Tegiwa GT86 Rally Build: K-Swap everything

Let’s address the elephant in the room – power. While our Toyota GT86 has been transformed with a serious weight reduction program and upgraded suspension, there’s no escaping the fact that the factory FA20 engine leaves a lot to be desired in the horsepower department. Our dyno testing confirmed what many critics have said over the years: with just 182 horsepower, the GT86’s power output simply doesn’t match its handling potential.

Farewell, FA20

The first step in our power transformation was removing the factory FA20 boxer engine. While this power plant has its charms – it simply doesn’t deliver the punch needed for our rally build ambitions. Even with tuning and bolt-ons, the FA20 struggles to make meaningful power gains without forced induction.

Enter the 4Piston Racing K400 Endurance Engine

To replace our departed FA20, we’ve gone with what might seem like a controversial choice to the Toyota purists – a Honda K-series engine. But not just any K-series. We’re installing a fully-built 4Piston Racing K400 Engine, a 2.5-litre monster capable of producing up to 400 naturally aspirated horsepower.

Of course, we’re no strangers to the Honda K-Series platform. Our Time Attack Honda NSX, Tsuki, is sporting a K-swap that’s currently producing a monstrous 700 horsepower from its Bourne HPP K22 engine. The proven power potential of the K-Series in our NSX build made this engine choice a no-brainer for the GT86 project.

This is no ordinary engine swap. The 4Piston K400 is a “no-compromises” approach to building a high-performance, high-reliability power plant. Let’s look at the impressive specification list:

• 4P rigid ductile iron sleeve Honda K20/K24 engine block with 99mm stroke x 89.5mm bore
• 4P I-beam long rod connecting to an 18mm tool steel wrist pin
• 4P Wiseco strutted box forged ultra lightweight pistons, armor plated, 89.5mm high compression
• ACL race bearings, ARP fasteners, exclusive 4P spec head gasket for superior sealing
• 4P Pro 163 CNC Cylinder head, 4P custom valves, Ferrea PAC HD valve springs, retainers, and locks
• 4P tool steel billet RR4 iVTEC camshafts
• 4P Ported oil pump and baffled sump
• All new Honda timing components and hardware

The 4Piston Racing K400 is specifically designed for maximum power output while maintaining exceptional durability. This isn’t just an engine built for peak power – it’s engineered to deliver consistent performance under the most extreme conditions. The durable I-beam billet steel connecting rods paired with ultra-lightweight, short-skirt pistons provide both strength and responsiveness throughout the rev range.

Perhaps most impressive is the “Pro 163” CNC cylinder head, flowing an incredible 400 CFM and representing the cutting edge of 4-valve cylinder head technology. Combined with the 4P RR4 billet camshafts, this head unlocks the breathing capacity needed to make serious naturally aspirated power.

Making It Fit: KPower Industries Race Package

Getting a Honda K-series engine to work in a Toyota GT86 isn’t as simple as just dropping it in. That’s where the KPower Industries race package comes in, providing all the components needed to make this swap work flawlessly:

• K24 to 86 transmission adapter plate with hardware
• 86 starter blockoff plate
• K24 to 86 custom steel flywheel
• Engine mount brackets with hardware
• Rubber engine mount pads
• 86 transmission mount bracket for relocated position
• Whiteline transmission mount insert
• Baffled aluminum oil pan that clears the stock subframe and undertray
• Cast aluminum intake manifold with IACV blockoff plate
• 3″ cold-air intake with filter
• 4-2-1 304 stainless race header
• 304 stainless midpipe with flex and hanger
• 3″ aluminum one-piece driveshaft
• KPower fuel rail
• E85-compatible fuel line kit
• Upper water neck for right-side engine bay routing

This comprehensive package ensures that our K-series engine not only fits physically but integrates properly with the GT86 chassis and drivetrain. The ability to retain the Toyota transmission is particularly valuable, preserving the excellent shift feel while gaining the power benefits of the K-series engine.

Speaking of the transmission, we’ll be retaining the original GT86 gearbox for now, but with one crucial upgrade – an MFactory 2-way plated limited-slip differential. This LSD is essential for putting down the substantially increased power, especially in rally conditions where traction is at a premium. The 2-way design provides lockup during both acceleration and deceleration, giving us better control when trail braking into corners.

