I Put a Real Gasoline V8 Inside a LEGO Koenigsegg
This is a 1:8 LEGO Technic Koenigsegg Sadair's Spear. 4,104 pieces, and it reproduces a lot of the real car's mechanical detail — the V8, the 9-speed gearbox, and Koenigsegg's triplex suspension. Power runs from the engine through the driveshaft, gearbox and differential before it reaches the wheels, the same path a real car uses.
The real car is unusual too. Only 30 were built, and all of them were sold before it was officially launched. At the 2025 Goodwood Festival of Speed it set the hill climb record for a road-legal production car.
LEGO went up the same hill. They built a full-size, driveable brick Koenigsegg and ran it at 111 km/h — the fastest LEGO Technic big build there's been. They know exactly how far the system can be pushed.
Building the model took me close to thirty hours.
When it was done I kept lifting the rear clam to watch ghost mode work — the doors, front hood and mirrors all sweeping open together. Whoever designed that linkage understands machinery.
So today I wanted to do something simple: put a real miniature V8 inside it and make it actually drive.
Everything works except one thing
LEGO reproduced everything that could reasonably be reproduced. The triplex suspension moves. The 9-speed gearbox shifts. The steering works. Even the V8 runs — plastic gears drive eight pistons up and down, the timing is correct, and there's a small ghost symbol printed on the side of the block.
It's display only, though. That isn't a shortcoming; LEGO never intended otherwise. That assembly is meant to be displayable, understandable and repeatable, and it is all three.
I like this car a lot. I finished it, put it on the shelf, and kept going back to it — lifting the clam, working the gearbox by hand, putting it down again.
Then Stirlingkit released the CISON LS-52.
And a thought turned up that I couldn't get rid of. What if that engine went into this car?
I spent a while looking into it before touching anything. As far as I could find, nobody had done it — a running gasoline V8 inside this particular model. There are good reasons why. I decided to try anyway.
I'd put a V8 in a car before
Before this, I'd already put a TOYAN V8 into an RC car and got it running. After that build, whether a miniature combustion engine could drive a radio-controlled car stopped being a question for me. The only question left was how far it could be pushed.
The LS-52 is a step up. The TOYAN FS-V800 is 28cc; the LS-52 is 52cc — close to double the displacement, plus water cooling and pressure lubrication. It also meant starting the whole driveline over. The 6-speed transmission I wanted to use isn't compatible with the TOYAN V8 at all — different output shaft, different bellhousing. Nothing from the previous car carried over except the thinking.
That earlier build is the only reason I was willing to try this one. Without it, I wouldn't have touched the LEGO.
→ Watch the TOYAN V8 RC car build
Why I Choose Cison LS V8 Engine for my Project?
The bay is barely wider than your palm. Most engines wouldn't physically go in, and most of the ones that would wouldn't survive being driven around. Four things about the LS-52 made me think this one might.
It has the torque, and it can sustain it. 52cc, roughly 6 hp, with a working range of 1,600 to 12,500 rpm. That's more than enough to move a 1:8 body. What matters more is that it holds together up top — the crankshaft is CNC-machined from high-strength aluminium alloy, and the main bearings use thrust plates to control endfloat. A conversion is harder on an engine than a display stand is.
The crankshaft has drilled oil passages. Most model engines rely on splash lubrication, because machining oil galleries at this scale is difficult. The LS-52 drills them straight through the crank, so pressurised oil reaches the rod bearings the way it does in a full-size engine. On a display stand you'd never notice. In a car that shakes, gets thrown around and runs continuously, it's the difference in service life.
The water pump is built into the head, with no external plumbing. This was the deciding factor for me. The Koenigsegg body sits very low, and LEGO packed that engine bay without wasting a millimetre. One extra coolant hose and the body panels don't close.
It was designed with modification in mind. CISON supplies both a large and a small ignition coil — the small one exists specifically for tight engine bays and custom builds. The block also has mounting points reserved at the flywheel for adding a clutch or a transmission later.
In other words, I wasn't forcing in an engine that didn't belong there.
Four problems that had to be solved
Even so, it took more than twenty days.
The driveline
LEGO's drivetrain is designed around the load of a hand turning it. The tolerances are good, but it was never meant to see real torque. The moment you open the throttle, plastic gears strip.
So the whole power path was rebuilt. I used Stirlingkit's 6-speed transmission — three forward gears plus reverse, with a high/low transfer case on top, which gives six forward ratios in total. Four steel clutch packs, shifting without lifting off, and a built-in brake. That last part matters on a gas-powered build, or you'd have to engineer braking separately.
One thing to be clear about: the transmission is currently matched to the CISON V8-440. The LS-52 version is still on pre-order. The interfaces don't line up, so I made an adapter.
It's an aluminium cylinder that sits between the engine and the gearbox, sized so it fits over the flywheel. I drilled a ring of holes through the wall, matching them one by one to the existing bolt holes on the engine. It's the only part of this project made completely from scratch, and it took the longest — everything downstream depended on whether it worked.
With that in place, the crankshaft, metal gearbox and metal differential run as one chain, all metal end to end.
The transmission is a four-wheel-drive unit with outputs front and rear. I only used the rear one; the front output isn't connected. And rather than running a propshaft, I added a pair of gears at the transmission output that take drive straight across to the rear differential, which then feeds the halfshafts.
