Camshaft Selection - Engine Builder Magazine

Camshaft Selection

When it comes to racing, sometimes the belief is that only custom-designed parts are good enough for a winning team. The question here is, do off-the-shelf components automatically have a performance handicap?

In order to get to the bottom of the “Custom Grinds vs Catalog Specs” debate Engine Builder magazine reached out to experts at the leading camshaft suppliers in the country. Some of them are legendary suppliers of performance camshafts from the earliest days of hot rodding, while some are relatively new names in the market. All of them have expertise that has come from in-house testing and real world field experience.

In order to allow them to speak candidly about the products they recommend, we offered them anonymity – they could speak freely about products and performance without revealing trade secrets. No names will be used in this article, but a listing of camshaft suppliers and contact information will be provided at the end of this article (contact information is compiled from the 2012 Engine Builder Buyers Guide).

If you’re building an engine for a typical racer, the initial question may be “how much power will these parts produce?” For the customer focused on muscle, it may seem counterintuitive but when it comes to camshaft selection, the more appropriate consideration may actually be to look at the brains versus the brawn.

Compared to other engine components, how vital is camshaft selection to a winning performance engine?

“How important is the human brain?” asks one expert. “The camshaft is the engine’s equivalent to the brain. A well thought-out cam is based on the following: the engine displacement, the potential of the induction system, the potential of the exhaust system, and given rpm range where power is needed. Based on these four key elements ‘lobe area’ can be calculated and the camshaft can be designed to reach the goals of the engine. If these four factors are not used, then get yourself a dart board – it’s a crap shoot.”

In some cases, the biggest isn’t always best. “The camshaft is probably one of the most critical parts in building a competitive race engine,” says another camshaft expert. “It can affect peak torque and peak horsepower, and where these two very important events occur it can also determine how the engine will accelerate. In engines were drivability is important the camshaft can be a powerful tuning tool. This is where you have to look at track times and listen to the driver and chassis tuner. In some instances the camshaft that performs the best on the track is not the camshaft that makes the most peak torque or horsepower.”

Of course, camshaft selection is also dependent on other factors. “The camshaft is only as good as the parts around it. There is no miracle camshaft that can make a winner out of poorly chosen components, so it’s important that we’re looking at an overall package that includes not only the engine, but also the vehicle, and the application that it’s used for,” explains another leader in the industry.

“All of the parts are important and should be considered when ‘specing’ the parts for an engine,” admits another. “Providing the parts are selected properly and the engine is built correctly, the maximum power is not necessarily the determining factor. The torque range and level will determine how the engine performs for the racer. Having said this, the cam package is vital to the airflow of the engine and therefore vital in determining the torque range of the engine. So, a really good engine with a really good cam that is really not the correct cam will not perform for the racer and the racer will not be happy.  Good engine, good cam, not matched cam = unhappy customer.  Good engine, good cam, matched cam = happy customer.”

Do racers typically understand what’s right for their engine’s needs? More importantly, specifically regarding cam selection, do engine builders?

“Some of the really experienced engine builders who build lots of engines that are relatively the same develop specific packages that work well for their combination. They know from experience and hard knocks what works for them. Most engine builders, even the most experienced ones, work with a tech guy from their preferred cam company when they veer away from their combination at all,” says one supplier with key involvement with NASCAR Sprint Cup teams.

He says partnering with a supplier can be a great way to move your engine designs to the next level. Develop a relationship with someone at the cam company to discuss how to cam a particular engine. “Taking a little time to do this is almost never wrong.  Not discussing it is frequently wrong,” he warns.

“Most engine builders depend on dyno results to determine if a camshaft is optimal for the engine they are building,” says one of our experts. “This is not necessarily a bad thing but you need to know what to look for in the dyno results. Peak torque and peak horsepower are not always the most important results.”

This, he explains, is where some engine builders struggle to understand what camshaft best fits the race engine they are building and why an engine builder with experience in building a certain type of engine really has an advantage over someone who is building his first engine to compete in a certain race application.

