Rock Your World: Maximizing Your Cam’s Potential With Better Rockers

How can changing rocker arm ratios be an easy way to increase the effective size of your camshaft? It’s simple really, when you increase the ratio of your engine’s rocker arms, you increase the size of the camshaft profile. More camshaft lift means more fuel and air enter the engine and deliver more performance – right? It’s a topic we wanted to test first hand, in order to check the reality of what seemed to be a logical concept. But as we were to find out, there were some far more interesting ramifications that occurred.

It was a test of what seemed to be an obvious free lunch – increase the rocker arm ratio and you increase the effective size of your camshaft. But as we were to learn, while there were some great advantages, there were some things that required our attention to avoid long-term problems.

We chose a small-block Chevy engine as our guinea pig for the test, and the standard rocker arm ratio is listed at 1.5:1. However, through testing at the COMP Cams research lab, the actual ratio for the standard stamped steel rocker arms are generally in the realm of a 1.46:1 ratio.

To pick up the effective specifications of the camshaft, both the COMP Cams Magnum and Pro Magnum rockers utilize a 1.52:1 ratio, which helps to wake up most enthusiast-level street-use and racing engines with no other required modifications.

As you will see from our testing, this simple move nets a nice little lift in power and torque, with the added benefit of the low-friction roller rocker technology.

As any non-engineering type enthusiast can tell by looking, the roller tip contact used to depress the top of the valve stem is a significantly better system than the friction-heavy stamped factory rockers where the tip simply moves down while sliding across the valve dependent on proper oiling to operate.

Things to Watch For

Before installing increased-ratio rocker arms, it is important to understand the dynamics of what happens when you start messing with these parts. An increased rocker ratio will increase the effective lift of the camshaft specifications at the valve. But it also affects the duration.

Simply demonstrated, the rocker ratio is the leverage comparison measured between these points. For a 1.5:1 ratio, the distance for “Y” is 1.5 times the size of “X.”

As noted by COMP Cams’ Lead Camshaft Engineer Billy Godbold, “a rocker ratio change of 0.05 (such as from 1.50:1 to 1.55:1), will add approximately a degree of duration along with that obvious enhanced lift.”

While that may seem inconsequential to most, think about how much a one or two degree difference means to lobe separation dimensions. This is important information that you should know before you start the modification process.

Next, there are a number of geometric changes that occur when you change rocker arm ratios. Probably the most important to you is that rocker arm travel is increased. Along with this increased travel, the pushrod also moves closer to the rocker mount.

In many engines, that is not a problem. But for some engines, including the venerable small-block Chevy, the stock pushrod holes through the cylinder head are not large enough to compensate for that movement. In many cases, the pushrod will actually contact the pushrod hole in the head.

When this occurs, there are several ways to handle the situation. First, you can assess the benefit of the high-ratio rockers, and whether such a change is right for needs. If you feel it is worth keeping the high-ratio rockers, you can enlarge the size of the pushrod holes. Lest you believe you are breaking new technology here, there are many who have encountered the problem before you.

Coil bind (the point when the spring ceases to spring and becomes a block of steel) is bad and will cause catastrophic damage to your engine. Before completing any rocker ratio swap, make sure you have proper valve springs that are in good condition and appropriate for an increased rocker ratio swap without encountering coil bind.

There is even a COMP Cams available fix, the Louis tool (COMP Cams PN# 4710) which will provide adequate clearance. In most heads, especially in the case of our small-block Chevy, there are no port or water jacket concerns in the area surrounding the pushrod hole.

The stock factory rockers (left) are rated at 1.5:1 but for our test, we installed these new COMP Cams High Energy rockers, since they were in much better condition and much higher quality. These COMP Cams Magnum rockers (right) utilize the same ball and stud mount as found with the factory and High Energy rockers, but have the added benefit of a roller tip that reduces friction and even engine oil operating temperature.

In addition to watching the pushrod hole clearance, there can be conflict with the pushrod guide plate. Cycling the engine before starting it will help note any potential contact in this area. If there is concern, changing to larger pushrod guide plate openings or machining them for additional area will avoid such power robbing interference.

While all this talk about interference and increase valve lift is great, one item has been left out of the discussion entirely to this point – valve springs. It is critical to make certain your valve springs are “adequate” to accommodate your new expected valve lift, based on the lobe lift of the cam and the calculated new valve lift.

Changing to a higher-ratio rocker arm will increase lift at the valve. It is important to know how close your valves are to contacting the pistons at all times. Don’t go blindly into rocker ratio swaps, or valve to piston contact could become a problem.

Most late-model factory valve springs are incapable of handling increased valve lift.  For instance, changing a 2000 LS6 rocker from the stock 1.7 to 1.85 ratio, increases valve lift to .600-inch – well beyond the safe capability of the factory spring. In a case like this, the high-ratio rocker swap should include a matching spring swap as well.

Late-model Ford Modulars and Dodge Hemi engines follow suite at well. On classic engines, such as our test SBC, it is a good idea to swap in a set of fresh valve springs a well – although the stock springs are somewhat more tolerant to increased lift than late-model pieces. If you increase valve lift without matching the right spring, the springs can break, float, or fatigue – resulting in disaster. Changing your springs to a high quality, more “adequate” spring just makes sense.

