title: Jacobs R-755
text: # Jacobs R-755
  
  The Jacobs R-755 (company designation L-4) is a seven-cylinder, air-cooled, radial engine for aircraft manufactured in the United States by the Jacobs Aircraft Engine Company.
  
  ## Design and development
  
  The R-755 was first run in 1933 and was still in production in the 1970s. With a bore and stroke of 5.25 in × 5 in (133 mm × 127 mm) the displacement was 757 cu in (12.4 L), power ranged from 200 hp to 350 hp (150 kW - 260 kW). The engine features steel cylinders with aluminum-alloy cylinder heads. An R-755E variant was developed for use in helicopters.
  
  ## Variants
  
  ### R-755A1
  
      The base-line direct drive production version.
  
  ### R-755A2
  
      300 hp variant.
  
  ### R-755A3
  
      Similar to A1 but with Scintilla magnetoes.
  
  ### R-755B1
  
      De-rated version of the R-755A to drive a fixed pitch airscrew.
  
  ### R-755B2
  
      De-rated version of the R-755A to drive a variable or controllable pitch airscrew.
  
  ### R-755E
  
      Up-rated engine with reduction gearing.
  
  ### R-755EH
  
      Developed to power the Jacobs Type 104 Gyrodyne.
  
  ## Applications
  
  * Anahuac Tauro
  * Beechcraft Model 17 Staggerwing (B17L, C17L, E17L)
  * Boeing-Stearman PT-18 Kaydet
  * Cessna AT-17 Bobcat
  * Cessna 195
  * Funk F-23
  * Grumman G-164 Ag Cat
  * Kellett KD-1
  * Lascurain Aura
  * Morane-Saulnier MS.505 Criquet
  * Waco F series (YMF, YPF)
  * Waco Custom Cabin series (YOC, YQC)
  * Waco Standard Cabin series (YKC, YKC-S, YKS-6)
  * Waco PG-3 (twin-engined powered version of Waco CG-15 glider, prototype only)
  
  ## Engines on display
  
  * A preserved Jacobs R-755 is on display at the Arkansas Air Museum.
  * A Jacobs R-755 is on public display at the Aerospace Museum of California
  * A preserved Jacobs R-755 is on display at Super T Aviation Academy in Medicine Hat, Canada.
  * A restored Jacobs R-755A is on display at the House of Whitley.
  
  ## Specifications (R-755-A1)
  
  Data from Jane's fighting aircraft of World War II, Jane's all the World's Aircraft 1938
  
  ### General characteristics
  
  * Type: 7-cylinder air-cooled radial piston engine
  * Bore: 5.25 in (133 mm)
  * Stroke: 5 in (130 mm)
  * Displacement: 757 cu in (12.4 L)
  * Length: 37 in (940 mm) overall
  * Diameter: 43.5 in (1,100 mm)
  * Dry weight: 505 lb (229 kg)
  
  ### Components
  
  * Valvetrain: 2 valves per cylinder, pushrod-actuated, sodium-cooled exhaust valves
  * Fuel system: Single Stromberg NA-R7A carburetor
  * Fuel type: 73 octane
  * Oil system: One pressure pump, two scavenge pumps
  * Cooling system: Air-cooled
  * Reduction gear: Direct drive, right hand tractor
  
  ### Performance
  
  * Power output: 225 hp (168 kW) at 2,000 rpm at sea level
  * Specific power: 0.32 hp/cu-in (14.8 kW/L)
  * Power-to-weight ratio: 0.48 hp/lb (0.8 kW/kg)
  