Geek speak

The complicated explained

by JEZ SPINKS

Dry-Sump Engines

How race cars, supercars and HSV’s W1 stay lubed-up O IL STARVATION sucks.

Poor pick-up is bad news for critical engine components, such as bearings, which need lots of the black gold to reduce friction and dissipate heat to avoid going kaput.

It’s why a dry-sump engine has for decades been employed by some of world’s fastest, nimblest vehicles – ranging from a World War II Spitfire to Formula 1 cars, supercars... and HSV’s new W1 muscle car.

The W1 follows the W427 in borrowing an advanced lubrication system from Chevrolet’s fastest Corvette to aid dynamic driving.

When you’re braking, accelerating or cornering with serious intent, the conventional wet sump system has the potential to suffer oil surge – where oil sloshes up the sides of the sump and leaves the pick-up tube exposed so it draws in air.

To avoid this, dry sumps employ a separate oil tank and multiple pumps in a multi-stage process.

O supercars and HSV’s W1 The deeper tank’s ability to store greater quantities of oil is also handy for performance cars. It helps the oil perform better for longer.

Benefits don’t stop there. A shallower oil pan allows lower positioning of the engine for improved centre of gravity, while extra power can be liberated by a lowered crankcase pressure; thanks to the combination of the lower oil level and scavenger pumps helping to remove air.

Ferrari, Lamborghini and Porsche have been incorporating dry-sump engines in various forms and models for decades.

That includes the original 911, though its sump was more of a wet/ dry hybrid – especially compared to today’s GT3 variant, which features W1 stay lubed-up no less than seven scavenger pumps to aggressively feed oil back to its separate reservoir. (Alternatively, the W1 features just one.)

Mercedes-AMG’s GT also employs a dry sump, linking it to the 300SL Gullwing – fortunately without being quite as problematic. The huge oil capacity of Benz’s 1950s race-car-turned-road-car was so effective at cooling the engine that you had to drive it like you stole it to ensure proper combustion and unfouled spark plugs.

There are several reasons dry sumps aren’t ubiquitous in the industry. The additional components and plumbing adds complexity, increases the weight of the engine, and costs a few hundred dollars more than a wet system. M

A dry-sump engine has for decades been employed by some of world’s fastest cars

From ZR1 to W1

As customised by HSV

MAY have inherited the dry sump lubricating system with the Corvette’s LS9, but it had to make modifications for its installation in the W1’s engine bay.

It took the upper (separation system) and lower (pick-up and transfer piping) sections of the Chevy’s oil reservoir, but features a different shape and geometry – and is positioned on the opposite side of the engine to the US sports car. HSV’s engineers also had to create some unique oil lines.

A dual-gerotor oil pump is carried over, integrated on to the crankshaft and featuring separate rotors for supplying and scavenging the oil.

Nick True, HSV’s managing engineer for powertrain, says while there are multiple benefits to a dry-sump system, its primary aim for the W1 was maintaining constant oil pick-up during fast and dynamic driving on road or track.

“You do get some benefit from scavenging the crankcase and reducing the crankcase pressure," he told MOTOR, "though I wouldn’t say you get a huge amount of additional power [with a dry sump] in this application. It’s principally for oil-handling.

“In a race car application, [engineers] might scavenge harder to get that crankcase pressure lower, but we’re not doing it for that reason.”

Pump It!

How the W1 avoids oil surge

1. SCAVENGE

A dual-gerotor oil pump is driven off the nose of the crankshaft, and comprises a primary supply rotor and a secondary ’scavenge’ rotor. The former draws oil from the bottom of the 58cm-tall, cylindrical oil reservoir/tank. Oil is then passed through a filter and distributed around the engine – covering the crankshaft, bearings, camshaft and piston cooling jets.

2. GRAVITY

Gravity then does its thing and the oil drains into the shallow sump via internal passages in the engine.

The scavenge pump inside the sump then picks up the oil and blow-by gas (an escapee from the cylinder combustion process) and pumps it back into the oil tank via a return pipe.

3. RIGHT ROUTE

A transfer pipe in the oil tank directs this oil/gas mixture to the oil separation system, where it’s projected onto the sides of the tank. Oil runs down a helical ramp, draining through slots back to the bottom, while the gas is directed to the top and onto the intake system to be burnt. (A perforated baffle plate prevents oil droplets from taking the same journey.)

4. RETURN

There can be aeration in the oil running back into the tank. The large oil volume allows for an increased residence time in the tank and permits de-aeration at the surface of the oil. Oil is then picked up again from the bottom of the tank to repeat the cycle.

5. STORAGE

The W1’s oil system holds 10 litres – a generous amount that is beneficial from engine degradation, cleaning and cooling perspectives.