Choosing the Right Cam for Your Engine Combination

Core Values

Richard Holdener Nov 28, 2016 0 Comment(s)
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Selecting the right cam for your performance street/strip or even full-race Chevy engine is difficult, especially if you don’t speak the lingo. Even before taking a look at things like cam lift, duration, and lobe separation angle, you have to get past the wide variety of different types of cams available. This is especially true for small- and big-block Chevy fans, as they must choose between no less than four different types: solid flat tappet, hydraulic flat tappet, solid roller, and hydraulic roller profiles. Heck, even the LS (and new LT) guys can choose between the solid and hydraulic roller cams for the new-generation small-blocks. Of course, no discussion on cams would be complete without also mentioning the associated lifters. To help you decide, we took a look at the pros and cons of all four different types and even provided recommendations. Each type offers something different to enthusiasts. The question now is, which one is best for your application?

Comp Cam 2/18

No matter what kind of engine you have, the right cam can make or break your buildup.

Hydraulic Flat Tappet

We begin our discussion with the most common cam type offered: the hydraulic flat tappet. Used in literally millions of production Chevy big- and small-blocks, to say nothing of the many V-6 applications, the benefits of the hydraulic flat tappet cam includes low cost, minimal maintenance, and the elimination of valvetrain noise. Looking at the benefits, it should come as no surprise that the OEMs chose to use the hydraulic flat tappet design for their production vehicles. From a purely cost standpoint, when you produce millions of cams, even a small cost savings starts to multiply very rapidly. The hydraulic flat tappet cam was used for not only all of the low- (base model) and medium-performance applications, but also made an appearance in a couple of powerful small-blocks in the muscle car era. Ask anyone who ever drove the 350hp L79 327 or the 350hp L46 350 how well the hydraulic cammed engines ran. Stuffed in a lightweight Chevy II, the L79 was a force to be reckoned with on the street. Toss in the added benefit of a set-it-and-forget-it valve adjustment procedure that eliminated periodic maintenance and whisper-quiet operation, and you can see why hydraulic flat tappet cams continue to be so popular.

Before getting to the next three cam types, we need to take a look at the inner workings of a lifter. The lifter’s job is to ride on the cam and (working with the pushrod and rocker) actuate the valve. Though simple in appearance, the hydraulic lifter is actually quite complex in design. Externally, the hydraulic flat tappet lifter appears to have a flat mating surface (where it contacts the cam), but the surface is actually crowned. Working with the angle ground into the cam lobe, the combination provides preload on the cam (to keep it from walking forward). Internally, the lifter features an oil reservoir and piston (actuated by the pushrod). This mechanism acts like a hydraulic shock absorber to soften the impact of opening and closing the valves during operation. Remember, running at 6,000 rpm, the valves open and close 300 times per second! As if this level of operation weren’t tough enough, add in the fact that customers expect zero valvetrain noise, 100,000 miles (or more) of trouble-free service, and want to pay next to nothing for it and you have the difficult design criteria for the hydraulic flat tappet cam and lifters.

Hydraulilc Flat Tappet Cam 3/18

The hydraulic flat tappet cam is the most common and least expensive type, and was used in literally millions of production Chevy V-8s.

Solid Flat Tappet

Next on this list are the solid flat tappet cams. Akin to the hydraulic flat tappet, the solid flat tappet differed both in design and application. The hydraulic and solid flat tappet cams actually look similar, but the lifters are unique. The solid flat tappet lifters lack the internal reservoir and piston assembly of the hydraulic lifters. This eliminates both the shock absorbing qualities and the ability to expand or contract with changes in engine temperature. Lacking this internal adjustability, the solid lifter requires external lash to allow for these changes. The solid flat tappet cams were used in the high-performance big- and small-blocks of the muscle car era. The most powerful performance combinations offered by GM all featured solid lifter valvetrains. Ask any Chevy guy (or gal) about their favorite factory performance engine and chances are it will have a famous, alphanumeric designation like DZ302, L88, or LS6. The solid lifter cams offered increased engine speed and more aggressive cam profiles (compared to the hydraulic). This allowed the solid flat tappet cammed engines to not only rev higher but also make more power doing so.

