TECHNICAL
Scorpion Racing Products Pushrods
Why can’t I use my stock pushrods?
Wear, length and strength are three reasons not to use your stock pushrods.
Wear on the ends of the pushrod where it contacts the rocker or lifter is always a concern. Because of the high loads, it’s important that the radius on the end of the pushrod match the radius of the seat in the rocker or lifter and that it be free of scoring. A used pushrod end may not be worn round and may have score marks on it.
Length is important on a stud mount rocker to assure proper rocker geometry. On a non-adjustable pedestal mount rocker, length is critical for proper lifter preload. Whenever you change anything in the valvetrain pushrod length must be checked.
Strength is always a concern as stock pushrods are marginal for stock cam profiles and spring loads. When higher load springs, faster cam profiles and higher rpm are involved the increased pushrod flexing (pushrod bends then springs back) disrupts valve timing, rpm stability and component durability.
What should I look for in a new pushrod?
Absolute minimum wall thickness of .080" to reduce pushrod deflection or flex, this also includes the ends (radius) of the pushrod. If you’re running pushrod guideplates the pushrod must be hardened and smooth to be compatible. The radius on the pushrod ends must be correctly sized and with a smooth finish free of tool marks to prevent galling of the pushrod seats in the rocker and lifter. Scorpion Racing Products pushrods have an .083" wall thickness on the 5/16" diameter units and .120" wall on the 3/8" diameter ones. Our radius ends are billet CNC machined for radius accuracy, finish and maximum thickness. SRP pushrods are hardened and centerless ground smooth for compatibility with guideplates.
I’ve never had a pushrod failure, why change them?
Most people think if they haven’t had a visible problem (broken, bent or galling) with their pushrods that nothing better is needed. This is wrong! Even on mild performance applications, a pushrod that is flexing can cause problems from power loss to component failures elsewhere in the valvetrain and there may be no actual pushrod failures.
Should I use a 5/16" or a 3/8" diameter pushrods?
Usually the cylinder head design limits the diameter you can use. Without having sophisticated testing equipment, the general rule is to use the most rigid pushrod that will fit. Naturally the 3/8" diameter is more rigid than the 5/16" diameter, so if it will clear the cylinder head, use the larger diameter.
Will the extra weight of the larger diameter/thicker wall pushrod affect rpm?
Added weight on the "pushrod side" of the valvetrain is not as important as on the "valve side". The added power, rpm and valvetrain durability from the lack of pushrod flex is more important.
What is pushrod flex and how does it affect power and durability?
The pushrod deflects or flexes upon valve opening and then again just prior to valve closing. As the cam tries to move the valvetrain to open the valve, it has the weight of the valvetrain against it and in the case of the exhaust valve, cylinder pressure also. Upon valve closing, the cam is trying to slow the valvetrain down. So on valve opening and valve closing the pushrod flexes and as rpm increases it gets worse. Here’s how it effects rpm, power and durability;
Rpm is reduced when the pushrod flexes, and then rebounds like a pole vault. It throws the rocker and valve out of control. As rpm increases, the more the pushrod flexes, the more out of control the valvetrain becomes and the more valve "float" or "bounce" to the point that the engine rpm no longer increases.
Power is naturally affected by the loss of valvetrain control at rpm, but something else happens. Remember the engine responds to valve timing not cam timing. Even if the valvetrain stays in control. When the pushrod flexes upon valve opening and valve closing, the valve opens later and closes earlier. The engine "sees" less valve open time (like a smaller duration cam) and as rpm increases it gets worse. Loosing 6 to 8 degrees of valve timing is not unheard of!
Durability is affected when the valvetrain parts are "thrown" out of control by the rebounding pushrod. When this happens the valvetrain parts are jerked apart from each other, and then slammed back against each other by the valve spring pressure. This "slam" can break parts anyplace in the valvetrain and at the very least break the lubricating oil film causing excessive wear. All of the above can happen without a pushrod failure!
