Boosting Power and Efficiency in a 1979 BMC 1.5L Diesel Engine
Updated: May 7, 2025
Written by Leonard Teasca, Engineer
Leonard Teasca is a Dublin-based engineer and innovator with a remarkable talent for translating complex technological concepts into accessible understanding. His unique combination of technical expertise and artistic experience allows him to bridge the gap between sophisticated engineering principles and practical applications.
In the world of marine engineering, improving the efficiency and power of older engines is always a challenge. In this article, I’ll share my experience modifying a 1979 1.5L BMC diesel engine by adding two... Intex air pumps... (1.2 psi each) to the air intake system, controlled via a... PWM module... The result? A noticeable improvement in fuel economy, power output, and overall engine efficiency. We’ll go through the calculations, the benefits, and the technology behind the modification.
The setup: Air pumps, PWM module, and engine modification
For this modification, I used two Intex air pumps rated at 1.2 psi each. These pumps are configured in parallel for airflow but wired in series electrically to ensure smooth operation. The pumps are controlled via a PWM module, which adjusts the airflow as required for efficient combustion. This simple setup boosts the amount of air available for combustion in the engine, enhancing the burn rate and improving overall engine performance.
The science of the modification
When you add air to a diesel engine’s intake, you improve the air-fuel ratio, allowing the engine to burn more fuel more completely. This leads to better efficiency, more power, and less wasted fuel. In my case, the addition of air has resulted in a measurable improvement in power and fuel economy. Let’s break down the numbers:
The math: Fuel economy, power calculation, and efficiency
Power before modification
The engine’s rated power is 30 horsepower (hp). With a thermal efficiency of 33%, only about 33% of the fuel energy is converted to usable power.
Energy consumed per hour: 4 liters/hour × 35.8 MJ/L = 143.2 MJ/hour
Usable energy per hour: 143.2 MJ/hour × 33% = 47.2 MJ/hour
Power output: 47.2 MJ/hour ÷ 3600 seconds/hour × 1 ÷ 0.7457 = ~30 hp (rated power)
Fuel economy improvement
After modifying the engine, the fuel consumption decreased by 15%, from 4 liters/hour to 3.4 liters/hour. This saved 60 liters of fuel annually, resulting in a 15% improvement in fuel economy.
With the added air and better burn efficiency, the engine’s power increased from 30 hp to 32.4 hp, an increase of 2.4 hp, while fuel consumption decreased. The combustion efficiency improved from 33% to 35%, resulting in a noticeable boost in power and efficiency.
Environmental impact: CO₂ savings
One of the greatest benefits of this modification is its positive environmental impact. By saving fuel, the engine emits less CO₂. The reduction in fuel consumption by 60 liters annually leads to a savings of 160.8 kg of CO₂ per year.
This modification not only improves performance, it also contributes to a greener, more sustainable marine operation.
Conclusion: A smarter, more efficient marine engine
The addition of air pumps to the intake system of a 1979 BMC 1.5L diesel engine has resulted in a real-world improvement in both performance and fuel efficiency. With a slight increase in horsepower, a reduction in fuel consumption, and a decrease in CO₂ emissions, this modification is a great example of how technology can breathe new life into an older engine.
The modification is simple, cost-effective, and highly beneficial for anyone looking to enhance the performance and environmental impact of their older diesel engines.
Read more from Leonard Teasca
Leonard Teasca, Engineer
Leonard Teasca stands at the forefront of innovative wellness technology research, specializing in the development of advanced healing chambers and therapeutic environments. His groundbreaking research focuses on integrating marine engineering principles with wellness technology to create state-of-the-art healing environments. Through meticulous study and development, Leonard has pioneered approaches to wellness chamber design that maximize therapeutic benefits while ensuring optimal safety and comfort...
