Swapping a K24 Into a Honda S2000

Omar Kaayal had to thank his lucky stars when a lightly-prepped Honda S2000 track toy rolled into his view with a drool-inducing low price tag attached to it. With all the HPDE essentials installed and plenty of room left for customization, Kaayal had a functioning car he could still put his stamp on and spend his free time planning his modifications.

Unfortunately, his time spent doing homework was all for naught. The relationship between them began beautifully, but after just two track days, the F20C dropped a valve. Suddenly he was considering five-figure solutions to his new problem.

It’s fairly common knowledge that the F20’s valvetrain is one of its weak links. Owners are advised to upgrade to the stronger valve retainers from the second-generation S2000 engine, the F22, to avoid such problems. Alas, the motor was toast and Kaayal had to make a decision to keep his recent acquisition from becoming an expensive tarp stand.

His options were limited. Rebuilding the F20 is challenging due to its fiber-reinforced metal cylinder liner design. FRM consists of a fiber-based material in the form of a cylinder sleeve, which is first inserted to the die of the block. Melted liquid aluminum is then poured into the die and integrated with the fiber sleeve. This fiber sleeve reinforces the block, allowing the distance between adjacent bores to be reduced while maintaining mechanical strength.

The problem is that the FRM cylinder liners can only be machined so much, and honing requires a special process that not every machinist knows. It’s likely that any scratches would warrant a re-sleeve. Clearly, this would not be the easiest path.

Alternatively, he could buy another F-series for $6,000, but that might pop just as quickly as the last one.

The wish to have a dependable, fast, and cost-effective S2000 over the long haul drove Kaayal to resurrect his car with another model of engine. Rather than source another F-series, he reached out to the wise guys at Walshmo Racing for a swap kit that in the short and the long term, promised peace of mind for a little more overhead.

The cost of swapping a new motor into a chassis never designed for it added to the up-front costs, but the possibility of replacing several motors over time meant turning to the popular K24 would save Kaayal some money in the long run. The K24 is ubiquitous and inexpensive. The going rate for a good example is roughly $800. The motor is also supported by the aftermarket and capable of providing comparable power and better mid-range torque than the motor it replaces in this case, so shortcomings of the swap are not innumerable, though there are several.

HARSH MY BUZZ

Eric Walsh of Walshmo Racing has performed a dozen of these swaps and has come to appreciate the availability and easy operation of the larger K24 engine, found in several dozen models ranging from sports sedans to minivans. “It’s really not that different from the F22. I think of them as brothers, really,” he says.

If there’s an obvious issue with the motor once it’s sitting in its new home, it’s vibration. To rev the K24 as high as the F22, one needs to install the oil pump from an RSX Type S. With this, it will buzz happily to 8,200 rpm, but not before making a few modifications.

The Type S oil pump does not have the harmonic balance shafts that the F-series’ pump does, and, besides, K motors are inherently buzzier than Fs. Therefore, an aftermarket damper pulley helps keep NVH levels tolerable. Kaayal prefers the one made by Fluidampr, though ATI’s is good, too.

“The stock balance shafts on the K24’s oil pump will rev themselves to bits if you raise the rev limit. Sometimes you’ll get lucky and eat a bunch of bearings, but I’ve seen some cases where they will explode out of their housing in the oil pump,” says Walsh.

“The NVH is bad enough to unscrew the oil filter, which is the cause of a surprising number of failures,” Kaayal adds. To stabilize the buzzy K24 as much as possible, “put Loctite on just about everything, add exhaust and intake bracing, use Nord-Lock washers wherever you can, and remote mount as many sensors as possible,” he advises.

Oiling, or the lack thereof, is less than ideal, though that can be said of many Honda motors. Most advise overfilling the engine. As mentioned before, aftermarket oil pumps are needed to raise the rev limit. There should be a baffled sump in place — preferably one with greater capacity. Lastly, just like the F-series engines, the K24 needs to have a catch can installed to divert the blow-by from getting sent back into the intake manifold.

SHOEHORN NOT NECESSARY

The K24 isn’t a drop-in, but it is surprisingly easy to install. Its dimensions are slightly different — the K24 measures about 1 inch taller due to its greater stroke than both F-series engines — though they both have the same 87 mm bore. The typical adapter plate used to mate the K motor and the S2000’s gearbox pushes the lump forward by an inch, too.

However, there still isn’t sufficient space between the firewall and the back of the K24’s head to run the standard coolant lines in the same way they’re routed around the S2000’s original engine. These coolant lines must be rerouted with an adapter.

