565: How’d We Do That – Part 1?

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?

The 565’s all new cylinder head flows about as much as is possible with a 2-valve.

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.)

565 crankshaft (pictured) has 4.25 inch stroke compared to 4.00 of Racing’s 525 EFI.

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!



Share Share

11 thoughts on “565: How’d We Do That – Part 1?”

  1. The torque definition was clear, but from a layman’s perspective how did/do you increase RPM?
    Because the 565 has a longer stroke than the 525, is the compression higher yielding a faster time-bomb explosion, equaling a higher RPM?

    1. I wish I could find a simple, layman’s answer to your question. RPM is the result of a multitude of design decisions. Most revolve (pun intended) around physical limitations: inertia, friction, lubrication, cooling, flow capacity. Compression is just one variable. The pace of explosions (RPM) is a function of how fast one can reload the cylinders with the right combustible mix.

  2. “…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’).”

    If you shorten the above lever arm does it increase RPM, the opposite of a longer distance increasing the engine’s torque?

    1. If one could maintain the same horsepower, RPM would have to go up. However, on this engine platform, the power would likely decrease. Why? Valve train is the limitation — not crank, rods and pistons. Engine design is always balancing many compromises.

  3. “…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’).”

    Does a V6 engine configuration yield more torque, than a comparable in-line 6 with the same cubic-inch displacement? I ask this because the connecting rods are pushing the crankshaft from a wider fulcrum angle/distance in the V6 layout.

    I would also like to think you for generous time, in the above answers to an inquisitive mind.

    1. Think about your question for a minute. Each individual combustion event pushes on its piston. For that push, it’s the same geometry — regardless of how the rest of the pistons and rods are laid out. It only changes if the stroke (crankshaft centerline to rod big-end centerline) changes.

  4. Torque x RPM = Horsepower.

    Could I properly deduct that increasing an engine’s torque will facilitate a boat’s faster acceleration from idle to planing speed? Likewise –inversely- raising the maximum RPM capability to a higher red-line numeric value, will equate to a higher top-end speed?

    I ask the above as a theoretical scenario, liken to a CAD model where you only change the RPM or Torque, as sliding-variables in the T x RPM = H.P. formula. (And hypothetically leave boat/hull/weight, propeller, and engine: displacement, valve train, etc. staying the same as a constant denominator).

  5. I am running 2 565’s in my recently repowered fastech 382. I am turning 4900 rpm with blade 5 blade props. Is the torque still climbing through the WOT range up to 5400 to any decent degree, such that i should try different props and get the WOT up higher to get the higher torque, thus pick up a few mph?

Leave a Reply

Your email address will not be published. Required fields are marked *