Honda R18A1 Specs: 81 x 87.3 mm (3.1890 x 3.4370 in), 140 hp

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Honda R18A1 specs: 1.8L (109.8 ci) 4-cylinder, 81 x 87.3 mm (3.1890 x 3.4370 in) bore and stroke, 10.5:1 compression. Rated 140 hp, 2006–2011.

The Honda R18A1 is undersquare — the 3.437" stroke exceeds the 3.189" bore by 7.2% — a layout that trades peak RPM for leverage and torque low in the range. The 3.437" stroke puts mean piston speed at 4,000 ft/min around 7,000 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 27.5 ci (450 cc).

10.5:1 is in the range that usually runs on pump premium.

It is one of 4 engines in the R-series family, all of them 109.8 ci — the differences between them are in compression, heads and rating, not displacement. 6 factory variants share these dimensions, rated at 140 hp across 2006–2011.

Dimensions

Displacement	109.8 ci / 1.8 L
Bore	3.189"
Stroke	3.437"
Cylinders	4
Configuration	I4
Compression ratio	10.5:1
Bore/stroke ratio	0.928

Construction

Valvetrain	SOHC
Fuel type	gas
Redline	6,800 rpm (factory limit)
Advertised HP	140 hp
Years	2006–2011

Factory ratings by year

Year	Version	HP @ rpm	Torque @ rpm	Comp.
2006	R18A1 net	140 @ 6300	128 lb-ft @ 4300	10.5:1
2007	R18A1 net	140 @ 6300	128 lb-ft @ 4300	10.5:1
2008	R18A1 net	140 @ 6300	128 lb-ft @ 4300	10.5:1
2009	R18A1 net	140 @ 6300	128 lb-ft @ 4300	10.5:1
2010	R18A1 net	140 @ 6300	128 lb-ft @ 4300	10.5:1
2011	R18A1 net	140 @ 6300	128 lb-ft @ 4300	10.5:1

Factory specification sheet.

What these numbers mean

Bore/stroke character	0.928 — undersquare — stroke exceeds bore, which favours low-end torque
Mean piston speed at 6,000 RPM	3,437 ft/min — conservative for a street engine
Displacement per cylinder	27.4 ci
Static compression	10.5:1 — in the range that usually runs on pump premium

Run the numbers for this engine

Each link opens the calculator with this engine's specs already filled in.

• Displacement from bore and stroke (calculator)
• Static and dynamic compression ratio calculator
• Piston ring gap for this bore
• Piston speed at any RPM
• Horsepower to torque at any RPM
• What size carburetor (CFM calculator)

Variants sharing these dimensions (6)

These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.

Year	Advertised HP	Code
2006	140 hp	R18A1
2007	140 hp	R18A1
2008	140 hp	R18A1
2009	140 hp	R18A1
2010	140 hp	R18A1
2011	140 hp	R18A1

What cars have the R18A1?

1 factory vehicle, 2006–2011. Each year opens that model's engine table.

• Honda Civic: 2006, 140 hp; 2007, 140 hp; 2008, 140 hp; 2009, 140 hp; 2010, 140 hp; 2011, 140 hp

Similar engines

• Honda R18A — 109.8 ci
• Honda R-series (2006–2022) — 109.8 ci
• Honda R18Z1 — 109.8 ci
• Honda A18A — 111.7 ci
• Honda ES2 — 111.7 ci
• Honda ES3 — 111.7 ci
• Audi 18T 20V Ea113 — 109.8 ci
• Hyundai G4GM — 109.8 ci

← All R-series engines