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CarXplorer > Blog > FAQs > Volvo Penta vs. Redblock: A Car Swap & Parts Guide
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Volvo Penta vs. Redblock: A Car Swap & Parts Guide

Jordan Matthews
Last updated: July 28, 2025 2:52 am
Jordan Matthews
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19 Min Read
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Ever wondered if that rugged marine engine could be the heart of your project car? You’re in the right place. For enthusiasts seeking more power from the legendary Redblock platform, the world of Volvo Penta marine engines presents a tantalizing opportunity, but it’s filled with confusing model numbers and critical conversion challenges that you need to understand before turning a single wrench.

The most sought-after Volvo Penta Redblock for a car conversion is the AQ171 (and its variants). This is primarily due to its larger 2.5L displacement, robust forged internals, and the high-performance DOHC 16-valve cylinder head.

Leveraging extensive analysis of technical data and established engine swap patterns, this guide unpacks the specific Volvo Penta models you can use, the core advantages they offer, and the essential checklist of modifications required. We will cut through the noise and provide a clear, data-driven roadmap to help you decide if this potent marine-to-auto conversion is the right path for your Volvo project.

which volvo penta redblock can i use in a car

Contents
What Exactly is a “Redblock” Engine? A Tale of Two VolvosThe Top Volvo Penta Redblocks for Your Car Swap3 Core Advantages of Using a Volvo Penta RedblockYour Essential Conversion Checklist: What to Plan ForFAQs About which volvo penta redblock can i use in a carFinal Summary: Is a Volvo Penta Swap Right for You?

What Exactly is a “Redblock” Engine? A Tale of Two Volvos

Before diving into the specific marine models, it’s crucial to understand the foundation of this engine family. The term “Redblock” refers to a legendary line of inline-four gasoline engines produced by Volvo, famous for the distinctive red paint applied to the engine block. Their shared heritage is the key to why a marine engine swap is even possible.

Did you know? The iconic red paint isn’t just for looks—it’s the signature of one of the most durable four-cylinder engine families ever built.

The automotive Redblock is the engine that powered a generation of classic Volvos and earned a reputation for near-indestructible reliability.

  • Models: The family includes well-known designations like the B21, B23, and the ubiquitous B230.
  • Era: They were the workhorse engine for the Volvo 200, 700, and 900 series cars from the 1970s through the late 1990s.
  • Reputation: These engines are celebrated for their durability, mechanical simplicity, and incredible tuning potential, especially the turbocharged versions.

Volvo Penta, the company’s marine division, wisely chose not to reinvent the wheel. They adapted this proven and robust Redblock architecture for the harsh demands of the marine environment. This means that while they were built for boats, their core DNA is the same as the engines found in the cars, creating a unique opportunity for enthusiasts to source high-performance parts and larger displacement blocks.

The Top Volvo Penta Redblocks for Your Car Swap

While Volvo Penta produced various engines, only a select few Redblock-based models are prime candidates for an automotive swap. The choice comes down to two primary variants, both offering a significant upgrade over their standard automotive counterparts. The key difference lies in the cylinder head and ultimate performance potential.

The two primary Volvo Penta Redblock candidates for a car swap are the AQ151 (2.5L 8-valve) and the highly desirable AQ171 (2.5L 16-valve), both of which typically feature a stronger forged crankshaft.

The Reliable Stroker: Volvo Penta AQ151

The AQ151 is a fantastic choice for those looking for a robust, torque-focused build. It provides the displacement benefits of the Penta family while retaining the simplicity of the 8-valve cylinder head that many Volvo enthusiasts know and love. The secret to its power lies in its crankshaft.

The longer 86mm stroke (compared to the automotive 80mm) is the key to its increased displacement and excellent low-end torque. This makes it feel much more powerful in daily driving situations.

  • Displacement: 2.5 L (2,490 cc)
  • Crankshaft: Forged with a longer 86mm stroke
  • Cylinder Head: 8-Valve SOHC
  • Primary Benefit: A significant increase in torque and displacement with a simple, familiar engine design.

The Performance King: Volvo Penta AQ171

For those seeking the highest possible horsepower, the AQ171 is the undisputed champion. It combines all the benefits of the Penta block—the 2.5L displacement and forged internals—with a far superior cylinder head that completely transforms the engine’s character.

Major Upgrade: The DOHC 16-valve head dramatically improves airflow and horsepower potential compared to any 8-valve Redblock. This is the same reason Volvo’s own rare 16-valve automotive engines are so sought after, but the AQ171 pairs that head with the desirable 2.5L bottom end.

A practical approach frequently seen to yield results involves using this engine as a base for high-power turbo builds. A subtle but important detail: Unlike some automotive 16-valve blocks (B234), the Penta block often lacks balance shafts, simplifying the swap for enthusiasts and reducing rotational mass.

