Getting to Know Your Engine

Engine Basics & Common Terms

Engine Specifics:

Rated at 197 horsepower, and 139 lb.-ft. of torque, the K20Z3 motor is one of the most efficient high revving four cylinder engines on the market.  The engine boasts a 2.0 liter displacement, an 11:1 compression ratio, and a multiple profile dual overhead cam i-VTEC valve train system that makes this engine scream once you get over 6,000 rpm.

What does DOHC mean?

DOHC stands for Dual Overhead Camshaft.  This is a valve train setup that contains one camshaft to control the inlet valves and the other to control the exhaust valves, allowing the engine to breathe much more efficiently than a single overhead camshaft valve train system.  It does this by allowing for multiple valves per cylinder, having intake valves on one side and exhaust valves on the other. 

What is the difference between VTEC and i-VTEC?

To delve into what i-VTEC is you must first understand the original Honda developed multiple camshaft profile setup, VTEC.  VTEC stands for Variable Valve Timing and Lift Electronic Control.  VTEC was introduced by Honda to give their engines better volumetric efficiency by electronically controlling two camshaft profiles, one optimized for low rpms, and another optimized for high rpms.  When the engine reaches the designated rpm switch point, a locking pin engages and locks the high-lift cam profile in place to open the valves further, giving the engine more power by increasing inlet and outlet flows.

i-VTEC was introduced to the US with the fifth generation Si (2002-2005).  i-VTEC or intelligent-VTEC works pretty similar to the way regular VTEC does in that it has two cam profiles, but the i-VTEC setup allows the intake camshaft to continuously, in low and high cam profiles, change the angles at which it operates from 25 to 50 degrees.  These changes to the angle of the cam are called phases, and if dialed in correctly, they drastically improve the torque output at all rpms.

What is the difference between an Exhaust Manifold and a Header?

First off an exhaust manifold is not a header!  Most cars come with exhaust manifolds.  Exhaust manifolds are usually made from cast iron making them easier to mass produce, and last longer.  They collect the exhaust gasses from the cyclinders and route it to your exhaust piping.  Headers are a set of pipes, usually mendrel bent, one for each cylinder, which are routed to a collector where they usually connect to the exhaust piping.  Each cylinder having it's own smooth pipe, allows for the gasses to flow faster and more efficiently to the collector where it connects to the exhaust piping.

What does the MAF Sensor do?

The MAF Sensor or Mass Airflow Sensor is a sensor located in between the throttle body and the intake air filter.  The MAF sensor determines the amount of air entering the intake manifold so the ecu can compute the correct amount of fuel to use.  The sensor works by heating a small wire in the airflow path which is then cooled by the passing air, it uses the conductivity of the wire (higher conductivity when the wire is cooler) to determine the amount of air entering the engine. 

This is directly correlated to the MAF Calibration table.  When you are calculating your MAF Calibration table in ATR, the values in the top row are the conductivity of the wire, and the values on the bottom row are the expected airflow of the intake.  This table tells the ecu that for each given voltage in the top row, it will be receiving the amount of air (g/s) in the bottom row.  The ecu then determines the correct amount of fuel to be used at that specified voltage.

What does an O2 Sensor do?

The O2 Sensor, Oxygen Sensor, or Lambda Sensor is located in the exhaust flow.  This sensor determines lambda or the amount of air in relation to one unit of fuel present in the exhaust gases that are flowing past, also called the Air to Fuel Ratio (A/F Ratio).  O2 sensors are extremely important as they can tell the ecu whether it is running too lean(not enough fuel, higher A/F Ratio) or too rich(too much fuel, lower A/F Ratio), and the ecu can then adjust itself accordingly.  This sensor also helps tuners determine the right amount of fuel to program when tuning the vehicle for wide open throttle.