Lunati Technical Information

The following collection of technical information should provide a basic understanding of everything from learning cam profile terms to more advanced topics such as verifying your valvetrain geometry.

Understanding Cam Profile Terms

RAMPS The parts of a camshaft lobe that actually initiate the lifting and descending movement of the lifter are called "ramps". Ramps include the lash ramp, the opening ramp, and the closing ramp. Camshaft lobe ramps are ground to have different rates of lifter movement in terms of velocity and degrees of duration, as measured in degrees of crankshaft rotation.

The "lash ramp" of a camshaft lobe is a mid-point location between the opening ramp and closing ramp.

The "opening ramp" of a camshaft lobe is the point where the lifter just begins to lift until the point that it reaches the nose of the lobe.

The "closing ramp" is the point of the camshaft lobe from the nose back down to the lash ramp.

NOSE The "nose" of a camshaft lobe is the top or the highest maximum lift point for the valve. It is where valves are kept open for as long as possible before making the transition to the closing ramp.

BASE CIRCLE The "base circle", also known as the "heel", is the lowest point of the camshaft lobe and is the place where the valve is in the closed position. The "base circle" is the point where all valve lash settings are made.

SYMMETRICAL is a term that refers to the "profiles" of the opening and closing ramps of a camshaft lobe. All "early technology" camshafts were ground on a symmetrical design, meaning both sides are exactly the same. That is to say the profile of the closing ramp is a "mirror image" of the opening ramp.

ASYMMETRICAL refers to a camshaft lobe profile where the opening and closing ramps are not exactly the same. The reason some camshafts are this way is to try to achieve an opening ramp profile that has a high velocity and a closing ramp profile that has a slower velocity. In this way the valve can be set down more "gently" than the rate at which it was first opened.

A DUAL PATTERN camshaft has an intake lobe profile design that differs from that of the exhaust lobe profile design. For example, camshaft "A" has intake lobes of 260 degrees duration while the exhaust lobes are 270 degrees duration. Camshaft "B", has intake and exhaust lobes that are both at 260 degrees. Camshaft "A" is referred to as a dual pattern, while camshaft "B" is referred to as a single pattern.

With the advent of emissions laws and the widespread use of computer systems, more modern single and dual profile pattern designs have been developed. A dual pattern camshaft is ground to "bias" the duration of either the intake or exhaust lobe. For example, if an engine is restricted on the exhaust side, compared to the intake side, the camshaft designer would try to compensate by grinding in more lift and/or duration on the exhaust lobe.

Why must I install new lifters with my new camshaft?

If you are installing a new flat tappet camshaft in your engine, you must install new lifters. The lifter/lobe contact area is under a tremendous amount of pressure, and the lifter and lobe must wear in together. The following illustration demonstrates why:

Understanding Camshaft Specifications

LIFT

Lift refers to maximum valve lift. This is how much the valve is "lifted" off its seat at the cam lobe’s highest point.

How is it measured?

Cam Lobe Lift Valve Lift is the amount (usually in inches) that the valve is lifted off of its seat. It is usually measured with a dial indicator at the tip of the valve. Lobe Lift is the amount (usually in inches) that the cam lobe increases in radius above the cam base circle.

Tip: To quickly find maximum lobe lift, measure the base circle of the cam and subtract it from the thickness across the cam lobe’s highest point (see the diagram below).

Tip: Maximum valve lift can be calculated by multiplying the maximum lobe lift times the rocker ratio. For example, a 0.310" lobe lift cam yields 0.496" of valve lift when using a 1.6 ratio rocker arm.

Formula: valve lift = lobe lift x rocker ratio

What does it do?

The intake and exhaust valves need to open to let air/fuel in and exhaust out of the cylinders. Generally, opening the valves quicker and further will increase engine output. Increasing valve lift, without increasing duration, can yield more power without much change to the nature of the power curve. However, an increase in valve lift almost always is accompanied by an increase in duration. This is because ramps are limited in their shape which is directly related to the type of lifters being used, such as flat or roller.

DURATION

Duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the cam lobe.

How is it measured?

Advertised duration is the angle in crankshaft degrees that the cam follower is lifted more than a predetermined amount (the SAE standard is 0.006") off of its seat. Duration @.050" is a measurement of the movement the cam follower, in crankshaft degrees, from the point where it’s first lifted .050" off the base circle on the opening ramp side of the camshaft lobe, to the point where it ends up being .050" from the base circle on the closing ramp side of the camshaft lobe. This is the industry standard, and is a good value to use to compare cams from different manufacturers. Both are usually measured with a dial indicator and a degree wheel.

