Building the winning Engine Masters Challenge motor means successfully applying theoretical knowledge. This sounds reasonable, but there are stumbling blocks-two, in fact. First, the theory has to be right, and secondly, it has to be functionally applied. Assuming the smarts for the first part, the second does not seem too difficult until a specific component is found not to function quite as well as hoped. At this point, things can get complex real fast. It's here that the difference between a totally theoretical engineer and a practical engineer really shines. If you've followed the EMC through the years, it's clear that whoever wins has to be well versed in both theory and practice. What we're going to do is start with applied theory and see how far it will take us before we run into a problem that might derail a winning combination and force us to make a hardware compromise to get better results.

This Year's Rules
The way this year's rules are structured means the contest boils down to a power-percubic-inch race. In simpli-fied form, the contestant can build an engine from 300 inches up. If it's just output we are looking at, then big inches has the best chance of winning, but if it's output per cube, then a whole different scenario applies. Just so you know where I'm coming from, I can be pretty specific about the application of the theoretical side based on experience. Quite a while back, I did a project for Chrysler UK which involved developing a 90-cube four-cylinder engine to optimize power bandwidth, driveability, and output. The car was tested by two magazines and deemed outstanding. The powerband was steam-engine like, starting at 400 rpm, and going all the way to 8,000 rpm. That said, let's start with the theory behind why smaller cylinders make more power per cube and work our way through the rest of the engine's components to see what's most likely optimal, and why.

Small Vs. Big Cylinders
At the end of the day, a successful high-output engine is all about geometry. That geometry has to most effectively allow the engine to inhale the maximum amount of air per cube, mix fuel into it, compress it, and burn it. At this point, the pressure in the cylinder must be transmitted efficiently via the connecting rod to the crank.

The first point on our list is inhaling air and how geometry affects that. let's assume as a starting point we have a 4-inch bore. For most practical purposes, the combined size of the valves in a typical 4-inch bore V-8 is 91 percent of the bore size. This is distributed as 51 percent for the intake, and 40 percent for the exhaust. using a stock bore and stroke 5.0 Mustang engine (302 inches) as a starting point, we find that this works out to a 2.04-inch intake and a 1.6-inch exhaust. If we scale up the bore and stroke by 25 percent, we now have an engine with a 5-inch bore and a 3.75-inch stroke, for 589 inches. At the same proportions, the intake valve size will be 2.55 inches, and 2 inches for the exhaust. At this point it looks (at least at first sight) like all the proportions have stayed the same, so nothing has changed in terms of cylinder size and breathing capability. unfortunately, nothing could be further from reality. The problem is that the valve diameter may have gone up proportionally, but the volume it has to feed has gone up by the cube. The result is we have valves 25 percent bigger, but the cubic inches have gone from 302 to 589-that's almost double!

At this point, someone is going to argue that it should be the valve area we have to consider. Namely, for a valve made 25 percent bigger, the area goes up by 56 percent, not 25 percent. unfortunately, the valve area does not come into play here in quite the way we might expect. The breathing capacity of a valve is dictated by the curtain area, and the curtain area for a given valve lift goes up in the same proportion as the increase in valve diameter. The extra area of the valve is not realized until it has been lifted higher than 25 percent of the diameter of the smaller valve we are considering. The bottom line is that the bigger the cylinder, the less valve breathing capacity we can get per cube to be fed. so at this point, assuming we can optimize everything else, we want the biggest valves possible in the smallest engine allowed by the rules.