Engine Masters Challenge - The Power To Win!
We Take A Hard Look At What It Takes To Win The Engine Masters Challenge.
From the May, 2008 issue of Popular Hot Rodding
By David Vizard
Photography by David Vizard
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.
The starting point for maximizing...
The starting point for maximizing power should always be at the cylinder heads. shown here is a 23-degree small-block Chevy head from AFr with proven power delivering capability.
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!
Bore here are the typical...
here are the typical proportions of valve sizing in relation to the bore diameter. With these proportions locked-in, we find that the smaller the cylinders are, the greater the breathing per cube is.
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.
Heads For Torque
Still on the subject of size here, what we should now consider are the port and valve sizes needed to make the most output between 2,500 and 6,500 rpm. First, let's dispel the myth about sizing valves for a motor that must make maximum low-speed output as well as high speed. smaller valves don't make more low-speed power than big ones. If a back-to-back dyno test shows otherwise, it's because the big valve situation was not optimized. If maximum output is the goal, the valves need to be as large as possible within the confines of the bore. What is critical is the sizing of the ports. Get this a little too far off and an attempt to win an EMC could be dead in the water.
The curtain area as shown...
The curtain area as shown here is the most important factor in an engine's entire chain of breathing events. Not only does it need to be maximized per cube, but also the rate at which it reaches that peak needs to be maximized.
Starting at the intake port, we need to develop the port so that it has the minimal cross-sectional area to meet the 6,500-rpm needs. Achieving a minimal cross-sectional area, along with enough flow for the top-end output means having a port that flows big numbers because it is efficient-not big. That port velocity is not just important for low speed-it's vital. here's a good clue to what is needed. When the engine's peak power rpm has been dictated by a requirement (just like it often is by the restraints of a street car budget), then the port size needs to be optimal for the cylinder it has to feed, not the valve-and there is a difference. When developing the port, it should have the highest average velocity possible and the least amount of velocity difference between the slowest and fastest part. The port should direct flow past the valve into the cylinder in such a way as to generate good, but not excessive swirl.
As for the valve and seat form, this needs to deliver strong flow right off the seat to a point a little higher than the valve lift to be used. If the flow continues to increase past the max lift point, it's a sure-fire bet the port is too big! As for low-lift flow (this is where I get to stir things up), this needs to be as good as possible. here is not the time to debate the subject in full, but the stronger a valve flows at low lift, the more the cylinder thinks it has a higher acceleration valvetrain. ultimately, strong low-lift flow ends up being the next best bet to variable valve timing with no extra moving parts. To make it work means reevaluating the valve event timing. Typically, the lobe centerline angle (lCA) needs to be widened, and the duration shortened.
Swirl Generation Cylinder...
Good swirl generation is an important factor toward low-speed torque. some heads, such as those for small-block Chevys, have port forms that are conducive to swirl. With about 70 percent of the airflow emerging from the "A" half of the valve, the charge has a very strong tendency to turn in the direction of the ghosted arrows.
At this point, we have to consider the combustibility of the mixture. This inevitably means checking out our porting work on a wet flow bench. A wet flow bench will always show problems. It's the nature of the beast, but the real trick is determining whether or not there are any big problems. Making the best of a fuel combustibility situation starts at the carb booster, and works its way to the combustion chamber. Minimizing the port size for the job in question is a good move toward a more ignitable and combustible mixture. As the charge enters the cylinder, it is important for it not to wash out the spark plug. In this context, the placement of the plug is critical not only to avoid too much wet fuel flow, but to minimize detonation. here we find that the combustion chamber's ability to resist detonation can be affected for better or worse. The charge is always hotter on the exhaust side of the chamber, so it burns faster. Also, detonation is also more likely to occur on the exhaust side because it is hotter. By biasing the plug toward the exhaust side, the charge is burned there first, and the flamefront progresses from there across to the cooler side by the intake. since this side started off cooler, it is less likely to detonate. All this may look easy to do, but in placing the plug, it has to be remembered that the charge and the flame-front are rotating, so everything is not quite as obvious as just looking at it and saying, "let's stick the plug here." This is where transparent cylinders and in-cylinder pressure measurement can really pay off. This used to be tech that only the big car companies could afford, but times have changed and top engine builders are now in a position to use such equipment. Then there is computer simulation of the burn characteristics, but that is a whole other story in itself.
Having burned the charge effectively, it now has to be expelled as effectively as possible. This brings us to the exhaust port, which in many ways needs to have many of the same attributes as the intake. An important one is that the port should not only have good flow, but also good anti-reversion properties. This is usually achieved by making sure the port is no bigger than it needs to be for an engine that will peak at 6,500 rpm. Making sure of this is a good move toward better low-speed output without any compromise in top end.
For an intake manifold, a single-plane is probably the way to go if the cam ultimately used is not too big. runner cross-sectional areas will be critical, as will the size of the carb and the booster selection. Making sure the carb is no bigger than needed will be the best bet toward good results at the 2,500-rpm checkpoint. A well set up vacuum secondary could also be the key to success here.
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.
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.
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."
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.