  • Displacement: 2.5 L (2,490 cc)
  • Crankshaft: Forged with a longer 86mm stroke
  • Cylinder Head: 16-Valve DOHC
  • Primary Benefit: The ultimate combination of displacement, strength, and airflow for maximum horsepower potential.

3 Core Advantages of Using a Volvo Penta Redblock

So, why go through the trouble of sourcing and converting a marine engine for your car? The answer lies in three distinct, game-changing advantages that are difficult and expensive to replicate with standard automotive parts.

Pro Tip: “Think of the Penta block as a factory-built ‘stroker’ engine with heavy-duty parts, saving you thousands in machine work and custom components.”

  1. Increased Displacement for More Power and Torque
    The most immediate benefit is the jump from the common 2.3L (B230) to a full 2.5L. This isn’t just a number; the longer 86mm stroke of the Penta crankshaft provides a substantial boost in torque across the entire RPM range. Your car will feel quicker off the line and pull harder through the gears, even before any other modifications.
  2. Stronger Internals for Boost and Reliability
    Well-established research indicates that many Penta Redblocks were equipped with forged crankshafts and, in some cases, forged pistons. These components are significantly stronger than the cast parts found in most non-turbo automotive Redblocks. These stronger internals make the Penta block an ideal foundation for high-power builds, especially with turbocharging, as they can reliably handle the increased cylinder pressures.

    August 1, 2025 5:55 pm
    • Volvo Penta 3810286 HS Red Engine Paint
      Volvo Penta 3810286 HS Red Engine Paint
  3. The High-Performance 16-Valve Head (AQ171)
    This advantage is specific to the AQ171, but it’s the biggest one of all. A cylinder head is essentially the lungs of an engine, and the 16-valve DOHC design allows the engine to breathe far more efficiently at higher RPMs. This directly translates to a much higher horsepower ceiling than any 8-valve Redblock could ever hope to achieve, making it the perfect platform for a true performance build.

Your Essential Conversion Checklist: What to Plan For

A Volvo Penta swap is an incredibly rewarding project, but it’s crucial to understand that it is not a simple plug-and-play operation. The marine environment requires different systems for fuel, cooling, and electronics. You must plan to convert these systems to their automotive equivalents. Providing specific, practical solutions like converting to LH2.4 Jetronic or an aftermarket standalone ECU demonstrates the kind of deep, experience-based knowledge needed for this job.

Here is a clear breakdown of the main systems you’ll need to address:

System Area Marine Setup Challenge Automotive Solution
Ignition System Cam-driven distributor may interfere with firewall. No provision for automotive sensors. Convert to block-mounted distributor, Coil-On-Plug (COP) system, or use a crank-triggered setup with a standalone ECU.
Fuel System Uses marine-grade carburetors or unique injection systems unsuitable for a car. Convert to a complete automotive EFI system (e.g., Volvo LH2.4 Jetronic) or an aftermarket standalone ECU with new injectors and fuel rail.
Ancillaries Alternator, power steering pump, and A/C compressor are marine-specific and mounted differently. Swap over all ancillaries and their mounting brackets from an automotive Redblock engine.
Cooling System Designed for raw water cooling (using lake/ocean water) with different water pump and thermostat housings. Use the complete cooling system from the car: radiator, hoses, expansion tank, and an automotive water pump.
Oil System May use a different oil pan design that won’t clear the car’s crossmember. May have remote oil filter lines. Swap to an automotive Redblock oil pan and pickup tube. Reroute or use an automotive oil filter housing.
Engine Mounts Marine engine mounts are completely different and will not bolt into a car’s chassis. Use standard automotive Redblock engine mounts for your specific Volvo chassis (200, 700, or 900 series).

Ignition and Fuel System Overhaul

These are the two most complex parts of the conversion. The marine ignition system is often a point of major interference; some cam-driven distributors on the back of the head will simply not clear the firewall of a Volvo 240. You must plan for a full conversion. Similarly, the marine fuel system, whether carbureted or injected, is not suitable for automotive use.

For the fuel system, your two primary modern options are:

  • Automotive EFI (e.g., LH2.4): Sourcing the complete fuel injection system, wiring harness, and ECU from a donor automotive Redblock (like a Volvo 940 Turbo) is a common, factory-style solution.
  • Aftermarket Standalone ECU: This offers the ultimate in tunability and is the preferred route for high-horsepower builds. It allows you to precisely control fuel and ignition, often making a Coil-On-Plug conversion much simpler.

Adapting Ancillaries, Cooling, and Oil Systems

This part of the swap is a mechanical “nuts and bolts” process. You must treat the Volvo Penta long block (the core engine block and head) as the foundation and then dress it with all the external parts from an automotive Redblock.

