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Roller Camshaft Conversions Engine Upgrade - Rockin’ And Rollin’
Roller camshaft conversions take the anxiety out of driving your classic Ford
It's been all the talk on internet forums, club meeting hangouts, and in enthusiast garages across the nation—the loss of zinc and other protective "barrier" chemicals in modern oil damaging traditional flat tappet camshafts and valvetrain components. From wiped out cams that didn't make it past initial break-in to long-serving engines simply losing valvetrain parts overnight from a simple oil change, the problem has had enthusiasts running scared for several years.
Why the change in conventional motor oils you ask? Why couldn't they just leave well enough alone? It's simple, really; major aftermarket oil companies and the parts stores that carry their products cater to the general DIY market for modern cars (considered less than 20 years old). Much like there hasn't been a Ford built with a carburetor since the early 1980s, the same can be said for a flat tappet cam application in a Ford. From factory roller cam setups (5.0L HO Mustangs for example) to more modern overhead cam valvetrains that use roller followers, these valvetrains simple don't need the protection from high pressure wear like a flat tappet cam does. When the OEs determined that additives in the oil package were affecting their emissions systems (catalytic converters, oxygen sensors, and so forth) the additive packages were removed. From an OE standpoint, it was an easy decision, as the additives were no longer needed in the first place with modern valvetrains.
Unfortunately, this decision affected us enthusiasts in a negative manner, since we stand in line at the parts counter buying the same 10W30 that the guy in front of us with an OE roller valvetrain buys. He goes home and pours in his oil and all is well. You do the same and a few days later, you have valvetrain failure. Today, the issue has been reduced somewhat by the fact that there are several oil companies that offer oil with these additive packages once again. Some are labeled as "high mileage," while some are called "muscle car oil." Still, others search out specialty oils for diesels and power sports applications and use these products due to their retention of these all-important additives. Lastly, you can buy the additive in a pour-in concentrate to add to your traditional oil change as a manner of protection as well.
While a somewhat expensive solution, converting to a roller camshaft/lifter setup is a permanent one. Whenever we see an engine being built, we strongly urge the owner to spend the extra coin to add a roller cam to their shopping list. There are several ways to add roller cam technology to a small- or big-block Ford engine build and reap the benefits of a roller cam valvetrain. The most basic is a roller cam conversion kit, which generally features a roller camshaft with a reduced base circle, roller lifters specific to the application, and some sort of installation hardware/retainer. These kits offer several popular cam grinds for street use and most manufacturers can even offer custom grinds. The reduced base circle of the cam is to allow the retrofit to work in early blocks (more on that later). Another option is to use a standard base circle roller cam with "link bar" lifters. Instead of the lifters being retained in the valley to prevent rotation, the lifters are linked to each other to prevent rotation. This allows a wider option of cam profiles, but is a bit more expensive when purchasing the lifters. The last option for retrofitting a roller cam is to use a roller-cam-ready block, either a production block or an aftermarket block. This allows the use of OE type hardware and everything just bolts together. This last option is probably best if you're planning to build a completely new engine.
One of the most confusing aspects of choosing a roller cam for many is comparing the roller cam specs to a traditional flat tappet camshaft. It's not a true apples-to-apples comparison of the specs on the cam card. Where you will find the key differences is in the lobe pattern. A flat-tappet cam lobe can only provide so much lift before the lobe literally comes to a point, which would fail very quickly. With a roller cam profile, the lobe lift can be more dramatic because of the roller cam's "broad shouldered" lobe, which provides more lift. For example, if you compare cams with similar durations at 0.050-inch lift, you'll see the roller cam has much more lift for a similar power range. Take Comp Cams' popular 280H grind flat tappet (230 degrees duration and 0.512-inch valve lift) and compare it to Comp's XE282HR roller (230 degrees duration at 0.050-inch lift and 0.565-inch valve lift). That's 0.053-inch more lift. "The lobe profiles are quite different because of the flat versus roller follower, but the engine only ‘cares' about how the valve moves and not at all about how fat the lobe ‘looks' to our eyes. The roller cams certainly give much larger gains on great flowing heads (especially the modern cast and/or CNC ports that work so well at high valve lift)," states Billy Godbold, Valvetrain Engineering Manager at Comp Cams.