Do higher ratio rockers affect the pushrods?
Higher ratio rockers will increase the load on the pushrod because the rocker is moving the valve side faster. This means more pushrod flex as the valve starts to open. To get the most performance from higher ratio rockers a rigid pushrod is a must.
Scorpion Racing Products Lifters
What is the difference between hydraulic and mechanical lifters?
On the outside they look the same, inside is where the difference is. The mechanical (or solid lifter) is just what it sounds like, solid with no internal movement. These lifters are designed to be adjusted at lash (clearance) and are to be used on camshafts that are designed for a lash setting. Mechanical lifters require periodic adjustment and are normally used for higher rpm. However the advantages are they have no internal parts to stick or fail and the lash can be varied to help tune the combination. Hydraulic lifters are designed to run at no lash and have a moveable pushrod seat controlled by engine oil to accomplish this. They are normally adjusted to a "preload" (how far down from zero lash) setting and use a camshaft designed for a "no lash" situation. They are basicly a set and forget lifter because of the preload type adjustment and are normally used up to approximately 6500 rpm. Hydraulic lifters (because of the hydraulic unit) are subject to bleed down issues caused by debris.
What are flat tappet and roller tappet lifters?
Flat tappets (lifters) have a flat face that rides against the cam lobe. In reality the face has a slight crown (convex) to help the lifter spin or rotate when the cam lobe moves past it. These are available in both hydraulic and mechanical. All Scorpion Racing Products flat tappets are made in the U.S.A. from a proprietary formula of hardenable cast iron for wear resistance. The face of the lifter has a high concentration of microscopic carbides and is mirror finished for durability in both street and high load race engines. Scorpion Racing Products mechanical flat lifters are available with and without a .015" oil hole in the face. Scorpion Racing Products hydraulic flat lifters are available with three different types of hydraulic units, race, short travel and variable duration. The race lifter has the travel and bleed rate of an "anti-pump up" race tappet, the short travel has .050 of hydraulic travel and a custom bleed rate for higher rpm. The variable duration lifter has a faster bleed rate to increase manifold vacuum and low speed performance. Flat lifters (hydraulic or mechanical) must be used with camshafts designed for that use. Roller lifters are noticeably different as there is a roller at the bottom that rides against the cam lobe and there is some means to stop the lifter itself from rotating in the lifter bore. These lifters are also available in either hydraulic or mechanical. All Scorpion Racing Products (hydraulic or mechanical) roller lifters are made in the U.S.A. from cold forged heat treated steel with a precision ground roller assembly using a tool steel axle. The hydraulic roller lifters are available in both "tie bar" and OEM style locking bar types. The tie bar style hydraulic roller is available with either race or with short travel hydraulic units. The OEM style are available with the race hydraulic unit only. The race hydraulic unit has the travel and bleed rate of a standard "anti-pump up" lifter while the short travel has .050 of hydraulic travel and a custom bleed rate for higher rpm. The Scorpion Racing Products mechanical roller tappets have a lightweight body with a proprietary tie bar design. They are available to fit taller lifter bore, hydraulic roller style engine blocks. Roller tappets must be used with roller lifter camshafts.
What is the best way to adjust my lifters?
The easiest way to explain this is to take it in three sections; engine position to proper adjustment, hydraulic lifter adjustment and mechanical lifter adjustment. These instructions will work on flat or roller lifter engines. Also if this is a new engine or a cam change where the intake manifold has been removed, leave the manifold off when doing your initial adjustments as it is easier to watch the lifters while positioning the engine and for adjusting. To position the engine for proper adjustment you will work on one cylinder at a time and always turn the engine in the normal direction of rotation. This procedure can be used on any engine with any camshaft. Remember to use Scorpion Racing Products assembly lube, SRPAL4-1, on all parts.
