There is a lot of science in our short-block assembly and cylinder head choice, as we have already outlined in this series of stories on our 388ci, LSX-based drag radial bullet. But even more crucial than those parts, the stuff that takes the most research and concentration (and often, custom work) is the valve train.
On a street motor, everything is normally bought “off-the-shelf”—you buy a camshaft out of the catalog, and it comes with the appropriate lifters, pushrods, and rockers, which assemble together with no drama. But when you start getting up into the extreme cam lobe ramp angles and velocities, and enormous lift numbers of a serious engine, it all gets exponentially more difficult. “There’s probably more time spent engineering a valvetrain system than on any other part of the engine,” said engine builder Shawn Miller at Virginia Speed.
There’s probably more time spent engineering a valvetrain system than on any other part of the engine. -Shawn Miller
Race Valvetrain Dynamics
The high-flow nature of the Trick Flow GenX 265 cylinder heads, chosen to cram in as much boosted air as the engine could swallow, needed a camshaft grind compatible with that goal. The way to get the maximum amount of air in and out of the chamber is to hold the valves open as far and as long as possible, and that requires excessively dramatic cam lobes. A flat-tappet cam designed for a street car has lobes that look almost like triangles, whereas a street roller cam’s lobes are much more rounded, meaning that from the base circle (valve closed) part of the lobe to the peak lift point, the lobe angle is steeper to accelerate the lifter (and therefore pushrod, rocker, and valve) faster, and the lobe’s peak is wider, holding the valve at max lift much longer than a flat tappet can. You can’t have that type of lobe with a flat-tappet lifter, since the lifter can’t follow the lobe. The roller lifter’s wheel can, hence the ability to open and close the valve much more quickly and hold it open longer.
Compare a street roller to a full-race roller, and the difference is even more dramatic. When you get up to almost a full inch of peak valve opening, as we are on this engine, everything moves so fast and so violently, that the parts need to get more serious as well. The valve springs must be bigger and stiffer to control the motion, and that combined with the radical cam lobes requires beefy lifters. Lifters and springs are usually the sacrificial lambs with a big roller cam motor, meaning they are usually the things that need to be replaced most often. To make this valvetrain as strong as possible, Miller went with 1.500-inch-diameter Comp Elite drag race springs (part no. 26956) with a whopping 950 pounds of open pressure (350 on the seat), and selected Jesel’s large-diameter, keyway lifters.
Jesel’s Keyway Lifters
388 LSX Valvetrain Components
Jesel LS Keyway Lifters – PN LFT-53450
Jesel Pushrods – 1/2-inch diameter, 8.650″ length
Jesel Custom LS Long Arc Rockers
Jesel LS Belt Drive – PN 31045-3489
COMP Custom Camshaft – 271/282 duration, .742/.715 lift
COMP 1.5″ Dual Valve Springs – PN 26956
Jesel’s Bob McDonald added, “The Jesel Full Body Keyway lifter features the roller surrounded by the lifter body for added strength and support in the thrust area on the lifter body. Available combinations include a .937 diameter lifter featuring a .785” diameter roller, a 1.062” lifter can be ordered with either a .785” or .850” diameter roller and our 1.095” diameter lifter includes a .940” roller. A centered, .050” or .150” offset pushrod cup is available.”
See, there are no such things as off-the-shelf-parts on an engine this serious. For this engine, we used the .937-inch-diameter Keyway lifters with a 1.060 bushing and an .850 wheel (part no. LFT-53450).
As shown in part one of this buildup, the Jesel lifters don’t use a conventional tie-bar to connect the pairs, but rather a keyway on the body of the lifter, and a bronze bushing in the lifter bore to keep it square to the face of the cam lobe. Miller said, “As spring pressure goes up you need a bigger and bigger [lifter] wheel to handle it. The only way to do that is with a bigger lifter, but then [the lifter] gets heavier. A keyway lifter gives us a big lifter but with lower weight because there’s no tie bar. They can also be rebuilt. Two years from now when we freshen up the motor, we can send ‘em back to Jesel and they’ll rebuild them for us.”
The Camshaft Selection
What they ended up with was a big roller with 271/282 degrees of duration at .050-inch lift, and .437/.421-inch lobe lift, which equates to .742/.715 valve lift with the Jesel rockers used (more on that later). Lobe separation is a big 116 degrees. Miller said, “We have limited airflow due to the cylinder head and blower rules so we need to trap as much air as possible, and keep the overlap down so that the intake charge doesn’t blow out the exhaust.”
- Virginia Speed worked closely with the experts at Comp Cams to develop the perfect roller cam for this engine. It features specs of 271/282 degrees of duration at .050-inch lift, and .437/.421-inch lobe lift, which equates to .742/.715 valve lift with the Jesel rockers used. The lobe separation is 116 degrees. The Cam Pro Plus software that Virginia Speed uses is available from Audie Technology (AudieTech.com). It is a software and sensor package for measuring and analyzing lifter and valve motion profiles, either on a test stand or in the engine, and is the shiznit tool for knowledgeable engine builders. It can be used to verify custom cam specs, make it easier to degree the cam, and many other factors. Check out Audie’s website for the full rundown.
Knowing that the camshaft would have to be extreme to meet our power goals, Miller first selected the lifters, Jesel ½-inch-diameter pushrods (8.650 inches long) and springs, and then turned to getting the best possible camshaft lobes and timing to match. Miller said, “We determined what we felt would be the proper ramp rates for what we needed and contacted Comp, and we worked with their engineers to get something that was close to what we wanted. We engineered the lobes and springs around the rest of the valve train parts.”