The Test

Our test at Westech Performance involved the use of a fairly typical street engine, enhanced with a COMP Cams XE268H hydraulic flat tappet camshaft – recommended for street use, this is the largest camshaft suggested for stock automatic transmission converter usage. In addition, the 383 cubic-inch engine sported a 750 cfm Speed Demon carburetor, dyno headers, and TFS aluminum cylinder heads.

We had been advised by COMP that the stock steel rocker arms were so bad, that we would not get a consistent dyno number if they were used – even for the baseline test. For our test and to simulate the factory rockers, we used the COMP Cams’ stamped steel 1.5:1 ratio Hi-Energy “friction” rockers.

After proper camshaft break in, the dyno pulls were completed. As noted in the graphs, the engine made excellent power, peaking at 389.9 horsepower at 5,700 rpm and 407.0 lb-ft of torque at 4,400 rpm. The engine required little tuning to achieve this figure.

Guide plates are critical with many engine applications, and cannot interfere with pushrod movement, which is changed when rocker ratio is altered.

Our first test was to install the COMP Cams 1.52:1 ratio Pro Magnum roller rockers. With our engine warmed up and ready to go, power jumped up nicely. In this case, the torque moved up 5 lb-ft, managing 412 lb-ft from 4,540 through 4,700 rpm.

In the horsepower department, we achieved more than 11 ponies, peaking at 404.1 horsepower, again at 5,700 rpm. In addition, we noticed a lower engine oil operating temperature – a nice benefit as well, the reduced rocker arm/valve step friction, and the slight rocker ratio increase, had clearly made a difference.

With some OE heads such as these early Chevrolet units, the pushrod holes are very small. A change in rocker ratio will create contact between the pushrod and the inside edge of the hole. To fix that problem, a Louis tool is used to mill out the hole providing greater clearance.

Step two of our rocker ratio test involved the usage of the COMP Cams Pro Magnum roller rockers, this time with a 1.6:1 ratio. These steel rocker arms feature the same rebuildable roller tip and base, with a steel body to resist flex.

We were not disappointed.  Our new peak figures were 422.8 lb-ft of torque (approx. 10 more lb-ft) at 4,700 rpm. In the horsepower arena, a new total of 413.6 horsepower, (more than 9.5 from the 1.52:1 test, and a full 23.7 more horsepower than the stock figures).

Cycling through the engine rotation and checking all clearances and valve spring bind conditions is a good idea.

The Rub

The improvement witnessed with the two rocker ratio changes had us optimistic concerning our final test with the 1.65:1 ratio COMP Cams Hi-Tech stainless steel rockers – after all the racer motto seemed to be ringing true here – “if a little is good, more is better and too much is just right.” Unfortunately, we were about to witness “too much.”

As noted earlier, the higher the rocker ratio, the more the movement of the pushrod closer to the valve spring.  The 1.65:1 ratio rocker was to result in only slightly higher power and torque – approximately one or two horsepower. So why no leap in performance? Simple – as promised, the pushrod came in contact with the pushrod hole.

In all fairness, the heads were are using were not the newest versions. In discussions with  Godbold, he knew of no currently-available aftermarket cylinder heads where such a conflict occurs. The problem is, however, a common one with stock cylinder heads.  For such a problem, the Lewis tool is the easy remedy.

So how did we determine that this was the problem? The lack of horsepower/torque increase, and the witness marks on the pushrod itself. In extreme cases, we have been told that horsepower and torque can drop by as much as 10 percent, and result in major damage. While the obvious parts wear is a problem, there is another problem due to the fact that the hydraulic lifters can bleed down reducing lift and duration.

These COMP Cams Pro Magnum rockers (left) features all steel construction and roller bearings to reduce frictional losses found with factory units. They come in a variety of different rocker ratios for a wide variety of engine applications. For our 1.65:1 ratio test, we used these high performance COMP Cams Hi-Tech rocker arms (right). These are amazingly strong rockers and capable of ultra high rpm use.

Lessons To Be Learned

So what have we learned?

Remember, quality valve springs are not only the most overlooked performance component in your engine, but also one of the most critical to making power. When changing rocker arm ratios, it is a good idea to change springs as well to achieve the most from this kind of swap.

Lesson 1: That increasing the rocker arm ratio can increase the power and torque from your engine.

Lesson 2: There are potential conflicts that can occur between the pushrod and the cylinder head, and camshaft duration is also affected as well as lift.

Lesson 3: it is believed by the COMP Cams tech folks, that when we used the Pro Magnum roller rocker arms, a significant part of the performance gain was a combination of the reduced roller rocker friction, and the increased rocker ratio. Separating them for our test was not possible.

Lesson 4: Overall, we netted a 5 percent increase in both power and torque – not bad for a seemingly simple change.

If you need to know if a rocker arm ratio upgrade will work for you, call the COMP Cams Tech line and ask about your application. You may be pleasantly surprised. This test verified the horsepower improvements that are possible with such as swap.  For those looking for even more power and durability, there are more complete valvetrain upgrades that can be had for not a lot more money. The COMP Cam tech guys can be very helpful guiding you to the right part for your engine.

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