The NASCAR Winston Cup engine...
The NASCAR Winston Cup engine you see here is not that much different from the engines that run every Saturday night at your local short track.
The techniques used to make...
The techniques used to make the Winston Cup engines so durable and consistent are within a short-track, weekend racers grasp.
Editors Note: Months in planning, this multi-part series deals with fundamental areas of engine building used in Winston Cup that can apply directly to other classes of racing. Chuck Jencks and Jim McFarland, each representing decades of involvement in circle-track racing, compiled the material. Jencks is a mechanical engineer, formerly with Summit Racing, a past powertrain engineer for Joe Gibbs Racing, and currently doing engine R&D for a premier Cup team. McFarland is a product-designing automotive engineer, 30-year journalist, and member of the Circle Track Tech Council.
Readers of this series will discover new thoughts and ample reinforcements for building consistent, powerful, and competitive Saturday-night engines. Jencks lays the hard-core foundation and McFarland provides the theoretical flavor.
There are certain aspects of Winston Cup engine programs that apply directly to engine building for other classes of racing. To make this clear, we must first examine some of the more important topics. So, first things first ...
Everyone wants to know the secrets of building a race- winning, 800hp Winston Cup engine. Well, here they are: excellent planning, a thorough understanding of the basics, an unbelievably hard-working and dedicated staff (team), fanatical attention to detail, a testing program second to none, and a budget to support the effort. And even if you can only adopt and apply portions of this set of secrets, your engine-building program will improve, even if its just you and your set of tools. No single piece of rocket science will make the power you want. Todays Winston Cup engine is an ultimate example of the process of continuous improvement.
Before you laugh and begin comparing the multi-million dollar budgets, scores of people, and state-of-the-art equipment to the appearance of your garage or shop, you may be interested in the similarities between successful programs on all levels of racing and how they might apply to your own. For example, a few years ago, a book entitled The Seven Habits of Highly Successful People was a best-seller.
Its core message was that by adopting common traits of successful people, its possible to become more efficient and more successful on your own. In a similar fashion, not all of what will be discussed here may be applicable to your particular racing program. But rest assured, the topics will at least be thought-provoking and worthy of consideration.
Many of todays Winston Cup head engine builders built winning engines at a variety of levels before rising to the top in Cup racing. So what goes on in a Winston Cup engine shop that could possibly benefit the Saturday-night builder?
What Is Important
You must first honestly evaluate what part an engine plays in the entire vehicle performance picture. Further, what part of its performance is the most critical? Circle-track racing is not drag racing. In drag racing, engine output is as important as any single element in the sport. In circle-track racing, engine output alone is probably not even one of the top three factors required for a winning car. Engines are important, but any Winston Cup head engine builder will say that durability and consistency are the key performance factors for winning races and championships, not engine power.
When it comes to engine performance, its production of torque and horsepower must be created in the rpm range that the driver will use the most. This is an important point to research and will be key information in the determination of what and how the engine will be built. For example, if the engine is to be raced at many different tracks and the rpm range varies widely, a much more flexible combination (in terms of rpm range) must be built. Also important, dont forget to take into account how much the rpm range drops on long runs due to tire wear.
What Are Torque And Horsepower, And What Is The Difference?
Technically speaking, torque may be defined as the potential to do work. Grab the knob of a locked door, apply a twisting force, and the knob doesnt turn.
This is torque. Upon unlocking, the knob will turn under force of the torque applied, time enters the picture and horsepower can be measured (torque acting over a period of time: pounds-feet/second or pounds-feet/minute). Stated another way, torque is the ability of a system (engine) to perform work. Horsepower is the rate of doing work.
Torque accelerates a race car (the rate of change in torque); horsepower makes it fast (the ability to sustain specific levels of torque). Many engine builders (Winston Cup and Saturday night alike) prefer building engines keyed on the production of torque.
An important ingredient in understanding the concept of torque is an engines ability to produce torque over a specific range of rpm at a rapid rate. Some call this transient torque or the rate at which an engine will accelerate under load through a range of rpm. Generally speaking, the higher the torque output of a given engine, the quicker it will accelerate under load. This is because its potential for rpm increase is linked to total torque output.
