In-cylinder pressure-measuring...
In-cylinder pressure-measuring gear, even just a few years ago, cost big bucks. These days, the cost has dropped dramatically. The Texas-based TFX Engine Technology entry-level system shown here can be had for less than $5,000. Add to this the cost of the type of sensors required, and even a small engine shop can be in business.
Options For Making Cubes
An engine gets cubes from a combination of bore size and stroke. so to make the best power, do we need a big-bore/short-stroke, or a small-bore/long-stroke combination? First, let's dispel the myth that a long stroke makes more torque just because the crank has a longer arm. For a given amount of cubic inches, a longer stroke will have a smaller bore. This means for a given level of cylinder pressure, less force will be pushing the piston down the bore because the area is smaller. Also, this smaller bore cannot accommodate valves as large, and that means holding them open longer to fill the cylinder for output at the top end of the rpm range. With a big-bore/short-stroke configuration, the larger valves can (and should) be opened later and (very important to low-speed output) closed sooner. An earlier closing on the intake means a greater amount of charge is trapped in the cylinder, thus creating more cylinder pressure upon combustion. This is a prime example of how meaningless a single change makes toward proving one concept or another. The only way to prove the superiority of a short-stroke engine is to test with the bigger valves it allows, and the revised cam timing. But there are limits to how big a bore and short a stroke can be used. As the bore gets bigger, so does the difficulty of making a suitably compact combustion chamber with good properties. Assuming a typical small-block sized bore of 4 inches (or thereabout), what stroke is most likely to give the best chamber configuration for the 10.5:1 compression ratio limit of the EMC? This is a good question. Certainly it will be easier to produce a good chamber for a 4-inch stroke combination than for a 3-inch stroke. so here we have a situation where having a few more cubes may actually help output production per cube, and that leaves us with the question of what might be best.
Here is a 350 Chevy intake...
Here is a 350 Chevy intake port with the valve lifted about .300-inches and the mixture flowing at a speed typically generated when an engine is running at about 5,000 rpm. The luminescent blue is fuel. Note the rotating vortex halfway down the port and the fact there is almost no fuel in the top half of the port where it approaches the turn. Fixing a wet-flow problem like this can be worth as much as 25 hp!
Part of getting the burn successfully done is to make sure the quench action between the piston crown and cylinder head is optimal. This usually means (but not always) making it as tight as possible.
We have talked crank for displacement; now let's talk rods and pistons. should the rods be long, with a shorter and lighter piston, or should we go with a short rod with possible lowspeed torque benefits? This is a subject that could take fifty pages, so let's cut right to the chase. If there was no bore friction, a short rod would be best, because it hangs around BDC longer and moves up the bore more slowly, thus producing more volume above the piston at the point of valve closure. This means a greater trapped charge, which is significant at low speed. But pistons do have friction; the longer the rod, the less angularity it goes through. This means the force into the major thrust side of the bore is less, and power lost to friction is less. Also, a longer rod delays the point of peak piston speed, and this makes for a valve opening which is greater at any point in the first half of the cycle. It's a small advantage, but that's what fine tuning a configuration is all about. As to what is optimum is hard to say with all the variables involved. If testing multiple configurations is out of the question, the best bet is to err on the long side. For instance, a stock 5.0 Mustang has, with its 3-inch stroke and 5.09-inch long rod, a rod/stroke ratio of 1.69, whereas the popular 5.4-inch long aftermarket rod would produce a 1.8 ratio. This may not sound like much, but it does represent a couple of degrees less rod angularity. Opinions aside, real-life testing (on my dyno) with typical pistons, heads, street cams, and compression ratios indicates that rod/stroke ratios between 1.75 and 1.9 can pay off over shorter ones (1.5 to 1.6) to the tune of 4-6 lb-ft in a motor of nominally 425 hp. That's not much, but it is a big enough difference to demote a possible EMC winner to third spot.
The uppermost curve is the...
The uppermost curve is the combustion temperature in degrees Celsius. The blue curve is the cylinder pressure. In this instance, it peaks at 1,536 psi. Note the spikes in the curve near the peak. This is the result of an inconsistent burn and/or a chemical reaction, such as the generation of oxides of nitrogen (NOX) absorbing a portion of the combustion heat. The lower curve is the cylinder pressure that would have occurred if the plug had not fired the charge.
One last point is on the bottom end. We need bearings tight enough so they do not dump an excessive amount of oil into the path of the rotating crank, and a pump of just adequate size to supply the volume of oil needed. This normally means keeping bearing clearances to a minimum and the use of lowviscosity oil.
Cam And Valvetrain
It may not be apparent at first sight, but we do have something of a dilemma lurking here. For the powerband sought on the smaller engines at least, the cam's off-the-seat duration will need to be about 278 degrees, give or take about five. This raises the question as to whether or not the mandated flattappet cam can generate sufficient lift. The bigger the engine is, the more lift will be required. For a 400-inch engine, intake valve lift may have to be .700-inch or more, but for a 300-inch engine, probably about .600-inch will get the job done. So the smaller engine is going to have an easier time with the valvetrain, but still the traditional 1.6 to 1.7 rocker ratios are probably not going to cut it. Fast opening of the intake is always a good move, and to compensate for the .842-inch lifter diameter on a Chevy (the Ford fares better with a 0.875-inch lifter and a Chrysler with its .904-inch lifter, even better yet), even a small motor can benefit from a rocker ratio of 1.8 or more. As for valvesprings, the beehive design is it for sure. The last part of the equation is the cam spec itself. We have mentioned duration at the seat, and this for a fast-opening flat-tappet will translate into a .050-inch lift figure of about 250 degrees. As for lCA, expect these to be considerably tighter on the big-inch, small-block engines. Numbers around the 102- to 104-degree mark may not be uncommon, whereas the 300-inch or so engines are more likely to be optimal in the 108 to 110-degree range.