Now that the K24 is established as the one of the more popular swaps for a number of different platforms, some of the ancillaries are getting a little harder to find.

If you’re fortunate, you can use the stock K24 ECU, but most people aren’t getting a full harness when they purchase a K24,” says Walsh. “All of the JDM K24s we bought came with chopped harnesses because the exporters in Japan just chop the harness in the most convenient place so they can rip the motor and transmission out of the car easily.”

The cheapest wiring solution involves an RSX engine harness and the widely available PnP kit from 2NRS, which runs about $500. Or, if one is willing to spend more, a custom Rywire harness brings that price up to $1,100, but can save the swapper the headache of brittle connectors and the like.

While wiring up the new lump, it’s worth considering a more sophisticated, controllable ECU. The ECU from both F motors will not work with the K24 in place, since the cam and crank sensors are different, and the K24 also has VTC (Variable Timing Control), which the F motors do not.

The easiest way to do this is with Hondata, though this also requires the K20 ECU from the RSX. Adding the Hondata KPro piggyback system works well enough for most racers, and it also supports OB2 functionality — “you might even be able to meet emissions,” Walsh suggests.

“Although Hondata is the “easiest” route to take, you can use KTuner, AEM, Haltech, Emtron, Motec, and just about any other ECU you’d like,” Walsh adds.

GO FOR THE GRUNT

The tradeoff in terms of powerband shape is clear. The F-series engines were made to make power at the top of their rev range, while the K-series were meant for more sedate driving around town in a heavier vehicle. That torque, however, is still valuable in a lightweight sports car. Crucially, the K24’s torque helps minimize the number of shifts. It can be “lugged” out of corners at 5,000 rpm and still pull strongly.

To help build upon the K24’s additional displacement and the accompanying bump in torque, an aftermarket ECU can drop the VTEC engagement point to a desired engine speed to help keep the engine “on the pipe” more of the time. An aftermarket ECU can control the K24’s VTC, which fatten up that much-needed midrange even more, as does the RSX Type S’ 50-degree VTC gear. “There’s a lot more torque starting from 3,500 RPM all the way to 8,000 RPM,” Walsh notes.

“The K24 quits earlier than the F-series do, especially with OEM cams. I advise my drivers to shift at 7,800 most of the time, although the occasional 8,200-shift is fine for passing or stretching a gear,” Walsh says.

Despite the increased ease of driving, outright power is still a determining factor when running in classes like TT4. To make the 240 average horsepower required to compete in TT4, one must upgrade the camshafts, since either major weight loss or a serious engine build are needed to be competitive. Simply put, Kaayal’s K-swapped S2000 is a more competitive package in TT5, where bolt-ons should provide adequate power for near-factory weight.

Walsh elaborates on the difference in powerbands. “We dyno all our cars with BBR, and what I’ve seen is that a freshly built or healthy F22 generally makes about 230 whp around 7,600 rpm, and 160 wtq at 6,500 rpm. In contrast, a fresh K24 with OEM cams usually makes something closer to 227 whp at about 7,000 rpm, but makes around 180 wtq at 5,300 rpm.”

IN WITH THE OLD

Being a Honda product, the F-series is dependable, and a lot of the original equipment can be reused with the new block. Along with the fuel rail, the throttle body, and the MAF sensor, both the intake and exhaust manifolds can be reused, but those two require some modification.

Fortunately, the F20’s intake manifold can be reused in the swap if a large chunk of the manifold is chopped. Roughly 2-3” of material must be cut for the intake to fit, which removes the area dedicated to the intake coolant passage, which in OEM configuration, runs coolant through the throttle body and the idle air control valve. Fortunately, there is another line running off the block that can be appropriated.

Recycling old parts saves on swap costs, but it’s still far from cheap. For the bare essentials required for a track-ready car, spending $8,000 is likely, and that’s without labor.

In the end, what is the owner afforded? They trade a heritage motor with a special sort of top end for something a little more commonplace that’s not as eager to rev, but — and this is the crucial bit for the racers out most weekends — is expendable. The K-series motor can be replaced quickly and cheaply. It’s also a low-maintenance motor when kept in neat-factory configuration.

To keep on top of K24 maintenance is nothing special. The valves need adjustment, the oil ought to be changed frequently, and the catch can must be cleaned occasionally. Stay on top of those, and the K24 runs as reliably as one would expect from a mass-produced Honda motor. It’s just as fast as the old F20 and F22, and the small savings Kaayal has enjoyed since swapping his motor has helped him master what can be an uncompromising chassis, and on the street, he can occasionally run a gear higher and save some fuel. Sounds like money well spent.