What does it do?

Increasing duration keeps the valve open longer, and can increase high-rpm power. Doing so increases the RPM range that the engine produces power. Increasing duration without a change in lobe separation angle will result in increased valve overlap.

LOBE SEPARATION

Lobe separation is the angle in camshaft degrees between the maximum lift points of the intake and exhaust valves. It is the result of the placement of the intake and exhaust lobes on the camshaft.

How is it measured?

Cam Lobe Separation Lobe separation can be measured using a dial indicator and a degree wheel, but is usually calculated by dividing the sum of the intake centerline and the exhaust centerline by two.

What does it do?

Lobe separation affects valve overlap, which affects the nature of the power curve, idle quality, idle vacuum, etc.

OVERLAP

Overlap is the angle in crankshaft degrees that both the intake and exhaust valves are open. This occurs at the end of the exhaust stroke and the beginning of the intake stroke. Increasing lift duration and/or decreasing lobe separation increases overlap.

How is it measured?

Overlap can be calculated by adding the exhaust closing and the intake opening points. For example, a cam with an exhaust closing at 4 degrees ATDC and an intake opening of 8 degrees BTDC has 12 degrees of overlap. But keep in mind that since these timing figures are at 0.050" of valve lift, this therefore is overlap at 0.050". A better way to think about overlap is the area that both lift curves overlap, rather than just the crankshaft angle that both valves are open. Therefore, one can see that decreasing the lobe separation only a few degrees can have a huge effect on overlap area.

What does it do?

At high engine speeds, overlap allows the rush of exhaust gasses out the exhaust valve to help pull the fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances the effect. Increasing overlap increases top-end power and reduces low-speed power and idle quality.

CENTERLINES

The intake centerline is the point of highest lift on the intake lobe. It is expressed in crankshaft degrees after top dead center (ATDC). Likewise the exhaust centerline is the point of highest lift on the exhaust lobe. It is expressed in crankshaft degrees before top dead center (BTDC). The cam centerline is the point halfway between the intake and exhaust centerlines.

ADVANCE/RETARD

Advancing or retarding the camshaft moves the engine’s torque band around the RPM scale by moving the valve events further ahead or behind the movement of the piston. Typically, a racer will experiment with advancing or retarding a cam from "straight up" and see what works best for their application. Lunati camshafts are ground to provide maximum performance and are designed to be installed to the specifications listed on the cam card.

How is it measured?

A cam with a 107 degrees intake lobe centerline will actually be centered at 103 degrees ATDC when installed 4 degrees advanced.

Most Lunati camshafts have a certain amount of advance ground in. "Ground-in advance" can also be found by subtracting the intake lobe centerline from the lobe separation.

What does it do?

Advance improves low-end power and response. For a general summary of the affects of camshaft timing, refer to the following tables:
Valvetrain Understanding

Understanding The Different Types Of Camshaft Lifters
The cam lifter (also called a "follower" or "tappet") is the component that makes direct contact with the cam lobes and "follows" the profile of the cam. There are generally four types of lifters:

Hydraulic Flat Tappet

The hydraulic flat tappet is self-adjusting, due to the valve controlled plunger within the tappet body. It operates to pre-load the push-rod by using the oil system pressure to maintain this pre-load in the closed valve position. Hydraulic tappets are quieter than mechanical tappet lifters since there is no lash or free-play. However, it is generally agreed that they fall short of offering optimum performance above 6,000 - 6,500 RPM. Many cheaper designs fall even shorter than this. This poor performance at high RPM is due mainly to the inability of the lifter to "bleed down" the excessive oil pressure , and thus does not allow the valves to seat.

Mechanical Flat Tappet

The mechanical (solid) tappet is essentially a solid "link" between the cam lobe, and the push-rod. In most cases it is a simple heat-treated cylinder with a radiused contact face. It allows more RPM potential than that of the hydraulic tappet since there are no worries about the inability of the lifter to "bleed down." Solid lifters do, however require lash or clearance to allow for part expansion as the engine heats up.

Mechanical Roller Tappet

The mechanical (solid) roller tappet allows for the most aggressive lobe designs. Roller tappets allow faster, "steeper" opening and closing ramps. This allows the cam to produce more lift for a given duration. They are not limited to a particular lifter diameter to obtain higher cam lifts. They also contain a roller that reduces friction between cam and followers. Roller cams require the use of higher valve spring forces making high engine speeds (over 10,000 RPM’s) possible.

