Honda K24 2.5 16v
The Honda K series car engine is a four-cylinder four-stroke engine introduced in 2001. The K series engines are equipped with DOHC valve train and use roller rockers to reduce friction. Honda i-VTEC system can be found on K series engines with both variable cam timing control (VTC) and the Vtec system. The K series engines came in 2.0l, 2.3l and 2.4l.
At Stafford Performance we have spent many years developing this engine. We have combined many high-end performance parts from different manufacturers around the world to produce an ultra reliable, high performing engine with a wide and smooth power band. Ideal for the tough conditions that rallying demands.
Our latest 2.5l, K24 high-spec engine now produces 350bhp and 244lb/ft of torque and revs to 8600rpm. These engines are not to be under-estimated for their drive ability, ease on drive train and reliability.
These K24 engines produced 190bhp from standard and depending on your needs we can produce an engine for you from 190bhp all the way up to our full spec power. We also stock many parts for these great engines. Contact us for more info.
Our Full Spec 2.5 K24 Engine
K24 Bottom end with K20 Type R head
Darton Wet liners bringing the engine to 2.5
Variable cam control on the intake cam and Vtec control
Custom Rally Cams
Jenvey Throttle Bodies
Dry sump Kit
DTA S60 ecu
Electric water pump
Contact for more info
Advantages of a Honda K25 over other 4 cylinder 2.5 Engines
As you can see from the power graph, our latest spec engine makes 354bhp @ 7900rpm and 244lb/ft @6200rpm. These peak figures are on par with other top spec class 14 engines. However, peak figures only tell a small part of the story. It's the power in every other part of the rev range that sets these engines apart. Note how straight the power line (Red) is, this gives you a very even and smooth power delivery throughout the whole rev range, This is particularly important in wet conditions. Also from the graph you can see how early the torque (Orange) comes in with nearly 210lb/ft at 3000rpm and stays above this all the way to the limiter at 8500rpm. Only engines with a Vtec system and variable cam timing could produce a power curve this straight and with so much torque in the first half of the rev range.
Essentially the VTEC system gives you two cam profiles for both intake and exhaust cams. The non-VTEC profiles on both cams are less aggressive and more suited to lower rpm. They provide maximum torque and power from low down in the rev range up to about 6000rpm where they are no longer effective. They also help provide a smooth idle and a snappy response. The VTEC profile however is more aggressive and much more suited to higher rpm. It works best from 4500rpm to 8500rpm. This profile is equivalent to the cam profiles of many other 2.5l engines. The transition from non-VTEC to the VTEC profile is controlled by the ECU. In the above graph, VTEC changeover is around 5000rpm providing a very smooth transition. The combination of both profiles gives a very broad power band from around 2500rpm to over 8000rpm. Only the Honda engines have this VTEC system. Other 2.5l engines depend on a single aggressive cam profile for each cam. This means they would have a narrower power band where the cam is working at it's best; usually between 5000 and 8000rpm. Even though these engines might have similar peak power and torque figures as the Honda they would be weaker in the low rpm to 5000rpm range. Also the transition from the off-cam to the on-cam area (4-5k rpm) can be very aggressive giving a feeling of lots of power where, in fact, it's just a transition from a low torque area in the rev range to a high torque one. This can make the car less driveable.
Variable Camshaft Timing
Honda K series engines also came with a variable inlet camshaft. This is controlled by the ECU and is capable of advancing the inlet cam up to 50 degrees. The control of the inlet cam is in a closed loop system where the ECU makes constant adjustments to the angle of the cam relative to the exhaust cam and crank position throughout the whole rev range to optimize the power output. This is another example of Honda's engineering excellence as these systems rarely give any trouble. The cam returns to zero degrees advance at idle allowing for a nice smooth idle and comfortable driving on low throttle. Both the VTEC and variable cam control use oil pressure to control them. Oil pressure is not a problem with these engines especially with the use of a dry sump system.
With the VTEC system and cam control combined we can produce an engine which is very smooth, very driveable and has instant power anywhere in the rev range.
The exhaust cam is set to it's optimum angle with the use of a vernier cam gear.
Most other 2.5l engines in class 14 apart from the Honda use a direct bucket style cam follower. These work very well with few issues. However, one disadvantage with these is the friction caused by the valve spring pressure acting on the bucket against the cam. This friction is not substantial but adds to the total valvetrain power loss. Proper lubrication helps to reduce this.
With the K series engine however we use a roller rocker set up. The cam acts against a needle type bearing roller that is part of the rocker. This reduces friction greatly and in turn reduces the power loss.
The other advantage that the roller rocker has over the bucket lifter is the speed at which the valves can be opened. Thanks to the rocker-lever effect, the valve can accelerate faster. This results in more air being drawn into the engine.
Due to the low friction cam and rocker system, wear is rarely a problem.
Electric Water Pump And Fan Control
On our 2.5l engines we have removed the bulky water pump housing that comes standard on the K series engines and fitted a tidy blanking plate in its place. This allows a lot more room for the dry sump pump and fittings. Instead, to control coolant flow, we use a powerful electric water pump. This water pump is controlled by the ECU in a closed loop system that controls it's speed to keep the engine running at optimum temperature. Electric water pumps draw less power on average from the engine than mechanical water pumps, with much better control. The pumps we use have proven to be extremely reliable and make very little noise when operating.
The radiator fan is also controlled by the ECU and is switched on and off when needed to help control the coolant temperature. We have found this system to work very well in preventing the engine from ever over-heating.
Coil Per Cylinder and Sequential Injection
As standard, all Honda K series engines came with a coil per cylinder set up and this proved to be very reliable. We have retained this on our engines as it is the most desirable set up. Individual coils work better than a single coil pack and plug leads. They produce a stronger spark with less voltage drop between coil and spark plug.
The DTA S60 ECU also provides us with sequential injection which allows us to inject the fuel into each inlet port at the optimum time for best atomisation with the incoming air to ultimately create the most power. Having the injectors placed further out the inlet manifold also helps in this process and gives more time for the fuel and air to mix higher in the rev range. This has not affected idling or throttle response which is still very sharp.
Aluminum Block And Head
In all forms of motor racing weight is an important factor. The less weight a car is, the less force it takes to move it. The k25 engines have both heads and blocks made from aluminium. This helps to reduce weight. These engines use a high quality aluminum unlike a lot of modern engines. The heads have large ports ideal for large capacity power. The blocks are very strong and they use a full bottom cradle for the main bearings as opposed to individual main caps found in other engines. To bring these engines to 2500cc, a large bore is required. This is achieved by installing steel wet liners on a CNC mill. These add to the strength of the block but also the stability of the liners themselves. When done correctly these liners are bullet proof.
- Full 2500cc capacity. (Some engines like the 2.5l Vauxhall are limited by their bore and stroke to 2430cc.)
- Modern engine. K series was first produced in 2001 making it a newer design than most other engines in the class such as the Cosworth based engines and Vauxhall XE engines.
- Under piston oil squirters. These help to lubricate the bores and also to cool the pistons.
- A harmonic balancer. This reduces destructive crankshaft torsional vibration, which is the end-to-end twisting/rebound motion, that is naturally generated during each power stroke. A harmonic balancer contributes to greater valve train and timing efficiency, plus reduces wear of critical engine components such as main bearings, oil pump and the crankshaft itself.
- Competitive price. Compared to other top spec engines in the class these engines are by far the best value for money.
- Looks good. Looks don't make much difference to performance but is still important to most people. The rocker cover has the oil cap and dip stick removed and then carbon dipped. The center plug cover is air brushed to give it a special look. Also a front billet timing cover adds a little extra something.