Engine position for adjustment: To adjust the intake lifter/rocker, rotate the engine and watch for the exhaust lifter to be on the low portion of the cam (valve closed) and continue rotating the engine until the exhaust lifter just starts to rise (valve just starting to open), stop and adjust the intake. To adjust the exhaust lifter/rocker, rotate the engine watching the intake lifter. The lifter will rise and then go back down, just as it stops moving down (valve just closes) stop and adjust the exhaust.
Hydraulic lifter adjustment: When adjusting hydraulic lifters, don’t install the rocker until you’re ready to adjust it. When you have the engine in the correct position (see above) for adjustment, install the pushrod and rocker, tightening the adjusting nut with your fingers (make sure the locking set screw is backed out far enough on the adjusting nut). When the free play or lash (up and down movement) has been taken out of the valve train (zero lash), use a wrench and turn the nut down (preload) the recommended amount. Then lock the set screw down against the rocker stud. Scorpion Racing Products recommends 1/2 to 1 turn down on all but our short travel. On our short travel lifters it’s 1/8 to 1/4 turns down. After reading this you now know that with the intake manifold off you can see when you’re at zero lash, because the free play is gone but the pushrod seat is still up against the snap ring in the lifter. You can also see when you’re preloading because you can see the pushrod seat move away from the snap ring in the lifter. If it is a pedestal mount, non-adjustable rocker the procedure is basicly the same. With the engine in the proper position, install the rocker and lightly tighten the attaching screw with your fingers. Once you’re at zero lash, set your torque wrench to the specified torque and tighten the attaching screw. The screw should turn another 1/4 to 3/4 (1/8 to 1/4 turn with short travel lifter) turn until the torque wrench clicks. If it is less than 1/4 turn, a longer pushrod is needed. If it is more than 3/4 turn, a shorter pushrod or shimming the pedestal is needed.
Mechanical lifter adjustment: When adjusting mechanical lifters, rotate the engine to the correct postion (see "engine positon for adjustment" above), install the rocker arm and set the lash to the cam grinder’s specs.. If you are not used to using a feeler gage, it would be best to have the feeler size you need for your adjustment and one that is .002 larger. Using the correct size to set your valve lash, then make sure the larger size doesn’t fit. This will stop you from having the lash too loose and will help you establish a "feel". When adjusting the engine cold; on iron head/iron block use the recommended lash, on alum head/iron block, subtract.006 from the recommended lash, on alum head/alum block subtract .012 from the recommended lash setting. Then recheck lash with the engine at operating temperature. Remember for initial startup or cam break-in with mechanical tappets, tighter lash is better than too loose. Naturally you don’t want it so tight it will hold the valve open.
Scorpion Performance Valve Springs
What Valve Springs are best for my engine?
There’s many factors in choosing the correct spring for your engine. Physical fit such as diameter and installed height, having enough travel in the spring for the valve lift, and proper closed and open pressures to control the valvetrain at the desired rpm. Lets take them one at a time:
Physical fit is determined by your cylinder heads and valve length. Many heads are restricted as to how large of a diameter spring can be used. The cylinder head (spring pocket diameter and depth) and valve length (along with spring retainers and locks) will determine your valve spring installed height.
Spring travel is designed into the spring. This is how much actual travel is in the spring from the installed height to coil bind (spring totally collapsed). This travel, minus .060, is the safe amount of valve lift the spring will accept. For example: .660 spring travel, minus .060 = .600 maximum safe valve lift.
Spring Pressures are determined by spring design and installed height. The spring design would be wire diameter, number of coils, spring diameter, number of springs (single, dual or triple) and type of steel. The installed height is how much the spring is compressed when the valve is closed. The recommended open and closed pressures are best gotten from your cam spec card or by calling your cam grinder. One thing to remember is that the cam profile, valvetrain weights, rocker ratio and rpm vary these recommendations. An example would be two engines with the same parts running different rpm would need different spring pressures. A combination turning 9000 rpm needs considerably more spring pressure than the same combination turning 7500 rpm. You could use the same pressure at 7500 rpm as 9000 rpm but using excessive spring pressures shortens the life of the valvetrain components and increases heat.
