"A lot of sanctioning bodies use the carburetor essentially as a restrictor plate to slow the cars down, and you have to account for that," Jones says. "Take a NASCAR Late Model Stock for example, since they are probably the most popular example of this. Because that two-barrel carburetor will only allow so much air, the engine's peak power will be at 6,500 rpm. But I know most racers are pushing well beyond that--usually around 7,200 rpm--to get the gear they need in the car. So instead of designing a cam for peak power, I'll want it to make the best possible power all the way to 7,200 rpm. We'll try to make that horsepower line on the dyno sheet as flat as possible. Now we don't have the best possible peak horsepower number, but the car runs better on the track because it holds its power better and doesn't lay down at the flagstand."
Another interesting problem Jones is helping many racers combat is spec tire rules. "I recently worked with a guy who was racing a dirt car that was having problems breaking the tires loose coming out of the turns," Jones explains. "His track limited the tire size, and the engine was simply overpowering the tires when he put his foot on the gas. Then, to make things worse, on the straights, when he could use the power, the engine was laying down.
"We didn't want to get rid of the torque the engine was making, but we did want to move it to a place in the rpm range where it would be more useable," he continues. "The engine was making peak horsepower at 6,500 rpm and peak torque at 4,200 rpm. We estimated at the rpm the driver was coming out of the corners, it was making around 500 ft-lb of torque! So I put the numbers into my program and started playing with them. I designed a cam with a wider lobe separation that moved the peak torque out to 5,000 rpm. The goal was to give the driver more manageable torque coming out of the turns, and then gain as he went down the stretch. Again, we gave up a little bit on the peak torque, but in this situation it's OK because the car couldn't handle it anyway."
The Profile Once Jones knows what he needs, the next step is to map out the optimum lifter location along 360 degrees of camshaft rotation. That's because the lifter motion relates directly to valve lift (with a multiple for the rocker-arm ratio). He then takes that information, along with the lifter size and the base circle of the cam, to CNC programmer David Taylor. Taylor can then use this information to design a cam lobe that fits it. It may seem a little backward, but this method means Taylor can easily design lobes for both flat-tappet and roller cams to fit this profile.
Once the profiles for both intake and exhaust cam lobes are programmed, aluminum patterns are cut on a four-axis lathe from solid 2.5-inch bar stock. These patterns, 1:1 models of the final lobes, allow Jones and Taylor to check out the final product before cutting steel. If the patterns past muster, they are used to cut the masters. Masters are 5-inch steel discs that are mounted to the cam cutting machine to cut the lobes. Over the years, Jones has collected a truckload of these masters, so unless somebody requests a proprietary lobe profile, it's likely he has the profile you need, and the previous steps won't even be necessary.
Cut And Run The final step is to grab the appropriate blank and start grinding. Once all the design work has been done, this is actually the least technical part of the entire process. There is one surprise here, though. Jones can actually build cams with inverse curves in the base of the lobes. He does this by using a 5-inch cutting wheel instead of the standard 18-inch wheel. The small concave curve this creates at the base of the ramp allows Jones to significantly slow the speeds at which the valve lifts off the seat and closes on the seat--the most critical events of the cycle. Of course, cutting cam lobes with a 5-inch grinding wheel is much more time consuming than with a big 18-inch wheel, so as you might expect, the costs are greater. Still, Jones has found many applications where the concave base is worth it.
 Machinist Tony Ellis checks...  Machinist Tony Ellis checks the pattern before handing it over to Jones. |
 The patterns are used to make...  The patterns are used to make masters, five-inch steel discs that thecam grinder uses to cut the desired shape into the lobes. |
 Depending on your needs, there...  Depending on your needs, there are several core options to choose from.These cores are all designed for the ubiquitous Chevy small-block. Fromthe bottom is an iron core for flat-tappet cams, an experimental steelcore for Winston Cup applications, a steel core for roller-tappetapplications, and finally, on top is a steel core for Trans-Am racingwith giant 55mm base circles. |
 Jones checks every core to...  Jones checks every core to make sure they are straight before setting itup on the grinder. |
 Here you can see the final...  Here you can see the final setup. The master is mounted to the grinder(left) and guides an 18-inch follower. The follower and the grindingwheel are the same size and follow the same path so that the final lobeshape matches the master exactly--only on a much smaller scale. If Jonesis grinding a camshaft with concave bases on the lobes, he uses asmaller 5-inch follower and grinding wheel. |