"Even though he has decades of experience building race-wining engines at every level, engine builder Keith Dorton of Automotive Specialists says he still works closely with the camshaft manufactures he trusts to help improve performance. Here, Dorton mock up an engine with a new roller cam from Crane Cams."
If you have ever flipped through a camshaft catalog it can be easy to get overwhelmed by the tables of data provided for each cam family. There are numbers for lift, duration, lobe split, and on and on. And if you don’t have an idea what you’re looking for, it’s easy to get lost.
What’s funny is that for an experienced engine builder or cam designer, all that information doesn’t even begin to tell the story. In today’s ultra-competitive world of stock car racing, there is a lot more that goes into race-winning camshaft design than just dialing in X amount of lift and Y duration. For example, did you know that most leading-edge cam designers break the cam lobe down not into simply the opening and closing faces, but they actually look at the opening face as at least eight separate zones? And, of course, they put just as much thought into the closing ramp as well. Outsiders might sneer at what they consider our ’50s-era carbureted race engines, but there is a lot of top-shelf science going on here, and you can take advantage of your competition by making use of it.
For this article we picked out three of the top camshaft manufacturers in our sport and asked them a very simple question, “Beyond basic lift and duration, what goes into building a camshaft capable of winning races?” And, as you might expect, representatives from all three manufacturers said that there was so much going on that explaining it all would not simply fill a book, but volumes of books.
We spoke to the experts at three leading valvetrain manufacturers to find out just what goes into a camshaft capable of taking ...
Still, all three were very happy to spend some time talking about advanced camshaft design, and we compiled the very best nuggets here for you to digest and use to advance your racing program. There is no way you can take this and go out and grind your own cams, but even if you aren’t building your own engines this information can help you ask the right questions when working with your engine builder or camshaft manufacturer for your next circle track racing engine.
Communication is Key
Just like a good marriage, the key to finding the absolute best camshaft for the engine in your race car is good communication. After all, who wants to waste the time and money cycling through three or four camshafts and paying for expensive dyno time trying to figure out which one is best. Instead, leaning on the experience of a quality cam designer/manufacturer can help you avoid wasting your precious time and money.
“There is a lot we can learn from a racer or an engine builder just over the phone,” Allan Bechtloff of Crane Cams says. “And that is way beyond the simple things like engine size and the limitations imposed by the rulebook. We will usually want to know what cam and engine combination you have run before and how well that worked for you. What do you need more of, low end torque or more pull in the high rpm range? What have you tried already, and have you opened the lash up or closed it down? Have you tried advancing your current cam? What about different rocker ratios? The type of cylinder head you are running is also important, especially the flow rates. Even whether or not you are having trouble spinning your tires off the corner is important for us to know. Sometimes it may not seem like much, but every little bit of information can help us tailor the cam to fit your needs.”
Lose on the Dyno, Win on the Track
There’s an old adage that says we don’t race engine dyno’s, we race on the track. That’s definitely true and a response to engine builders who try to claim that their product is better by simply throwing out a peak horsepower number. But smart engine builders and cam designers know that a big peak number is often fool’s gold when it comes to actual performance on the track.
Instead, the cam should be used to mold the power band to the race car and the track. If you are on a short, tight racetrack running hard compound tires, there is often little use putting a ton of torque to the wheels low in the rpm range. It may feel like the engine has lots of power when the driver spins the rear tires every time he gets on the gas, but that’s probably not helping him lower his lap times.
But, however, if you are racing a Sprint Car or a Dirt Late Model on a track that stays tacky with lots of grip, you probably want a ton of torque down low so that you can set up a pass coming out of turns.
“A lot of times if a driver is spinning the rear tires, we’ll find that we need to bleed off some torque,” explains Ron Iskenderian of Isky Racing Cams. “You want to make the cam worse on the dyno in order to make the car faster on the track. But how do you do it? Well, the trend would be toward a little wider lobe separation. You can also use a little longer exhaust duration. So you would tend toward making the camshaft a little longer or bigger overall, except in the case of a restricted intake class where you have to be careful about that. Also, if you are trying to bleed off to torque, you want to make sure not to advance the camshaft.”
The idea is to build a cam that is a little more gentle on the torque curve at the low-end rpm range but then comes on strong around the flag stand and pulls all the way to corner entry at the end of the straight. If you get it right, a well-designed cam can function as a poor man’s very legal traction control. It may not win on the dyno, but it can definitely help a low-traction race car get around the track faster, and that is what racing is all about.
The Cam Doesn’t Matter
OK, that’s really not true, but we did at least get your attention with that headline, didn’t we? But we still have a point, and that is the engine doesn’t really care what the camshaft is doing. All the engine cares about is the motion of the intake and exhaust valves -- specifically, when they open and close and how far they open to allow air and fuel to move into an out of combustion chambers.
That’s why Billy Godbold of Comp Cams says that when he is designing a camshaft for any application one of the first things he does is determine when he wants the intake valve to close on the compression stroke. Godbold was even kind enough to share with us his own checklist he begins with when designing a cam. He says that generally he starts with these reference points and then works back to determine the ideal duration and lift.
1. Rpm (What limit do I need to set?)
2. Valvetrain mass and stiffness
3. Cylinder head flow relative to engine displacement (cfm/cubic inches)
5. Required durability (Pro Stock drag racing vs circle track vs Le Mans)
6. Valve sizes
7. Valvesprings available and lift rating
“Basically,” he explains, “you want to figure out what lobe families would work best before you try to nail down the duration. This is in part because an aggressive lobe with shorter seat timing (duration) will support more airflow and rpm than if you have to go to a smoother family. However, you always need to select a lobe family that will meet both your rpm limit and service interval requirements that are dictated by questions one, two, and five.” In other words, Godbold visualizes the valve opening and closing events that the engine wants, makes sure the valvesprings can handle that loading and then selects the cam shape that will make it happen.