Forget all the jargon about “increasing volumetric efficiency” when it come to how supercharging and turbocharging work to create more power in high-performance marine engines. It isn’t that the verbiage is wrong—in fact it’s technically correct. It’s just that for most folks trying to understand the basics of turbochargers and superchargers, it’s mind-numbing gibberish.
Instead, think of it this way. An internal combustion engine burns fuel through the use of an oxidizer—with the igniting help of a spark—meaning air. The more air you bring into each cylinder, the more fuel it is able to burn and, if tuned and calibrated correctly, the more power the engine is able to make. But unlike fuel, air can be compressed.
So what happens when you compress the air used in the combustion process in an internal combustion engine? Simple—you get a “bigger bang.” Manage and control that bang correctly and you get more horsepower from a given engine without increasing its displacement, meaning without “making it bigger” by adding cubic inches.
Superchargers (also called blowers) and turbochargers simply add more air—they call it “boost”—to the combustion process without the need for added displacement in the form of larger cylinders bores and increased piston stroke. Pretty easy to understand, right? Of course, there are a number of types of superchargers and turbochargers, but that’s one of those discussions that, while interesting, would sidetrack us from getting the basics. Another time, perhaps.
A supercharger is driven off the crankshaft of the engine. In a supercharger application, a pulley and belt are added to the engine’s original pulley and belt system to drive the blower. A turbocharger, on the other hand, is driven off exhaust gas pressure. It gets a free ride, so to speak, off the final part of the combustion process.
Because superchargers and turbochargers essentially compress air, they create heat. Too much heat translates to power loss in internal combustion engines, so both superchargers and turbochargers usually are set up with some kind of intercooler system.
So Which System Is Better?
Until recently, supercharging has been the preferred method for boosting power in high-performance marine engines. That’s because, as noted earlier, superchargers are driven directly off the engine’s crankshaft. Response, and hence boost, to throttle input is immediate.
In a turbocharger application, however, exhaust gas pressure—the force that drivers the turbo—is the final stage of the combustion process. So in traditional marine turbocharger applications, there was a distinct lag between the driver nailing the throttles and turbo kicking in. Aptly named “turbo lag," it was enough of an issue to turn off most go-fast boat enthusiasts in search of more power, who instead found it in supercharging applications. So, while turbocharged gasoline engines did exist in the go-fast powerboat world, they were thought to be an oddity and generally inferior to the their supercharged counterparts. At least that was case until 2010, when Mercury Racing introduced its twin-turbo, quad-overhead-cam 1350 engine masterpiece.
Thanks to design and engineering developments including exhaust pulse tuning and sophisticated computer control, the 1,350-hp engine and its 1,100- and 1,650-hp siblings (the 1650 Race version was introduced this at the 2013 Miami International Boat Show) have no turbo lag. They develop power “on a straight line” and don’t require massive amounts of engine operating speed (rpm) to make their peak power and torque. They simply require massive amount of money—$203,000 retail with a Mercury Racing M8 drive—to buy.
So much of a game-changer and so technologically advanced is the quad overhead cam 1350 turbo platform that no builders are even trying to copy it. Instead, they are sticking for the most part with their supercharged engines, which are by no means bad products. But next to the Mercury Racing 1100, 1350, and 1650 they are dinosaurs.
This certainly doesn’t make supercharged engines “bad.” Mercury Racing still offers two—the 600SCi and 700SCi. Independent engine builders such as Teague Custom Marine build 700- to 1,500-hp supercharged engines. And for those who prefer to go the naturally aspirated—mean no turbocharger or blower—route, Ilmor Marine makes a nifty 730-hp V-10 engine with own, in-house-built Indy drive.
So what if you don’t have the boat, much less the bank, for a Mercury Racing 1350—or any new engine for that matter. What if you have an out-of-warranty Mercury Racing 525EFI or MerCruiser 495 Mag HO ECT engine that you want to hop up? Do you go turbocharger or supercharger?
Well, as far as current kits go, your only choice is a supercharger. A little more than a year ago Hardin Marine announced it was building a 700-hp turbocharger kit for the popular 525EFI, but that kit is not yet on the market. (According to sources at Hardin, shipping should begin by summer 2013.)
So your choice really is made for you. You need to look at supercharger kits, and the leading manufacturer of these kits for marine and automotive applications is Whipple Industries in Fresno, Calif. Whipple makes an array of kits for different Mercury Racing and MerCruiser engine products, as well as kits for do-it-yourself engine builders. The kits generally come with a Whipple supercharger, an intercooler, a new intake manifold, a remapped control (either supplied by Whipple or sent to the company by the client for reprogramming), and all the requisite installation hardware. Kit prices start at approximately $7,000.
But here’s what none of the kits come with: The upgraded stern drive and bigger-pitch propeller you’ll definitely need to handle the extra power. Those are additional costs to be aware of. Try to avoid them and you’ll end up spending the money anyway when your stern-drive fails. Plus, you end may end up with a hefty bill from whatever on-water service tows your boat back to the dock.
So now you’re ready to blow some cash on a supercharged engine. Or you’re all revved up to make a big-ticket buy for the latest and greatest turbocharged mill. At least now you’re armed with a few basic facts and a little understanding of how it all works. But don’t stop here. Keep looking and asking questions. For like boost, knowledge is power.