Full Answer
What is a rocker arm ratio?
The rocker arm ratio multiplies the lift on the cam lobe and applies it to the valve. (Follow this link to learn more about Camshaft Lift .) For example, if the cam provides 0.312 in. of lobe lift and uses 1.5 rockers, the valve will lift 0.468 in. How do I know what my rocker ratio is? Most rocker arms have the ratio marked on them.
What size rocker arms do I need for a 320 lobe?
For instance, a cam with a .320-inch lobe lift and a 1.5-ratio rocker arm will have .480 inches of valve lift (.320 inches x 1.5 = .480 inches). If you were to install 1.6-ratio rocker arms, the valve lift would increase to .512 inches (.320 inches x 1.6 = .512 inches).
How much valve lift do I need for a rocker arm?
For instance, a cam with a .320-inch lobe lift and a 1.5-ratio rocker arm will have .480 inches of valve lift (.320 inches x 1.5 = .480 inches). If you were to install 1.6-ratio rocker arms, the valve lift would increase to .512 inches (.320 inches x 1.6 = .512 inches). The engine will respond as if a slightly larger lift cam had been installed.
What is the rocker ratio for COMP Cams?
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.
What ratio are stock rocker arms?
The rocker arm ratio is the relationship between the 2 halves of the rocker arm. The halves are: The center of the valve stem to the center of the pivot point....How do I know what my rocker ratio is?Engine TypeStock Rocker Arm RatioChevy LS71.8Gen. 5 Chevy LT Engines1.8Big Block Chevy1.7Small Block Ford1.62 more rows•Feb 6, 2019
What is the stock rocker arm ratio for a small-block Chevy?
1.5:1 ratioEven though Chevrolet made the decision easy for us when it engineered the small-block to run around a 1.5:1 ratio, (Comp Cams says most stock rockers are actually about 1.46:1), it's well known that the inconsistencies of stock rockers and the friction and heat they create mean there's power lost with them.
What does 1.5 mean on rocker arms?
One of the most popular ratios is 1.5, and what exactly does that mean? It means the rocker arm will open the valve 1 and a ½ times the amount the cam moves the lifter and the push rod, or what cam manufacturers refer to as cam or lobe lift.
How do I know what rocker arms I need?
2:5916:04How to Choose the Right Rocker Arms - YouTubeYouTubeStart of suggested clipEnd of suggested clipApplication under 5000 rpm uh torque engine off-road you know type of engine where it's low rpm aMoreApplication under 5000 rpm uh torque engine off-road you know type of engine where it's low rpm a lot of torque.
How much lift does 1.6 rockers add?
With a 1.6:1 rocker, this gives us 0.508-inch valve lift at max lift, an increase of 0.031 inch. It doesn't sound like much, yet it was enough to show a sizeable gain, mainly because it increases the amount of time that the valves are open at higher lifts, allowing more air to flow through the heads.
What do higher ratio rockers do?
A high-ratio rocker arm increases valve lift at every point. It boosts gross valve lift by several hundredths of an inch, but it can make a camshaft seem a few degrees larger as well.
Do changing rocker arms increase horsepower?
Whether you're dealing with a mostly stock junkyard small-block or a highly modified race engine, rocker arms play a big role in freeing up horsepower and helping reduce friction in the valvetrain.
How much HP do roller rockers add?
Most rocker arms are designed to increase the lift of the cam by having a positive ratio. Rocker arms are commonly designed to increase lift at the valve by about 1.3 to 1.6 times the lift at the cam. This setup also slightly increases duration, but not by the same ratio.
How does rocker arm ratio affect lift?
Essentially, changing to a rocker arm ratio that is larger, is comparable to increasing the lift of your camshaft. Increasing the opening distance of both valves can usually increase power because your engine can move more air.
Are roller rockers better than stock?
Besides the potential power benefits of an increase in rocker ratio, roller rockers have several additional power-adding advantages compared with a stamped rocker. The advertised ratio of aftermarket roller-tip rockers is more accurate than the claimed ratio of typical stock stamped rockers.
