The 1.7 Litre Engine, a workhorse in various vehicles, often draws comparisons with other powerplants like the Porsche 356’s engine. While the 356, especially later models, boasted impressive horsepower figures (around 95 HP DIN), achieving this output involved more than just carburetors and camshafts. A key factor was the high compression ratio, rumored to be as high as 9.5:1, significantly higher than the 7.6:1 found in US-spec 1.7 litre engines.
Compression Ratio: A Key Differentiator in 1.7 Litre Engine Performance
Compression ratio plays a crucial role in engine power. A jump from the US-spec 7.6:1 to the Euro-spec 8.0:1 in a 1.7 litre engine could yield a 5 HP increase. This illustrates the impact of compression. While a direct extrapolation to a 9.5:1 compression ratio might not be entirely accurate, it highlights the potential for increased power output. The difference between the 8.2:1 compression ratio of the standard 1.7 litre 914 engine (producing 80 DIN HP) and the 7.3:1 ratio of the California-spec 1.7 litre engine (72 DIN HP) further underscores the significance of compression.
Head Design and Flow: Optimizing the 1.7 Litre Engine
Beyond compression, the design of the cylinder heads significantly influences performance. The 356 heads, with a more hemispherical combustion chamber compared to the wedge-shaped design of the VW Type IV, facilitated higher compression ratios and improved flow. This superior flow, partly attributed to the 356’s dedicated design compared to the 914’s adapted VW sedan engine, contributed to increased power.
Intake and Exhaust Systems: Breathing Life into the 1.7 Litre Engine
The intake and exhaust systems also play vital roles. The 356’s carburetors and shorter intake path optimized high RPM breathing, while the 914’s longer fuel injection path favored low RPM performance. The exhaust system design, with the 356’s front and rear exhaust port placement versus the 914’s bottom placement, potentially impacted performance, though the optimal configuration remains a topic of debate. Ideally, intake and exhaust ports should be on opposing sides of the head, a characteristic not fully realized in either engine.
Power Band and Torque: Defining the Engine’s Character
Analyzing the power band reveals further distinctions. The 356, known for its high-revving nature, concentrated its torque in the 5000-6000 RPM range. In contrast, the stock US-spec 2.0 litre 914 delivered a broad torque curve from 2800 to 4200 RPM, prioritizing low-end torque over high-end horsepower. This difference in philosophy stemmed from the Type IV engine’s original purpose: powering heavier Volkswagen vehicles. Ultimately, understanding power generation requires considering various factors, including compression, head design, intake and exhaust systems, and the intended application of the engine. The 1.7 litre engine, with its unique characteristics, stands as a testament to the intricate relationship between these elements.