Why do prices vary so much for the same size and pressure valve spring?
The quality of the steel used in the spring (and damper if used), the inspection processes and the surface treatments of the finished spring all add costs to the finished product. Scorpion Racing Products valve springs are made from "superclean" alloy, with increased inspection levels, coiled and ground on CNC equipment and surface treated using sophisticated processing. These processes produce a durable, consistant spring that resists load loss and failure. It is not uncommon to see only a 4 to 6 pound load loss after use. Lesser priced springs may skip a process or use a lower quality steel. The bottom line here is, the valve spring is the most highly stressed part in your engine, using a premium Scorpion Racing Products valve spring is money well spent on power and durability.
What is valve spring installed height?
Installed height (or assembled height) is the measurement of what just the valve spring itself measures when it’s installed on the cylinder head with the valve closed. This means from the bottom to the top of the spring only. Do not include the retainer or spring seat in this measurement.
What if I change the installed height?
Obviously, a valve spring is a coil spring. If you put a light coil spring in your hand and squeeze, the more you squeeze the higher the tension. The same with the valve spring. The shorter the installed height (squeezed more) the higher the pressures, both when the valve is closed and valve open. Naturally the opposite happens when taller installed height is used. Also when the installed height is changed the amount of travel (valve lift) that the spring will accept changes. The shorter the installed height, the closer the spring is to coil bind resulting in less travel (less lift).
When checking the pressure of a valve spring should a retainer be used?
A single spring with a damper, a dual spring or a triple spring should be checked with a retainer. The steps on the underside of the retainer will change the pressure and coil bind numbers. When checking the spring pressure, you will have to add the thickness of the retainer (from where the outer spring sits to the highest portion on the top of the retainer) to the installed spring height to get your checking distance.
A word of caution:
As I said earlier, the valve spring is the highest stressed part in your engine. The specialized surface finish of the spring is very important to it’s durability. Any damage to the spring surface can cause it to fail in that location. This includes scratches from mishandling, marring from incorrectly fitting retainers or spring seats and pitting from rust.
Scorpion Racing Products Rocker Arms
Why not use my stock rocker arms?
Stock stamped steel rocker arms are not durable enough to handle the more aggressive loads of current performance camshaft profiles and valve springs. Ratios will also vary considerably on stock rockers from one to another, that coupled with the added heat and friction of the stock type pivot robs power. Scorpion Racing Products rocker arms are fully CNC machined for ratio accuracy and strength. The roller bearing centerless ground fulcrum and roller tip lowers friction and heat.
How much power will I see by switching to Scorpion Racing Products roller rockers?
Typically you will see as much as a 15 horsepower gain from the ratio accuracy and reduced friction. A side benefit from the reduced friction is lower oil temperature, Scorpion Racing Products roller rockers generate half the heat of a stock type "ball" center pivot!
Which rocker ratio should I use?
Most engine/cylinder head combinations will respond to higher rocker ratios especially on the intake valve. When installing higher ratios, the engine "sees" more valve lift and a faster valve opening and closing rate. Remember the engine responds to valve movement not lifter movement! Any change in the valvetrain (camshaft, rocker ratio or stiffer pushrods) that increases valve movement will increase power. When installing higher ratio rockers the remainder of the valvetrain must be checked for clearance. Items to check are; valve spring travel (coil bind), retainer to seal clearance, pushrod to head clearance and in some cases piston to valve clearance.
How much more lift will I get with higher ratio rockers?
You’ll need to do some math here. Divide your valve lift by your rocker ratio, that will give you your cam lift. Now multiply your cam lift by the new rocker ratio to get your new valve lift. An example of .550 lift with 1.5 ratio going to a 1.6 ratio is, .550 divided by 1.5 equals .366 multiplied by 1.6 equals .586.
Will Scorpion Racing Products rockers fit under my center bolt valve covers?
