An internal Combustion Engine is essentially an air pump and the key to making more power is pumping more air in and out of the engine.  The 2 most effective ways to pump more air is increased displacement or RPMs. Increasing displacement increases the amount of air per pump and increasing RPM increased the number of pumps per unit of time.  Increasing engine displacement or redline entails building a custom bottom end with larger bore or stroke or lightening internals to increase RPM. 

The next opportunity to increase power is to improve the air flow in and out of the engine.  Most common air flow upgrades are less restrictive intake, header or exhaust.  However, no matter how much you optimize the ends of the intake and exhaust systems, there is always a bottleneck, the head itself.  The head ports are the last influence of air flow in and out of the combustion chamber and are the most critical part of the air pumps flow tract. 

S2000 Head History

More than 20 years later, the S2000 is still one of the best flowing normally aspirated heads ever.  When it was launched, it out flowed every Sport Compact head by a large margin, even heads that had larger valves and bores.  Honda designed the S2000 for is 50th anniversary and the original power goal was 220 hp to hit a target power to weight ratio.  However, the S2000 ended up overweight and Honda needed to increase power to 240 hp to hit its target power to weight ratio.  Most of the power increase came from enlarging the head port improving the head flow.  The problem with the larger ports is that it made the engine lazy at lower RPM as it didn’t rev hard until 5000 RPM.  The 2.0L engine needed higher RPM to reach a port air velocity to become responsive.  The future increase to 2.2L improved port velocity as it starts to come alive at 3500 RPM. 

New Direction

We have spent a few years looking for a new head porter after our original legendary head porter retired.  To find someone that focused on air velocity and not head flow, we went in a new direction.  High performance motorcycles rev much higher and have a larger operating range than S2000 thus port air velocity is even more critical.  We believe we found the best head motorcycle head porter in the world and when we interviewed him about head flow, he noted “I haven’t flowed my heads in years”.  They scan the shape of the port, look for areas of slow air velocity, optimizes them and then runs them on a dyno or on track. 

We would like to reintroduce our NEW velocity head program with new designed head by a world class motorcycle head porter. 

Air Velocity Focus

Most head porters benchmark themselves on head flow or the amount of air the head will flow at various valve lifts.  Our head porter has not used their flow bench in years.  Its relatively easy to achieve high head flow simply by opening port dimensions as much as possible.  However, head flow alone will not create the fastest accelerating cars, increased air velocity is the key to revving faster. 

The most critical part of air intake is how much air comes in after BDC due to air momentum during the expansion stroke.  A slower moving air column due to lower air velocity will slow and reverse limiting the total amount of air in the cylinder.  A faster moving column of air will continue to flow into the cylinder, even after BDC during the initial part of the compression stroke achieving over 100% volumetric efficiency. 

Additionally, high air velocity in the ports also improves transient response or the ability to increase RPM per time.  An engine with lower air velocity ports will feel lazy with slow throttle response, especially at lower RPMs.  High air velocity ports improve engine response and creating a feeling of wanting to rev through the redline and reduce tenths of seconds along straights or acceleration runs. 

Headwork Process

Each port is cut using a 5 axis CNC to reach the critical parts of the port that need to change and ensure consistency.  Heads are intentionally not polished and left with rough surfaces as they are proven to reduce surface drag improving air velocity.  Similar to how the dimples on a golf ball significantly improve the distance it flies.  Additionally, there may be parts of the head left uncut because they don’t improve flow.  Most head porters cut the entire port as the head might look unfinished, but cutting areas that don’t improve flow will increase port size without flow gains and slow overall velocity.  Our headwork is function over form, rough surfaces, some surfaces uncut, all in an effort to maximize air flow AND velocity to have the fastest accelerating motor. 

The highest air velocity and most critical head flow is through the seats and around the valve.   Each Valve seat received a full radius valve job (vs more typical 3 or 5 angle) to ensure the best possible flow at the valve opening.  A full radius valve job can yield up to 3% in horsepower by itself. 

Finally, we don’t offer different stages.  Each head gets the best possible port and valve job based upon valve diameter.  If oversized valves are used, the port design and shape are scaled to support the larger valve. 

Side by side comparison of URGE designs Velocity intake port vs the cast OEM