The D4 was designed from the outset as a marine engine. In other words, it is not like most marine diesels which were originally designed for trucks and then refitted for marine use.
Small But Mighty
The 3.7 liter, in-line four-cylinder diesel measures just 36.7” (93.cm) long x 29.9” (75.9 cm) wide x 30.7” (78 cm) high, and weighs 1,420 lbs. (664 kg.) It is generally recognized in the marine industry that this engine is appropriate for all sorts of applications ranging from a singe engine runabout to a twin engine express to a single engine long range cruiser that will go displacement speeds.
Because of its compact size it is ideal for repowering. New boat buyers will find it more and more on the option list for all manner of boats.
The big buzz-words in diesel for the last decade have been “common rail fuel injection” -- which is, surprisingly, not as sexy as it sounds but very efficient and beautiful in its simplicity. A single fuel line, or "rail," supplies all of the injectors. Unlike conventional systems where fuel must be pressurized with each pulse of the injector before it can be squirted into the combustion chamber, the fuel in this rail remains under constant pressure. That means the lag time between advancing the throttle and getting a power response is a thing of the past and now you are rewarded with much crisper, and faster throttle response.
Mating the D4 to the new IPS pod drives was a no-brainer, and opened up a new market of boat specifically configured to accommodate the new propulsion system.
Volvo Penta’s 4-cylinder D4-300 is developed from the latest design in modern diesel technology. In addition to the common rail fuel injection system, it has double overhead camshafts, 4 valves per cylinder, a turbocharger and an aftercooler. Given its relatively small size, it has a large swept volume and high torque during acceleration. Because it was designed specifically for marine applications, it has a minimum of hoses.
This acronym stands for Electronic Vessel Control and it’s the latest development in engine control and instrumentation. Once you’ve experienced it, we don't think you will ever want to go back to the old ways of engine control.
Because this isn’t a full blown EVC report, the short version is that EVC allows for plug and play installation between the motor and both the engine controls and helm gauges. This allows you to not only control the flow of data to the helm but electronically control the engines.
That means that all those mechanical connections between the helm and the engine are long gone, and adding a remote location for your engine controls, say at the stern or for wing controls, is as easy as running another cable. And the digital controls are opening up a whole new breed of capability. Cruise modes, tow modes, trim assist, single lever modes… all are available at the push of a button.
The D4 is a compact package that packs a wallop.
Smoking Is Prohibited
The D4 carefully monitors and controls the fuel injection and burning process with what Volvo Penta calls its EMS-2 unit. EMS stands for Engine Management System and it began life as the need to meet stringent exhaust emission standards began to take effect back in ’06. It’s basically a system of microprocessors and proprietary coding that calculates how much fuel the engine needs, and does it up to 100 times per second.
EMS-2 significantly reduces fuel consumption and minimizes exhaust emissions by controlling fuel pulses into the combustion chamber. So not only is lag time between hitting the throttle and the engine delivering power reduced to near zero, range is extended and operating costs are lower. And, of course, the engine meets all U.S. and European environmental standards.
Testing the Metal
Test numbers of a Regal 42 Sport Coupe powered by twin IPS400 systems which incorporate the D4 engine.
Our test boat was a new Regal 42 Sport Coupe with twin D4 engines driving through IPS400s. The boat displaces 18,800 lb. (8527 kg.) dry, has a 13' (4 m) beam, draws 3'5" (1.04 m) and has a deadrise of 18-degrees. We tested the boat on a windy day with one to two feet of chop, which is just the kind of condition where you want a high-torque diesel engine powering your boat.
As you can see from the chart above the Regal had a top speed of 32.3 knots and a best cruise of 25.8 knots at 3,000 rpm. At that speed the boat burned 21.2 gph (80.2 LPH) and got 1.4 miles per gallon -- which is very good for a boat weighing over 20,000 lbs. with fuel and crew aboard in the conditions we encountered.
Even more telling, perhaps, was the boat's time to plane -- 6.5 seconds -- which is only about two seconds slower than most sportboats weighing only a few thousand pounds. Zero to 30 mph was 13 seconds. These two measurements attest to the powerful torque curve of this engine at the low rpm range.
We feel a boat's engine package is far too important not to be given a serious amount of consideration by the consumer, just as the boat brand and model itself. If you have ever had a chronic engine problem in a boat that you otherwise loved then you will know what we mean. When buying a boat remember that you can usually specify the engines that go into it.
There are a number of things that we like about the D4. First, it was designed specifically for marine use, unlike most marine diesels on the market in this size range which have virtually all been designed for trucks. That is one reason why it is so compact. It also has a minimum of hoses, which means fewer items to check, and fewer things to go wrong in your engine room.
There is also a strong benefit in having all parts of the engine system made by one company. With the D4, the EVC controls, the marine gears, the pod drives or outdrives are all made by Volvo Penta. If something goes wrong with your power system, there is no finger pointing or confusion as to who should fix it.
If you are repowering or buying new, we would definitely advise considering the Volvo Penta D4 for power in the 225 to 300-hp range. If it is not on the builder's engine option list, ask if there are any plans for adding it. Since the advent of the Great Recession more and more builders today are glad to install a brand engine not on its option list if that will make the sale.