Scorpion Racing Products offers rocker arms in both 1.5 and 1.6 ratios and 1.5/1.6 ratio sets (all with a 3/8 stud) in narrow body self-aligning and narrow body non self-aligning that were designed for the center bolt covers. You will still have to check for interference upon installation as there were many different covers produced with different internal baffling. You may have to do some minor modifications to these baffles.
How do I know if I need self-aligning rockers?
A stud mounted rocker arm needs to have a means of keeping the rocker aligned with the valve tip. The two common ways are guiding the rocker from the pushrod side (guide plate or slot in the cylinder head) or by capturing the valve tip (self-aligning) in the rocker arm. It is important that this is only done by either one of the two methods. In otherwords, the rocker must be held in alignment with the valve tip, but it cannot be guided from both the pushrod and the valve side at the same time. If your cylinder head has a slot machined into it or a pushrod guide plate, the non self-aligning rocker should be used. If you don’t have either of these then look at your stock rockers, if you see and indentation in the underside of the rocker that would capture the valve tip, then you would use a self-aligning rocker. A word of caution, some aluminum heads from GM had a "guide plate" on it and used a self-aligning rocker. This "guide plate" had wide pushrod slots in it and was used for engine assembly purposes at the factory only. This type of "guide plate" is not for holding the rocker in alignment, this head would use a self-aligning rocker.
How do I determine the correct pushrod length on my Scorpion Racing Products rocker arms?
When any component is changed in the valve train the pushrod length must be checked. The pushrod length on a stud mounted rocker determines the rocker geometry which is very important for power and durability throughout the valve train. When the pushrod is the correct length the rocker arm roller tip will sweep in the middle of the valve tip when the valve travels from closed, to full lift and closed again. This can be checked using an adjustable checking pushrod and some type of marking compound (bluing, grease etc.). With some marking compound on the valve tip and the lifter at the low portion of the cam lobe, install the pushrod and rocker. Adjust the pushrod length so that the roller tip is about a 1/3 across the valve tip towards the rocker stud. Install the rocker adjusting nut to zero lash and rotate the engine to valve open and around to valve closed again. Remove the rocker, the pattern or sweep across the valve tip should be centered. If the pattern is closer to the rocker stud, then the pushrod is too short, lengthen it and check again. If the pattern is towards the outside of the engine, then the pushrod is too long, shorten and check again. Keep in mind if you are using a hydraulic lifter you will need to bottom out the lifter (subtract the amount the lifter is depressed from the ending pushrod length) or use a light checking spring in place of the valve spring. You do not want the lifter to be compressing while checking the pushrod length. Once the correct pushrod length is found, measure the overall length and contact us at Scorpion Racing Products for your pushrod needs.
What is the difference between the Scorpion Racing Products Race Series and the Platinum Series?
Both rockers use the same premium components, materials, will handle the same loads and will clear a 1.625 O.D. spring. The main difference is the rocker arm body itself. The Platinum Series rocker is profiled for up to a 34 gram weight reduction and has a reinforced top "strap" for additional strength and rigidity. Because the Platinum Series rocker body is profiled, it has a better chance of clearing lower profile valve covers. If you’re looking for maximum strength with minimum weight the Platinum Series is the one to choose.
Can I use high spring pressures with pedestal mount rockers?
Pedestal mount rockers are meant as a bolt on, mild performance alternative to the higher cost of removing the heads and machining for screw in studs, You have to remember there is only a 5/16" screw attaching it to the cylinder head! The rocker itself is plenty strong enough, the attaching bolt is the weak link. However, when everything is correct it is possible to use open pressures as high as 350 lbs. spring load. The everything I’m refering to is: Hydraulic lifters only, Proper lifter preload, Correct spring loads for the cam and rpm, Do not tighten or loosen the attaching screw with spring pressure against it, Use a torque wrench on the attaching screws, No mechanical interference in the valve train (coil bind, retainer to seal, etc.), Use a rigid Scorpion Racing Products pushrod, Do not over rpm the engine into valve float.