CLOSE
Sign up to get news on contests, pro events, new products and special offers.
RistoThink back. Among your first skiing impressions you will likely recall being neck-deep in the water, looking down a long rope, staring at the business end of a stern-drive framed by a pair of wobbly combo skis. The stern-drive, or inboard/outboard – I/O if you prefer – is the family ski powertrain of choice.
More hours of skiing, wakeboarding, kneeboarding, tubing and general family fun are logged every year behind stern-drive boats than either inboards or outboards. Perhaps more significant is that skiers are more likely to learn to ski behind an I/O family runabout than any other type of ski boat.
This popularity was earned through years of trusted performance. While stern-drives may not provide the ultimate in tournament-level skiing performance, when you balance overall daily boat drivability and ease of operation with solid performance, the modern stern-drive is a tough package to beat.
In an age when we are constantly bombarded with a wider range of products and more choices, the 1997 stern-drive lineup is something of an anomaly. Rather than offer more variations on the ever-popular I/O theme, marine manufacturers are refining their lines, trimming down to concentrate on the most popular models. In recent years we've also witnessed a number of significant product-line changes. The most notable was the consolidation of the OMC and Volvo Penta stern-drive packages to form a new powerhouse in the I/O market. Never a major player in the stern-drive market, Yamaha dropped stern-drives from its marine line in 1995 to instead concentrate on outboard technology and the emerging PWC/jet-boat market.
Like the rest of the marine market, stern-drives are relying heavily on electronic fuel injection and computerized engine controls to improve both performance and efficiency. Out-drive technology is also advancing, with more efficient ways to put that additional power to the water. Pioneered by Volvo Penta, counter-rotating props are now offered on a variety of MerCruiser out-drives as well.
GM powertrains now rule the stern-drive market. MerCruiser has always been a staunch GM engine supporter, and for 1997 it appears that Volvo Penta, MerCruiser's primary competition in the stern-drive market, has jumped ship, fielding an exclusively GM engine lineup. For '97, Volvo Penta has dropped all the 5.0 and 5.8 Ford V-8s from the line.
A hot rod at last year's test, Extreme Watersports is back for '97 with new marketing plans and more diverse selection of high-performance engines for Ski-Pro boats. The engine line has grown to incorporate both a 4.3L V-6, and several 5.7L (350-cid) small-block Chevy V-8s in addition to the monster 400-cid aluminum small-block we reviewed last year. If small-block Chevys turn your crank shaft, then Extreme is worth a serious look. You can order a fairly basic carbureted 5.7 V-8, EFI 5.7, Extreme ZX 300 TPI or add aluminum heads and you get the Extreme ZX 350 TPI V-8. The Extreme ZX 400 Supercharged EFI V-8 is a stroked small-block with impressive torque out of the hole.
The neat thing about the Extreme approach is that all its powerplants can be custom-built to suit your skiing needs. They are offered exclusively in Ski-Pro boats and all are fitted with Volvo Penta DuoProp drives. The goal is tournament inboard performance with the advantage of a “tunable” wake shape through trim changes. Trim the DuoProp down for a flat slalom wake or up for wake or kneeboarding.
MerCruiser is fielding 135-hp V-6s on up through the outrageous 415-horse 502-cid big-block. Both throttle-body and multi-port fuel injection systems are offered, utilizing the company's electronically controlled high-pressure injectors.
MerCruiser's electronic control module (ECM) is among the most advanced in the marine industry. It monitors all vital engine functions and continually adjusts fuel/air mixture and spark timing for optimum performance regardless of atmospheric conditions. The result is improved power, better throttle response and easier starts while improving overall efficiency. When it comes to marinizing GM engines, nobody has more experience or a closer working relationship than MerCruiser. Stern-drives are offered in three skiable engine families: Sport, Competitor and Magnum.
MerCruiser has gone to roller cam designs on all their V-6s and small V-8 engines for better torque and overall efficiency. The company is also fielding a wide range of engines with new Gen1+ cylinder heads. The new heads, which are hot in the inboard industry, provide considerably more airflow for generous horsepower gains. Other mechanical improvements, like single serpentine accessory drive belts, water-cooled fuel systems and one-piece exhaust manifolds keep MerCruiser on the cutting edge for 1997.
And MerCruiser's stern-drive technology can't be ignored either. The company passed the 2-million-unit mark a long time ago and continues to refine its proven propulsion systems. Most ski boats will utilize either the Alpha, Bravo One or Bravo Three series drives. The Alpha series, with anti-feedback power steering, is designed for quicker planing on smaller runabouts and family boats. The Bravo One combines heavy-duty drive shafts and bearings with precision-forged gears in a trim case for higher-performance ski boats. The Bravo Three is MerCruiser's twin, counter-rotating prop model. It supplies more punch out of the hole with less torque steer.
As mentioned, Volvo Penta discontinued the 5.0L and 5.8L Ford engine offerings from its stern-drive lineup for 1997. That's not to say that the line is lacking – it's as diverse as you'll find – you just can't buy a DuoProp propelled by a Ford V-8 anymore. Though the company still offers a good selection of carbureted models, like the rest of the marine industry Volvo Penta has jumped on the EFI bandwagon in a big way. For 1997, Volvo Penta offers a complete range of EFI models with both SX Cobra single-prop and DuoProp configurations.
Always an innovator in the worldwide marine industry, Volvo Penta was the first to offer twin inline counter-rotating props to the water-ski market. For 1997, DuoProp stern-drives are offered with 10 different skiable engines, ranging from the thrifty 4.3GL V-6 on up to a 300-propshaft-hp 7.4 Gi big-block V-8. Three new 5.7L V-8 fuel-injected models have been added to the line as well. The most prominent is a 280-propshaft-horsepower 5.7 Gsi, which should win over small-block performance fans. For high-performance applications, Volvo Penta offers the DPX DuoProp with its exclusive Xact steering system. The Xact design has two integrated external hydraulic power steering cylinders on the drive unit.
The SX Cobra drive series of engines is available in 11 models for 1997, starting with a base 3.0L four-cylinder that makes a respectable 135 horses on up through a healthy 7.4L Gi big-block V-8 that rocks with 330-prop hp. SX Cobra out-drives feature pattern-matched, helical-cut gears and a cone clutch for smooth, precise shifting and quiet operation. The distinctive case, formally an OMC design, offers minimal drag with a substantial rudder area for solid steering control. The SX Cobra design also places the prop farther aft than most other designs for more propulsion authority under power.
The SX Cobra single-prop owner can now easily convert a stern-drive to a DuoProp with a kit recently introduced by Volvo Penta. Essentially, the kit replaces the single-prop SX Cobra lower unit with a new DuoProp lower unit. The swap can be made on SX-C and SX-C1 model SX Cobra stern-drives on 4.3L, 5.0L, 5.7L, 5.8L and 7.4L gasoline engines. According to Volvo Penta, the conversion increases total boat performance, including top speed and fuel economy, by providing 60-70 percent more prop blade surface than a conventional three-blade single propeller design.
