Gemini is a very smart AI assistant!
I asked about tye disadvantages of ported exhaust at BDC:
Some early four-stroke engines did have an exhaust port at the bottom dead center (BDC) in addition to the usual top exhaust port. This design aimed for better cooling of the cylinder head, but it came with several disadvantages:
**Loss of efficiency:**
* **Incomplete exhaust:** With the BDC port open during the exhaust stroke, some of the unburnt fuel-air mixture and hot exhaust gases could escape prematurely. This reduces the pressure available for pushing the piston down on the power stroke, leading to lower power output and wasted fuel.
* **Fresh air loss:** As the piston starts its upward stroke for the intake phase, the BDC port might still be slightly open. This allows some of the fresh air-fuel mixture being drawn in to escape through the bottom, reducing the amount available for combustion and further impacting efficiency.
**Lubrication challenges:**
* **Oil loss:** The BDC port's location near the crankcase could lead to engine oil escaping with the exhaust gases. This increases oil consumption and requires more frequent top-ups.
**Complexity:**
* **Design and manufacturing:** Having two exhaust ports adds complexity to the engine design and manufacturing process. This can make the engine more expensive to produce and maintain.
**Overall, the efficiency and lubrication drawbacks of the BDC exhaust port outweighed the benefit of slightly better cooling. Modern four-stroke engines rely on improved engine design and materials for efficient cooling, eliminating the need for this less effective approach.**
Here are some additional points to consider:
* This design was more common in very early four-stroke engines, likely single-cylinder models.
* The BDC port might not have been a fully open port but rather a timed opening or slot that remained open for a shorter duration to minimize the efficiency losses.
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