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Dry Sump Secrets

Most people who want a dry sump know its most important function -- it provides oil to the pump even in high-G turns and sweepers. But there are many inobvious facts about its functions.

1. Fact. A dry sump system removes foam from the oil so it lubricates better. Subfact: It doesn't do it perfectly. NASCAR uses centrifugal oil/air separators added to the dry sump system. The rest of us rely on an anti-foam agent in our oil to reduce foaming, which is the same as in stomach pills: Simeticone!

2. Fact. Dry sump tanks must be round in order to maximize oil swirl on entry, which greatly helps "deaeration" (getting the bubbles out) of the incoming oil. Subfact: Round is better but there are many square or tall rectangular tanks that race every day. Swirl counts, but apparently depth matters. Depth gives the oil more of a chance to deaerate as it gets sucked down to the outgoing hose.

3. Fact. A dry sump system still needs an oil cooler. Subfact: A dry sump, like a deep sump, contains more oil than a standard system and therefore it takes longer to get too hot, but it will get there. And a dry sump tank and lines contribute to cooling, but not as much as you'd suspect.

4. Fact. Dry sump systems still need catch cans. Subfact: A dry sump tank should be filled to about 7/8th capacity, to provide expansion room (the "headspace" for the hot oil. Most guys never think about oil expansion, but it does expand. When an over-filled dry sump "burps" out of its vent, you are likely to get a litre of oil out of it all at once.

5. Fact. Most dry sump systems need an oil tank heater for 40-degree (F.) or less weather. Subfact: Heaters commonly are AC current and consist of a "electric blanket" wrapped around the tank. But most hobby or daily driver VW's do not have heaters, so a respectful warm-up interval is advised to avoid blowing oil filters or coolers just getting out of the driveway. Special plumbing configurations with thermostatically controlled bypass valves can be installed to dump oil pump overpressure back to the oil tank until you reach about 180 degrees F.

6. Fact: A small oil tank, depending on application, can serve as well as a large tank. Porsche ran 6-litre oil tanks on their Type 547 engine 4-cam Spyders. One reason was oil is heavy and the factory only wanted to carry just enough to do the job. Today, the average round oil tank for the VW holds a heavy three gallons. Subfact: There is always more oil in a 6-litre system than 6 litres. Don't forget the oil coolers (2 each on a 550 or 550A Spyder), the oil lines, the engine case residual, and the oil filter.

7. Fact. The CB Performance dual-stack dry sump pump is only a single pickup pump, as opposed to pumps that have scavenging pickups in the heads, valve covers, etc. Subfact: Even being a single pickup, the CB withstands endurance racing, 7 to 24 hours at a time very well. With the engine running, the CB system will show about 1/4 inch, or 6mm of oil at the bottom of the stick. Kind of scary the first time you see it. The truth is, the VW dipstick exits its guide tube and fully depressed, stops about 11mm short of the case floor.

8. Fact. The CB pump system is simple but so efficient it sucks all the running oil out right down to the oil pickup level. Subfact: This fluctuates, and at times, the pump is also evacuating case pressure, which really helps internal case windage and adds a little power on its own.

9. Fact. A dry sump system is really two oil systems as opposed to one. Subfact. This takes a little getting used to -- one oil system is delivering oil to the engine bearings. The other oil system is pulling oil out of the case and sending it to the filter, cooler, and oil tank. As a real-world example of the two systems, we've had the case pickup get clogged (long story how), but the oil delivery side of the system was working. The engine case filled up because no oil was being returned to the oil tank. And the opposite can happen as well.

This is by no means all there is to know about a dry sump system, just a highlight overview.

FJC

Great info. Thx.

Fact: the oilfilter would protect the engine better is it was not placed in the returnline of the scavanger pump, but was plumbed as a full flow system.

Hi Blue Thunder,

Can you give is a drawing of your routing?

FJC

@Blue Thunder, the CB style dry sump pump is not capable of running full flow. Thus you only have a choice of running the oil filter on the return line or on a external oil cooler as plumbed from the top of the engine case.

When using the autocraft 3 stage style pumps then the oil cooler can be fitted before the engine on the full flow line.

