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Q1. What are roller rockers?

A. Roller rockers are highly engineered levers designed to overcome the many faults of low cost factory rocker arms, which in performance applications are prone to failure, which can result in an expensive engine rebuild.


Q2. How are these constructed and what are the benefits?

A. Budget priced STREET TERRA rockers use a high strength die cast aluminium alloy arm. Premium YELLA TERRA rockers utilise an extruded aircraft alloy arm - computer designed and machined.

These strong arms resist breakage; they house huge needle roller bearings and roller tips that reduce friction. Your engine will run cooler, smoother and quieter, lower operation temperatures result as well as reduced engine oil foaming.

A roller rocker equipped engine responds more quickly than its standard counterpart. In high performance engines with roller rockers and strong valve springs, quiet considerable horsepower gains are common over conventional rockers.


Q3. Are roller rockers a new invention?

A. No, they have been around in many forms since World War 1 - originally used in aircraft applications. Today many expensive cars use them standard, BMW, Mercedes Benz, etc. Today it would be hard to find any serious motorsport or marine competition application using standard rocker arms.


Q4. How do roller rockers extend the life of cylinder heads? 

A. The standard non-roller type of rocker arm pushes and pulls the valve stem sideways every time the valve is opened. This causes the guides to wear prematurely, which in turn causes the valve seat to deteriorate. With a roller rocker, the roller tip prevents this side loading, giving the guide and stem the best chance of survival, making them ideal for not only performance engines, but standard engines as well.


Q5. What is the difference between PRO STREET rockers and STREET TERRA rockers?

A. Both PRO STREET and STREET TERRA rockers use the same hardware; the difference is in the material and design of the aluminium arm (rocker body). STREET TERRA arms are made from high density, vacuum die cast aluminium, and they are vastly superior to original rockers and many aftermarket brands, at an affordable price. 

The even stronger PRO STREET rocker arms are machined from heat-treated certified aircraft grade aluminium extrusion. This combined with their "beefy" but well balanced design, makes them one of the strongest aluminium rockers available.

All steel components, bearings etc. are identical in both series of rockers, should replacement components or overhaul be required these are readily available.


Q6. Why are YELLA TERRA rockers not anodised to nice colours?

A. Anodising degrades the aluminium reducing its tensile strength and reducing the life cycle of the arm. 

An anodised arm is weaker! Anodising is an electrochemical process that produces a clear or coloured coating on the rocker arm. This coating is extremely hard and is "notch sensitive". Even slight "dings" from careless handling or slight scratches like those from feeler gauges can cause a "stress riser" precipitating cracking and subsequent arm failure


Q7. Will standard rocker covers fit?

A. The majority of stud mounted and bolt-on EF rockers will fit under the standard covers, but some bolt-on adjustables and the wide body adjustables may require taller covers. Often using two rocker cover gaskets glued together and longer bolts is a quick and easy fix.


Q8. What are the advantages of shaft mount rockers?

A. Shaft mounting makes the rockers more stable and reliable at rpm and in many cases results in a significant horsepower gain over stud mounted rockers, where the studs are prone to flexing, particularly where heavier springs are used in performance applications 

The majority of YELLA TERRA & PRO STREET rocker kits are of the Easy Fit "EF" shaft type. Independent tests and millions of kilometres of race reliability over 50+ years have proven YELLA TERRA shaft rockers to be the most used and reliable.


Q9. What rockers do I fit with a solid lifter camshaft?

A. Ensure you fit one of the adjustable models. Reground or high lift camshafts need to have compensation for changes in the length of the lifter-pushrod assembly; these length variations can be easily compensated with adjustable rockers.


Q10. Should I run a higher than standard rocker ratio? 

A. Many cam grinders today specify rocker ratios higher than standard for specific camshaft grinds but in most cases, unless specified, the standard ratio gives you the best result.


Q11. I am fitting larger diameter valve springs. Will I have any problems?