We’ve opted not to mess with any gear sets at this stage, as there’s potential to upgrade the entire gearbox at a later date once we’ve evaluated the car’s performance with the K-swap. The stock gear ratios should work well with the K-series’ power delivery characteristics for our initial phase.

Keeping It Cool: Mishimoto Cooling Package

With such a significant increase in power, managing heat becomes critical. That’s why we’ve installed Mishimoto’s range of GT86 cooling products, including their aluminum radiator, high-flow fans, and oil cooler kit.

These cooling modifications are particularly important for our rally car application. Unlike traditional circuit racing where airflow is constant, rally cars often sit stationary for longer periods between stages or may run at lower speeds through technical sections with reduced airflow. It’s absolutely crucial that everything remains at an optimum temperature to maintain performance consistency throughout an entire rally day.

The Mishimoto radiator offers significantly improved cooling capacity over the stock unit, while their fans provide better airflow at idle and low speeds. The oil sandwich plate ensures that the engine oil reaches operating temperature quickly but never exceeds the optimal range, protecting our high-performance K-series engine even under the most demanding conditions.

Brains of the Operation: Haltech Elite 1500 ECU and Digital Dash

To harness all 400 naturally aspirated horsepower, we need a serious engine management system. Enter the Haltech Elite 1500 ECU – a fully programmable, race-proven engine management system that gives us complete control over every aspect of the engine’s operation.

The Elite 1500 offers features that are critical for our application:

• Full sequential injection and ignition control
• Multipoint adjustable traction control
• Data logging with 64MB of onboard memory
• Dual lambda sensor inputs for precise air/fuel ratio monitoring
• Real-time tuning capability

Complementing the Elite 1500 ECU is Haltech’s IC-7 7″ digital dash display, which provides us with comprehensive real-time data at a glance. The fully customisable interface allows us to monitor critical engine parameters, with configurable alarms and warnings to alert us to any issues before they become serious problems.

The dash integrates seamlessly with the ECU, displaying not just basic information like RPM and temperatures, but also advanced data like air/fuel ratios. For our rally build, this level of data feedback is invaluable both for tuning and for driver information during competition.

We have to give a massive thank you to the team at Haltech for making this entire project possible. Without their extensive knowledge, technical support, and hands-on assistance, getting our K-swapped GT86 up and running would have been an infinitely more challenging task. The Haltech team went above and beyond, providing not just exceptional products but also the expertise needed to integrate everything seamlessly. Their commitment to supporting builds like ours is what makes them such an invaluable partner in the motorsport community. From initial setup through to final tuning, their support has been absolutely first-class.

Milltek Exhaust: The Perfect Finishing Touch

As a major retailer of Milltek exhaust systems, it made complete sense to showcase yet another one of their exceptional products on this build. We opted for Milltek’s primary cat-back system, finished with their brushed titanium tips that fill the rear diffuser perfectly and provide that distinctive, purposeful appearance our rally build deserves.

The sound from the Milltek system is sublime – it perfectly complements the character of our K400 engine, providing that deep, resonant note that lets you know this GT86 means business. What was particularly impressive about the Milltek system was how perfectly it mated up to the KPower Industries exhaust manifold with absolutely no modifications required whatsoever. This kind of compatibility speaks volumes about the quality and precision of both manufacturers’ engineering.

We’ll put out some more images of the Milltek exhaust soon when we reveal the wrap and the body kit!

The Power-to-Weight Equation

Our GT86 has undergone a comprehensive weight reduction program and even with the addition of the Safety Devices roll cage, RRS carbon bucket seats, R6 Evo harnesses, and other safety equipment, we’re still looking at a car that will weigh substantially less than stock.

While we won’t know the exact figures until we get the car on the scales and dyno, we’re hopeful that once tuned our K400 engine will produce around the 350bhp mark – nearly double the output of the factory FA20. If we achieve these targets, the resulting power-to-weight ratio will be absolutely transformative, putting our GT86 into territory to challenge the front runners of our rally class.

What’s Next?

With our engine swap complete and the car ready for its first fire-up with the new power plant, our next steps will include:

1. A comprehensive dyno tuning session to optimize the Haltech Elite 1500 ECU for our specific build
2. We are currently working on a full body kit to go on the car and this will also have a livery applied over the top
3. Testing the car on track to evaluate the newfound performance and make any necessary adjustments

Stay tuned for our next update where we’ll share the dyno results and first driving impressions of our K-swapped GT86!