Two reasons. The Koenigsegg is rear-wheel drive to begin with, and gear drive is far shorter than a propshaft, which lets the whole power pack sit tighter. That saved me on the next problem.
Cooling
The framework through the middle of the body was hollowed out, and I made a small radiator and coolant tank by hand to fit the space that was left. The radiator has a fan and stands vertically ahead of the engine.
This only worked because of the LS-52's internal water pump. With an external pump the layout wouldn't have been possible at all.
Ride height
The Koenigsegg is mid-engined and rear-wheel drive. The transmission alone is 13.8 cm long and weighs a kilogram — noticeably longer than a typical RC gearbox — and once it's stacked with the differential the assembly sits higher than the original floor allows. The body wouldn't close.
Those gears I mentioned absorbed part of the height difference between the transmission output and the diff. The rest came down to adjustment: I reworked the drive angles repeatedly and shaved the chassis mounting points down by microns until the whole pack sat back at the original height. Raise the stance and it stops looking like a Koenigsegg.
Suspension
By this point the rear was fully occupied by the block, the gearbox and the differential.
The triplex suspension is one of the things that makes this car what it is, and LEGO reproduced it well. I didn't want to throw it away just to fit an engine. So the coilovers were moved inboard and mounted longitudinally, operated by pushrods and rockers, front and rear. The rear pair sits above the transmission; the front pair runs along the chassis rails. It's a common racing layout, and it gets the bulkiest part of the suspension away from the wheels. The parts aren't LEGO's any more, but the mechanism and the travel survived.
Questions people asked
Won't the vibration shake the brick structure apart?
Not straight away, but sustained high-frequency vibration does work the pins loose over time. I spot-glued the load-bearing connection points. Spot-glued — not flooded, or you can never take it apart again to service it.
The exhaust gets hot. Did it melt the bricks?
No. There's a 5 mm air gap between the exhaust shielding and the body panels. It's enough.
Where did the ignition, battery and tank end up?
Nowhere hidden. Not by choice — there was simply no room.
Once the interior was hollowed out there was less space left than I expected. After the engine, gearbox, differential and cooling system, the electronics had nowhere to go. So they sit out in the open.
It turned out to be the better arrangement anyway. This car needs constant adjustment — ignition timing, coolant level, battery swaps. Sealing all of that inside the body would mean stripping it down every single time.
The radiator and fan stand ahead of the engine, with the clear coolant tank beside them, so the green level is visible at a glance. The battery pack sits behind that. Power runs through a locking connector, which is easier to work with than soldered joints.
The ignition system has a small display on a lead, so it doesn't have to be mounted in the bay at all. It shows rpm, water temperature and voltage live, and logs peak rpm. You can hold it in your hand while the car runs — one reading was 4,155 rpm at 63°C. During setup that's far more useful than listening to the engine.
Refuelling is done through a hose from above, without removing the body. The tank is a 100 ml plastic unit; a full tank runs for about half an hour. At the end of a tank the water temperature is in the low seventies, well short of needing a cool-down. What limits this car isn't heat, it's fuel.
Underneath it all is the aluminium chassis — one plate and two rails. Engine, gearbox, differential and suspension all mount to that. The brick body only handles the shape; it carries no load.
What did it cost you?
The LEGO set itself. After drilling, cutting and gluing, it isn't going back together.
I put it off for a while before starting. That was thirty hours and 4,104 pieces of finished work, and taking it apart wasn't easy. If all you want is the car, don't do what I did — it's a very good model exactly as it is. This is irreversible. Think it through first.
First start
Fuel in, ignition connected, one pull on the starter cord.
It fired on the first try.
The exhaust note is lower than I expected. The rods are turning over fast, you can feel the heat coming off the pipes, and the whole body shivers slightly.
The lines are still there. The stance is still there. Ghost mode still opens the way it should. It just has a voice now.
The V8 sounds great, and LEGO Technic's engineering is just as impressive. Those two things aren't in conflict.
If you want to try something like this
You don't have to start by cutting up a LEGO set.
The engine in this car is the CISON LS-52: 1:5 scale, 52cc, water-cooled OHV four-stroke V8, pressure lubrication, internal water pump, MCU digital ignition, 12,500 rpm ceiling. It runs perfectly well sitting on a desk — or it can be the starting point for something else.
One warning: the LS-52 is not a beginner project. Rocker and pushrod installation, valve clearance on all eight cylinders individually, timing gear alignment — CISON's own manual flags these as difficult steps, and a timing gear one tooth out means it won't fire at all. If this is your first model engine, start with one of CISON's inline engines.
CISON LS-52 Full SetEngine + MCU ignition + metal base 6-Speed TransmissionHigh/low transfer case, reverse and brake — LS-52 version on pre-order 62 Build Tips & Full LS-52 FAQFrom assembly to first startQuestions about your build? service@stirlingkit.com
This article documents a personal modification project involving irreversible structural changes, high-temperature exhaust and gasoline handling. Do not attempt without relevant experience.
LEGO® and LEGO Technic™ are trademarks of the LEGO Group. Koenigsegg® and Sadair's Spear are trademarks of Koenigsegg Automotive AB. Neither company sponsors, authorizes or endorses the modification described here, and neither is affiliated with Stirlingkit. Modifying a product in this way voids its warranty.
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