Isotta Fraschini Asso 750
# Isotta Fraschini Asso 750

The Isotta Fraschini Asso 750 was an Italian W 18 water-cooled aircraft engine of the 1930s. Produced by Isotta Fraschini the engine displaced just under 48 L (2,900 cu in) and produced up to 940 hp (700 kW). Together with the Asso 200 and the Asso 500 the Asso 750 was part of a family of modular engines, that used common and interchangeable components to lower production costs.

## Technical description

The W-18 Asso 750 had three six-cylinder in-line banks made of chrome-manganese steel, each joined by a single cast aluminum head for each bank of cylinders.

## Operational history

A version with an effective power of 940 hp (700 kW) was optimized for the Savoia-Marchetti S.55X used for the trans-Atlantic flight of Italo Balbo.

## Variants

### Asso 750

    Direct-drive, unsupercharged.

### Asso 750 R.

    Development with modified crankcase and crankshaft, fitted with a 0.658:1 reduction gear. Maximum power output 940 hp (700 kW).

### Asso 750 R.C.35

    The 750 R. fitted with a supercharger, rated altitude of 3,500 m (11,500 ft).

### Asso 750 M

    A 57.25 L (3,494 cu in) racing development with 150 mm (5.9 in) bore and 180 mm (7.1 in) stroke, for the Macchi M.67, re-designated Asso 1000 Ri.

## Applications

* CANT Z.501 (early versions)
* Caproni Ca.111
* Macchi M.C.77
* Savoia-Marchetti S.55
* Savoia-Marchetti S.62
* Savoia-Marchetti S.78

## Engines on display

At the Italian Air Force Museum two Isotta Fraschini Asso 750 are exhibited: A direct-drive Asso 750 and an Asso 750 R.C.35 with reduction gear and supercharger.

## Specifications (Asso 750)

Data from Il motore Isotta Fraschini Asso 750

### General characteristics

* Type: W-18 liquid/water-cooled
* Bore: 140 mm (5.5 in)
* Stroke: 170 mm (6.7 in)
* Displacement: 47.6 L (2,900 cu in)
* Length: 2,196 mm (86.5 in)
* Width: 1,060 mm (42 in)
* Height: 1,060 mm (42 in)
* Dry weight: 630 kg (1,390 lb)

### Components

* Valvetrain: Overhead valves 2x inlet and 2x exhaust per cylinder
* Supercharger: No supercharger fitted to this variant: supercharger available in other variants - (R.C.35 rated to 3,500 m (11,500 ft)).
* Fuel type: Gasoline 87 Octane
* Oil system: pressure
* Cooling system: Liquid/water
* Reduction gear: Not fitted to this variant: reduction geared variants available (0.658:1 R. and R.C.35).

### Performance

* Power output: Normal 800 hp (600 kW) at 1700 rpm; Take-off 850 hp (630 kW) at 1750 rpm; Max 900 hp (670 kW) at 1900 rpm
* Compression ratio: 5.6:1
* Specific fuel consumption: 0.295 kg/kWh (0.485 lb/(hp⋅h))
* Oil consumption: 0.00114 kg/kWh (0.00187 lb/(hp⋅h))
* Power-to-weight ratio: Normal 0.95 kW/kg (0.58 hp/lb) max 1.129 kW/kg (0.687 hp/lb)
