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Roll It Over

The Details Behind Converting To A Hydraulic-Roller Cam

Jeff Smith Apr 10, 2003

The new buzz for hot street engines are hydraulic-roller cams. These cams offer significant advantages for additional lift and more power when properly combined with the rest of the engine combination. That's what has everyone so excited. But there are some practical pitfalls that you should be aware of before you dive in the roller-cam pool. That's what this story will detail. The big limitations are cost and all the other details that must be accomplished before you can take advantage of everything that hydraulic-roller cams have to offer. Let's jump in and see just how deep the waters are, shall we?

In the Beginning

Small-block Chevys first came out of Detroit with hydraulic-roller camshafts in 1987 in some passenger cars. Because the small-block was first on the scene, this story will deal with just the small-block. You big-block guys will have to wait. The concept was to reduce friction and improve mileage, which really didn't generate great results. However, the roller wheel on the end of the hydraulic lifter allows greater lift-curve capabilities, delivering much more lobe lift--and therefore valve lift--than a flat-tappet camshaft. But there's much more to this puzzle than just rollers on the end of the lifter.

Installing a roller cam isn't difficult, but it does require some specific parts depending upon the type of small-block you're working with. Early (pre-'87) small-blocks require a retrofit-style hydraulic-roller cam and valvetrain while most '87-and-later small-blocks can use much, if not all, of the original roller-cam valvetrain. We'll get into a late-model small-block first to show you how the factory designed a hydraulic-roller-cam valvetrain. Then we'll get into the aftermarket version that reconfigures a flat-tappet block for a roller cam and lifters.

OEM Roller

The most important point about roller lifters is that they must not be allowed to spin in the lifter bore for obvious reasons. The factory takes care of this by designing two small flat spots on the lifter that accommodate a rectangular alignment bar that slips over a pair of lifters that prevents them from spinning. This requires the lifter to be slightly longer in overall length both for this alignment bar and to create room for the roller. Otherwise, the hydraulic part of the lifter operates the same way as a flat-tappet hydraulic tappet. To keep the alignment bar in place, Chevy uses an eight-legged "spider" that places one leg over each of the eight alignment bars in the lifter valley. Roller cams also cannot be allowed to move fore or aft in the block for several reasons. The most important reason is that the roller tappet can be easily damaged if the cam moves far enough that a lifter might crash into an adjacent lobe. Another good reason has to do with the angled or helical cut of the distributor gear. The camshaft has a tendency to move rearward when loaded by the distributor gear. The higher the engine speed, the more the cam wants to move. This requires some kind of limiter to prevent the cam from moving in either direction. Factory roller-cam blocks employ a limiter plate that bolts to the block in front of the cam. This requires a step be placed in the cam nose to be able to bolt on the cam drive gear.

One advantage to roller cams in general is that you can reuse lifters on a new or different camshaft. This means that if you are upgrading a late-model roller-cam engine, you don't need to purchase new lifters as long as the tappets are in good condition. If you need to purchase new lifters, the OEM replacement lifters are far less expensive than aftermarket retrofit hydraulic roller tappets because of the sheer volume of production. For example, a set of 16 Crane replacement lifters cost around $200, while a set of Crane retrofit hydraulic rollers will run you $390--almost twice as much.

This leads us to an interesting point. If you are planning on a hydraulic-roller cam in a rebuilt small-block, you might be money ahead to invest in a hydraulic-roller-cam block. You should be able to find a basic short-block with the spider, retainer plate, and perhaps even the one-piece rear-main-seal crank for under $200. For those who choose a passenger-car roller-cam small-block, most '87 to '91 engines come with a mechanical-fuel-pump boss. We've seen some truck engines with a fuel pump boss, but no block-off plate because the hole is not drilled for the pushrod. Comp Cams also sells a hydraulic-roller-lifter installation kit for those who have a block and lifters but none of the guide pieces. The kit includes the spider, the lifter guides, cam retainer plate, and the fasteners for a reasonable amount of money. Of course these pieces could also be found in any old small-block roller-lifter engine. While we're on the subject of factory roller lifters, the small- and big-block lifters are not interchangeable as they are with flat-tappet engines. The flats on the lifter body that the lifter guides fit over are in different places on small-block versus big-block lifters, so they are not interchangeable.

One other interesting note is using hydraulic-roller lifters in the late-model hydraulic-roller blocks with small-base-circle cams or >> cams with significantly greater lift than stock. The smaller base circle drops the lifter deeper in the lifter bore, which is already taller than the older blocks to provide more lifter stability. Dropped farther down, stock lifters can actually push the lifter guide off the lifter, causing all sorts of mayhem. Crane makes a taller body lifter that prevents this from occurring.

One of the more budget-oriented conversion kits from GM Performance Parts is the Hot hydraulic-roller cam. This particular cam was originally designed for the LT1 small-block and used with 1.6 roller rockers. GM Performance Parts has packaged it with the cam, 1.6 roller rockers, springs, retainer, keepers and shims for the respectable price of $500. Add the lifter and retainer kit that uses OEM-style lifters (with an '87-and-later block) for another $192 and a pushrod kit for $24 and you have everything you need to do the conversion with all-new parts. This is a great cam; in a 355ci small-block with Vortec heads and a GM Performance Parts dual-plane intake, it made 412 hp and 422 lb-ft of torque with 9.75:1 compression ("Hot, Hot, Hot, Part II," Nov. '01, pg. 80).