Hydraulic Roller Tappet

The hydraulic roller tappet camshaft can provide the best of both worlds. Diesel engines and some motorcycle engines have used this design for many years. They provide most of the virtues of a solid mechanical roller tappet while providing the benefits of quiet operation and ease of valve lash setting.

This type of design still has the limitations of an oil bleed-off control type follower. If your application requires high RPM potential you should use a solid roller tappet design.

How To Verify Valvetrain Geometry

The following is a method of verifying proper valve train geometry. After you have estimated the required pushrod length using a Lunati Pushrod Length Checker, use this method to verify that the valve train geometry is correct (using the rockers you are using in your engine.)

1. The first step is to install a solid lifter and an adjustable pushrod. Mark the tip of the valve with a marker.

2. Install your rocker arm and set it up with zero lash. Rotate the crankshaft clockwise several times. Remove the rocker arm. The contact pattern of the rocker tip will be where the marker has been wiped away from the valve tip. The pattern should be centered on the valve tip, and as narrow as possible. If it is not, experiment with varying the pushrod length to yield the best pattern.

3. Rotate the crankshaft clockwise several times. Remove the rocker arm. The contact pattern of the rocker tip will be where the marker has been wiped away from the valve tip. The pattern should be centered on the valve tip, and as narrow as possible. If it is not, experiment with varying the pushrod length to yield the best pattern.

4a. Pushrod Too Long: Notice how the pattern is wide, and shifted to the exhaust side of the valve tip

4b. Pushrod Too Short: Notice how the pattern is wide, and shifted to the intake side of the valve tip.

4c. Pushrod Length Correct: Notice how the pattern is narrow and is centered on the valve tip.

Valve Spring Tech
Valve Spring Pocket Clearance

Valve spring pocket clearance is the gap between the inside diameter of the valve spring pocket (or cup, if used) and the outside diameter of the valve spring.
- Too much clearance will result in the spring "dancing" around in the head, which "beats up" the spring mounting surface and the spring itself. If this is the case, a spring cup may be used. Additional machining of the spring pocket may be required to accept the spring cup.
- Not enough clearance will bind the spring in the pocket, overstressing the bottom coil by limiting its movement and not allowing the spring to "grow". This will cause the bottom coil to wear against the head and/or prematurely fail. Machine the valve pocket using a Spring Seat Cutter if not enough clearance exists.
Valve Spring Retainer Fit

The valve spring retainer should fit the valve spring being used. A slightly snug fit is acceptable, however a fit that is too tight can overstress the top coil, and cause it to fail. A fit that is too loose can lead to spring "dancing."

Valve Spring Installed Height

The installed height of the valve spring is the distance between the valve pocket (or cup, or shims) and the outer edge of the spring retainer (which is the height of the valve spring) when the valve is closed. To check installed height, follow the following procedure:
- Install the valve in the guide.
- Install the retainer and valve locks.
- Install all spring cups and/or valve spring shims (basically, everything except the valve spring).
- Hold the valve closed by pulling the retainer up tightly against the valve locks.
- Measure the distance between the outside edge of the valve spring retainer and the spring seat. A snap gage or a height micrometer should be used.
- Check the distance against what is recommended on the camshaft specification card. An installed height of +/- 0.020" is acceptable.
- If the installed height is not within 0.020", either machining of the valve pocket, or removal/installation of valve spring shims is necessary.
- Repeat this procedure for the rest of the valves.
Valve Spring Retainer to Valve Seal Clearance

The distance between the innermost step on the valve spring retainer and the valve guide must be 0.090" larger than the maximum valve lift of the camshaft. Measure the distance between the top of the valve seal to the bottom of the valve spring retainer. After adding 0.090" to your measurement, it should still be larger than the maximum valve lift of the camshaft. If not, machining of the valve guide in necessary for adequate clearance.

Valve Spring Coil Clearance

Coil clearance is the distance between the valve spring coils when the valve is it maximum lift (fully open). A minimum of 0.060" must exist between the coils at maximum lift. Coil bind is when the valve spring is compressed fully-to the point that all of the coils are "stacked up" on top of each other. For high RPM applications, .100" is recommended . Coil bind is a catastrophic condition that will result in valve train failure. Disassemble each spring (if multiple springs are employed at each valve). Check all the springs (both inner, and outer springs) If there is not 0.060" - 0.100" minimum of clearance between the coils, the solutions are: the valve retainer, the valve locks, the valve, or the spring must be changed; the spring pocket must be machined. Keep in mind that these modifications will change the valve spring installed height

Valve Spring Retainer to Rocker Arm Clearance

When installing the rocker arms, check to see that the inside of the rocker arms clear the spring retainers. Many rocker arms have a "relief" to accommodate large valve spring retainers.

