Flat-Eight Engine — Marvin Scott

Flat Eight Engine

Background

I am working on this engine design for fun. Flat-six engines are a great engine choice for any vehicle, especially engines placed towards the middle of the vehicle. Their low center of mass ensures optimal cornering, and low understeer. Porsche is most famous for its flat-six engine design, so why not take it a step further? Only 5 flat-eight engines have been made by Porsche, the last being made in 1971. What would happen if we designed this using modern engineering practices? I know that the flat-eight engine can be quite a ways larger than a flat-six engine, but certainly if a luxury brand were to release this in a car, it would be an instant hit. Nowadays, engineers are extremely focused on creating turbocharged, and supercharged four cylinder engines. This usually comes at the cost of reliability, and for many, the enjoyment of the sound of a roaring engine. Another issue with reduction of cylinders includes more issues with engine shaking, and then issues with actually feeding a turbo properly.

The Challenge

For this work in progress, I am challenging myself to design an 8 cylinder horizontally opposed engine.

My Role

I am in charge of designing every aspect of this engine, which includes motion studies, any FEA studies, and feasibility studies.

Process

This engine design started with the most important part of the engine, in my opinion, the pistons. I want this design simply to be a design for feasibility, simplicity, and assembly, so the decision was made to simply make the piston head at a diameter of 1.5in. Small bore, large stroke. The stroke is 3.15in, which gives a stroke to bore ratio of 2.1. In total, this would represent a total displacement of .71L. A laughably small displacement. However, I believe this is important to actually make an engine that can fit in most modern cars. A smaller engine in and of itself would be important to actually pull this off. When it comes to sound, I’m sure this engine would sound something reminiscent of a 1960’s era 12 cylinder engine (with 1.5L of displacement, yes Ferrari actually made that as a V12, one of their first cars). After I made the piston, I did a simple design study to determine if the rod could actually resist the forces with the pressure being around 200psi at the piston head. As shown, the actual piston rod would hold just fine. Other design considerations for this engine include the assembly. Notice, the pistons have been made to be a two sided snap assembly, as they connect to the crankshaft mechanism. The final design consideration thus far, has been the actual crankshaft. I made the firing order on this crankshaft in a “wave” order. (1, 2, 3, 4, 5, 6, 7, 8) This wave order evenly disperses the inertia of the rods upon the crankshaft by making them fire closely along the crankshaft. This, hopefully, would minimize any shaking that would actually occur along the crankshaft, therefore making a smother firing engine. As this is a work in progress, this is all subject to change as I learn more about engine design.

Final Outcomes

All in all, this has been a fun project to work on. It is interesting learning more about design considerations in internal combustion based engines. There’s a whole fascinating world in engineering related to these engines. I do not think I know enough about internal combustion engines to fully satisfy the design requirements of completing the engine, but as I learn more I will add more parts.