Tuesday, May 12, 2009

A Diversion

In an effort to keep these postings interesting, some blogs will stray from the task at hand and offer some level of general insight into the automotive field. Refraining from ‘Science Content’ warnings or Nerd Alerts, I will try to present technically-riddled subjects in contextual format with my own brand of whimsical nonsense. I don’t think the physics behind air/fuel mixture vortices would provide much value unless reflecting upon a certain Honda’s ancestral roots and the Compound Vortex Controlled Combustion (CVCC) engine that it sported. But, I digress with purpose.

You’ve heard of the Honda Civic and you’ve also heard terms like V8, Straight Six, Cubic Inches, Liters, 4-Stroke/2-Stroke, etc. when referring to automotive engines. Aside from sounding neato, these are all useful in determining what you’ve got under the hood (bonnet, if you’re British).

V8 refers to two things: 8 cylinders in a V formation – that is 2 rows of 4 cylinders set at an angle to each other (a V6 has two rows of 3 cylinders and so forth). Straight/Inline is an arrangement of 1 row with all cylinders lined up: I8, I6, I5, I4. Since the ‘70s, American manufacturers wandered from the standard straight six to pursue V6s and never looked back. The choice was made for economical reasons, rather than performance reasons and many auto makers have followed. I6s are still out there, though - BMW has built quite a reputation on theirs (the “i” following most of their model numbers means inline). Engine configurations are not limited to Vs and Is - there are many more including (but no limited to) Slant, Flat, Opposed, W, and H, but I’ll let The Internet answer your questions on those. All of these types of engines have their benefits and drawbacks and are very useful in certain applications.

Intermission: The Parts of an Engine
Depicted below is an exploded view of an Inline 4, similar to the TR4A’s engine. The cylinders are merely guides for the pistons to move up and down in. The pistons go through strokes to achieve power:
1. Intake Stroke: Down, sucking air/fuel mixture in.
2. Compression Stroke: Up, creating compression – the spark plug causes detonation at the top.
3. Combustion/Power Stroke: Down, pushed from the ignition/explosion.
4. Exhaust Stroke: Up, pushing out spent gasses; and back to 1.
Each piston is connected to the crankshaft, which translates the up-and-down to rotation. The crankshaft is also connected to the camshaft, which controls the timing of intake and exhaust valves. This is all shown in the second graphic, which I obtained from howstuffworks.com.

Engine displacement is measured in cubic inches (CI) or liters (L) and represents the volume of all cylinders added up - it’s a measure of the amount of total space available for internal combustions or, simply, how much explosive force can be transformed into motion. Forgetting about many other aspects that factor into torque and horsepower, the size of an engine is the most basic gauge to how ballsy it is. By numbers alone, it seems logical that a Chevy 350 (that’s 350 CI) would be more powerful than Toyota 2.0L, but what about a Buick 215 versus a Ford 5.0L? A 1-liter engine would equate to about 61 cubic inches and each 100 CI equals roughly 1.639L, so you’d need to level the playing field for comparisons. Also, ad men get into the mix sometimes and screw up the math: the Ford 5.0L is closer to a 4.9L since it’s just a re-badged 302, but 5.0 sounds so much better than 4.9. A more-precise habit of manufacturers and automotive enthusiasts is to use the cubic centimeter (cc) to refer to an engine’s volume: 1L = 1000cc’s. This curious method is what Triumph used, so I will talk about the TR4A’s engine as a 2138 cc instead of a 2.1L or a 130 CI.

Strokes were brought up earlier and they will be the last item of discussion for this journal entry. If you notice, the verbiage describes four diff’rent strokes. What I’m talking about, Willis, is a 4-stroke engine. The neat and orderly separation between these strokes is good for emissions, but not so good for power. Thinking more about this, a complete cycle requires the crankshaft to rotate two times - during which, there is only one power stroke per cylinder. The four-cylinder engine pictured above would have four explosions for every two revolutions of the crankshaft so you’re getting two explosions per revolution. Now, here’s the interesting part: a 2.5L Inline 4 produces as much power, per cylinder as a 5.0L V8. Since only one cylinder fires at a time and individual cylinders are the same size for both engines – the V8 just has more cylinders, which means more explosions per revolution and, therefore, more total power. The 2-stroke engine is similar to this comparison because there are only two strokes per cycle rather than four - so, you’re getting more explosions per cylinder per revolution - all cylinders have their power stroke every revolution of the crankshaft. Taking it all in, a 2-stroke, 4-cylinder would potentially match the total power of a 4-stroke V8 twice its size. But, because of the nature of mixing exhaust with fresh air/fuel and the need for oil to be mixed in with the fuel, 2-stroke engines are dirtier and produce more harmful emissions than comparable 4-strokes. A visual aid for this comparison:

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