Naturally, both the hydraulic and solid flat tappet cam profiles each have their downsides. Both the hydraulic and solid flat tappet cams are limited in terms of longevity, as the sliding-contact design accelerates cam and lifter wear (especially compared to hydraulic roller combinations). The hydraulic lifters limit both the cam profiles and rpm potential, leaving high-rpm and aggressive lobe profiles for the solid crowd. The lack of the internal reservoir and need for external lash greatly increases valvetrain noise on the solid lifter cams. The design also necessitates periodic valve adjustments to keep them running properly. When purchased new and installed in a fresh rebuild or buildup, both of these cam designs require a dedicated break-in procedure to ensure the cam and lifters get properly acquainted before subjecting the engine to extensive loading and/or rpm. This requires break-in oil or additives with elevated zinc content to ensure the cam will survive the break-in procedure. Once properly broken in, the wear pattern generated during operation dictates the lifters can only be used on that cam (in the right order).

Solid Lifter Cam 4/18

If you are dead set on building a reproduction solid lifter muscle car small- or big-block, Comp Cams offers reproductions of many famous factory grinds.

Hydraulic Roller

Hydraulic roller cams were employed by the OEMs to help reduce wear, decrease friction, and simultaneously improve fuel mileage and power. The hydraulic roller cam takes everything we like about the hydraulic flat tappet cam and improves it. The hydraulic roller retains the quiet operation and minimal maintenance, then tosses in a dramatic increase in longevity and the ability to offer much more aggressive cam profiles. The key to the success of the hydraulic roller cam and lifter package is the increased strength of the cam core itself (improved metallurgy, some even employ billet cores) and the replacement of the crowned sliding surface of the lifter with a roller. The roller not only greatly reduces the friction of the contacting surfaces, but allows the lifter to easily follow much more aggressive ramp rates without wear or contact issues. Factory hydraulic roller cams also featured cam-retaining plates to keep them positioned properly on the rollers (which do not rotate like the flat tappets). Basically, the hydraulic roller cam and lifters combine the best attributes of the solid roller and hydraulic flat tappet cams.

Hydraulic Roller Cam 5/18

Starting in the mid ’80s, GM switched over to the hydraulic roller cam design and never looked back. Both the LS and LT engine families continue this design.

Solid Roller

Just like its solid flat tappet counterpart, the solid roller is really designed for high-performance, high-rpm race usage. They (solid rollers) can be run on the street, but the solid roller was not designed for extended, low-rpm operation. Street engines, even wild street combinations, would actually be better served with a hydraulic roller cam. Solid roller cams in small-blocks, big-blocks, and LS applications have exceeded 10,000 rpm, though more realistic numbers are usually in the 7,500-8,000–rpm range. Solid roller cams and lifters provide the opportunity to run the most aggressive cam profiles and maximum engine speeds. This combination affords impressive power production if teamed with the proper heads, intake, and a short-block capable of running at the desired rpm. Part of their success is the ability to withstand the massive valvespring pressures needed for high-rpm power production. Like the solid lifter, the solid roller requires an external lash adjustment to allow for changes in running temperature.

Naturally, there are downsides to both types of roller cams. On the hydraulic roller side, the two major limitations are cost and rpm potential. Compared to a flat tappet cam, hydraulic roller cams and lifters are considerably more expensive. You trade cost for the increased efficiency (both power and economy) and longevity. There really is no free lunch, but the cost is partially offset by the ability to run trouble-free for considerably longer compared to a flat tappet cam. The weight of the hydraulic roller lifter requires additional spring pressure (compared to a flat tappet), and so, too (usually), do the more aggressive ramp rates. Excessive spring pressure may damage the hydraulic roller lifter, so a balance must be met between spring pressure, longevity, and desired rpm. The advent of limited travel lifters (that reduce the reservoir and plunger movement) combined with cam profiles allow for hydraulic roller cams to exceed 8,000 rpm (Comp Cam’s Billy Godbold recently spun a hydraulic roller LS above 9,000 rpm!), so hydraulic rollers are certainly bridging the gap with solid rollers. The solid roller cams increase valvetrain noise, require periodic adjustment, are not suited for (low-rpm) street use, and they cost considerably more than flat tappet cams.

