Stealth Powerhouse V-Six

The skateboard craze has abated, but its legacy is a number of hybrids. These days, no self-respecting skydiver would leave an aeroplane without a skyboard attached to the feet. Similarly, cool impressions are made on snowboards at ski resorts. And now it's skis out/wakeboards in at favourite waterski spots.

Wakeboarding has become increasingly popular, as is the practice of towing the skier make that boarder with a big, single pole.

It's surprising that very few boat engineers have drafted alternative designs, as the pole (and particularly the associated support ropes) are not aesthetic. Seating is also limited due to the ropes being anchored in the cockpit.

Clearly then, Powerhouse Performance in Perth has something unique on its Sterling Marine Stealth skiboat.

But the aluminium tubing structure isn't the only feature that's alternative on this boat. Most Stealth skiboats are powered by 350ci Chevrolet V-eight engines, but this WA-version carries a V-six engine as found in VN model Commodores.

Oh, did we also mention the Sprintex supercharger onboard?

Sterling Marine's Stealth skiboat kits from Adelaide are quite well known and held in high esteem around the country.

A combination of good ergonomics for the driver and plush cabin features, including ski-rope lockers, have made the Stealth a popular choice for skiers.

Danny Williams, managing director of Powerhouse Performance, bought his Stealth from WA state distributor Devil Marine in Morley.

"For a big boat, it handles really well," enthused Devil Marine's Keith Florence. "The quality of workmanship is also exceptional."

SUPERCHARGED SCEPTICISM
The idea to put a supercharged Commodore V-six engine into one of these boats was initially viewed with scepticism by Florence who helped fit and align the motor, plus set a few things up.

A Borg Warner soft clutch is standard fitment to these boats, however, this is anything but a standard Stealth.

"It's got a Commodore clutch we adapted to suit the marine application," explained Williams.

"We put a shaft, a coupling and a support bearing through the standard Commodore bell housing, then coupled it to the prop shaft. Not being the more usual powerplant seen in these boats did necessitate a few custom parts here and there, including a specially-made prop," added Florence. "The prop that's supplied with the Stealth kit is designed for a V-eight engine but the V-six torque curve is totally different, so we had to manufacture a custom item."

The 3.8lt V-six Commodore engine is basically standard internally, although Greg Gower in Perth did flow the heads for improved breathing with the supercharger.

The S102 Sprintex supercharger hasn't been in the spotlight for a few years now... But that's all set to change.

With the financial backing of Advanced Engine Components Ltd (formerly Transcom International), Sprintex superchargers will go into series production in Australia later this year. The S102 supercharger is one of the few screw superchargers on the market.

AIR APPARENT
This is not the time or place to delve into supercharger technology, suffice to say that screw superchargers are true air compressors and don't just blow extra air into the combustion chambers of an engine.

Mounted on the stock V-six Commodore inlet manifold, this particular S102 produces up to 12psi which is claimed to be good enough for 300hp not bad for an old Commodore donk!

The engine is managed by the standard Holden EFI and ignition systems, although a Chevy heat exchanger takes the place of the original car radiator.

The exhaust system comprises ceramic-coated custom stainless headers set up by Geoff Garland of Exhaust Dynamics.

But it's what's happening behind the scenes that's of interest... "There's a stainless line that dumps discharge water out of the heat exchanger into the exhaust manifolds," explained Williams.

"So, with the ceramic coating and the water cooling, we don't have any exhaust heat problems."

Although this arrangement is nothing unusual on the marine scene, there's more than a touch of custom engineering in this application.

"We've basically got two cooling circuits on the boat, the first being a closed loop system which flows through the engine itself and which contains coolant much like your typical car circuit," added Williams.

"The secondary circuit uses river water for intercooling and exhaust cooling, so there's a pick-up on the bottom of the boat with a pump driven off the front crankshaft pulley. Then it's into the intercooler, through to the heat exchanger and a dump exit."

"At the dump exit on the bottom of the boat we've plumbed in a T-piece, plus a variable gate valve and a splitter box to feed the exhaust manifolds. Obviously, this allows us to control how much water is used for exhaust cooling."

COOL RUNNINGS
No doubt, much of this cooling and intercooling plays a key role in the claimed 300hp figure yet the entire package highlights that supercharging can make a small and light engine behave like a much larger powerplant.

The V-six Commodore engine weighs significantly less than the obligatory Chev V-eight, which is a major benefit.

With similar or greater power output, the supercharged V-six unit improves the boat's power-to-weight ratio and that's a benefit every watersports enthusiast can appreciate. But the aim with this project wasn't just to create some ballistic, water-based hoon missile.

"The supercharger does produce extra power which is great for towing, but supercharging is all about making the internal combustion engine much more efficient," explained Williams.

It should be noted that Williams and his Powerhouse business are corporately involved with Advanced Engine Components, and the resurgence of Sprintex.

Being the Australian distributor for Eaton and Whipple, means Powerhouse is in a perfect position to supply a wide range of supercharger kits for virtually any application marine or otherwise.

The Stealth boat featured here has been a test bed for the past couple of years, with the aim to make a fuel-efficient powerplant for a skiboat that meets forthcoming emissions requirements for recreational vehicles.

The choice of Eaton, Sprintex or Whipple, and the engine alternatives to which the supercharger is attached, is a personal selection. But at least the variety is there!