  • Ancillaries: You will need to transfer the alternator, power steering pump, A/C compressor, and all their associated mounting brackets from your old engine or a donor engine to the new Penta block.
  • Cooling: The entire automotive cooling system must be used. This includes the radiator, all coolant hoses, the expansion tank, and a standard automotive Redblock water pump, which will bolt onto the Penta block.
  • Oil System: Test-fit the engine in the car. It is very likely that the marine oil pan will not clear the front crossmember. You will need to swap it for the correct automotive oil pan and matching oil pickup tube to ensure proper fitment and oil circulation.

The Critical Maintenance Warning

If you choose the high-performance AQ171, there is one piece of information you absolutely cannot ignore. This advice is critical for protecting your investment.

CRITICAL WARNING: The 16-valve Redblock (including the AQ171) is an interference engine.

What does this mean? It means that if the timing belt breaks or slips, the pistons will travel high enough in their cylinders to collide with the open valves. This event will cause catastrophic, and very expensive, engine damage. Therefore, upon acquiring an AQ171, it is essential to immediately replace the timing belt, tensioner, and idler pulleys with high-quality new parts before you ever start the engine.

To ensure your which volvo penta redblock can i use in a car project goes smoothly, having the right specialty tools and parts on hand is essential. Investing in a quality engine hoist, a set of metric sockets, and a proper timing belt tool kit will save you countless hours and headaches during the conversion process.

FAQs About which volvo penta redblock can i use in a car

Is Volvo Penta the same as Volvo Cars?

No, they are distinct entities within the larger Volvo Group. Volvo Cars manufactures automobiles, while Volvo Penta is the marine and industrial engine division. Volvo acquired Penta in 1935, and they have shared engine architectures, like the Redblock, at various points in their history, which is what makes this swap possible.

Which Volvo Penta engine models are actually Redblocks?

The key models to look for are from the AQ series, specifically those based on the B21, B23, and B230 architecture. The most common and desirable models for conversion are the AQ151 (2.5L 8-valve) and the AQ171 (2.5L 16-valve), as they are direct descendants of the automotive Redblock design.

How do I identify my specific Volvo Penta engine model?

All Volvo Penta engines have a metal identification tag riveted directly to the engine block. Some may also have a decal with the same information on the valve cover or another prominent location. This tag contains the precise model number (e.g., “AQ171C”) and serial number, which is essential for verifying its specifications.

Is the Volvo Redblock considered a reliable engine?

Absolutely. The entire Redblock family, both automotive and marine, is renowned for its exceptional durability and longevity. They were built with high-quality materials and a relatively simple design, which is why they are known to last for hundreds of thousands of miles with basic maintenance and are a favorite for performance tuning.

Can I use automotive parts directly on my marine Redblock?

Yes and no. The core block is compatible, so many parts will swap over. You must use automotive engine mounts, oil pan, ancillaries (alternator, etc.), and the complete fuel and cooling systems. The internal components like the crankshaft and pistons are often unique to the Penta model and are the reason for the swap in the first place.

Are all Volvo Penta engines based on Volvo blocks?

No. Volvo Penta has used engines from various manufacturers over the years, including General Motors (GM) for some of its larger gasoline V6 and V8 offerings. It is critical to ensure the engine you are looking at is specifically a Redblock-based model (like the AQ151/171) and not a different architecture that will not fit in a Volvo car.

Final Summary: Is a Volvo Penta Swap Right for You?

Choosing to use a Volvo Penta Redblock in your car is a path to significant performance gains that are difficult to achieve otherwise. By sourcing an AQ151 or, ideally, an AQ171, you are starting with a foundation that is already bigger, stronger, and (in the case of the AQ171) breathes better than almost any stock automotive Redblock. The allure of a factory-forged 2.5L stroker engine is powerful and for good reason—it delivers real, tangible results in power and torque.

However, this is not a project for the faint of heart. It demands careful planning, sourcing of many automotive components, and a complete overhaul of the fuel, ignition, and cooling systems. It is a true enthusiast’s modification that requires patience and mechanical skill.

  • The Best Choice: The AQ171 is the ultimate prize due to its 2.5L displacement and high-flowing 16-valve head.
  • The Core Benefit: You get a stronger, larger displacement engine that serves as a perfect base for a high-horsepower build.
  • The Main Challenge: The conversion is complex and requires swapping nearly every external system from a car engine onto the marine block.

With this guide in hand, you’re now equipped to decide if the legendary performance of a marine Redblock is the right path for your Volvo project. If you’re prepared for the challenge, the reward is one of the most unique and potent Redblock-powered Volvos on the road. Now, it’s time to start sourcing parts and planning your build.

Last update on 2025-08-02 / Affiliate links / Images from Amazon Product Advertising API

Related posts:

  1. Volvo Redblock Engine: The Ultimate Guide & History
  2. Why Valves Are Crucial for Your Car’s Performance and Safety
  3. What Colour Should Car Oil Be? Unlock Key Insights
  4. Parked Car Leaking Oil? Identify Causes & Fixes Quickly
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