What Makes the Volvo Redblock Engine So Special?

Reviewed by

Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on September 26th, 2025

Reading Time: 4 minutes

Summary

  • The Volvo Redblock engine is considered special because of its simplicity, durability, and high tuning potential, making it a reliable and iconic choice for enthusiasts.

  • It was produced between 1974 and 1998, powering Volvo’s 200, 700, and 900 Series, and was widely praised for its non-interference design, forged components, and ability to exceed 300,000 miles.

  • Its cast iron block, low compression piston configuration, and straightforward design made it ideal for turbocharging and modifications, with some enthusiasts achieving up to 300 hp.

Recognized for its striking red paint, Volvo’s Redblock engine is more than just a pretty face. It’s known to be the most iconic engine that ever came out of Volvo and one that’s been able to withstand the test of time. 

History of the Redblock Engine

Produced between 1974 and 1998, the Volvo Redblock engine一also referred to as the B21, was introduced as a replacement for the B20.

A lot of enthusiasts saw the B21 as the Swedish equivalent of a small block V8, although it wasn’t exactly known for its power. 

Still, the Redblock remained a popular pick for those who enjoyed swapping engines long after it was discontinued, mainly because of how reliable and tunable it is when paired with a turbocharger. 

The Redblock first made the headlines when it was fitted into the Volvo 200 Series in 1974 with a 2.3L displacement, as well as a single overhead camshaft, two valves per cylinder, and a Mitsubishi TD05 or Garret turbocharger. 

Aside from the 200 Series, the same engine (and different versions that came from it) also powered the 700 and 900 Series with 90 to 180 hp tucked under its belt. 

The Redblock engine wasn’t exactly the most powerful workhorse during its time, but many enthusiasts believe that the lack of power is a safety feature instead of a defect or liability. 

In 1995, the Insurance Institute for Highway Safety issued a report claiming that the Volvo 240 had the lowest death rate of any car in the US from 1990 to 1994.

Volvo’s Redblock engines are non-interference machines, which means the piston heads won’t collide with the valves in case the timing belt breaks.

What Makes the Volvo Redblock a Swedish Masterpiece?

A Volvo Redblock engine | Image Source: Richard McCuistian

Volvo enthusiasts praise the Redblock for defining what it means to have a proper Turbobrick. Here are some basic bullet points for why enthusiasts love the Redblock:

  • Most SOHC versions are a non-interference design: If the timing belt breaks, the valves won’t be damaged.
  • Many versions are “overbuilt,” meaning they have forged crankshafts, sodium-filled valves, and very strong connecting rods.
  • The B230FT has great tuning potential, meaning that it can handle boost and other tuning modifications with minimal upgrades
  • Redblock engines regularly exceed 300,000 miles; some hit 1 million with proper care
  • They’re easy to work on, and have a huge enthusiast and parts support community

Here are more reasons why the Redblock is iconic:

Remarkably Simple

When the entire industry decided to make the shift to producing more aerodynamic vehicles during the ‘90s, Volvo was seemingly left behind, sticking with the trend of the ‘80s. 

Volvo didn’t change how its vehicles looked throughout the ‘90s. 

In fact, most of the models retained their boxy aesthetics and remained unequivocally Swedish. 

While this move might seem like a step in the wrong direction, Volvo stood by its simplistic nature, opting to market its vehicles as utilitarian and reliable. The same ideas were applied to the Redblock engine.

The Swedes made sure to develop an engine that’s easy to pack, workable, and simple enough to prove its worth. 

Designed to Perform

Efficiency was at the forefront of Volvo’s priorities in developing the B21. Cast iron was used to craft the engine block, producing a solid and sturdy deck. 

The configuration of the pistons was made in such a way that lowered compression, making it a great fit for a turbocharger. 

Full of Potential

With the Redblock engine, it seemed as though the Swedes designed it to accommodate high-end upgrades that made factory figures almost non-existent. 

The simple design meant that Redblock owners could go crazy with their engines. The sky was the limit when it came to discovering the Redblock’s potential.

A lot of enthusiasts had fun tinkering with their own B21s, with some of them unlocking up to 300 hp.

To this day, you’re guaranteed to find a couple of modified Redblocks that work just fine, with some of them even crossing the 300,000-mile mark. 

Redblock Engine Specs

There’s not one set of specifications that can perfectly describe the B21, mainly because there have been tons of iterations made to the original. Still, each version that came out of the first Redblock carried the same vision and purpose.

Redblock Specs In the Volvo 240, 300, and 740 Series (B19, B21, B23)

  • Stroke: 80 mm (3.150 inches)
  • B19 bore: 88.9 mm (3,500 inches)
  • B21 bore: 92 mm (3.622 inches)
  • B23 bore: 96 mm (3.780 inches)
  • Con-rod length (c to c): 145 mm (5.709 inches)
  • Crankshaft main journal diameter: 63.45 mm (2.498 inches)
  • Con-rod’s bearing’s journal diameter: 54 mm (2.126 inches)
  • Wrist pin diameter: 24 mm (0.945 inches)
  • Piston height:
    • B19A: 46 mm
    • B19E: (->1983) 46 mm
    • B19E: (1984->) 46.7 mm
    • B19ET: 46 mm
    • B19K: 46.7 mm
    • B21A Europe: 46.7 mm
    • B21A: 46 mm
    • B21E: 46 mm
    • B21ET: 46.5 mm
    • B23A: 46.4 mm
    • B23E: 46.4 mm
    • Firing order: 1-3-4-2

Redblock Specs In the Volvo 240, 300, 740, and 940 Series (B200, B230)

  • Stroke: 80 mm
  • B200 bore: 88.9 mm
  • B230 Bore: 96 mm
  • Con-rod length (c to c): 152 mm
  • Crankshaft main journal diameter: 55 mm
  • Con-rod’s bearing’s journal diameter: 49 mm
  • Wrist pin diameter: 23 mm
  • Piston height: 39.7 to 41.9 mm
  • Firing order: 1-3-4-2

Redblock Specs In the Volvo 240, 300, 740, and 940 Series (Late B200, B230)

  • Stroke: 80 mm
  • B200 bore: 88.9 mm
  • B230 Bore: 96 mm
  • Con-rod length (c to c): 152 mm
  • Crankshaft main journal diameter: 63 mm
  • Con-rod’s bearing’s journal diameter: 49 mm
  • Wrist pin diameter: 23 mm
  • Firing order: 1-3-4-2

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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Published by
CarParts.com Research Team and Richard McCuistian, ASE Certified Master Automobile Technician