Lunch tasted like shoe leather dipped in engine grease.

  I sat on the rusted, moss-covered foot of the "Centurion"—the derelict Siege Walker that occupied the far corner of the Rust Yard. It was a mountain of dead metal, missing its head, its arms, and most importantly, its power core.

  "This jerky," I muttered, gnawing on a strip of dried meat Rax had provided. "Is this... are you sure this isn't just a dried belt?"

  Rax laughed, taking a swig of dark, foamy ale from a battered tin mug. "It's Rock-Lizard. Tough skin, but it keeps you going. Stop complaining, city boy. You have fifty thousand credits; buy your own lunch."

  "I'm saving the credits for the parts," I said, finally tearing a piece off. My jaw clicked in protest.

  Amelia sat next to me, picking at the meat suspiciously. She looked up at the towering legs of the Walker. "Julian, even with the metal we bought... how are we going to move this? A Centurion usually runs on an Eternal Mana Core. Those cost millions. And even if we stole one, I can't power a Siege Walker. I'm a Wind Mage, not a nuclear reactor."

  "We don't need an Eternal Core," I said, chewing thoughtfully. "We just need torque. We need something that pushes hard."

  Rax grunted. "Good luck. The only thing cheap enough to burn around here is Fire Dust from the mines. And that stuff is useless."

  I stopped chewing. "Fire Dust?"

  "Yeah," Rax kicked a bucket of red, sandy powder sitting near the forge. "Waste product from the Fire Crystal mines. It's too unstable to enchant. If you look at it wrong, it flares up. We usually pay people to haul it away and dump it in the river."

  I walked over to the bucket. I picked up a pinch of the red dust. It felt warm to the touch, vibrating with latent energy. I tossed the pinch into the small campfire we were using to heat the tea.

  WHUMP.

  A mini-mushroom cloud of orange flame erupted, singing Rax's eyebrows. "Hey!" Rax shouted, spilling his ale.

  I grinned. The jerky suddenly tasted delicious. "It oxidizes instantly," I murmured. "High energy density. Unstable. Cheap." I looked at Rax. "Don't dump it. I'll buy every ounce you have."

  "You want to build a bomb?" Amelia asked, wiping soot from her nose.

  "No," I looked up at the empty chest cavity of the Walker. "I want to build a heart."

  The design phase was a nightmare of translation. I drew a V8 engine block on the concrete floor in chalk. "This is an engine," I explained to the baffled team of Iron Guild blacksmiths Rax had assembled. "It eats Fire Dust and spits out power."

  "It explodes?" the head smith, a dwarf named Gorn, asked skeptically.

  "Controlled explosions," I corrected. "Thousands of them a minute. Inside these cylinders."

  Amelia raised her hand. "Julian, wait. If it explodes thousands of times a minute... who is lighting the fuse? Me?" She looked horrified. "I can't cast a Spark spell that fast! My fingers would fall off!"

  "I know," I said. "That's why we don't use your reaction speed. We use geometry."

  I drew a new component: The Distributor.

  "This," I pointed to the spinning rotor in the diagram, "is a distributor. Amelia, you don't cast thousands of spells. You just channel a steady stream of fire mana into this central copper post. The machine spins. As it spins, it connects your power to each cylinder in the perfect sequence. You are the battery; the machine is the finger that pulls the trigger."

  Amelia tilted her head, looking at the diagram. "So... I just hold on and let it spin?"

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  "Exactly."

  "And the heat?" Gorn pointed at the cylinder walls. "If you explode fire dust inside steel that fast, the metal will soften. The pistons will weld themselves to the block within thirty seconds."

  "Cooling jackets," I tapped the drawing. "We don't cast solid blocks. We cast them hollow. We pump water through the walls to carry the heat away."

  Gorn spat on the floor. "Casting hollow steel with water channels? That's master-level work. It'll cost you."

  "We have fifty thousand credits," I said. "Start melting."

  The next three days were a blur of heat, noise, and swearing.

  Making a V8 engine by hand wasn't like assembling a LEGO set. It was a war against tolerance. The blacksmiths could forge the heavy shape, but they couldn't do the precision work. A piston had to fit into a cylinder so tightly that gas couldn't escape, but loosely enough that it could slide at 3,000 RPM.

  That was my job. I stood at the lathe, my hands covered in oil and iron filings. "[Skill: Internal Oscillation - Micro Mode]."

  I vibrated my fingertips against the steel piston rings. I wasn't sanding them; I was honing them on a molecular level. I could feel the microscopic peaks and valleys of the metal. Bzzt. Bzzt. I smoothed them down until they were mirror-bright.