Roller cams are generally made from billet steel or specially hardened steel, unlike the standard cast iron of a flat-tappet camshaft. This holds true whether you're discussing hydraulic or solid roller camshafts. The lifters, or tappets, are similar to a traditional flat tappet, except that they have a hardened roller wheel on their end that rides in needle bearings in a linear fashion against the cam lobe. The lifter does not rotate in its bore like a flat tappet (the flat tappet has a radius on its bottom which creates the rotation when the cam lobe rotates against it), and due to the roller wheel on its end, must be held in place by a retainer of some sort. Otherwise the roller tappet would rotate and the wheel would be perpendicular to the cam lobe (think a car's tire in a slide) causing immediate and extreme wear. This retainer aligns the tappet to the cam lobe. Roller tappets are also taller than their flat tappet cousins and require shorter pushrods in retrofit applications. The taller body of the roller tappet can also cause a problem with early blocks and their shorter lifter bores, which is why these applications must use a small base circle cam if using OE-style roller tappets; otherwise the tappet would continually crash into the tappet retainer, causing damage and eventual failure.
When converting to a roller cam, it's not just the camshaft, lifters, and pushrods you need to consider, but the whole valvetrain. From the valvesprings on the cylinder heads to the timing chain setup at the front of the engine, everything needs to be upgraded to handle a roller cam's higher loads. Yes, a roller valvetrain produces less friction, but it does impart higher loads on the valvetrain due to the quick valve opening and closing rates. While this is not necessarily new information, as long-time wrenchers will remember a full cam swap "back in the day" included appropriate valvesprings, double roller timing chain setup, and so forth, it is worth a mention again here to not allow the presumption that a roller cam can just be dropped in with flat tappet springs, timing chain, and so forth.
Roller Cam Options
Solid Roller Cam Retrofits-A solid roller camshaft is similar to a mechanical flat tappet, in that there is no hydraulic "cushion" from the lifter/tappet and periodic maintenance/adjustment is necessary to maintain optimum valvetrain specifications. These tend to be race-level parts with high power output in mind, including extremely high lifts and duration. You won't find too many solid roller users on the street, but for our quarter-mile fans, this is certainly an option.
Hydraulic Roller Cam Retrofits-Hydraulic roller cams are similar to their solid counterparts, however, they use a tappet with an oil-filled chamber, just like a hydraulic flat tappet, which provides some valvetrain cushion and allows for valvetrain wear by taking up the slack via the pressurized oiling system of the engine. You get the best of all worlds with roller cam efficiency and low valvetrain maintenance for a quiet and performance oriented valvetrain; perfect for street driven performance engines.
Factory Hydraulic Roller Cams-A stock 5.0L Mustang roller cam can be used in a vintage engine application with the use of the proper lifters. You get all the benefits described above in the retrofit, but you can use an OE or aftermarket-spec replacement cam (intended for the original roller application), greatly increasing your cam choices. OE cams are also a good choice if you're using a late-model roller-specific engine block or aftermarket roller-ready block in your engine build.
Roller Cam Pros/Cons
While flat-tappet camshafts are what most of us grew up with, their popularity is still strong due to their relatively low cost. Generally a cam and lifter kit is all you need for a cam swap unless you've got some decent lift that requires a spring change. With roller camshafts, however, the velocity and lift can be far higher than a flat-tappet camshaft and still be very streetable. Roller cams are also able to tolerate higher spring loads than a flat-tappet cam. For most street applications, roller cams are "all done" at 6,500 rpm. You can get a bit more rpm out of them with lighter valves, stiffer rocker arms, and short travel lifters while using modern design valvesprings.
"Anything above 7,500 rpm becomes a significant challenge," Billy explained; although, their new 4-Pattern roller cams are capable with matched components. A solid roller cam will easily take higher rpm if you need it for a free-breathing track engine, but on the street, a typical performance grind hydraulic roller and the 6,500 rpm threshold is fine in our opinion.
