Topic: Power From Your Rocker Arms

[bluedevil]

We find out if changing the rocker arm ratio is an effective way to increase horsepower.

It’s a simple premise: increase the ratio of your engine’s rocker arms and you increase the size of the camshaft profile. More camshaft lift means more fuel and air into the engine and more performance - right? It’s a topic we wanted to test first hand 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. No free lunch!




With a small-block Chevy engine used as our guinea pig for the test, the standard 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 beginning to install 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. As noted by COMP Cams Lead Camshaft Engineer Billy Godbold, a rocker ratio change of 0.05 @ .050-inch lift (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 of a difference a degree or two 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 most important to you is that the rocker travel is increased. Along with this increased travel is the fact that the pushrod 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 are not big 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 it. 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. 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.



In addition to watching the pushrod hole contact, there can be conflict with the pushrod guide plate. Cycling the engine before firing 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 expected new valve lift, based on the lobe lift of the cam and the calculated new valve lift. Most late-model factory valve springs are incapable of handling increased valve lift. For instance, changing a 2000 LS6 rocker from stock 1.7 to 1.85 increases valve lift to 0.600-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.




te-model Fords Modular and Dodge Hemi engines follow suite at well. On classic engines, such as this test SBC, it is a good idea to swap in a set of fresh (and capable) valve springs as well – although the stock springs are somewhat more tolerant to increased lift than the springs used on late-model engines. If you go over on valve lift without matching the right spring, they can break, float, or fatigue – resulting in sure disaster. Changing your springs to a high quality, more “adequate” spring just makes great sense.



The Test

Our test at Westech Performance involved use of a fairly typical street configuration engine enhanced with a COMP Cams XE268H hydraulic flat tappet camshaft – recommended for street use, the largest camshaft suggested for stock automatic transmission converter usage. In addition the 383cid engine sported a 750cfm 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 rocker method, we used the COMP Cams stamped steel 1.5:1 ratio Hi-Energy “friction” rockers.




After proper camshaft break, the dyno pulls were completed. As noted in the graphs, the engine made excellent power peaking at 389.9 hp @ 5700 rpm and 407.0 lb. Ft of torque @ 4400 rpm. The engine required little tuning to achieve this figure, impressive power for certain.




Our first test was to install the COMP Cams Pro Magnum roller rockers in the 1.52:1 ratio configuration. With our engine warmed up and ready to go, we found power jumped up nicely. In this case, the torque moved up 5 lb. ft managing 412 lb. Ft from 4540 through 4700 rpm. In the horsepower department, we achieved over 11 more ponies, peaking at 404.1 again at 5700rpm. 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, clearly had made a difference.




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 flavoring. These steel rockers feature the same rebuildable, roller tip and base with a steel body to resist flex. We were not disappointed. Our new peak figures, 422.8 lb. Ft of torque (approx. 10 more lb. Ft.) @ 4700 rpm. In the horsepower arena, a new total of 413.6 hp, (more than 9.5 more hp from the 1.52:1 test and a full 23.7 hp more than the stock figures).


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.” 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 hp. 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 Billy Godbold, COMP Cams’ lead camshaft engineers, he knew of no currently available aftermarket cylinder heads where such a conflict occurs today. The problem is, however, a common one with stock cylinder heads. For such 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 inherent due to the fact that the hydraulic lifters can bleed down reducing lift and duration.




Lessons




So what have we learned? Lesson 1: That increasing the rocker arm ratio can increase the power and torque resulting 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 moved to the true Pro Magnum roller rocker arm, a significant part of the performance gain was a combination of the reduced roller rocker friction and the increased rocker ratio. Separating them for out test was not possible. Lesson 4: Overall, we netted a 5 percent increase in both power and torque – not bad for a seemingly simple true bolt on change.




Need to know if this will work for you? Call the COMP Cams Tech line and ask about your application. You may be pleasantly surprised. This test proved the small step horsepower improvements that are possible with such as swap. For those looking for even more power and durability, there are more complete valve train 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.