Specifically, the Comp lobes are numbered 4312r on the intakes, 4032r on the exhausts. Miller said, “The intake lobe is getting up there, it’s pretty aggressive. The exhaust lobe is a little milder, since the valve is heavier. We have to be careful of float because of the heavy valve, but we can open and shut the intake faster to get more area under the curve, and get more air in the chamber. The faster we can do that and get everything in there, the better we’re gonna be.”
Again, Miller worked closely with Comp Cams to sort the camshaft out, and we talked with Comp’s Chris Mays on how he approaches a custom cam profile. Mays said, “After we look at all the variables, bottom to top, how much power we looking to make, how much boost, and what kind of rpm are we looking to run, that gives us a pretty good idea where we need to start leaning towards. Based on the engine’s displacement, the cylinder heads’ airflow, where the heads max out for airflow, then we look at mid-lift numbers more so than the peak flow because it’s going to be in that area longer than it’ll be at peak lift.”
Mays also said that after years of experience, he and the techs at Comp know roughly where they need to be duration-wise with a power adder combination, and how a supercharged engine is different than a turbocharged one in regards to the cam, especially in the case of a small-tire car like our Camaro. “With a small-tire car, you can lean on the exhaust lobe a little harder, and make it bigger because it’s going to run out the back end pretty good like that, and with a small-tire car you don’t want to shock it too much down low.” Plus, electronics have helped a ton over the years. “Modern EFI systems like the F.A.S.T. system have let us alter the camshafts over the past few years because we can ramp in timing and traction control variables, where we couldn’t do that years ago.”
In the end, reliability is just as important as ultimate peak power. Mays said, “A lot of these guys building combinations like this don’t have the budget of John Force. We’re trying to make the most power we possibly can but also be easy enough on the valve train. They don’t want to be chucking valve springs out of the valve covers every weekend.” As for those valve springs, they are Comp part number 26956, a 1.500-inch-diameter dual drag race spring that Mays describes as “a very good spring. It has a higher quality than the average spring from a wire standpoint, and goes through more stress enhancements when the coiling is being done. It’s a good, high-end spring but not something that’s going to break the pocketbook too bad.”
It’s all top-line stuff. There’s nothing better than what Jesel makes, it’s as simple as that.
With the valve train parts figured out, there was one big roadblock standing in the way of making them work on the LS engine—the factory design of the cylinder heads. Trick Flow had to follow that design to make these heads compatible with a bunch of different applications, but that design features very narrow valve cover rails which dictates short rocker arm bodies. With the short rockers and lots of valve lift, anything over about .750-inch lift, the rocker will roll off of the top of the valve. And that’s not a good thing to have happening.
“We didn’t touch the heads,” said Miller. “We sent them to Jesel and they did their long rocker arm conversion to them.”
Jesel Long LS Rocker Arm Conversion
Jesel’s conversion modifies the heads to accept a much longer rocker arm. They have to machine down the valve cover rail to below the height of the rocker to accept their longer rocker, and they move the pushrod holes up, and cut them into the rail. This allows more than .800-inch lift without the rocker/valve alignment problem, but brings with it a few challenges. The rocker ends up hanging over the rail by about 3/16-inch, and the pushrod does on the other side, requiring a special Jesel cover that wraps around the rockers and attaches to the rail.
Jesel’s Bob McDonald tells us, “The main advantages of a longer pivot rockers over a the stock pivot length rocker, is that on a longer pivot rocker the tip travels in a much larger arc, which results in a smaller travel pattern and minimized the scrubbing motion across the valve tip. The stock pivot rocker with the shorter pivot length will sweep further across the valve tip which results in increased friction and binding. Also, with the longer pivot rocker, you are capable of using a larger diameter spring and increasing rocker ratio.”
“No other type of rocker system can compare to the performance, strength and maintenance advantages of a shaft rocker system.” McDonald said. “Performance advantages include such as improved geometry from increased pivot length, decreased valve guide wear, stability at high rpm, and accurate ratio and lift numbers. Strength advantages include a stable mounting surface and rocker tensile strength capable of handling over 1200lbs of open spring pressures with less mass on the valve tip to increase spring life. There are also multiple maintenance advantages including ease of setting the valve lash, stable lash settings, on-engine spring removal and elimination of pushrod guide plates.”
Jesel LS Belt Drive
Finishing off the valve train is a Jesel belt drive (part no. 31045-3489) for the cam-to-crank connection. From the factory the LS uses a conventional chain to drive the cam, but a serious race engine can benefit from a belt drive in a number of ways. As Miller put it, “The belt drive, that’s an important part. It seems simple in theory and it is, but the beauty of a belt drive is twofold. For one, it’s easy to change the cam timing—in five minutes we can change it up to 20 degrees. It also takes a lot of harmonics and doesn’t transfer them into the cam like a chain or a gear-drive can. It’s almost like a damper for the cam.”
According to Jesel, “All Jesel Belt Drives feature extremely accurate, externally adjustable cam timing to fine tune the engine’s power curve. The camshaft can be changed by simply removing the upper pulley and cam seal plate. Teflon coated cam and crank seals insure proper oil and vacuum sealing. The Gates High Torq Drive belts are engineered to handle well over 1,200 lbs of spring pressure and are custom made to Jesel specs to insure the proper belt tension. And on certain applications, we have cam adapter assemblies capable of reducing camshaft endplay down to as low as .001-inch.”
And there you have it, the Comp/Jesel valvetrain for our 388ci LSX bullet. One of these days, we’ll get that puppy on the dyno and see what she’s got!