Selecting the carb to get...
Selecting the carb to get the best of the engine at the 2,500-rpm checkpoint is very much a question of making sure it is not too big. This is even more critical for the smaller-inch engines. For best allaround performance, a vacuum secondary carb such as this Barry Grant 650 road Demon would probably be a good choice.
Exhaust
The exhaust tuning on a successful EMC entrant will need to be well sorted. The positive effect the exhaust lengths and diameters can have on an engine's power curve are far greater than the intake tuning, and can operate over a range of as much as 4,000 rpm. We talk about long, small-diameter pipes favoring the low end, and short large-diameter pipes favoring the top end. While there is a lot of truth to this, the reality is far more complex. This is especially so on a two-plane crank V-8, where the exhaust pulses are far from evenly spaced. The key to success is going to be an exhaust system that scavenges the combustion chambers; to do that with a relatively short cam will mean having the lCA tighter than might normally be expected. As for the mufflers, these must flow sufficient to keep backpressure to an insignificant amount. About 2.2 cfm (at 1.5 inches mercury) per horsepower will see to that. The other factor that is of at least equal importance, is that the muffler should not alter the tuned length characteristics of an open pipe. If a muffler with an open internal design and of sufficient volume is selected, then the muffler can actually enhance pressure wave tuning. This could mean an extra half dozen horses just for well-sorted noise reduction, and that is definitely a win-win situation.
Minimizing the mass of reciprocating...
Minimizing the mass of reciprocating parts like the pistons and rods means less mass to counterbalance on the crank. By maximizing the efficiency with which the counterbalance mass is used, the crank can be made significantly lighter. The scat crank shown here is a typical example. under the accelerating test conditions, lighter parts show a power advantage.
Challenger's Comments
Here is what our top three 2007 EMC contestants thought about the route they took toward building a successful engine:
Tony Bischoff Of Bes Engines:
"In a contest like this, you must start with a good idea of what would be best in theory. That said, what's needed and what's available may be so far apart that the only viable starting point is to take a combination you know works, and build it. At this point, the fine tuning can start. Again, you look at what should work in theory, and temper it with what is available and can be done in the real world. If I had an F1 budget, what I would have entered would have been quite a bit different from what I actually built."
Jon Kaase Of Jon Kaase Racing Engines:
"Our experience is with long-stroke/big-inch engines, but I suspected that a 302 with its bigger valves per cube might do well, as our fourth-place guys proved with a 302 Chevy. To check where things might stand, I rounded up some shop parts and built a mule. It was fine at the top end, but the low-speed output suggested we might have to do a lot of head work. In addition to this, the Ford's short-block height meant a single four-barrel intake would have very short runners for the middle four cylinders. Not good for low speed. A tall deck would get the runner length needed for significantly better low-end output, so we made that our next move. since this was a longer stroke big-inch engine, we were on home turf. That meant homing-in on a parts combination much more quickly."
Judson Massingill School Of Automotive Machinists:
"Our starting point for an entry was, like several other contestants, a small-displacement engine. We put together a 302 Ford, and although the results were good for a typical 302, it was evident that it was not a winning combination. At this point, it was not so much back to the drawing board, but back to what we knew worked. since results are all about good heads and utilization of such, we built a 351 Ford and a 400-inch Chevy using some really effective heads. Taller blocks, longer intake runners, and more appropriate port cross-sectional areas for the cubic inches resulted in a far better combination of parts. This more than offset the fact that, in theory, what we put together was less likely to produce results. What this tells me is that a stock bore/stroke configuration 5.0 is still short of optimal heads and intakes; after all these years, that's something of a surprise."
Conclusions
It does not take much to see that there is a common theme here. These contestants have had to adopt an engine building position falling somewhere between total engineering theory and total parts availability. They have proved that not only are there some really good parts out there, but also there is still, in some quarters, room for significant improvement.
 Making sure the rods and pistons...  Making sure the rods and pistons are no heavier than needed is the first step toward minimizing the moment of inertia (MOI) of the rotating assembly. The Q-lite design from scat is a prime example of a cost-effective lightweight rod that can hold up to 700 hp. |  This lightweight JE piston...  This lightweight JE piston epitomizes the current high-tech piston design. here we see a dished crown, thin rings (.043-inch compression and 3mm oil) a thermal-barrier top coating, and an antifriction skirt coating. |  Rod To Stroke Ratio The rod/stroke...  Rod To Stroke Ratio
The rod/stroke ratio is B divided by half of A, as indicated in the drawing. The shorter the rod, the more the piston loads the lefthand side of the bore on the power stroke. If the piston and ring package had zero friction, this would not be a problem, but since it does, this makes a longer rod (up to a point) a better deal, as friction losses are lower. |
 To allow good heads to work...  To allow good heads to work effectively means having a valvetrain that opens the valves fast, high, and at the right time in relation to the crank. |  The popularity of beehive...  The popularity of beehive springs is rapidly increasing. The reason is that they deliver more rpm for less spring load as well as better valvetrain control on the way up to valve crash speed. |  Ultra high-lift rockers will...  Ultra high-lift rockers will most likely be needed by any configuration within the rules. This means shaft rockers of 1.7:1 or more (such as these Crane items) are going to be needed. |
 Getting the exhaust system...  Getting the exhaust system right will make or break the engine's final performance. This optimization process will start with the headers and finish at the mufflers. | | |