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Maximum Effort Valvetrain MAXIMUM EFFORT VALVETRAIN 1 ENGINE MAXIMUM EFFORT VALVETRAIN CIRCLE TRACK takes a look at one of the hard- est working valvetrains in motorsports—the Late Model Stock—and the tricks some engine builders are taking to push it to its limits Text and Photography by jeff Huneycutt n circle track racing the Late Model Stock classes have a now-classic set of rules that mostly haven’t changed in over a dozen years. The heads must come from the manufacturer, typically the Chevrolet Bow Tie 23-degree and Ford N351, and must be iron with no port work besides a three-angle valve job. Valves must be steel and the stock size. The cam Ihas to be a flat tappet solid, the carburetor is a restrictive two barrel (usually either 350 or 500 cfm), and the intake is an alumi- num dual-plane stock-style intake that legally, you aren’t allowed to do anything to beyond dust it off and bolt it up. But the Late Model Stock class is also normally the head- liner at asphalt racetracks all across the country. And as such, it draws the most dedicated race teams that put the most effort into winning. So even though the rules package is pretty limiting, competitive engine builders have been finding ways to continually push the engine package to ever higher limits. And the one area with some of the most innovations is the valve- train. As the camshaft gets more radical, more and more steps have to be taken to help keep the valves under control as well as making sure everything lives. With the idea of helping racers—no matter the class—gain some insight that may help them improve their own engine program, we spent some time at race engine specialists KT Engine Development to get the latest advancements in Late Model Stock valvetrain technology. Not every idea will work in every situation, but we’re betting there are at least one or two things here that apply to any class you race. CIRCLE TRACK • july 2011 2 ↑On the left is a standard valvespring. On the right is a valvespring that has gone through a surface treatment pro- cess to polish it. The spring isn’t coated, but the polishing process smoothes the surface to reduce or eliminate any imperfections that can create an originating point for a crack to develop and cause a spring failure. Also notice how the edges of the spring on the right at the very top where it contacts the spring retainer have been chamfered to eliminate any sharp edges. ↑Conventional Late Model Stock rules don’t specifically limit compression. Instead, they require flat top pistons and have a minimum volume for the combustion chamber. Compression equals power, so to maximize it, make sure the valve pockets in the piston tops are no larger than necessary and that the combustion chambers are all right at the minimum size (normally 62 cc’s). ↑Here’s one concession to economics. If you get much variation after cc’ing Sometimes you may be allowed to use the combustion chambers, you can titanium retainers, but these are steel. sometimes deck the head so that the The titanium units are lighter but they smallest chamber is slightly undersized are quite a bit more costly and wear to bring the larger chambers closer to out more quickly. Some new coating the minimum and then dish the valves processes help increase the lifespan of on a lathe to open the smallest chamber titanium retainers, but that only adds back up a bit. to the cost. Well made steel retainers, however, don’t add significantly to the overall valvetrain weight. No matter which you use, do make sure that the retainer fits the spring tightly and that there are no sharp edges on the spring where it contacts the retainer, which can lead to a failure ← Valves have to be steel with a stan- dard 0.34375-inch diameter stem. The maximum valve size is normally Chevy Even with a restrictive standard 2.020 inches for the intake two-barrel carbure- and 1.625 for the exhausts. One trick tor, modern Late Model you can do, however, is used undercut Stock engine packages valves. It is hard to see here, but the are delivering 8,000-plus darker portion of these Ferrea valves is rpms in some situations. actually 0.3125-inch. This is the portion Keeping the valvetrain of the valve stem that stays below the under control at those valve guide. The smaller diameter not rpms requires real atten- only reduces the valve’s weight but also tion to detail. creates room in the lower portion of the port to allow for more air and fuel to enter the combustion chamber. www.circletrack.com • CIRCLE TRACK MAXIMUM EFFORT VALVETRAIN 3 ENGINE ↑Notice how the installed valves aren’t sunk into the chambers, but instead the seats are cut so that they sit right on top. This helps get the air and fuel moving as soon as the cam lifts the valve off the seat and improves overall flow into the chambers. ↑The installed springs are set up to have a very light opening pressure (approximately 160 pounds) but then ↑As the lift rates on the racing cams ramp up quickly to 400 pounds of pres- get extreme, the flat tappet lifters want 7 sure when fully opened. The ⁄16 rocker to start digging into the face of the ↑Here’s a comparison of pushrods. studs are the largest that will fit to help lobe instead of sliding up and over. As The pushrod on the left is the standard 3 reduce rocker arm deflection. a result, lifter technology has made ⁄8-inch diameter steel unit. It works well, 5 some pretty significant advancements. but the larger ⁄16-inch pushrod helps The idea is to make the lifter as hard limit deflection and improves valve con- and slick as possible so that it will slide trol. A smaller pushrod may be lighter, with no deflection to limit the chances but it flexes the result is that the valve of grinding against the lobe. This lifter opens later and the lifter can loft off of looks pretty standard at first glance, the cam lobe—neither of which is good. but it’s constructed from tool steel and If you experiment with tapered wall ↑Just about everything in the val- given a DLC (diamond-like carbon) coat- pushrods, you can sometimes get even vetrain comes right back to allowing ing to make it extremely tough. bigger units to work. the camshaft to be as aggressive as possible. With flat tappet cams this can be difficult because the extra sliding friction between the cam lobe and the → A less expensive option are these Ferrea lifters Troutman also lifter tappet makes extra aggressive sometimes uses. Instead of the DLC coating these lifters have an designs hard on parts. One way to help anti-friction coating that helps the face of the tappet slide up and this is a treatment called “nitriding” over the cam lobe. You can also see the pressurized oiling hole in which makes the cam both harder and the face of the lobe that injects a steady stream of oil between the slipperier. Engine builder Ken Trout- tappet face and the cam lobe for extra lubrication. man uses a custom grind developed with the help of Comp Cams and not only did he not want to share the cam specs—which we can understand—he didn’t even want pictures taken of the thing. So instead, this is an off-the-shelf nitrided cam from Comp. Eagle eyed readers may also notice it’s for a big block, but you get the idea. CIRCLE TRACK • july 2011 4 ↑The total valve lift on this Ford Late Model Stock that Troutman is building is 0.550 inches on the intakes and 0.575 on the exhausts, which is necessary to help the unported heads flow more air. One way to get such extreme valve motion without stressing the flat tappet cam too much is to use high-ratio rocker arms. Here, Trout- man mixes 1.65:1 ratio intake rockers with 1.60:1 exhausts to get the valve motion he wants. ↑When working with large valve move- ments, it becomes critical that the rocker arm’s roller tip is centered over the valve stem. If the movement isn’t centered over the valve it can press the valve stem into the wall of the valve- guide which reduces the efficiency of the valvetrain and can lead to a broken valve. If you are mixing and matching rocker arms with different ratios, be prepared to use two different pushrod lengths in your race engine. SOURCES Comp Cams • 800/999-0853 • www.compcams.com ↑A rocker stud girdle can significantly improve valve control. Without it, the stability Ferrea • 888/733-2505 • www.ferrea.com 7 of the rocker depending on the stiffness of the ⁄16-inch rocker stud. But the girdle KT Engine Development • 704/784-2610 ties all the studs together, and since all the rockers aren’t activated at the same time it means the strength of multiple studs come into play every time a rocker arm is rolled forward to open its corresponding valve. CT www.circletrack.com • CIRCLE TRACK.
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