Back in the Eisenhower days of the late ‘50s, everyone thought by 2015 we’d be piloting flying cars, living on the moon, and sending men to Mars. Clearly that was a bit optimistic, but if a writer had taken a shot at 21^st Century performance engines he would have expected at the very least that hot rodders would be using pneumatic or electronic valve control by now. But as we plow midway through the century’s second decade, our engines still rely on valve springs and even pushrods just like our grandfathers did a century ago. The big difference is second century engines spin a wee bit faster.

But do not be fooled – there’s plenty of science in valve springs. We’ll approach this story from the street performance standpoint and deal with how a typical enthusiast can upgrade his valve springs when installing a performance camshaft. The evolution of cam lobe profiles is really a study in the ability of the spring to control the valve. So this means as valve spring quality has improved, so have engine speeds and durability . As engine speeds increase, all this places even more demand on the valvetrain to maintain control over the valves.

Spring Selection

Valve spring selection is first determined by the type of camshaft the engine will use. Flat tappet cams do not demand nearly as much valve spring pressure as roller cams, and hydraulic rollers are typically less radical than their mechanical cousins. Much of this demand for valve control is based on lifter velocity rates. The big issue is flat tappets are limited to a finite rate of lift (in terms of fractions of an inch of lift per degree of cam rotation) that is defined by the tappet diameter. Smaller diameter lifters have a lower velocity limit than larger lifters. This gives advantage to Ford lobes, which enjoy a 0.875 inch tappet over the Chevys that are only 0.842. Chrysler engines are better yet with a 0.904 diameter tappet. Each larger tappet allows a higher lifter velocity, which increases the tappet’s maximum velocity potential. This can be viewed in terms of greater lift for the same amount of duration.

Roller followers as a family will require more spring mainly because of the roller’s ability to generate very fast valve opening rates. It’s beyond the scope of this story to get much deeper into this, but it is the dynamic conditions imparted on all the components in the valvetrain (especially on the spring side of the rocker arm) at high engine speeds that place very high loads on the valvetrain. It’s the spring’s job to maintain this control. As  you might imagine, it’s a tough job.

Installed Height

Most professional engine builders will agree that the installed height–dictated by the cylinder head and valve length–is the most important criteria to begin the process of selecting a spring. The installed height is defined as the distance from the spring seat in the head to the bottom of the valve spring retainer. When a spring is compressed to this height, it creates the seat load exerted on the valve keeps it closed. Right here it’s important to emphasize that spring pressure or load is expressed in terms of pounds of force – which is not psi. The term pounds per square inch (psi) is used to express pressure exerted in all directions as in pressure in an air tank. When expressing spring load, the pounds of force we are talking about are exerted in a single, uniform direction.

Engine builders are forever referring to spring catalogs and each spring’s specs, so it’s best to know the terms that will be referenced in this story. Spring rate is expressed in pounds per inch (lbs/in) and is determined by a multitude of factors including wire diameter, overall spring diameter, and the spring’s height. A typical spring might have a rate of 500 lbs/in. As you can imagine, as the spring is compressed, the load increases. A spring’s installed height load is the amount of force created by the spring at a specific height. As an example, a spec of 120 pounds at 1.700 inches means when the spring is compressed to the height of 1.700 inches, it will require a force of more than 120 pounds to open the valve.

Most enthusiasts think that valve float occurs when the spring loses control of the valve and launches the lifter off the nose of the lobe of the cam in a ballistic curve. This is referred to as lofting, which can and does occur. But Spintron research has proven that the most common loss of valve control begins when the valve bounces off the seat upon closing. This is a critical event, because when the intake valve bounces after the desired intake closing point, a certain amount of pressure already building in the cylinder is lost. If this loss of control continues – the valve bouncing several times – each time this occurs, more cylinder pressure is vented back up into the intake tract and power drops dramatically. So based on this, seat pressure is a very important part of blueprinting valve springs to ensure that this loss of control does not occur within the engine’s intended power band.

 

Coil Bind

Coil bind is another critical valve spring spec as it helps define the total amount of valve lift possible with this spring. Coil bind is the height of the spring in its fully collapsed position. This is an important spec because the spring must be compatible with the overall lift created by the combination of the cam lobe and the rocker ratio. As an example, let’s use a big-block Chevy with an installed height of 1.900 inches. Our camshaft maximum lift is 0.650 inch.

