techXXX
Designing the 3.0L NA 11.5k-rpm V12 Engine—If I Had a Car Company 02
As promised previously, today I lay out the specifications of the 3.0L NA V12 engine that I would build if I had a car company for the working enthusiasts.
As promised previously, today I lay out the specifications of the 3.0L NA V12 engine that I would build if I had a car company for the working enthusiasts. One point that I should note is that a strong alternative design would be a 4.0L V12 with 9k rpm redline, which would be considerably simpler and cheaper. This 3.0L V12 is viable, though we are entering exotic territory.
Let us name this engine PC301, as in P for Petrol, C as hexadecimal for 12, 30 for 3.0L, and 1 for mark 1.
Bottom-End
- Bore x stroke: 74mm x 58mm
- Cylinder spacing: 82mm
- Rod length: 110mm => 1.9 rod ratio
- Piston compression height (CH): 27mm
- Deck clearance: .8mm
- Deck height: 166.8mm
- Bank angle: 60°
- Water jacket: Closed deck
- Timing: Straight-cut gears
- Block material: Hypereutectic aluminum block + Nikasil coating
- Piston: Forged 4032 aluminum pistons
- Piston pins: 9310 steel, 21mm OD, 16mm ID, DLC coating, Fully floating
- Small-end bearing: Plain bronze
- Crankpin journal: 45mm diameter, 38mm width
- Main journal: 54mm diameter, 23mm width
- Bearing clearance: .038mm
- Bearing material: Tri-metal
- Dry-sump oil pump: 50% crank speed, 5 stages (1 pressure + 3 pan scavenge + 1 valley scavenge), Pre-oiling before engine start
- Oil viscosity: 5W40 or 5W30
- Flywheel: Single-mass, Billet steel *size, weight need engineering
- Fastening: Waisted studs, ARP bolts
Starting with the bottom-end, the key metrics that determine the characteristics of this engine and render it viable are the bore, stroke, cylinder spacing, and rod ratio. This is a small-displacement, highly oversquare engine with a high rod ratio. It will use a strong aluminum alloy for the block with Nikasil cylinder coating paired with forged aluminum pistons. Bearing sizes are moderate but sufficient. Straight-cut timing gears and dry-sump oiling will be used, too.
Top-End
- Shallow combustion chamber: Small, 30% squish band, Central spark plug, 40° valve angle (20° per side) *need engineering
- Target compression ratio (CR): 13:1
- Combustion chamber volume: ~ 16.8cc
- Cams: DOHC (quad cam)
- Intake valve: Titanium, D 34mm, Lift 12.5mm, Duration 280° @ 1mm, Mass < 40g
- Exhaust valve: Titanium, D 29mm, Lift 11.5mm, Duration 265° @ 1mm, Mass < 35g
- Springs: Dual ovate-wire steel springs, Titanium retainers, Finger followers
- Valve timing: VVT only for intake, +/-20°, Locked at high rpm / default to 30° overlap, Electric actuator
- Valve overlap: 18° idle / cold, 45° full power, *need engineering, Only by adjusting intake cam
In the top-end, the key metrics are moderately high compression ratio, titanium valves, and conservative VVT for the intake cams only. The top-end is the main reason I think a 4.0L V12 would be simpler and cheaper to build. In that alternative, VVT can be eliminated, and a cheaper valvetrain will be viable. In a sense, as the words of wisdom go, there is no replacement for displacement. However, if we go for displacement, nothing beats a supercharged pushrod V8, but that cannot meet today’s emission requirements without worse compromises.
Fuel, Intake, Exhaust
- Fuel delivery: Port injection
- Injectors: Need high-performance injectors
- Air intake: ITBs (individual throttle bodies), Short total intake runner length ~ 3” *need engineering
- Airbox: 10.5L airbox directly on top of ITBs
- Bank switching: Alternate bank shutoff with 10s intervals
- Equal-length exhaust headers: 6–2–1
- Firing order: 1–7–5–11–3–9–6–12–2–8–4–10
- Belt-driven accessories: Water pump, alternator, AC compressor (optional)
- Radiators: Main rad + condenser M, Oil cooler L, Cold air intake R
In terms of the accessories, the key metrics are port injection, individual throttle bodies (ITBs), and equal-length exhaust headers in a 6–2–1 setup.
Performance
- Target redline: 11.5k rpm
- Idle: 1200rpm
- Target power: 450hp to 530hp
When it comes to performance, tuning this engine means adjusting the valve timing. More aggressive cam profiles and more overlaps will contribute to top-end power at the expense of idle and drivability. I think a conservative tune of 450hp should provide a thrilling experience without drivability issues, thanks to VVT. Emissions will be under control, too, thanks to cylinder bank switching at idle. This engine should provide a “pure” feeling, thanks to its characteristics timing gear whine and symphonic exhaust note from equal-length headers in a V12.
In the next few posts, I will delve deep into why each metric is chosen. Specifically, the next one will cover the engine block.