How do you calculate valve lift with rocker ratio?
of valve lift with a 1.6 rocker ratio. Valve Lift = 0.270 x 1.6 = 0.432 in. Example #2: A camshaft with 0.468 in. of valve lift with a 1.5 rocker ratio has 0.312 in.
How can I improve my cam lift?
Besides grinding a lobe with more lift, you can increase the lift of an existing cam profile by going to a higher rocker arm ratio. For example, small-block Chevys where the cylinder head runners are not maxed out may benefit from moving up from the stock 1.5:1 ratio to 1.6:1 rockers.
How much does a rocker ratio increase valve lift?
For example, going from 1.5 to 1.6 rockers on a SBC will increase valve lift by about 0.030 in.
How do I know what my rocker ratio is?
Most rocker arms have the ratio marked on them. If you look and can’t find a marking, you will need to measure.
Where is the dial indicator on a valve?
When the valve is fully closed, set up your Dial Indicator so it rests on the tip of the valve stem.
Do you need pushrods for proper geometry?
To maintain proper geometry, you might need New Pushrods.
What does "rocker arm" mean?
It means the rocker arm will open the valve 1 and a ½ times the amount the cam moves the lifter and the push rod, or what cam manufacturers refer to as cam or lobe lift.
Which side of the pushrod is 1.5 times longer?
The valve side Y will be 1.5 times longer than the pushrod side X
Does rocker arm increase horsepower?
Typically increasing rocker arm ratio will increase horsepower at higher RPMs but there are some drawbacks such as less power at lower RPM’s and more stress on the engines valve train as well as the rocker arm itself, and as always make sure there is sufficient valve to piston clearance.
jimmer Well-Known Member
What is the easiest way to tell what ratio that my stock small block rocker arms really are ? I know mopar syas they are 1.5 ? I have heard they really very to as low as 1.3 ? I have a 292/509 cam in the 360, I don't really want to open my wallet for roller rockers. I do know many people have run the stock rockers with know problems.
70aarcuda Master Hoader of SBM FABO Gold Member
put a set of 1.6 rockers on it...then you will be all that you can be....
jimmer Well-Known Member
Not trying to be a jerk lonewolf ? No wonder you call yourself lonewolf . J/k Well I have like 3 different sets of stock rocker arms from what I have been told they very . So if I can check them I will use the set with the most ratio. That is why I ask. I have used the same cam in a different 340 and it worked well with stock rockers.
70aarcuda Master Hoader of SBM FABO Gold Member
the rocker ratio will vary within a set as the production tolerance vary also...only way to know..is the mock up and check EACH rocker...
What is the rocker arm ratio?
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.
What happens when you increase the ratio of your engine's rocker arms?
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.
What is the ratio of a camshaft to a rocker?
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.
Why increase rocker ratio?
An increased rocker ratio will increase the effective lift of the camshaft specifications at the valve. But it also affects the duration.
How much does horsepower drop on pushrods?
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.
What is the lesson 2 of the pushrod?
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.
How to increase lift at valve?
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.
How Is It calculated?
What Does It do?
- The rocker arm ratio multiplies the lift on the cam lobe and applies it to the valve. (Follow this link to learn more about Camshaft Lift.) For example, if the cam provides 0.312 in. of lobe lift and uses 1.5 rockers, the valve will lift 0.468 in.
How Do I Know What My Rocker Ratio is?
- Most rocker arms have the ratio marked on them. If you look and can’t find a marking, you will need to measure. 1. Rotate the engine by hand and watch the valve. (Any valve on any cylinder will do.) 2. When the valve is fully closed, set up your Dial Indicatorso it rests on the tip of the valve stem. 3. Set the dial to zero. 4. Rotate the engine by hand. Watch the dial. 5. Note the max lift me…
How Does It Affect Performance?
- Increasing rocker ratio is the same as installing a higher lift camshaft. For example, going from 1.5 to 1.6 rockers on a SBC will increase valve lift by about 0.030 in. Before installing rocker arms with a higher ratio, you should consider the following: 1. Added lift could cause Coil Bind. 2. You could have an issue with Piston to Valve Clearance. 3. To maintain proper geometry, you might n…