Honda K-Series Engines
As the production of B and H series ended in 2001, Honda has relased a new line of inline 4 engines to be used in compact and mid-sized vehicles. This new engine family continued Honda's tradition for naming its engines. The first letter in engine code indicates the engine family. Two numbers behind the letter indicates the displacement, and the following letter and number indicate the version. This new family is named K-Series and currently consists of 3 different displacements, K20 and K24 are naturally aspirated, the third one, K23 is turbo charged.
K-Series engines have cast iron sleeved aluminum short blocks and chain driven DOHC aluminum heads with 4 valves per cylinder. Roller rockers are used to reduce friction. The distributor is replaced with a coil on plug ignition system which enabled ECU to manipulate ignition timing. K-Series has two short blocks with same design; only difference between them is the deck height. K20 uses the short block with deck height 212mm where K23 and K24 block has 231mm of deck height. K-Series is equipped with a segregated, chain-driven oil pump and one-piece crank girdle, which reduces the chance of crank walk at higher engine speeds.
The distinctive feature of K-Series is VTC, or Variable Timing Control. VTC uses a spool gear, and oil pressure to automatically adjust the overlap between the intake and exhaust cams. VTC mechanism is attached to the end of the intake camshaft and it can change the intake timing by plus or minus 30 degrees. VTC is active at all RPM ranges and continuously optimizes the valve timing depending on the load of the engine.
All K-Series have the i-VTEC badge, Honda describes i-VTEC as a combination of VTEC and VTC, however the way i-VTEC operates is not the same on all K-Series. Basically there are two different systems under i-VTEC name. Both have VTC and VTEC, but one of the systems aims performance where the other is focused reducing fuel consuption.
The way first system operates is almost the same with older DOHC VTEC engines. Both intake and exhaust camshafts have three lobes for each cylinder's pair of intake and exhaust valves. At low RPMs, outer lobes with normal profiles are active to provide a smooth idle and fuel economy. When VTEC kicks in, middle lobes, which have a high-lift, long-duration profile, are engaged to increase high-end power delivery. Along with VTEC mechanism, i-VTEC engines also have VTC on the intake cams. VTC continuously optimizes valve overlap no matter VTEC is active or not.
The second i-VTEC system, which emphasis on fuel economy also have VTEC and VTC. VTC opearates the same way it optimizes the valve overlap, but the way VTEC operates is very different. First of all it is only found on the inkate cam and there are two lobes instead of three; one has a round profile and the other one has a regular profile. At low RPMs the lobe with round profile is active. With this cam profile engine operates as a 12-valve engine. One of the intake valves does not open fully, thus decreasing fuel consumption. What VTEC does is to activate the rugular lobes on the cam to operate the engine in 16 valve mode. This might sound odd when the older VTEC applications are considered but, you end up with very efficient combustion and significantly reduced fuel consuption.
For more information on spesific engines please check out related pages.