Subscribe Twitter Facebook

Sunday, December 5, 2010

Bass Ackward but Amazing (Caution: nerdy ramblings ahead)

This year Porsche released their GT3 RS, which pumps out 450 horsepower from a 3.8 liter flat 6.  This is the latest version of Porsche's horizontally opposed 6-cylinder range.  It has evolved over the years more than a Pokemon.  Any motor that produces 100 horsepower per liter of displacement is a marvel of engineering.  Complete this thought with the fact that this motor doesn't have forced induction or direct fuel injection and this motor seems to be the pinnacle of Porsche's legendary engineering pedigree.  Although, I can't help but think that the limits of the iconic 911 may be drawing near.

In the world of high performance cars, it seems like having about .5 liter of displacement per cylinder is the Holy Grail of engine design.  This allows the pistons to remains small with an oversquare bore.  An oversquare bore in itself contributes to an engine's ability to reach stratospheric rpm.  Take for example the Honda S2000 and the current BMW M3.  They each have a displacement of .5 to .6 liters per cylinder.  The BMW hits its redline at 8400 rpm while the S2000 will shriek to a staggering 9000 rpm (in its 2 liter form).  The skyrocketing rpm allows a small capacity motor to make great horsepower due to the equation:
                                              Horsepower = (Torque X rpm)/5252

So, while these engines don't produce the torque of a small block Chevy or 8 liter Dodge Viper V10, they are still able to produce amazing horsepower numbers due to their ability to rev higher.  What does this all mean in terms of Porsche's engineering?
3.8 liter courtesy of

For the 2010 model year, Porsche developed a new motor to replace their aging 3.6 liter powerplant.  The new motor displaces 3.8 liters and makes 450 horsepower without a supercharger, turbocharger, or, to a lesser extent, direction injection.  As stated above, this is phenomenal!  However, this is getting further and further away from that beautiful .5 liter/cylinder ratio.  Not to pooh-pooh this motor, it is an award winning mill after all but I am hesitant to believe that this motor can evolve much past its current state.

The addition of direct injection will definitely improve combustion efficiency for better fuel mileage as well as horsepower.  After that, the only solution to making more power is higher engine speeds to comply with the formula above or to bore out the cylinders to increase displacement and torque yet keep the oversquare cylinder ratio for high revs, which are a necessary trait for sports cars.  Either way, a weight loss program needs to be enacted for everything from connecting rods to valves.  To increase engine speed, lighter materials like titanium and magnesium need to be employed or the engine will tear itself apart due to the reciprocating mass.  The same can be said about option 2, enlarging cylinder diameter.  Increasing the bore would necessitate a bigger piston diameter as well as larger valves to accommodate the needed air, fuel, and exhaust flow.  These larger parts would not change direction as easily as the smaller bore siblings and also require lightweight materials.

The lightweight approach would work but it would also cost a premium for the consumer.  Maybe this new motor is part of a tiered approach to improving driving dynamics and efficiency.  Take a step back and look at the whole picture.  Perhaps the goal isn't to increase power but to maintain it in the most efficient manner while reducing the overall weight of the car.  Reducing overall weight would maximize performance across the board as opposed to just acceleration properties.

Porsche has been a powerhouse in the automotive world for close to 80 years.  I'm sure their engineering group has its wits about them.  If not, they should call me for a job.

1 comment:

  1. New Diet Taps into Pioneering Idea to Help Dieters Lose 15 Pounds within Only 21 Days!