Sidebar:




Rocker Terms 101




Rocker Geometry
Rocker arm geometry is absolutely critical to valve train stability, durability, and accuracy. The relationship between the shaft height and the tip of the valve is a significant factor in valve train geometry. The correct shaft position will ensure that the roller tip of the rocker arm will be located at the same position on the valve tip no matter if the valve is closed or at full lift. With the valve closed, the roller should be slightly ahead of the valve stem centerline, moving to slightly ahead of stem centerline at mid lift, moving back to slightly behind stem centerline at full lift.




Mass Moment Of Inertia
Mass moment of inertia is the relationship between the center of
gravity (CG) of an object with a geometrically irregular shape, and its rotational axis. The further the CG is from the axis of rotation, the higher the mass moment of inertia. The higher the mass moment of inertia, the more spring pressure is needed to control the rocker arm instead of the valve. The more the mass moment of inertia is reduced, the higher the operational RPM capability of the engine goes up.




Sidebar #2




Gross Valve Lift Explained




Piston to valve clearance, like many other engine characteristics, is highly variable between individual engines. The consequence of not checking for yourself (or having your engine builder or mechanic check it) is that should your camshaft have more lift than clearance, you could easily wind up bending your valves, or worse, punching holes in your pistons with them -necessitating anything from a full engine teardown to a ground-up engine replacement.




Note the following equations for figuring out what effect altering rocker arm ratios has on valve lift -as an example, we’ll look at a common rocker ratio swap. Small Block Chevy, switching from the factory 1.5-1.52:1 ratio to a 1.6:1 ratio. Assuming a 0.500-inch lift camshaft (based on a 1.5:1 ratio); we will first need to calculate camshaft lobe lift. The lobe lift equation is as follows:




Valve lift/Rocker Ratio = Lobe Lift




Plugging in the numbers for our current cam and rocker ratio gives us 0.500/1.5, which equals 0.333-inch of lobe lift.
Rearranging the equation a bit gives us the means of figuring our gross valve lift with the new rocker ratio:




Lobe Lift X Rocker Ratio = Valve Lift




Inserting the specs for our cam and prospective rockers gives us 0.333 X 1.6, which equals 0.534-inch –a substantial difference in lift. Note that a lot of guys like to say “switching to a 1.6 from a 1.5 gives .030-inch more lift!” –this is true in some cases, but as this number is a ratio, not a constant, it is unwise to assume that the lift increase will be any set number –do the math, record the numbers, and verify that you have clearance, and you’ll never have to guess or worry about putting a valve through your brand new forged racing pistons! Also, remember that if you are running a split pattern cam with a difference in lift between the intake and exhaust lobes, you’ll want to do the equation twice (once for each lobe) in order to accurately calculate your gross valve lift. And last but not least, when swapping to a higher rocker arm ratio, you must verify that you have enough valve spring coil bind clearance to accommodate the increased lift.




Sources:
COMP Cams
Memphis, TN 38118
(800) 999-0853


Westech Performance
Mira Loma, CA
(951) 685-4767


The stock factory rockers are rated at 1.5:1 but for out rest we installed these new COMP Cams High Energy rockers as they were in much better condition and much higher quality.


These COMP Cams Magnum rockers 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.


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


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.


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


These COMP Cams Pro Magnum rockers 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. These are amazingly strong rockers and capable of ultra high rpm use.


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.

[Main One]

Good info!   :thumb:

[KY_BOB]

At one time I strongly considered a set of SLP 1.85 ratio rockers but they cost almost as much as a cam.  :-\

Also, the Gen3 truck valve springs are pretty close to maxed out even with a stock cam and rockers.  I did talk to a SLP rep at a Corvette show about this and he told me that it would be a good mod even with the stock springs if you stayed at rpm of the factory tune.  I'm spinning mine more than stock and Main One is spinning his more than me.  They would probably work fine with stock springs but "probably" scares me a little.

