Camshaft And Valvetrain Technology Insight - On The Lobe's Edge

A Look At The Latest Camshaft And Valvetrain Technology Straight From Its Creators

John Nelson Feb 1, 2009 0 Comment(s)
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One of the most exciting innovations coming out of the Comp camp is the company's work with GM's variable valve timing system, which is controlled by cam phasers as shown on this L92 cam. The phasers are computer-controlled to optimize cam timing based on engine rpm. Designing performance cams is difficult due to the constantly varying valve timing movement and the varying piston-to-valve clearance.

Competition Cams
We decided to approach our subjects in alphabetical order, which meant we began our conversations with our friend Billy Godbold of Comp Cams. We had no problem getting him to talk with gusto about the latest innovations coming out of Comp. "If you check out the components we're looking at today," he began. "We're figuring out how to make valvetrain pieces lighter, stronger, and stiffer. For example, we're testing pieces that run as many as 10 million cycles in big-block circle track applications." The method to this madness is pretty clear: "If we make the valve spring better, we can take so much better advantage of the cam."

Although Godbold returned to this subject, it quickly became obvious that he had other ideas aching to burst out of his mind. Ideas that can be summed up in the initials VVT-that's variable valve timing to you and me. "The L92 truck motor is incredibly impressive, making 400 SAE corrected horsepower stock and 430 hp with headers," he began. "With one of our cams and the phaser limiter kit, we made 500 hp, and it did not lose power anywhere. It's a great cylinder head, then you add the variable valve timing. We start out by giving the smaller cams lots of advance, up to 10 degrees, then you can retard those about 16 degrees. With the larger cams, piston to valve is tighter on the intake so we go down to 5 degrees advance. These designs run best with a sweep curve of about 12-degree retard, which helps the engine carry at high rpm."

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Comp worked around this obstacle with its XFI SPR Cams & Phaser Limiter Kit for Gen IV VVT engines. The Cam phaser limiter kit restricts the range of timing movement from 50 to 20 degrees. This allows the needed valve clearance for these performance cams but still takes advantage of the VVT technology.

Why should this matter to you or me? "I'm certain the automatic 6.2L Camaro will have VVT," Godbold disclosed. "Also, retrofits for other GM VVT LS applications will come available soon. The whole thing is better. You can move the cam around in the motor. Say you do a NASCAR cam with a 110 LSA. You can run it at 102, 106, 110, and 114 centerlines and get an idea of how it responds. It may fill in a gap, 104, 108...look at torque curve...102 best torque, 114 best high-end power. Good teams look at the specific track, look at where the engine spends time. This is something that would have taken us a lot of time and four guys on the dyno, and analyzing data in the past. Then, after you do it, you have to compromise. With the cam phaser, you can advance or retard the cam centerline to the position it runs best at each rpm. That's cool, really cool. You can get a 60-plus horsepower gain, with no loss anywhere. You can have control of the cam timing by tweaking a curve in your ECU, just like typical electronic ignition timing. It's like going from points to coil-on-plug.

"It's probably ahead of its time," Godbold continued, "but eventually it will be in many applications. GM uses it almost solely as an mpg device (they even refer to it as active fuel management), but that's not the way we're going to use it. We want to use VVT to enhance power and performance, hence Comp Cams designed the XFI SPR Cams and Phaser Limiter kits to work together in Gen IV VVT engines. Some competitors tell their customers to throw the phasers out completely. Comp has proven how robust and advanced this phaser technology can be for high-power applications. There are four grinds in this line so far."


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