130 to 140hp four-strokes compared, and DFI two-strokes

HONDA BF130
Released on the Aussie market in 1998, the BF130 is an up-rated version of the overweight BF115 and is based on the superseded Honda Accord engine, although it does weigh more than its much-newer BF135 counterpart, despite having belt drive for the camshaft and twin counter-rotating balance shafts.

Since June 1998 I've tested seven of these engines on a variety of hulls and all have performed better than expected, with significantly lower vibration levels than the BF135.

But perhaps the best matching was on a Markham 622 Calais half cab and spinning a 16-inch pitch Quicksilver Vengeance prop.

Pushing a total of 1400kg, including two adults, the demo engine trolled at 6km/h on 650rpm, using 1.6lt/h, and cruised quietly at 39km/h on 4000rpm, using 25lt/h with no prop ventilation occurring through tight figure of eight turns at these revs.

The wide open throttle average was 69km/h on 5800rpm, using 49lt/h. At these revs, we could hold a normal conversation at the helm.

Because of its SOHC powerhead, servicing is straightforward with components such as the engine oil dipstick and oil filter easily reached.

Providing the engine is freshwater-flushed after each use in saltwater, corrosion resistance is good.

But, as a result of ongoing product development for the BF135/150 Honda opted for chains to drive the double overhead camshafts. This was a very sensible move because, with this engine, the camshaft chain also has to drive the twin counter-rotating balance shafts.

The only belt drive on the BF135/150 is for the alternator atop the engine.

Based on the 2.4lt Euro Accord engine, the powerhead is entirely new and has been reversed 180 degrees from the BF130 engine, so instead of the camshaft drive belt drive being atop the engine and flywheel below it, the camshaft drive is now below it and the flywheel atop it, with the air intake and exhaust manifolds on the opposite sides.

The BF135 misses out on the VTEC of its 150 counterpart but still retains its Variable Air Intake System.

This lengthens the air intake flow at low speeds to increase bottom-end torque, but shortens the flow at high revs (above about 4000) to improve engine 'breathing' and increase power.

Mounted on a Cruise Craft Outsider 575 and spinning a 17-inch pitch Solas four-bladed stainless steel prop, the demo BF135 provided plenty of power combined with very good midrange fuel efficiency.

Pushing 1650kg, including three adults, the trolling average was 4.1km/h, using 1.6lt/h, although there was some harmonic vibration through the hull structure between 1000 and 2000rpm.

At 4000rpm we averaged 44.2km/h, using 20.6lt/h.

Through full lock figure of eight turns at 4500rpm, there was no prop ventilation. The four-bladed prop also reduced the hull leaning to windward across a beam wind, but due to prop blade drag, compared to a three-bladed prop, the WOT average was 65.1km/h on 5500rpm, using 50.6lt/h, at which speeds we could still talk as normal at the helm.

Servicing the BF135 appears straightforward, with the shrouded alternator drive belt and the engine oil dipstick and oil filter easily reached. Its resistance to saltwater corrosion should be comparable to the BF130.

Because of this relatively small displacement, the DF140 needs careful propping to ensure it reaches the upper end of its WOT rev range. However, correctly propped, it delivers performance unmatched by its Honda competition, despite this engine having a substantially larger piston displacement and variable air induction.

The DF140 has chain-driven camshafts, an offset driveshaft with two-stage gear reduction for a very effective ratio at the propshaft and an air-cooled under-flywheel alternator.

Mounted on a 5.5m Southern Star SF550WR walk-around and spinning a 19-inch Suzuki alloy prop, the demo engine provided all the power you'd ever need for this deep-vee hull.

Pushing a total of 1350kg, including four adults, it trolled us at 4.5km/h on 700rpm, using 1.5lt/h. It cruised effortlessly at 41.9km/h on 4000rpm, using 20.9lt/h.

From 4000rpm to WOT, the acceleration was much stronger than expected of a two-litre powerhead, and the WOT average was 68.1km/h on 6000rpm, using 52.4lt/h. Noise levels were so low we could still talk normally at the helm.

Despite not having the twin counter-rotating balance shafts of the BF135, vibration levels across the entire rev range were lower.

Servicing the DF140 is straightforward, with no drive belts to replace.

The hydraulically-tensioned camshaft chain is designed to last the lifespan of the engine.

The DF140 has proven its resistance to saltwater corrosion since being release in Australia a couple of years ago.

In essence a four-cylinder version of the Verado 200 to 275 straight six range, the 135 has four valves per cylinder and a massive sump capacity.

SmartCraft Digital Throttle and Shift with electronic throttle and SmartCraft Engine Guardian, which progressively reduces revs or even shuts down the engine should it overheat or experience low oil pressure, are standard features.

Hydraulic power steering systems are available. However, after testing the Verado 250, the latter would be my choice.

The Verado 135 is the only engine in this power range I haven't yet tested.

MARINER/MERCURY OPTIMAX 135
The least powerful of a trio of engines based on the reliable 2.5lt V6 powerhead, the OptiMax 135 complies with CARB 2008, whereas its 150 and 175 counterparts don't.

As with these engines, the 135 is SmartCraft compatible and can also be fitted with TrollControl to reduce engine revs to only 400 for slow-speed trolling.

The OptiMax 135 uses the Orbital Combustion Process, which mixes fuel pressurised to 80psi with air at 90psi, which is then injected directly into the combustion chambers.

A mix of stratified and homogenous combustion is used, with the air/fuel ratios varying from 40:1 to 25:1.

Being so under-stressed, the 135 produces a lot of torque for its output and, on a Signature 520R runabout, the demo engine was the maximum power for this hull.

Insufficient time prevented us conducting trolling trials, but pushing 950kg, including two adults, and spinning a 19-inch Quicksilver Laser 11 prop, the average at 4000rpm was 56.4km/h using 25lt/h, with no prop ventilation occurring through tight figure of eight turns at these revs.

The WOT average was 80.5km/h on 5400rpm, using 48lt/h.

The noise levels above 4000rpm were considerably higher than Honda's quiet BF135.

Servicing the OptiMax 135 appears straightforward, with the fuel injectors and belt-driven air compressor and alternator easily reachable.

The air compressor belt should be checked every 100 hours or once a year for damage. Resistance to saltwater corrosion is excellent.

The DF140 also meets EU2005, which takes into account noise emissions. All engines in this guide have three years of warranty coverage.

Recommended servicing requirements for the Johnson/Suzuki DF140 and Mariner/Mercury Verado 135 is every 50 hours, and every 100 for the BF130 and BF135.

The water pump impeller should be replaced every 100 hours.

The first service is at 20 hours, when the valve clearances should also be checked.

All the four-strokes have canister-type oil filters.

The two-stroke OptiMax 135 requires servicing every 100 hours after the first 20.

AND THE WINNER IS
The Suzuki DF140 is a beautifully light weight, compact, fuel efficient and clean-running engine that suits a wide variety of hulls from bass boats to cuddy cabins around 5.5m, and is therefore my choice in this power range.