We found a spring in the Comp catalog that seems to fit the requirement for the seat pressure (PN 26094), but we need to know if it will handle the 0.650 inch valve lift. The coil bind figure for this spring is 1.200 inch. If we subtract the maximum valve lift from the installed height: 1.900- 0.650 = 1.250, this tells us that we will have 0.050-inch of clearance at maximum valve lift before the spring goes into coil bind. Comp Cam’s recommendation is 0.060-inch, but many engine builders tell us that they will tighten this clearance for rpm engines because a shorter stack at peak lift tends to help dampen springs oscillations at high engine speeds. Generally speaking, a clearance of 0.050-inch ends up roughly 0.012-inch in between each of the active spring coils.

 

Retainer to Seal

Besides coil bind, selecting a valve spring also requires a dedicated retainer. Generally, the bottom of the retainer will come closest to the valve seal located on the guide. When measuring for installed height, this is also the best time to measure for retainer-to-seal clearance. This is a simple procedure where the distance between the retainer and the seal should be at least 0.050-inch more than the total valve lift. This prevents the retainer from bottoming on the seal and causing damage to the seal or preventing the valve from opening fully. This will cause major damage such as bent pushrods, damaged seals, cracked or broken valve guides and a host of other maladies that will be expensive to repair.

 

 

Retainers and Locks

It’s important to always follow the manufacturer’s recommendations for matching the retainer to the springs. This is important not only for the outer spring but also because the step in the retainer is used to locate the inner spring on dual- and triple-spring applications. We could probably do an entire story on just retainers and all the different variations and materials. A critical issue is retainer weight, especially when it comes to big-block engines with large diameter springs where the weight of the retainer is especially important.

A common misperception is that locks use the tang to prevent movement of the retainer. The reality is that the tang is only used to temporarily position the locks in relation to the retainer. Once load is applied to the retainer, the taper angle (7 or 10 degrees) serves to nest into the matching angle in the retainer and the whole assembly binds itself in place. The more force applied to the locks, the more load is applied to retain their position.

The important consideration is to choose a lock intended for the size of the valve. With so many different valve stem diameters, from 5/16 to 3/8 and metric size like the 8mm LS valve stem size, a specific lock is required for each valve size. Retainers are also intended for a given valve stem size, so choosing these components is critical to ensuring your valve train will function as intended.

 

Blueprinting Techniques

When it comes to installing a valve spring, you can run into all kinds of small issues that may require creative solutions. A common issue is a 0.100-inch taller valve is added to the heads, which now makes the installed height 0.100-inch too tall. While purchasing new valves with a lower lock position is one solution, that can be expensive. Another avenue is to use a spring seat. Spring seats are used to locate the spring, but they can also be used to decrease the installed height.

Spring seats are differentiated from basic shims in that seats also locate the spring either from the id or the od. Some engine builders may prefer one over the other, but the idea is to securely position the bottom of the spring to minimize the chance of it “dancing” or moving its seat location at high engine speeds.

Another technique that can be used to adjust installed height is with different height valve locks. For example, within the 10 degree Steel Super Locks, Comp offers two different locks that can adjust the installed height either up or down by 0.050 inch. These locks are only for 11/32-inch valves, but it does offer another option for adjusting the installed height. Keep in mind that adding 0.050-inch of install height will reduce the clearance between the retainer and the underside of the rocker arm and also the distance that the valve tip is above the level of the retainer. What is undesirable is the rocker arm hitting and possibly unloading the retainer from the valve stem. Lash caps can be used in this case to increase the height of the valve stem tip to increase this clearance.

 

Applying What We’ve Learned

Let’s put all of our new-found knowledge to work with a 496ci big-block Chevy that we want to eventually run with a hydraulic roller camshaft. According to our accompanying chart, a good place to start would be 180 lbs. of seat load with 420 lbs. open pressure. Note that these generic recommendations do not specify the actual valve lift or an installed height.

