Written by Jason Reiss
Photography courtesy of Pro Line Racing/Alan Johnson Performance Engineering
In the world of high-stakes, no-holds-barred drag racing, one of the most successful over the last 15 years is Pro Line Racing in Ball Ground, Georgia. The company found record-setting success through the partnership of tuner Steve Petty and engine builder/driver Tim Lynch in its early days, setting a blistering pace on the racetrack that proved to be a hard act for the competition to follow.
Since then, co-owners Eric Dillard and Doug Patton took the company to the top of the heap in many race classes through a combination of determination, experience, and the right people on their team. Many of the industry’s most accomplished tuners are on the PLR staff, including Jamie Miller, Brandon Stroud, Josh Ledford, and several others.
In addition to engine-building and tuning services, PLR forged a unique partnership with Alan Johnson Performance Engineering. It is through this collaboration that the company’s Raised Cam Hemi came to life and left a direct imprint on the racing world.
“Eric Dillard pushed this to happen sooner than it probably would have. With the 548, there were failures in extreme applications with lots of boost, right at the point where the rod was profiled to clear the camshaft. We knew that the valvetrain stability was going to get better, but it’s crazy how much power it added. It’s the same head with the same port design. The valvetrain is so much happier,” says Pro Line’s Jamie Miller.
As a simple function of the deep-breathing cylinder head configuration of the Hemi engine, it is natural to see 75 pounds of boost pressure and 10,000-plus rpm on the track with lock-up transmissions in these 4,000-horsepower cars. These situations are hard on parts, especially the valvetrain components that see massive stresses, particularly in turbocharged applications that pack big boost into the engine.
It is with these challenges in mind that the PLR team worked with AJPE to develop the raised-camshaft design. By raising the camshaft .650-inch over the stock Hemi position, the user gains the ability to do several things—all of which combine to provide improved durability in a platform that is known for eating parts. With the camshaft out of the way of interference with the crankshaft, a larger core can be used, which provides strength and reduced effects from harmonics, which is a big deal in these engines.
“You no longer have to have rods that are profiled to make sure they don’t hit the camshaft. You can run a rod that has more material around that area. We have different cubic-inch platforms available to us; we can go all the way up to maybe a 588, but on the older-style Hemi, 548 cubic inches was around the max, and most of them were 521 to 526 cubic inches because of NHRA rules,” Miller explained.
He says that Steve Petty is working to figure out the best platform regarding cubic inches versus weight breaks with both a lockup and non-lockup converter package. Since more engine displacement combinations will work due to the raised cam architecture, the PLR team would be leaving potential on the table if it didn’t test each possible option.
The raised camshaft height means shorter pushrods, which significantly improve rigidity—the shorter the pushrod is, the more resistant it will be to damaging harmonics and out-of-control situations where the pushrod beats up the rocker gear. Additionally, the rocker system is revised to take advantage of the improved geometry.
Traditional Hemi valvetrain—such as what you see in a Top Fuel-type application—consists of a massive assembly. It includes intake rockers on one shaft, exhaust rockers on another shaft, individual springs to keep them all in line, and beefy mounting plates to tie the whole assembly together. These systems are incredibly robust as you would expect them to be for use in a 10,000-plus-rpm application, but that strength also comes with a weight penalty.
The new platform uses a rocker setup with individual rockers, according to Miller. If there is an instance where a spring change is necessary, it is as simple as removing that single rocker from the head to change the pushrod or spring. With the shorter, stiffer pushrods of the raised-cam design, the entire system needs less material throughout its components to control the valve action yet provides vastly superior stability.
Since the valvetrain is more stable, the valve gear components will enjoy longer lifespans between changes. Controlling the valves—especially with boosted applications—means that the engine can make more power.
“What we have found is that maintenance-wise, there was a lot more going from the 481-X to the standard Hemi. The operating range from that engine is typically 1,000 rpm higher, so valve spring life was lower. Typically, on a max-effort Pro Boost-type car, you might change four or five or six springs throughout a weekend. Also, rods and things need to be changed more frequently because of the rpm level, things like that,” says Miller.
“Fast-forward to the Raised Cam Hemi coming out. Jeff Rudolf’s car was one of the first that we outfitted in an Outlaw format. It just makes unbelievable power compared to the standard-cam-location Hemi,” he added. “Jeff’s car has about 70 passes on it, and we have changed three sets of connecting rods, but just one valve spring in the engine. These valve springs stay at 600 pounds on the seat with 70-something passes on it, and we do not see any fatigue in the springs. With the older style, you’d make two hits, and see them down in the 425-pound range.”
Miller says that they make a bunch more power because the valvetrain is so much happier.
Additionally, the revision to the block eliminates the Hemi’s traditional inner head-bolt hole. The removal of the hole makes it easier to service the engine between rounds. For example, if a racer is pressed for time between rounds to change a piston, every minute counts, and not having to pull the intake manifold to do so saves valuable time.
“In thrash mode, when we’re racing and have an issue, you can get it apart much easier. You can slide the head right off; the pan and intake have O-rings. You can rip these things apart very quickly. They are designed to be able to be serviced at the track,” says Miller. “We’re all very happy with this raised cam platform.”
When the tuner is happy with the equipment, you know it’s performing up to snuff.
Alan Johnson Performance Engineering
Pro Line Racing