EDIT: there's so many new runs since i last checked so i'm fixing up this guide!

tl;dr:

• Chassis: Flying Chassis
• Engine: Angel's Engine
• Tires: Devil's Tires
• Brake: Devil's Brakes
• Steering: Dead Quick Steering
• Transmission: 7-speed MT (i'm pretty sure the gear ratio for 8 is like 420+ km/h which is is only ever reached for like 0.1 seconds)
• CPU: 4GB CPU Board
• Turbo: Nitro Charger
• Wheel: Dish Wheel
• Front: Lip Spoiler 2
• Hood: Bare Block (2)
• Top: Surfboard Carrier 2
• Wing: Drag Wing
• Rear: <depends>
• Side: <depends>

CHASSIS: Flying Chassis - 35 000 G to synthesise:

• UFO (Rosspury - bean event)
• Chassis Parts (Lafnek or Norsh)

ENGINE: Angel's Engine - 140 000 G to synthesise:

• Shining Piston ("Last Gift" reward after beating the game)
• Angel Wings (Mektakarit's time travel game - in a red chest hidden in the trees)

TIRES: Devil's Tires - 50 000 G to synthesise:

• Black Ring (Birthday "Gift 4")
• Devil's Carving Knife (Laltapass)

BRAKE: Devil's Brakes - 10 000 G to synthesise:

• Black Rubber (Norsh)
• Devil's Egg (Boyna, RNG prize for a "good name")

STEERING: Dead Quick Steering - 6 000 G to synthesise:

• Super Bearing (Norsh)
• Steering Parts (Norsh)

TRANSMISSION: 7-speed MT is good enough

CPU: 4GB CPU Board - 30 000 G to synthesise:

• 4GB CPU (Arbuk)
• Motherboard (Gedluna, Lafnek or Zeltaf)

TURBO: Nitro Charger - 20 000 G to synthesise

• Nitro Kit (Laltapass)
• Charger Parts (Laltapass)

FRONT: Lip Spoiler 2 from parts store; may need Mole Claw for URL and JRL (and possibly PJ - need to double-check)

• Mole's Claw (Zeltaf)
• Spoiler Parts (Lafnek)

HOOD: Bare Block (2) - 12 000 G to synthesise

• Big Block (Arbuk)
• High Mount (Arbuk)

TOP: Surfboard Carrier 2 - 4 000 G to synthesise

• Surfboard 2 (Letoba)
• Carrier Parts (Letoba)

WING: Drag Wing - 30 000 G to synthesise

• Weird Medicine (Murtica for donating to the Hospital)
• Dead Wings (Laltapass)

REAR: Drag Shoot or Propeller 2 from parts store

SIDE: Side Exhaust 2 - 5 000 G to synthesise

• Catalyzer (Norsh)
• Heat Resistant Pipe 2 (Norsh)

of course if you want to fully complete the game you will need to synthesise more parts for the Parts Race races, but that's outside this guide ok bye