Our AFR heads came with valves that placed the installed height at 1.900 inches. This is 0.100 inch taller that the standard big-block because AFR expects us to combine these heads with a big camshaft with lots of lift. So now that we have a goal for our seat pressure and an installed height, this narrows the field of selection.

We decided to go with a traditional (non-tapered), dual spring combination and looking through the Comp Cams catalog, our aforementioned PN 26094 dual spring appears to be a great choice. It offers 178 pounds of seat load against the recommended 180, so that’s a great place to start. The hydraulic roller cam we selected is an Xtreme Energy XR294 with 242/248 degrees of duration at 0.050 with 0.540/0.560 valve lift. Looking at the 26094’s spring chart in the Comp Cams catalog, spring force is listed every 0.050 of inch of valve lift. Our cam is nearly 0.550 lift which means this spring will deliver 425 pounds of open load, which is nearly spot-on to the recommendation. On the exhaust side, the open load becomes slightly higher due to the added lift.

We have also considered adding a 1.8:1 rocker ratio to this beast, and if we do, we wanted to know how much additional lift this would generate. The easiest way to do this is to simply divide the lift number by the rocker ratio. In this case, on the intake side the information lists 0.540 inch for intake lift. Divide this by the rocker ratio of 1.7:1 and we get 0.3176-inch for lobe lift. Then merely multiply this number by our desired 1.8:1 rocker ratio and we come up with 0.571, which is roughly 0.030-inch more lift.

So now with a max lift of 0.571, we can estimate our open spring load will be halfway between the rated 0.550 load of 425 lbs. and the 0.600 lift load of 447 lbs., which gives us around 435 pounds of load, which is less than 5 percent over our 420 open load recommendation, which will work just fine.

 

So as you can see, there’s not a small amount of material to deal with when selecting and blueprinting valve springs. If you follow these recommendations you will be leagues ahead of many other enthusiasts who don’t realize how important valve spring selection and installation is to engine performance. But now you know, which makes you powerful in your own right.

 

Valve Spring Load Chart

The following generic chart is a starting point for selecting valve springs for serious street engines. These are not one-size-fits-all numbers but rather recommendations that you can use as guidelines when selecting a valve spring. This chart does not differentiate between traditional springs, beehive, or conical springs. But keep in mind that a conical spring with a smaller retainer will experience a substantial reduction in inertial load due to its small retainer.

Small-Block Street Engines	Seat Load (lbs)	Open Load (lbs)
Flat Tappet Hydraulic	120	280-300
Flat Tappet Solid	130	350
Hydraulic Roller	160	380
Mechanical Roller	220	550
Big-Block Street Engines	Seat Load (lbs)	Open Load (lbs)
Flat Tappet Hydraulic	150	350
Flat Tappet Solid	150	380
Hydraulic Roller	180	420
Mechanical Roller	250-300	600-650

 

 

We thought a couple of dyno curves might be enlightening to show what happens when you improve valve control. Both of these horsepower curves are from a flat tappet mechanical 496ci big-block Chevy. The lower curve illustrates what happens to power when the valve springs lose control of the valve. While most people associate poor (not necessarily weak) springs with peak power problems, note how even at a very low 3,600 rpm, there’s an 11 hp difference in power. But the real problems start at 5,200 rpm where the lines dramatically diverge. With good springs and lightweight retainers from 5,700 to 6,300 this engine made between 576 and 578 hp with a nice, wide peak power curve. At 6,500, the better valve train added 54 hp over the previous package. This is probably the shift point for this engine on the drag strip and 50-plus horsepower will show up on the e.t. slip every time.

Spring Chart

We used the Comp PN 26094 spring in this story so we thought showing all the specs for this spring would to illustrate the information that’s available.

Specs:

Outside Dia.:             1.550

Inside Dia. (inner):   0.752

Damper:                     Yes

Coil Bind:                  1.200

Spring Rate:              449 lbs./in.

Installed Height(inches)	Spring Load (lbs.)
1.950	156
1.900	178
1.850	200
1.800	223
1.750	245
1.700	268
1.650	290
1.600	313
1.550	335
1.500	358
1.450	380
1.400	403
1.350	425
1.300	447
1.250	470
1.200	492

Source

COMP Cams
compcams.com