On a personal note, I would be more scared to do this with my stock springs than on a NA engine.  FI put pressure on the intake valve (not very much but some) when under boost making valve float occur easier than on a NA engine.


That article is very informative but I'm not sure that this is the most cost effective mod for the buck on our trucks.

[FlaBouy]

This is one of two of the unique mods in my motor buildout that puts my motor over the 600HP mark... the other is is setting the cam at 5*.........

[KY_BOB]

This is one of two of the unique mods in my motor buildout that puts my motor over the 600HP mark... the other is is setting the cam at 5*.........

I certainly agree that rocker arms can increase power.  I do however feel that it's not the most bang for the buck for a otherwise stock motor.  Your motor is nowhere near stock.


If someone wants to give me a set, I'll be glad to install them.  ;D

[FlaBouy]

Not sure I understood we were talking about a stock motor. When spinning up the rpms on even a stock motor, you get into valve float at around 5800 rpm or so. I believe this is why GM tuned the stock tune to 5400-5600 rpm shifts. Granted this is due to weak springs, but if you are considering boost at high RPM (or higher than stock rpm), I think new dual springs are in order. While we are in there changing the springs, we might as well get at least a higher ratio rocker..... I even went one step further and got an accelerated lift higher ratio rocker.

What did all that gain me? Instead of the expected 60-65 HP gain with the head/cam/rocker package, we saw over 100 rwhp gain on the dyno. The combination used in the selection of all the components as a package can sometimes be major factor in exceeding even the expectations of your designer/installer.

Is a rocker package worth it in and of itself? Dunno.... but when added to other considerations it might just net you an advantage or two over the competition......

[KY_BOB]

The thought has crossed my mind that a set of LS6 springs (which are cheap) and 1.85 ratio rockers might be worthwhile.  It would be a heck of a lot easier than a cam swap and would still give me more rpm to in turn build more boost as well as a little increase in lift for better flow. 

Two things have stopped me from trying this, cost of the rockers and the fact that LS6 springs wouldn't handle a aftermarket cam if I did change it later and would require being replaced again.

 

[FlaBouy]

The thought has crossed my mind that a set of LS6 springs (which are cheap) and 1.85 ratio rockers might be worthwhile.  It would be a heck of a lot easier than a cam swap and would still give me more rpm to in turn build more boost as well as a little increase in lift for better flow. 

Two things have stopped me from trying this, cost of the rockers and the fact that LS6 springs wouldn't handle a aftermarket cam if I did change it later and would require being replaced again.

 

Comp 918's or Patriot Golds should get you beyond .600 lift....   and if you go to the expense of the rockers... talk to Vinci on their accelerated lift 1.85's..... I am stopping just shy of .600" lift on my truck with lightning fast opening and closure rates on the valves.... helps with the scavenging while running the 2.02 titanium valves with the stock bore block...... that coupled with lack of cats helps my truck breathe better than a bottle of fine wine.... ;D


oh, did I mention my truck idles like stock?   :o

[Main One]

Ahhh.  It's so nice to have you guys talking performance on a forum where I can ask a question if I need some clarification!  Good to see you here FlaBouy!   :thumb:

[FlaBouy]

Ahhh.  It's so nice to have you guys talking performance on a forum where I can ask a question if I need some clarification!  Good to see you here FlaBouy!   :thumb:

Had to move somewhere...I think I wore my welcome out on the other site... Something about you cannot build horsepower without destroying your truck and using all the broken pieces to verify that you indeed have built horsepower, and since you were running through the traps when it broke, then you must indeed have the fastest truck since you were on a NHRA track to start with. We all know there are no other verifiable means to gauge 0-60 or 0-100 mph to a thousanth of a second... ;)

Give it time...I bet I piss all you guys of too......

BTW..back to the thread....   My jewels....