  "It leaks!" Amelia shouted from the water test bench. We had welded the water jacket shut, but steam was hissing out of a hairline crack. "Weld it again!" I yelled back, measuring the crankshaft clearance. "And put more flux on it!"

  By the end of the third day, it was finished. It sat on a heavy iron test stand in the middle of the warehouse. It was ugly. It wasn't the sleek, chrome-plated engine of a sports car. It was a rough-cast, black-iron beast. It was covered in weld marks, bolt heads, and copper pipes that looked like veins. It smelled of oil and raw potential.

  "The V8 Mana-Combustion Engine," I announced, wiping my hands on a rag that was dirtier than my hands. "Mark I."

  Rax walked around it, looking wary. "It looks like it wants to kill me."

  "It might," I admitted. "Amelia, connect the ignition."

  Amelia stepped up to the front. She grabbed the copper handle of the distributor. "I just... push mana in?"

  "Steady flow," I instructed. "Low voltage, high consistency."

  I walked to the rear. I grabbed the throttle lever—a simple valve that controlled how much red Fire Dust fell into the intake manifold. "Rax," I pointed to the heavy iron crank handle on the front. "You're the starter motor. Spin it. Hard."

  Rax grunted. He grabbed the handle with his mechanical arm. "On three. One. Two. Three!"

  He heaved. The massive flywheel turned. Chug... Chug... Chug...

  The pistons moved up and down, sucking in air and dust. "Ignition!" I yelled to Amelia. She closed her eyes and flared her mana.

  BANG.

  A gout of orange flame shot out of the open exhaust headers. Rax jumped back, cursing.

  BANG. BANG. The engine coughed. It shook the floor.

  "More dust!" I shouted, pushing the lever. "Feed it!"

  ROAR.

  It caught. It didn't hum. It didn't buzz. It screamed. The sound was a rhythmic, violent series of explosions that blurred into a continuous, chest-thumping roar. BRRRRRRRAAAAAAAAAAP!

  Black smoke poured from the exhaust, filling the warehouse ceiling. The cooling water in the side tank instantly began to bubble, sending jets of steam hissing into the air to mix with the smoke.

  It was loud. It was dirty. It was magnificent.

  The flywheel was a blur of motion. The air around the engine distorted from the sheer heat. Amelia was screaming something, but I couldn't hear her over the mechanical violence. She looked terrified, but she held onto the distributor, her eyes wide as she felt the machine eating her mana and turning it into raw force.

  I watched the tachometer I had jury-rigged. 1000 RPM... 2000 RPM...

  "Hold it there!" I bellowed, pulling the throttle back slightly. The roar settled into a steady, menacing idle. Thump-thump-thump-thump.

  Rax stared at the spinning shaft. He picked up a heavy iron crowbar and carefully touched it to the output gear. The crowbar was ripped from his hand and flung across the room, burying itself in a wooden crate. Rax looked at his hand, then at me. His eyes were huge.

  "That..." Rax shouted over the noise, "is not magic!"

  "No!" I shouted back, grinning like a maniac, my face covered in soot. "That is Horsepower! About four hundred of them!"

  I cut the fuel. The engine sputtered and died. The flywheel spun down. The silence that rushed back into the room was heavy. Steam hissed softly from the water tank. The iron block ticked as it cooled.

  "We have a heart," I said, patting the hot metal flank of the engine.

  Amelia let go of the distributor and collapsed onto a crate, breathing hard. "It's... angry. It feels like holding onto a dragon's tail."

  "It's perfect," Rax declared, kicking the tires of the test stand. "So we bolt this into the Centurion, and we march on the Academy?"

  I looked at the engine, then at the massive, legless corpse of the Siege Walker in the corner. My smile faded slightly. I ran the math in my head. The engine produced rotation. Fast, violent rotation. The Walker needed slow, powerful linear motion to move its legs.

  If I connected this spinning beast directly to the Walker's old, rusty joints, the torque would snap the drive shafts like twigs. The engine would tear the Walker apart from the inside out.

  "Not yet," I said, wiping the sweat from my forehead. "We have the power. But it's too fast. It's too violent."

  "We need a transmission," I muttered, looking at the pile of gears Rax had scavenged. "And hydraulics. We need to turn this scream into a push."

  "Hydraulics?" Rax asked, confused.

  "Fluid power," I said, turning to the blueprint. "We're going to build a blood system for the giant."