Peak Torque Vs. Area Under The Torque Curve
Based on a previous definition of torque that it is the potential for doing work, it is the area under the torque curve that will indicate the magnitude of this potential (see illustration on pg. 56). Here, its critical to differentiate between a value for peak torque and a value for the area computed (or shown) below a given curve.
At the risk of oversimplification, we are dealing with an engines ability to produce power, based on its torque potential. In other words, the greater an engines torque potential over a range of rpm (as represented by the area under the torque curve), the greater its ability to produce race car acceleration. As opposed to the importance of a value at peak torque, its possible to produce quicker acceleration by increasing the area under the torque curve (a broader torque band), even though there may be an accompanying slight decrease in peak torque (see Illustration of Torque Curve Areas).
Equally important are the benefits gained from selecting engine components (parts integration) that are functionally intended to enhance torque in a pre-determined range of engine speed. It is from this base of power that other vehicle components (particularly the powertrain) can be suitably matched to track length and conditions.
Start With A Plan
Know the rules. In general, circle-track racing engines (from Winston Cup to your local track) are tightly regulated to manage both engine output and cost. You must know the rules intimately in order to build the best engines possible within the rules. Analyze rules carefully and put emphasis only in the area(s) where the greatest return is possible. For example, if you are running an engine in an intake-restricted class that creates airflow limitations (such as a 2-barrel carburetor), use just enough valvespring to keep the valvetrain stable since more spring will absorb horsepower with no benefit.
How long must the engine last (how many races or miles)? How much maintenance will be performed or required? What does the power curve need to look like? (There are many shapes to a power curve, all of which may exhibit the same peak power.) As an example, an engine that is raced in a lightweight car on dirt can afford to sacrifice torque at the corner exit speed for power at the flag stand. A heavier car on pavement must have more torque for corner exit speed to help with acceleration.
And dont forget the budget. Even Winston Cup engine shops have a budget they must work within. Your planning must include how much time and money you can spend. Building successful racing engines is about using your resources of time and money better than your competition.
Where Is The Power?
Power comes mainly from the valvetrain, cylinder heads, and intake manifold, no matter what type of race engine you are building. So when looking for more power, this is the place to spend the time and available money. The trend in circle track racing is similar to most other forms of motorsports: more engine speed and higher numerical gear ratios. Crankshaft speed and gear will make more torque at the tires contact patch than crankshaft torque by itself. The multiplication factor that gear gives to engine torque is what provides you the advantage. The effect is similar to putting an extension arm on a breaker bar when breaking something loose. The downside of this trend, however, is its hard on valvetrain parts and difficult to pursue (time and cost).
increasing volumetric efficiency: cams, heads, and intake manifolds Part of an engines ability to make power depends upon how efficiently fuel and air can be induced on each inlet cycle. The amount of useful fuel it can ingest depends upon how much air (oxygen) can be supplied during this same time. Therefore, the limiting factor to the amount of power (work) that can be produced is the air capacity of each cylinder.
Now, depending upon several factors (many of which involve parts or systems that affect intake airflow), the goal is to try to achieve the highest levels of cylinder filling efficiency as possiblethroughout the rpm range.
Heres how all this is tied to torque. The greater the level of cylinder filling efficiencywhich, for purposes of this discussion, well call volumetric efficiency (VE)the greater the potential for optimizing torque. In fact (as noted in the illustration on pg. 56), an engines VE curve and torque curve very closely resemble each other. Combustion efficiency influence notwithstanding, its a pretty good rule of thumb that volumetric efficiency increases represent corresponding gains in torque ... again a reflection of the similarity between the two when represented graphically, as shown.
In studying the illustration of VE and torque curve similarities, note that the torque curve lies beneath the VE curve both below and above peak torque rpm. Generally, this is caused by poor air/fuel mixture quality. Below torque peak, a lack of flow velocity (related to air/fuel mixing) reduces combustion efficiency (power). Above peak torque, either mechanical separation of mixtures, combustion residue (exhaust gas), or a combination of both, also tends to penalize power. Later in the series, this issue will be examined more closelyparticularly regarding parts selection and/or modification.
