Triumph 91ci Specs: 73.7 x 87.5 mm

Triumph 91ci specs: 73.7 x 87.5 mm (2.9000 x 3.4450 in) bore and stroke. Displacement, compression and factory ratings, plus rod ratio.

At a glance

Displacement	91 ci
Cylinders	4
Bore	2.900"
Stroke	3.445"
Advertised power	53 hp
Years	1974–1980

This engine

Engine	Displacement	Bore × Stroke	CR	HP
FM	91 ci	2.9" × 3.445"	—	53

Factory cars with a Triumph 91ci

• Triumph Spitfire: 1974, FM; 1975, FM, 53 hp; 1976, FM; 1979, FM; 1980, FM

What varies across the family

This family is represented by a single engine in the database: 91 ci, 4 cylinders, a 2.9" × 3.445" bore and stroke.

All are undersquare — stroke larger than bore, favouring torque low in the range.

Each engine page carries rod ratio, mean piston speed, bore/stroke character and cylinder head specs where published, and links into the calculators with its dimensions already filled in.

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