@FJC: I don't have a drawing of the way I have routed my system, but I have an Autocraft 2 stage pump (1 stage 26mm, 1 stage 52mm). The 52mm scavenger side outlet runs to a thermostat and can run through a frontmount cooler, or straight back to the drysump tank. The 26mm inlet is connected to the tank and the outlet is connected to a remote oilfilter before it goes to the engine (full flow).
@4agedub: you are 100% correct, The CB pump is not a true 2 stage pump, and cannot be used for full flow connection

Interesting read, FJC. Will the CB pump fit below a stock sized pulley and rear tin in a Beetle? Also, what are you guys using for sump tanks? Most of the ones I've found online start in the $250-$300 range.

Kafer_Mike wrote: ↑Tue Jan 22, 2019 6:59 pm Interesting read, FJC. Will the CB pump fit below a stock sized pulley and rear tin in a Beetle? Also, what are you guys using for sump tanks? Most of the ones I've found online start in the $250-$300 range.

No it won't Mike.
BMD used to offer a correct ratio serpentine belt system for those dry sump pumps.
No longer in business unfortunately.
MST makes their version of a dry sump kit but the alternator pulley is not small enough to get the fans speed where it needs to be.
I've used Scat power pulleys, machined the backside to clear the cover, then a T3 generator pulley.
It's not perfect but it's close.

This photo was taken before we countersunk the oil cover plate bolt holes for flush-fit bolt heads.

On the subject of standard pulleys being used with the CB system, CB provides a slightly more narrow in thickness pulley with their kit, which requires a narrow belt. It is the same diameter as a power pulley, made for use with a press-in sand seal. Of course, press-in seals can be trouble. They spin, seize, and leak. We have to JB Weld ours in if using an unmachined case. And we've had to lightly machine the inner surface of the CB pulley hub to insure smooth no-galling rotation against the sand seal body.

One day we had no CB pulleys and a race to run. We had a standard sand-seal power pulley, standard belt thickness. We quickly discovered we could place shims behind the sand seal to stand the pulley out a bit, and use a thin steel pump cover with flush-mounted bolt heads. And we had to shim out the alternator pulley to match.

Using a regular thickness power pulley and a regular belt, it worked. You'd have to do some precise cutting to use stock sheet metal that fits behind the pulley because you have oil in and out lines on both sides of the pump.

All three of our oil tanks we use are Ebay items. About $30 each.

FJC

A "secret" I learned years ago from someone smarter than I, was to modify the CB 4 gear pump for true Full Flow use. By plugging the internal port from the pressure stage back into the case and tapping a 3rd fitting into the housing, you can route the oil from the sump tank, through the 21mm pressure stage, right back out of the pump to an external filter (cooler if you want to) and then into a tapped Full Flow fitting on the case. It's been working GREAT on my baja for years and thousands of miles. I run a 0W-40 Mobil 1 full synthetic with a half a bottle of Comp Cams break-in additive with every 8qt oil change and maintain ~ perfect oil pressures with the stock oil control springs/plungers and doghouse cooler in a modified shroud with functional T-stat and flaps. Another good idea is to open up the Pressure pump inlet fitting from -8 AN to -10 AN. With the "small" 21mm pressure stage being fed easily from a large line and gravity from the tank, it can easily supply what the engine needs. This pump feeds a mild 2110cc EFI Turbocharged T1 putting 240hp/tq to the ground through and 091 trans, 930 CVs and 31" BFGs.

Is 21mm pressure really enough?

Considering dry sump on my 2165 turbo engine.

21MM is enough. It is all I have ran ever. 2275cc big engine in both my bugs.

Steve Arndt wrote: ↑Mon Mar 04, 2019 9:51 am 21MM is enough. It is all I have ran ever. 2275cc big engine in both my bugs.

Thank you. Even with a turbo and external filter/cooler etc?

Seems kind of small. I use a 30mm pump today

I also run 0W40 like Karl. Yes on external cooler/filter. I don't have a turbo but the oil line orifice to those is very small.

bug66 wrote: ↑Mon Mar 04, 2019 1:23 am Is 21mm pressure really enough?

Considering dry sump on my 2165 turbo engine.

Yep, it's actually perfect! Mine is pushing through a filter and feeding a turbo, and I grooved all my lifters to feed more oil up the pushrods to keep the valvetrain a little happier. Pressure as well as temperature are absolutely perfect, wouldn't change a thing. All "high" oil pressure means is a restriction to flow. High oil pressure also heats up the oil more, wasting energy pumping oil through the relief valve, etc. Blueprint the pump and it'll keep 10psi on a hot idle. Oil pressure is one of those things where more is not better, especially in our air cooled Type 1 platforms.