Valve Spring Run-In

Each set of Lunati valve springs are hand-selected to keep load variations below +/- 10% of the next. However, it is important to "run in" your new valve springs at low RPM using the following procedure:
- Start the engine and run the engine between 1500 and 2000 RPM until the engine reaches operating temperature.
- Shut off the engine and allow the springs to cool.
- After initial run-in, most springs will lose a slight amount of pressure. Re-check and shim up the valve springs if necessary. After the springs are "run in", spring pressure should remain constant until the point of replacement.
Compression Height
The below topics will help you answer the question above:
- Calculate Block Height
- Calculate Connecting Rod Length
- Calculate Stroke Length
Before selecting a piston, the desired compression height must be known. As shown, compression height is the distance between the centerline of the pin bore and the top of the piston. To determine the compression, three things about the engine must first be known: block height, connecting rod length and crankshaft stroke length.

Calculate Block Height

Deck height is measured from the crankshaft centerline to the deck (cylinder head mounting surface) of the block.

Calculating Connecting Rod Length

Connecting rod length is measured between the centers of the "big end" (journal end - rotating) and the "little end" (piston pin end - reciprocating).

Calculate Stroke Length

Stroke length is twice the distance from the centerline of the crankshaft main bearing journals to the centerline of the connecting rod journals. It is also the distance the piston moves up and down in the cylinder.
Helpful Calculations
Immediately below is a list of the various charts/calculations on this page. Clicking on an item in the list below will take you to the respective section of this page.
- Engine Displacement
- Stroke Length
- Cylinder Bore Diameter
- Formula For Milling Pistons
- Compression Ratio
- Total Combustion Chamber Volume For a Specific Compression Ratio
- Cylinder Head Deck Machining To Reduce Total Chamber Volume
Machining Tolerances
Connecting rods probably receive the highest stresses of any bottom end engine component. The forces the rod receives when the piston direction reverses from top dead center can exceed 12,000 lb. in a 500 C.I. Pro Stock engine. This is why Lunati rods are forged from the finest premium quality 4340 alloy steel for strength and utilize Lunati/ARP rod bolts for superior clamping forces on the rod journal.

Closer tolerances and pride in workmanship, along with strict quality control are what makes Lunati Connecting Rods the only logical choice for serious racers. We at Lunati feel that no other manufacturer will hold the close machining tolerances in manufacturing that we do.
- Center to Center Distance: +/- 0.0001
- Bend and Twist: +/- 0.001 over 2.000"
- Rod Width: +/- 0.002
- Large End Bore: +/- 0.0002
- Small End Bore: +/- 0.0002
- Bearing Tang Location: +/- 0.0025
Rod Installation

Apply the molybdenum base lubricant under the head of the bolt and on the threads.

With the bolts installed hand tight, install the guage and zero the dial indicator. The stretch guage must fit into the dimples on each end of the bolt.

Alternating from one side of the rod to the other, tighten the bolts.

DO NOT STAMP THE ROD NUMBERS ON THE RODS! ETCH THE NUMBERS. STAMPING WILL DISTORT THE ROUNDNESS!

Rod Length

Connecting rod length is measured between the centers of the big end (journal end) and the little end (piston pin end). Below is a table with stock connecting rod lengths for various engine families.

Lunati Technical Information

LIFT

DURATION

LOBE SEPARATION

OVERLAP

CENTERLINES

ADVANCE/RETARD

Understanding The Different Types Of Camshaft Lifters

Hydraulic Flat Tappet

Mechanical Flat Tappet

Mechanical Roller Tappet

Hydraulic Roller Tappet

Valve Spring Pocket Clearance

Valve Spring Retainer Fit

Valve Spring Installed Height

Valve Spring Retainer to Valve Seal Clearance

Valve Spring Coil Clearance

Valve Spring Retainer to Rocker Arm Clearance

Valve Spring Run-In

Calculate Block Height

Calculating Connecting Rod Length

Calculate Stroke Length

Engine Displacement

Stroke Length

Cylinder Bore Diameter

Formula For Milling Pistons

Compression Ratio

Total Combustion Chamber Volume For a Specific Compression Ratio

Cylinder Head Deck Machining To Reduce Total Chamber Volume