Many engine builders have a good handle on what is needed in the camshaft department, agree all our experts. Very often this is due to personal experience, says one veteran who cautions that, while this is valuable information, it is often difficult to relate 20 or 25 year old cam lobe designs to modern lobe designs. Modern lobe designs often need to be much shorter duration.

“Good engine builders should be aware of what’s needed to produce a winning package, explains one representative. “They may not be fully aware of new developments that his cam company has recently introduced, so for a serious competition application, it can’t hurt to check with the camshaft manufacturer for any advancements and improvements that have been made.”

The key may be to occasionally put aside what you think you know. “True engine builders understand what’s needed, parts assemblers may not,” says one cam builder. “There is a huge difference between the two. And sometimes what’s needed is to set aside the ego and ask for help.”

We all know guys who think they know more than they know. It doesn’t always help to out-think the experts. And in quite a lot of cases, our experts say, a very successful race engine can be built with “off the shelf” parts.

In most classes of sportsman racing, a very competitive engine can be built using parts in stock if an engine builder works with the correct distributor, explains one key supplier.

“We work hard to make sure we have the most competitive components ready to deliver to the engine builder when they need them. Working with a distributor with experienced people in key positions gives the engine builder an edge because we can provide them with the parts in a timely manner allowing them to keep work moving through the shop and spend less time ordering parts and more time making money,” he says.

“We have over 25,000 cam designs. As we figure out a cam that works with a specific combination we frequently take the lobe designs and cam specifics and assign it a part number so that it then becomes ‘off the shelf,’” says an industry leader. “It may not be literally off the shelf but it can be ordered by part number and be shipped the next day.  Some of the part numbered cams that sell well will actually be ground and put on the shelf. It is very likely that if the cam company has LOTS of part numbered cams there will be one that will be right for the application.”

The key, confirm all of our experts, is the selection of the right combination of parts. Expensive or inexpensive, the combination is the key.

“A competitive engine may be built with off the shelf parts but a winning race engine may require a lighter rotating assembly, a professionally built carburetor, (especially 2 bbl carbs) and a custom ground cam,” says one cam grinder. “A well- prepared chassis and a really superior driver can overcome some of these things but as the other drivers improve with time then that advantage decreases significantly. The better-prepared engine will usually have considerably longer total life with regular freshening.”

Of course, if the race series you’re building for requires it, an off-the-shelf item may be your only option. And that, say experts, isn’t usually a problem. “You can certainly build a competitive engine using shelf parts,” acknowledges one supplier. “There are a number of racing series that have engine restrictions that are designed around readily available components. We have folks winning major championships using camshafts right out of our catalog, so that is definitely a viable choice.”

Of course, this being an industry built on innovators, modified parts to make cars go faster are a natural development, admit even the catalog suppliers. Tweaking or “out of the box” ideas give racers advantages and progress our industry.

“In addition,” explains one supplier, “most two-barrel classes perform significantly better with custom cams, a fact even more true of classes that require mufflers. They also require specially prepared carburetors as ‘box’ carbs tend to go very rich at high rpm. This makes a stock two-barrel carb impossible to jet properly.”

But does a custom-grind inherently offer a performance advantage?

“Inherently, no,” says one expert. “Potentially, yes.  Once again, the more an engine is built using standard ‘off the shelf’ parts the less advantage there will be for a custom grind. For instance, if an engine builder is using a standard set of CNC heads, a certain manifold, compression, etc., chances are there is a part numbered ‘off the shelf’ cam for that combination.  When the engine builder begins to ‘tweak’ the heads, manifold, etc., the cam should be ‘tweaked’ as well and a custom grind will likely work better.”

Could be and will be are far apart on the scale, experts agree. “A custom grind could certainly be of benefit. However, the reason we offer many catalog grinds is that they have been successful in competition applications,” comments one supplier. “We don’t put grinds in the catalog just to make it thicker.”

