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Dry Sump. Pump it up!

I am pleased to bring you the 4th in a series on the technology of our 1350 engine.

Efficiency. The purpose of dry sumping is efficiency: Put enough oil in the right places to lubricate and cool moving components, but not so much as to produce drag. Then, more power comes out.

The term, “dry sump,” simply refers to scavenging the oil from the lowest point (sump) of an engine – making it “dry.” Except, it’s never really dry. Oil goes almost everywhere and wants to collect wherever there is a low spot. Wherever oil gathers near moving parts, there is not only lubrication, but also risk of drag and even damage.

One of the greatest potential sources of power waste is the crankshaft. But, not in our QC4v engine!

No tranquility. The oil doesn’t pump gently to the valve train or rod bearings, lubricate and peacefully trickle back down, to make the rounds again. It’s violent in there: Oil goes “weightless” and smashes down when a boat launches and lands. It splashes with every wave impact. It wants to pile on one side, when you round a turn marker. Just think about how your body moves around at speed – and you’re not ducking under a spinning crankshaft!

A crankshaft’s relationship with oil is turbulent. Big slugs (counterweights) come whipping around and can whack right into pools or flying gobs of oil. Same for cam lobes in a cylinder head. Whack the oil enough, it’s like whipping egg whites – it froths and becomes a lazy lubricant. It reluctantly flows; there’s more air than oil. (Lube engineers have additives to help, but it’s the engine designers’ job to manage it.) If oil doesn’t get where it belongs, there is mechanical drag. And if it does, there is viscous drag on things that spin, slide or reciprocate. Every time, a little bit of that kinetic energy becomes heat. Add up all the little bits: Oil temp goes up. Power output goes down.

So engine designers work to: 1) put oil exactly where it needs to be (for lubing the “wiggly, spinning pieces”), 2) channel it away from getting beat up or doing evil, and 3) maintain enough oil volume so it can do the job within its temperature limits. Even wet, oil pan engines have windage trays to keep oil out of the crank.

Hardware. Now you know why; in Racing’s 1350, here’s how: by sucking, pumping, hosing, and cooling; by passing through reservoirs, holes, nozzles, and more holes; down channels, past baffles, and into sumps. Yes! Really!

The heart of a dry sump engine: its pump. There are three scavenge stages and a pressure stage.

High volume return of oil from valve train lubrication is through two passages (grey highlights) cast into the front cam chain cover.

Engine oil is scavenged from three locations by a gang of three pumps. It is then pushed through an oil cooler and out to a remote reservoir. The engine, reservoir and its hoses contain 11 to 13 liters of oil. After a brief respite in the reservoir, it’s back to work! From the pressure side of the pump, oil is directed to individual bearings and friction faces where it is metered (by small nozzles or jets) to the precise lube requirement at each location.

With quad cams and 32 valves, lots of oil goes to the heads – and back. Most of the oil in the cylinder heads returns through two, huge passages in the front cam chain cover and into the sump.

Five ports, at low points in each cylinder head, drain oil from valve train lubrication through block passages and into the sump.

In this view of the side of the block, from below, trace (yellow) how five ports in each cylinder head connect to three block passages to either side of the pan and its sumps.

Oil that happens to escape the big ports is collected at five smaller ports in each cylinder head. From there, it drains back through passages to the pan and its sumps. The pan is designed with ribs and other surfaces to keep residual oil away from the crankshaft and direct it to the sumps. There suction pickups do their thing, and the process begins again.

All that, so next time you crack open the throttles, all the ponies are there – roaring to put a smile on your face.

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4 Responses to “Dry Sump. Pump it up!”

  1. Stefan Eriksson says:

    What is your oil recomendation for sci1075?
    Thanks Stefan

    • Fred Kiekhaefer says:

      MerCruiser 25-40 is our recommended oil for 1075SCi engines. This is standard merCruiser oil (non-synthetic) available at any merCruiser dealer.

  2. chris m says:

    What high grade synthetic can be used in the 1075 package and others that are similar? AMSoil, Redline and a few other brands come to mind but I want to be sure.
    Thanks.

    • Fred Kiekhaefer says:

      Follow the owner’s manual: use MerCruiser 25W40. Our oil is tested extensively and found to function superbly in use. We do not recommend synthetics because they fail to adhere to components during periods of inactivity, common in boating. Synthetics tend toward excessive component wear from dry, cold starts. If you are racing, and have a pre-oiling system, that’s a different story: Then AMSoil, Mobile 1, and other synthetics may do fine. However, we have not validated their performance. I can say, they are a waste of money in typical recreational use.

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