Talking Torque: Petrol Alternative

Some cruisers just ain't suited to diesels.

Not long after I'd started working as boating writer in 1983, Harvey Halvorsen of Lars Halvorsen and Sons employed me as a casual charter boat skipper on Sydney Harbour. The regular charter boat was being re-fitted, so Harvey supplied his own Halvorsen 40 Kirribilli, originally launched in July 1967.

Kirribilli was a masterpiece of construction, with beautiful joinery work and completely dry bilges, not expected in a 16-year-old timber hull. Though getting a little tired, the twin big block 7.2L Chrysler 300 brake horsepower V8 Golden Lion inboards were perfectly matched to the hull. And the exhaust burble at low rpm was music to my ears.

Due to her fairly shallow deadrise hull, in calm water Kirribilli with a couple of adults aboard could be coaxed up to 25kt for (very) short periods, but best of all was her ability to cruise effortlessly and quietly at 6kt at 1200rpm, sipping fuel. 

With heat exchanger cooling there was no need to worry about condensation build up in the sumps or cylinder bore glazing at extended low rpm and loads, unlike mechanically-controlled diesels. No exhaust fumes either in following winds to make paying guests heave up — less mopping for me at the end of a charter.

Regrettably the position was only casual so later that year I concentrated on just testing marine engines. It wasn't until 1989 when Harvey sold Kirribilli that I heard of her again. Harvey put the new owner in touch with me and he asked what type of replacement engines would I fit? After my wonderful experiences with the Golden Lions I suggested new V8 petrol engines, as diesels would kill the character of the boat. He went ahead and had twin MerCruiser 7.4L inboards installed, which developed 310bhp each. He clocked up 650 reliable hours on the engines before Kirribilli was sold again and I lost touch of her movements.

So if you're lucky enough to come across an original petrol-powered Halvorsen 40 or 42 for sale, what would be suitable inboards nowadays? In my opinion the logical choice would be the MerCruiser 8.2 H.O. DTS, which has replaced the 8.1 H.O. In 2005 I tested twin 8.1s in a Sea Ray 40 Sundancer and they instantly brought back memories of the Golden Lions.

THE NITTY GRITTY

The 8.2 is a development of the 8.1 which unusually was an ‘undersquare’ engine with bigger cylinder stroke dimensions than bore diameter. Thankfully the 8.2 is oversquare with larger bore than stroke for reduced piston ring wear at higher rpm. The 8.1 and 8.2 develop maximum power of 419.6 and 424.9bhp, both at 4600rpm. The additional torque and top end power over the old Golden Lions should return speeds approaching 30kt in a Halvorsen 40. 

Mercury Marine is coy about publishing torque figures but I estimate the 8.2 develops around 750 Newton Metres at 3000 to 3200rpm, which coincides with where the Sea Ray planed cleanly with the 8.1s. Both engines use the ZF 63A or 63 IV hydraulic gear boxes, which are capable of transmitting this much torque. 

The 8.2 retails all the features of the 8.1, such as relatively simple two valves per cylinder and push rod valve actuation with hydraulic valve lifters. But with its lower 8.75:1 compression ratio the engine can run on fuel octane as low as 90 (standard unleaded is 91) though I'd use premium 95 because it's a denser fuel and lasts longer in underfloor fuel tanks. A knock control retards ignition timing if poor quality fuel is detected. Multipoint EFI is standard and the high-intensity digital (distributor-less) ignition ensures a longer spark plug life.

The standard alternator has a voltage-regulated output of 65A although reasonable chunk of this is used to power the engine management computer.  

The 8.2 is clearly designed for a long life in a salty environment and has a brass sea water cooling pump, 316 stainless steel dry exhaust joint elbows and uses an antifreeze coolant with a five-year life expectancy. 

Mercury Marine recommends using semi-synthetic Quicksilver SAE 25W40 oil in temperate climates (see “Oils ain't oils” Trade A Boat issue 525) and I recommend changing the oil and filter every 100 running hours or annually. Oil filter access is good and all fluid reservoirs are mounted on the top of the engine. The serpentine accessories drive belt has an automatic tensioner.

Perhaps the biggest change since I tested the 8.1s is the standard DTS, which replaces throttle and gear shift cables with wires and sensors. DTS gives way better control than cables which can stretch or corrode if not checked regularly. Installing controls in upper and lower helm stations is easier too. No more stupid twin lever controls!

Mercury Marine lists bobtail engine dimensions and weight for the 8.2 but as the width and height (crankshaft centreline, not overall) are the same as the 8.1 it's fair to assume so is the length with ZF 63 A. The 8.2 is 1194mm long, 838 wide and 610mm high though in reality to the bottom of the sump it's probably closer to 700mm. Complete with ZF 63 A box the 8.2 has a dry weight of 493kg, slightly heavier than diesels having comparable torque outputs but lighter than diesels with similar power outputs. As the 8.2 revs higher than comparable diesels, the higher rpm of the maximum torque band is not an issue. However gear reduction of around 2.5:1 is needed to reduce prop rpm to below 2000 and if you're re-powering from older MerCruiser inboards upgraded prop shafts and coarser-pitch props may be needed. The exhaust system may also need enlarging to prevent excessive back pressure.

THE WRAP

Of course the 8.2 uses way more fuel than comparable torque-output diesels but is easier to service. Away from MerCruiser Service Centres any competent auto mechanic can work on the 8.2 and with its low-pressure MPI (especially compared to common rail) the fuel delivery system is simpler.

In my opinion the 8.2 reflects what the Halvorsen 40 or 42 are all about. Relaxed pottering with the ability to sprint when needed, such as home before approaching storms. And relatively simple engineering in line with the way simpler age in which these cruisers were conceived. At the time of writing, deals of less than $35,000 for new engines make the 8.2 good value for what it offers.

For the location of your nearest MerCruiser dealer Google Mercury Marine Petrol Inboards.

QUICK SPECS

Engine type 90 degree V8 MPI petrol inboard

Rated output 424.9bhp/431mhp at 4600rpm*

Max torque Estimated 750NM at 3000 

to 3200rpm

Displacement 8.2L

Bore x stroke 113.5 x 101.6mm

Dry weight with gear box 493kg

*Brake horsepower/metric horsepower or PS