He points out that having a custom grind is not an assurance that it will be head and shoulders above a shelf grind. “This gets back to the overall package that surrounds it. Yes, there may be new items that have been developed since the catalogs are published that may provide a competitive edge, but we’re now looking at incremental improvements.”

Agreed, says another expert. “The correct camshaft gives a performance advantage and that may well be a shelf cam. We are dealing with an air pump that requires a given amount of air to operate in a given rpm range. The correct camshaft controls this. Again, it’s based on the proper combination.

Admittedly, guys like numbers – and the bigger the better. “Many people only pay attention to peak power numbers,” says one supplier. However, “Average numbers are more meaningful. A longer, flatter power curve is much more important than peak numbers. For street applications a huge hp number at 6,500 rpm is usually pretty worthless but 450-550 lb-ft. of torque at 3,200 rpm will be waiting for you at the next light as soon as you touch the gas.”

So what are the keys to getting the right cam for your build? What factors need to be taken into consideration when specifying a cam, whether off the shelf or custom grind?

“A simple school of thought from me,” says one expert, “is, if you give it a lot of cylinder head then it won’t need cam. If you don’t give it enough head then it will need cam. Duration is the ability to sustain power at a given rpm range and lift is the ability to make potential power.”

Another offers this: “When choosing a camshaft, it’s usually best to be slightly conservative. Having a bit more low-end torque at the possible expense of top rpm power, will provide superior results to having a lack of torque. Don’t hesitate to call your camshaft supplier if you’re building something out of your usual realm. Virtually all of the performance camshaft manufacturers have technical assistance departments for their customers.”

Be aware, cautions one manufacturer, that big cam companies have many tech people. “They all can’t be knowledgeable about everything. Your salesman may be a good place to start. Try to find out who the best tech guy is for your particular need. The drag race guru is seldom the oval track expert as well. Neither one may be much help with a Bonneville application.”

Do your research yourself and make your selection – then ask for help. The “cam guy” at your preferred supplier will discuss the package that works best for your application.

A few key points to remember, courtesy of the cam experts responding the this article are these:

• Stay safe. Unless the engine needs to produce the last possible fraction of a horsepower, stay safe.  There is a fine line between safe and sorry. Most racers and customers don’t want to be working on their engines all the time. They need to work on their cars.

• Smaller is better than bigger when talking about cams. If you are ever trying to decide between a larger cam and a smaller one, ALWAYS pick the smaller one. The customer will feel the torque and almost always be happier.

• For circle track racing, engine size, the minimum rpm in the corners and on restarts is most important. With unported factory heads it is often possible to have too much lift. High ratio rockers are usually desirable, but not always maximum lift.

• For street use cruising rpm is very important. Also top speed in high gear (not overdrive) is important. Many people seem to want their small block Chevy or Ford to be capable of at least 6,500 rpm or more, only to find out they had a 2.73 rear and 29 inch tall tires. 6,500 rpm = about 200 mph. Not likely they’ll ever do that! Meanwhile all low end and mid range throttle response is gone.

For drag racing the car weight, gear ratio, tire size, trans type and stall speed are all-important. Serious bracket racers usually don’t need the last 1/10th or so because consistency is what is most important.

• Vintage road racing requires a long flat torque curve while more sophisticated cars with 6-speed transmissions may often do better with a peaky torque curve since they can easily keep the engine in a pretty narrow rpm range.

• Don’t expect the cam grinder to tell you what your competition runs. He may make the same thing for you but don’t expect him to tell you that.

In short, remember this: Determine the goal of the engine; what does it need to do for the customer? What kind of budget do you have to work with to build this engine? Then a combination of parts must be selected and machined to make the build.

Properly recommending a camshaft requires a thorough comprehension of exactly what the overall combination is. The more information that’s provided, the better the cam selection will be.

Special thanks to Charles Reichert, Camcraft Cams; Chris Straub, Clay Smith Cams; Scooter Brothers, Comp Cams; Chase Knight, Crane Cams; Dave Crower, Crower Cams; Dick Boyer, Erson Cams/PBM; and George Richmond, Melling Select Performance, for their contributions to this article.

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