Tool Steel

CAM CORES

High Toughness / Proprietary Designs

As aftermarket cylinder heads evolved with much larger ports and bigger flow numbers, it became apparent that increasing valve lift would result in more power. Unfortunately, cam lobe lift had been maxed out for a number of years and the only way to achieve more lift was with higher rocker ratios. Engine builders and racers were “pushing the envelope” with rocker ratios over 2:1 and as a result, valvetrain stability and durability were going downhill fast.

Why You Need a Larger Cam Core
While this was going on, Dan Jesel was running in the opposite direction – he was looking for ways to reduce rocker ratio to take load off of the valvetrain. At the time Dan was working on a program to stabilize a NASCAR Xfinity engine valvetrain above 11,000rpm. The traditional high rocker ratio technology would allow racers to flirt with the 10,000rpm range, but above that valvetrains had a way of self-destructing. Dan’s idea was to take the ratio and load off the rocker and put the lift back on the cam lobe. However, that required a larger diameter camshaft core with larger bearing diameters.

When you look at the numbers, it is easy to see Dan’s logic. A 2.00 ratio rocker places approximately 33% more load on the lifter, pushrod and camshaft than a 1.50 ratio rocker. In a NHRA Pro Stock motor that runs 1350psi open spring pressure that would amount to 432-pound static force reduction – on one valve! Multiply that by 16 valves and 10,000rpm and you get a better picture of the gains in durability and force (hp) required to rotate that high rocker ratio valvetrain. So, the lesson learned was that a larger diameter cam core with more lobe lift and less rocker ratio was smoother and easier to rotate than a smaller cam core with higher rocker ratio.

Once the aftermarket block manufacturers realized this was the direction serious race motors were headed, they put more material in the bearing bosses so they could be bored to fit the largest cam cores available. Not only were cam diameters growing but the materials were evolving from a surface hardened cast iron to tool steel. The ever increasing spring pressures and rpm rendered 8620 and 9310 materials unacceptable, especially as lobes were made more narrow to accommodate their relocation.

To that end Jesel CNC machines its cam cores from a grade of tool steel that exhibits high-toughness and a high surface strength. It is through-hardened and heat treated for the high contact stress and shock loading caused by current spring pressures, ramp speeds and rocker ratios. Jesel is one of the few industry companies that has its own metallurgical laboratory to check all incoming raw metal stock to ensure that it meets Jesel’s specifications.

Relocating Cam Lobes
Part of Dan Jesel’s mission in life is to convince engine builders and racers that one of the primary objectives in good pushrod engine valvetrain design is as straight a path from the cam lobe to the valve tip as possible. In order to accomplish that objective Jesel makes lifters with offset pushrod cups and offset and angled rockers to reduce pushrod angles as much as possible. The newer aftermarket blocks with generous lifter bosses allow the lifter bores to be moved so that the pushrod will clear the intake ports. But, if you move the lifter bore, you must also relocate the camshaft lobe.

When you start moving cam lobes around you quickly run out of room. That is why the Jesel tool steel billet cam cores have narrow cam lobes. As custom engine design evolves, billet blocks like Mike Moran’s Pro Mod Hemi actually use relocated cam bearing journals as well. The cool thing about machining cam cores and blocks out of a solid billet is that you can make them any way you want.

Slowing Cam Bearing Surface Speeds
Lobe profiles can be more precisely ground on larger cam lobes. Smoother lobes provide smoother valve action and better durability for the entire valvetrain. But bigger is not always better, especially when it comes to camshaft bearing speed. For that reason Jesel introduced its Clamshell cam core.

With a typical cam running babbit or needle bearings, the lobe base circle can’t be any larger than the I.D. of the cam bearing. The clamshell design utilizes aluminum split clamshell bearings that bolts together on the core itself. This allows you to increase the diameter of the core as well as the lobes by the bearing thickness. The clamshell cam core assembly is installed into the block and locked in place through the lifter valley. The advantage to the clamshell bearing design is a smaller cam bearing journal which significantly reduces bearing surface speed over a traditional 70mm cam using babbit bearings. The clamshell assembly with a 1.500” bearing diameter reduces surface speed by 84%.       

Jesel also makes coated babbit cam bearings for its 54mm – 70mm cam cores. The babbit bearings start out as a precision centerless-ground stainless steel shell. Then a lead based alloy is applied to the surface that is coated with a dry film polymer lubricant to protect the bearing surface from damage due to dry starts or a catastrophic loss of oil pressure. The babbit bearings also feature an annular external oil grove with three oil feeds to the cam journal. 

For those engines with restricted oil flow to reduce windage losses, Jesel offers encapsulated needle bearings for 50mm – 70mm cam cores. They are low friction rollers designed to operate with a minimal oil supply. Jesel’s sales representatives and Custom Shop personnel can guide you through this new camshaft technology.

Jesel believes in providing racers with every detail required to install and use its products. For this reason they offer finished camshafts with your proprietary lobe profiles accurately machined on CNC equipment. Your specifications will be safeguarded and kept totally confidential.

What started out as Dan Jesel’s quest to reduce rocker ratio and to increase valvetrain durability resulted in another major Jesel innovation that literally changes everything for high-end pushrod race engines.