More to the point, because of their influence on volumetric efficiency, the selection of cylinder heads, camshafts, and intake manifolds is critical to not only torque output but also the production of torque within specific ranges of engine speed. Because more airflow does not always equate with increased power, both flow volume and quality must be considered in choosing these parts. This is especially true of cylinder heads and intake manifolds. More on this topic will be discussed as the series later digs into the essentials of these components and the similarities between their application in Winston Cup and Saturday-night engines.
It is by the application of gears and their respective ratios that mechanical advantages can enhance the application of power to the track. It was mentioned earlier that the rate of torque application (torque delivered vs. delivery time) can improve race car acceleration. By the method of tooth number and diameter differences, degrees of leverage can be created that allow an increase in the rate at which torque is applied to the driving wheels.
Even if only one or two forward transmission gears are used, proper selection of gear ratios that allow quick acceleration into the desired span of rpm most often used on the track helps keep a race car competitive. In the consideration of gear ratio (torque multiplication) choices, matching track length and surface conditions to the ratio that allows acceleration into the desired rpm span is critical. For example, an engine with a narrow torque band that will be run in a high rpm range will benefit from a ratio that allows it rapid acceleration up into that range. Larger displacement engines with more area under the torque curve, and at a lower rpm, can pull lower numerical gears and still provide acceleration based on sheer torque.
It is also worth remembering how tire wear affects on-track rpm. Generally, as tires become worn, it becomes necessary to race with less throttle opening (to maintain traction). This reduces the rpm in which the engine runs, thereby causing it to fall lower on its torque curve. Gear selection (torque multiplication) that factors in this condition (particularly on asphalt surfaces) will allow improved torque delivery as traction is reduced by tire wear.
Quality control is the key to durability Every part, every clearance must be checked every time. Do not ever assume that a part is dimensionally acceptable now, just because it measured correctly when it was purchased or the last time it was checked. Do not let other peoples dimensional problems become your engine failure. Do not check piston-to-valve clearance on one cylinder. Check them all. Just as flying has been described as hour after hour of boredom with a few moments of sheer terror, building race engines often involves long hours of incredible repetition (the checking and re-checking of dimensions), brightened with a few hours of excitement when it finally hits the dyno or racetrack.
Keep records. A notebook containing all of the information on its build should accompany every engine. This should include every important dimension and clearance in the engine with parts lists, dyno time (if applicable), and the amount of run time (even time on the track).
Build them the same. In Pro Stock drag racing, it is common that each engine build is slightly different from every other, in a continuing search for more power. Most circle-track engine programs will benefit from consistency, build to build and engine to engine. A tightly controlled recipe yields engines of similar power.
When an improvement is (or can be) found, the recipe is updated. For racers who only build one or two engines per season, freshening whenever required, the need for careful parts selection and combinations becomes even more critical to success. Choose parts and make changes carefully, only after serious consideration of all the consequences of such choices.
Avoid the tweak of the week. Hard work and good testing will see you through, not the latest fad. Just because someone else is running it doesnt necessarily mean its right for your combination. The valvetrain is one area where you see this problem, again and again. You hear someone is making great power with a new cam, but it may not work in your engine package. It would be unwise to ignore what is going on around you, but keep it all in context. The best engine programs are the ones that steer their own course, guided by sensible parts decisions and assembly techniques, not simply following the path of someone else.
In my opinion (Jencks), the top Winston Cup shops do one thing better than any other form of racing in the world. Yes, even better than all the mighty F-1 programs in Europe and Asia. That is testing. It is routine for a Winston Cup engine to be able to see variances of 0.5 hp out of 800. That amounts to a resolution of 0.0625 percent and is simply incredible. This allows a head engine builder to separate truth from fiction, as far as changes or improvements are measured.
Technology Transfer, Part II
Technology Transfer, Part III