :
- Open sump, no control - Highly likely to have issues under some circumstances or other. Bad.
- Open winged sump, no control - This will help however not as much as you might hope. The period of low oil pressure will *probably* be reduced, however it will still be present. Because at any given angle of overall G there is more oil up-hill at the beginning the pickup will remain covered for a longer time. Still far from good.
- Open winged sump with trap doors - The idea here is that the trap doors swing inwards towards the pickup thus allowing oil that is up-hill to run down to the pickup, and the oil around the pickup to not run away from it as the doors are shut in those directions. Unfortunately because their is no lid the oil still slops over the doors and moves away from the pickup faster than we would like. Trap doors should never be used with a sealed top as they will only trap air in the wings and the oil will not be able to flow out of the wings quickly anyway.
- Normal sump with sealed flat top - The biggest single improvement is found here. By putting a sealed lid on with only a hole for the pickup to hang through and the dipstick to measure through, the oil that is in the sump can not move significantly when "shaken" by the movement of the car. Furthermore because the oil down-hill of the pickup can't move, the oil up-hill that runs down sits on top of it and provides the maximum volume for the longest dry out free time. Because the pump is pulling volume out of the area below the top plate oil is assisted in not overflowing, and anything available is drawn down into the lower region by the flow. It is important that the level of the top plate is correct. It should be placed at the height that the oil level would be sitting at with the engine at redline continuously (ie, 1 or 2 litres up in the head etc). Any lower means less oil available in the reservoir to drink during a turn/braking zone, and any higher means air under the plate at extremes and more room for up-hill oil to move away from the pickup into. It is important that the holes for pickups and dip sticks are as small as possible because the surface of the oil will extend across on an angle perpendicular to the G line from the lowest lip of that hole.
- Winged sump with sealed flat top - This carries all the same advantages as the previous configuration with the added bonus of more "up-hill" oil to feed the pickup while the returned oil from the engine is running away from the pickup. i.e. the dry period is minimal with this configuration.
- Dry sump - I won't cover this here as :
- I have no expertise/experience in the area (yet)
- It's fairly expensive
- It's fairly complex
- It's touchy and easy to get wrong (aerate the oil while trying to clear the sump to the tank)
- I haven't proven that a good wet sump isn't good enough
It has been suggested to me that oil will have a difficult time getting down under the plate through the small holes. I reject this notion because the pump is drawing oil into that region as fast as it uses it from above the plate. Additionally, when under brakes for example, the oil is falling down to the far end away from the pickup regardless of whether there is a top plate or not. In essence it would not have gone to the pickup anyway, and when the G's go away, it will quickly fall down right on top of the pickup.
Someone also said that air will be trapped under the plate displacing oil, any small amount of air will naturally find it's way out of there as quickly as possible due to our friend gravity pulling the heavy oil down and helping the light air up.Extras :
Some of these are useful, but do not address the core problem.
Description of my sump :
- Crank Scraper (clears the oil from the crank as it moves past and collects airborn oil returning it all to the sump)
- Windage tray (prevents the wind from the fast moving crank from whipping the oil in the sump up into a froth)
- Wings (add oil capacity, and importantly add it up hill of the pickup for various wing directions. Effective, esp when combined with a sealed top. Caution, the roof line of these must be flat, or tapered up hill to the main roof to prevent trapping air and reducing effectiveness)
- Trap doors (attempt to keep oil around the pickup, ONLY effective when the sump is open topped. If closed top, the trap door effect is caused by the roof anyway...)
I added extra oil capacity of 0.5 litres to each of the four directions (front, rear, left, and right). I also used a windage tray from another related engine model to keep the oil above the top plate being whipped up into the air/foam before it could fall. I used a 10mm plasma cut sump spacer and block skirt brace to gain an extra litre of capacity and to stiffen the block for high rpm use. In total I went from 4 litres to 7 litres of oil. I increased surface area for cooling, and above all else, I gained good oil control by using a top plate. The top plate combined with the wings means very little chance of oil surge in most normal braking zones and corners.
Ideally I would have liked to have a funnel shape leading down to the lower region to help get more oil in faster, and the same leading up to get the air out faster. This would add significant height to the setup however so is not really practical. The next step is a full dry sump if that doesn't work out. Dry sumps also allow you to lower your engine and move it rearward aiding good weight distribution.
Ultimate wet sump (diagonal lines in blue and green represent oil level at 1g) :Examples :
OEM open topped long inline sump (bad) :
My winged sump pre top plating (poor) :
Trap doored open top sump (mediocre) :
Trap doored and semi-closed sump (trap doors are not good to have here) :
Toyota OEM closed top, semi winged lower section (good) :
My custom winged top-plated sump (ultimate wet sump?!) :
The sump mods I did for our C series Cummins :
That engine was suffering from surge in heavy seas :
Now it doesn't :-) I hindsight I would not have used the baffles, and would have put the top plate on an angle (engine sits on angle in the boat) however it is still a vast improvement over how it was before me taking to it with the grinder and MIG.
Mazda OEM windage trays :
I welcome any dry sump expert to share their knowledge on effective scavenging from the sump to the tank. The only way I can see to 100% guarantee non aerated oil is to run a very shallow wet sump design and enough oil to keep both the tank 100% full all of the time, the lower region 100% full most of the time and finally enough to hang around up in the head(s) at high rpm and still meet these conditions. In this way the scavenging pumps can be larger than the main oil pump and a return from the top of the tank to the lower wet area can be used to ensure that oil is pumped round in circles rather than oil AND air pumped to the tank directly. The late model corvette uses a system like this from the factory with a twin crank driven pump and external tank. One pump moves 1.5x the volume and it takes it from a single central pickup point in a conventional wet sump setup. Corvette setup :