We've seen factory hydraulic roller cam engines easily surpass 100,000 miles of use, and even our own 347 stroker with stout hydraulic roller cam, double springs, and roller rockers made it to 118,000 miles of daily beatings before a lifter failure took out a few cam lobes. It is common to pull a hydraulic roller cam out of an engine for an upgrade and see little to no wear on the lobes due to the roller cam's low-friction roller tappets. Even OE shop manuals state that roller tappets can be reused with a new cam and maintaining lifter-to-cam lobe pairing isn't critical like it is with a hydraulic flat-tappet cam where the lifter base and cam lobe wear together in a marriage of sorts. Of course, this is all only possible with a thorough inspection and finding the used lifters in sound order. Any question and you should replace the lifters when swapping from one roller cam to another—stock replacements are dirt cheap at about $100 a set.
Your typical street engine sees valvetrain loads in excess of 1,500 pounds per square inch as the valvetrain is compressed by the lift of the cam lobes. These loads are actually higher than the buckling load of your standard 5⁄16-inch hollow pushrod. However, the load is applied and released so quickly that the pushrod does not have time to buckle from the pressure! A flat-tappet cam tends to have higher acceleration rates to make up for some of the limited velocity and lift that is inherent to the cam design. This, in turn means, just as high, if not higher, loads as a roller cam profile. Interestingly, most people associate high spring loads as the main contributor to valvetrain stress and failure, when in fact the valve mass, rpm of the valvetrain, and profile acceleration rates are much more critical to valvetrain stress and associated failures, Billy explained to us.
Arguably one of the worst "cons" to retrofitting a roller cam to a classic Ford engine setup is the cost; especially if you are using a retrofit kit of matched parts with link-bar style lifters. You'll spend anywhere from $700 to well over $1,200 depending upon cam grind, type of roller lifter, roller retrofit hardware, valvesprings, pushrods, and so forth. Meanwhile a traditional flat-tappet camshaft and matched lifter/spring/timing set kit is roughly going to set you back around $450. So you can see how just shopping by price makes a roller cam conversion a bit of a bitter pill to swallow. However, spending that extra money up front (especially if you're building a complete engine) is cheap insurance, as there are thousands of horror stories across the Internet of brand-new engine builds and crate engines not making it through their flat-tappet cam break in, and taking bearings and other hardware with it during the failure.
Gears of Change
One of the most confusing aspects of converting to a roller cam in an early non-roller application is that of the distributor gear material, and what material is compatible with what cam. More confusion ensues when you consider that even within one manufacturer (like Comp Cams), there can be several different cam gear requirements depending upon the roller cam line being discussed. For OE-type camshafts, the roller cam is high-grade steel, sometimes billet, and that includes the cam gear. Ford, in turn, used a treated steel distributor gear. This offers the best life and wear and is compatible with many aftermarket roller cams as well. It is imperative that you know what your aftermarket roller cam material is and if the gear itself is the same material. Some cams utilize a pressed on gear to allow compatibility with flat-tappet iron distributor gears while others, like Comp Cams, use a ductile-iron cam core that is austempered on the lobes to harden just the lobes for the roller tappets, leaving the cam gear area as the standard ductile iron and compatible with iron gears. These cam cores are called Selective Austempered Ductile Iron (SADI) and are denoted by the "-8" on the end of their part numbers.
For the longest time, the sacrificial bronze distributor gear was considered the answer for roller cam use. This may have been fine for a weekend race car that gets constant tear downs and inspections, but for a street driven car, it can quickly become a nuisance. Worse yet is using too hard of a distributor gear and destroying the gear on the camshaft. Besides bronze gears and the stock treated steel gear from Ford, you'll find additional options such as aftermarket steel gears and even polymer gears. When purchasing a new roller cam, the cam manufacturer can point you in the right direction for the proper matching gear, or they can tell you if the gear you have now on your distributor is compatible. Ensuring you have the right hardware means a long life for your camshaft and your distributor.