Mercury Racing’s 565 – with digital throttle and shift (DTS), better fuel economy and more grunt – prompted more than a few questions. Mostly variations of: “How’d you do that?” We agreed to blog and provide some answers. In Part 1, I’ll discuss about torque and power. Part 2, fuel and DTS.
Torque. How big are the bombs and where do they push?
As I said in discussing our QC4v 1350, “The Valve Train That Could,” bigger bombs make more power. We pack more air because we designed the heads and inlet valves to flow better. Admittedly, they’re still two valve heads and not as free flowing as our four valve engines, but they’re better than our previous two valve designs. With more air, more fuel is added for combustion and makes a bigger bomb. Yet, fuel economy is better! How? Improved and more precise fuel delivery to each combustion event makes less wasted (unburned) fuel. Easy to say; hard to do – but we did it. (More about that in Part 2.)
The 565’s greater torque is due in part to its longer stroke. The lever arm (from center line of the crank to the center line of the rod’s big end) is 4.250 inches compared to 4.000 for Racing’s 525 EFI. When combustion force pushes on the connecting rods with their “big end” farther from the crank center line, it develops more leverage yielding greater torque (defined as “force acting at a distance from a fulcrum”).
Horsepower. How fast are the bombs going off?
Essentially, we make 565 horsepower because the bombs are bigger and go off more often than our 525. Several design elements are at work here. The bomb frequency (explosion rate) creates the input forces on the pistons. Frequency and the crankshaft’s lever arm makes the torque. The explosion rate dictates RPM. Torque x RPM = Horsepower (with a numerical constant to make the units of measure work out). Mechanical drag sucks up some of the input force (rings against cylinders, bearings against races, pinion teeth against gear teeth, turning pumps and alternators, etc). Fluid drag takes a little more (pumping coolant and lubricants around). Thermal losses of combustion energy (through cooling) sucks still more of the input force (cooling keeps parts from self-destruction). Minimizing the drag and thermal losses, without sticking up the mechanism, is the trick. The net result of doing all that very well is 565 delivered POWER!