The benefits and limitations listed for each cam should provide an indication about the designed usage. For the vast majority of street and street/strip applications, the hydraulic roller is certainly the hot setup. It provides more power, a longer life, and minimal maintenance compared to the rest. The downside is obviously cost, as the hydraulic roller (especially as a retrofit) is more expensive than a traditional flat tappet cam. To reduce costs, it is possible to substitute a hydraulic flat tappet cam, but be prepared to sacrifice power. For the LS guys, the hydraulic roller is the only way to go, even on 1,000+ hp turbo, nitrous, or blower applications. Leave the solid roller stuff for dedicated race engines, and by that we mean very high-rpm or very high-boost stuff that requires excessive spring pressure. There are plenty of hydraulic roller LS engines running safely to 8,000 rpm, so why go to all the trouble of setting up for a solid roller on your 7,500-rpm combo? Small-block and big-block guys, leave the solid rollers to the race engines and stick with a hydraulic roller for street/strip use. If you are building a reproduction DZ302, L76 327, or LS6 Chevelle, then by all means go with a solid flat tappet, but otherwise the modern roller profiles are really the way to go.

Solid Roller Cam 6/18

Solid roller cams offer the most power and rpm potential, but were not designed for extended low-rpm (street) use.

Small Block Engine 7/18

Mild crate engines like this GM Goodwrench 350 are still available with hydraulic flat tappet cams.

Cam Installation 8/18

When installing a cam (especially flat tappet cams) for the first time, it is critical to lube the bearing journals and cam lobes with assembly lube. Then make sure to run high-zinc, break-in oil or a similar additive during initial startup.

Timing Chain 9/18

Regardless of the cam type, proper cam timing is critical for maximum performance. Lining up the dots with the number one piston at TDC ensures accurate cam timing.

Cam Install Ls Small Block 10/18

There is no better way to improve the power output of your LS small-block than to perform a cam swap.

Rocker Arm 11/18

Rocker arms work with the cam, lifters, and pushrods to actuate the valves. The rockers act to multiply the cam lift by the designed rocker ratio. Typical factory rocker ratios for the Chevys include 1.5:1 for the small-block (shown), 1.7:1 for the LS and BBC, and 1.8:1 for the LS7.

Valve Springs 12/18

Your cam choice must be accompanied by the correct valvesprings. Both for the desired lift and intended rpm range. Inadequate spring rates (or coil bind clearance) can create valve float and coil contact issues.

408 Stroker Engine Crane Cam 13/18

Would you believe that by replacing the stock LM7 (5.3L) cam with a performance grind from Crane Cams the power output of this 408 stroker increased by over 150 hp?

Roller Cam Button 14/18

The installation of a solid or hydraulic roller cam in a block not originally designed for one requires a cam button to properly locate the cam. Failure to do so will allow the cam to move forward and the roller lifters to ride off the side of the cam lobe (not good).

Retrofit Hydraulic Cams 15/18

Retrofit hydraulic or solid roller lifters feature link bars to properly orient the rollers on the cam lobes.

Piston Valve Clearance Cam 16/18

When installing a high-lift, long-duration cam, make sure to provide adequate piston-to-valve clearance.

Valvespring Piston Clearance 17/18

Larger valves (like on this BBC) require additional valvespring pressure, especially when run with an aggressive cam profile.

Forced Induction Engine 18/18

Forced-induction (turbo or blower) engines require not only dedicated cams but additional spring pressure to offset the presence of boost (and/or back-) pressure.

Sources

Crane Cams
Daytona Beach, FL 32117
866-388-5120
http://www.cranecams.com
Comp Cams
Memphis, TN 38118
901-795-2400
http://www.compcams.com

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