You probably know Dart Machinery for their high-end race parts like billet blocks and 500-plus-CFM cylinder heads, but you might not realize that this company was born in Richard Maskin’s two-car garage during 1981. Though Dart has grown to an industry giant, they have never forgotten their roots.
Today they’re still supporting racers at every level with three decades of experience building horsepower and durability. You might not be building a Pro Stock motor in your own garage, but the lessons Maskin and his crew have learned from hard experience in NHRA and on the dyno can make your project more successful. In this first series of tech videos and how-tos, we had a chance to pick Dart’s brain to come up with engine-building advice thatanyone can use.
Our first stop at Dart was with Jack McInnis, who explained that the idea behind their ongoing efforts to educate their customers was to help give them extra value for their money, and of course, keep them coming back for more. “We also want to answer some of the common questions which frequently occupy our tech lines,” he added.
Oiling System Preparation
One of the big advantages of going with a Dart block instead of a lesser aftermarket piece or even an OEM block is improved lubrication. For the sake of manufacturing convenience, stock blocks typically use a system of passages that supplies oil to the camshaft journals and lifters first, then to the main bearings. While that might be fine for a daily driver, Dart has reengineered the setup in their blocks to provide “priority main” oiling, feeding the critical crankshaft bearings first, then the cam and valvetrain.
Priority main oiling, used in all of Dart’s performance blocks, sends oil to the main bearings first, then feeds the cam journals and lifters.
Not only does this help protect the crank should oil pressure falter a bit, but it can also reduce the amount of oil that ends up in the top end of the engine. While scrapers and windage trays can help keep drain-back from the valve covers away from the crankshaft, a good way to prevent parasitic loss and oil aeration from the crank thrashing it is to not put more high up in the engine than is really needed.
Some builders run restrictor orifices in the cam feed galleries, but McInnis cautions, “It’s important to stress that restrictors are only needed on racing engines with solid roller lifters. Using restrictors with hydraulic lifters would not be a good idea. As to orifice size, there really is not a simple guideline. It’s generally influenced by the oil viscosity/type of racing, as well as other factors like whether or not the lifters are bushed. This is an area that’s best left to an experienced engine builder for that specific type of engine.”
Per Dart’s McInnis, unless you’re running unusually loose main bearing clearances, or your builder has a specific reason, there’s no call for a high-volume or high-pressure oil pump when using a Dart block.
The rule of thumb for oil pumps used to be that bigger was always better, but thanks to improved oiling in a Dart block, using a high-volume, high-pressure unit isn’t typically necessary. How much power does it take to run an oil pump? “I really don’t know,” McInnis jokes, “We’ve never tried to run an engine without one!” Even so, an overkill pump will definitely put more of a parasitic load on the engine.
So when do you need a high-volume or high-pressure pump? “One scenario would be if you were going to run very loose bearing clearances, which would shed a lot of oil,” McInnis explains. “Other specific applications could be the preference of an engine builder for a given type of racing engine. Stock blocks generally require more oil pressure than a Dart block, because the oil has to run through the cam bearings and is fed off to the valvetrain en-route to the more critical main and rod bearings.”
Valvetrain Geometry 101
One of the most potentially perplexing topics Dart’s tech gurus cover with customer is valvetrain geometry. No matter how carefully designed and machined a block and pair of heads are, it will still be necessary to do some adjustment to the valvetrain to maximize power and longevity. Ideally, you want the tips of your rocker arms centered on the tops of the valve stems, and the arms themselves moving through an even arc to avoid as much side-load on the stems as possible. The key to getting where you want to be is having pushrods of the proper length, because without having the right dimension there, every other aspect of rocker geometry will be off as well. An adjustable “checker” pushrod is an essential tool in setting up the valvetrain.
An adjustable-length pushrod (shown here, with knurled sides) lets you mock up your valvetrain and measure the right length for proper rocker geometry.
Pushrod length should be set so that when the valve is half-way though its maximum lift, the angle formed by the arm and the stem is as close to 90 degrees as possible. That ensures an equal amount of travel on either side of that half-way point and , but due to tolerances in the placement of rocker studs and the dimensions of the rocker arms themselves, there will always be some tweaking necessary. Mocking up the engine and painting the tip of the valvestem with a marker will allow you to turn it over by hand and see where the tip of the rocker is actually going.
Dart’s patented adjustable guideplates make pushrod alignment easy.
Once you’ve gotten the right pushrods, setting the side-to-side alignment of the rockers is the next step. Typically, hardened pushrods and fixed guideplates are used to keep things in line, but they offer very little adjustability. Dart has a unique and patented solution in their adjustable guideplates, that will let you precisely position your rocker arms side-to-side. This helps avoid excessive load on both the pushrods and the valvestems, making them a win-win addition to your build.
Stud Girdle 101: Strength in Numbers
Even with perfect geometry, there are considerable dynamic loads placed on the valvetrain from both directions, and these loads are working on a good-sized lever arm in the form of the rocker stud. Switching from stud to shaft-mount rockers is one way to fight unwanted deflection of the rocker arms, but budgets and rulebooks don’t always allow them. An elegantly simple solution is a valve stud girdle that clamps on to extended rocker nuts, allowing the strength of all the studs to work together as a team. “Generally, the spring pressures encountered with mechanical roller cams are where they become necessary,” says McInnis. “Typically, stud girdles aren’t really necessary with hydraulic lifter applications.”
While a valvetrain girdle makes valve lash maintenance a little more complicated, the advantages in rocker stability make it worth the extra effort.
Though girdles do make it a little more difficult to set valve lash, per McInnis, “It does add some effort because you have to work around them, but it’s not excessive, really.” The rule to remember with a stud girdle is to leave it snug rather than fully tightened while you’re setting valve lash. Once they’re lashed, then you can tighten down the girdle to its final torque spec.
While we’ve just scratched the surface of all the tips and advice Dart has to offer the DIY engine builder, there’s plenty more available on their website at www.dartheads.com, and we’ll be bringing you more in our next installment as well. Until then, remember that nobody’s born knowing this stuff and you have to start somewhere – maybe even a two-car garage of your own – so start turning wrenches!