Most people will be retrofitting roller lifters into early pre-'87 small-blocks. The good news is that cam companies have everything you need to pull this off--it's just more expensive than with an OEM roller-cam block. Let's get into the details. The most important point when doing a roller-cam swap in an early block is that the cam not be allowed to move fore or aft in the engine. Flat-tappet cam lobes are ground at a very slight angle to prevent the cam from moving. Roller cams cannot be machined this way, so a roller-cam button is employed to limit cam movement. The spec for this is 0.003 to 0.005 inch. This is because load from the distributor drive gear (which also drives the oil pump) tries to push the camshaft rearward, which usually retards ignition timing. The button prevents this from occurring.

In the old days, engine builders would reinforce the flimsy tin timing-chain covers with a piece of steel welded to the the cover. Now most use cast-aluminum timing-chain covers like those from Bo Laws, Comp Cams, Milodon, and others. If you don't want to spend that $220, you can use an Edelbrock aluminum water pump, which includes a thrust-limiter boss that can use a threaded stud to contact the timing-chain cover and limit deflection. In order to use a hydraulic-roller cam in an early block, you must also use retrofit hydraulic-roller lifters equipped with tie bars that keep the roller lifters from rotating inside the lifter bore. These taller lifters also require a shorter pushrod that is in between the length of a standard small-block flat-tappet pushrod and an OEM replacement roller-lifter pushrod.

Keep in mind that a hydraulic-roller cam will also need much better valvesprings than what worked for a flat-tappet cam. Roller cams tend to pump up the acceleration rate of the lifter, so it's best to step up to a larger-diameter valvespring, like a 1.440-inch dual spring. The best bet is to go with the valvespring recommended by the cam grinder. If you are thinking of using a roller cam with stock iron heads, remember that not all OEM iron heads, especially the older iron castings, can accommodate larger springs. Often if you attempt to cut for larger springs, it's possible to hit a water jacket and ruin the head. So be careful.


As you can see, there's quite a bit more to swapping to a hydraulic-roller camshaft than just buying a cam and lifters. By keeping track of all the details and knowing where the good deals are, it's possible to build a stout small-block without spending all of next year's power budget on this year's fun.


Hydraulic-roller cams (top) are generally built on harder camshaft cores to withstand the higher unit loading pressure of a hardened roller follower. Flat-tappet cams (bottom) are generally hardened cast iron. This is the main reason why roller cams are more expensive.

Hydraulic-roller tappets are 0.630 inch taller than hydraulic flat tappets. The factory compensated by increasing the height of the roller-tappet boss in the block. This increased height also means hydraulic-roller tappets are also much heavier and therefore harder to control at high rpm.

In order to use a hydraulic-roller cam in an early (pre-'87) engine, you must use aftermarket retrofit lifters that use a tie-bar system to prevent the lifter from rotating in its bore.

Roller cams must also not move more than 0.005 inch fore or aft in the block. This roller-cam button is the way to go and fits inside the center hole in the cam gear.

The easiest way to check cam-thrust clearance is with a dial indicator on the back of the cam accessed by removing the rear cam plug. The cam-thrust bearing must not deflect the timing cover.

The elegant solution is a two-piece front timing-chain cover from Bow Laws Products (BLP) or Comp Cams that also offers an access hole for the dial indicator as well as the ability to easily access the timing chain and gear.

If you don't want to invest in a trick timing-chain cover, Edelbrock's aluminum water pumps come with these thrust-limiter mounts that allow you to install a threaded stud to contact the tin timing-chain cover to prevent deflection.

Factory hydraulic-roller-cam blocks use this tin "spider" to place a load on the cast retainers that fit over the stock roller lifters. The spider bolts to three threaded bosses cast into the center of the lifter valley.

When using a roller cam with a mechanical fuel pump, you must use an aftermarket fuel-pump pushrod that offers one of several tips to prevent wear on the steel cam. Comp offers a ceramic tip, bronze tip, or roller-tipped fuel-pump pushrod for these applications.

Pushrod length changes dramatically when converting an older block to hydraulic-roller lifters. Comp Cams' retrofit hydraulic-roller tappets use a 7.300-inch pushrod length while stock flat-tappet engines generally employ a 7.800-inch pushrod. OEM roller-cam engines spec a much shorter 7.200-inch pushrod. As you can see, it pays to pay attention to pushrod length.

Swapping in a hydraulic-roller cam also requires bigger and better valvesprings. Assume you will need to run a 1.440-inch diameter dual spring with good retainers and 10-degree machined locks.

All factory hydraulic-roller-cam blocks employ a step on the front of the camshaft to locate the camshaft behind the factory thrust plate. With the step face, the cam is intended for a hydraulic-roller-cam block. These cams can be used in earlier blocks but will require using a modified late-model thrust plate with the ears removed.

Virtually all street hydraulic- and mechanical-roller cams now come from the major cam companies with iron gears pressed onto the end of the camshaft to allow the use of stock-type iron distributor gears instead of the softer and less durable silicon-bronze gears.


Crane Cams
Daytona Beach, FL 32117
Comp Cams
Memphis, TN 38118
Chevrolet Performance Parts
Detroit, MI 48232
Iskenderian Racing Cams
Gardena, CA 90247-9990

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