A. It is imperative that you check for clearance between the rocker arm and the spring retainer combination in the fully open and closed positions. Allow at least .60" (1.5mm) clearance. Most YELLA TERRA rockers have adequate clearance.


Q12. Do roller rockers need special push rods?

 A. Usually no, with the exceptions being

1) When screw-in studs and hardened guide plates are to be fitted (on engines not fitted with them originally). These need hardened pushrods.

2) When extremely heavy valve springs are fitted a more robust push rod than standard may be required.


Q13. What tappet settings do I use when fitting roller rockers?

A. Whether using roller rockers or standard rockers, the tappet settings remain the same as specified for your camshaft.


Q14. My rockers are 1.7:1 for a BB Chevy, can they be used on another type of engine with a similar ratio, such as a Cleveland.

A. Yes, No - Maybe! Although the same or similar ratio, there are subtle differences that can cause serious problems like pushrod cup angle and depth, roller position and valve spring/retainer clearance. It's very easy to overlook a slight difference that can cause serious problems.


Q15. Should I reduce the oil supply to the top end when using roller rockers?

A. A roller rocker requires far less oil for lubrication than a standard type of rocker, so it is not uncommon for engine builders to restrict the amount of oil to the top end.


YELLA TERRA roller rockers incorporate an oil passage in the front of each rocker arm to supply oil to the valve spring. In highly stressed engines the cooling effect of the oil on the valve springs can be critical, so the decision to reduce oil supply should not be taken lightly.




Q1. How much better will my vehicle be with a YELLA TERRA head?

A. Compared to standard reconditioned head, which can give no better than original performance, the difference with YELLA TERRA is dramatic. The sensation of less throttle being required to maintain a given speed is the first thing you will notice. A performance improvement of 15-30% could be expected (depending on model) resulting in improved torque, power, economy and reliability. 

Considering the performance, economy and durability benefits, the relatively small cost difference between a standard reconditioned and a YELLA TERRA is well worthwhile.


Q2. How do YELLA TERRA heads improve performance?

A. Compared to an athlete's breathing exercises to improve performance, YELLA TERRA heads improve the breathing of an engine i.e. "cylinder filling" and increase performance by allowing more air/fuel mixture into the cylinder and burning the mixture and exhausting the spent gas better than standard - yielding extra power.


Q3. Will a YELLA TERRA head(s) affect my fuel economy?

A. With the power improvement gained, you use less throttle for the same speed so the economy is generally improved. 10-15% is not uncommon.


Q4. Will YELLA TERRA head(s) shorten the life of my engine?

A. No engine life is generally increases, as you no longer have to rev your engine as much to produce good usable power. Of course if you drag race from every stoplight, your engine life will be shortened and fuel consumption increased.


Q5. Quoted compression ratio appears to be about standard, wouldn't it be better to have a higher compression ratio? 

A. In road applications today's fuels cannot tolerate higher compression than original, knocking, pinging or severe engine damage can result from too high compression ratio. What really matters is the breathing and cylinder-filling efficiency of the head at medium to higher engine speeds, that's what really improves power and performance.


Q6. Do I need different or special tuning?

A. No, in most cases standard tuning specifications will give the best result.


Q7. Would roller rockers be a good idea to fit with my new head?

A. Yes, the best time to take most advantage of roller rockers is when you fit a new cylinder head. The combination will delight you in performance and reliability - most likely outlasting your ownership of vehicle. Cylinder head wear will be almost negligible. A smooth, quieter more responsive engine will be the result.


Q8. Do I need to change carburettors, manifolds, camshaft and exhaust system?

A. No, however each of these modifications if selected carefully, aloe or in combination will yield increased performance and perhaps economy. It is important to seek professional advice before committing to such modifications. 

Poorly selected items will cause annoyance and frustration.


Q9. Do YELLA TERRA heads require special head gaskets?

A. In most cases no. A good quality standard replacement gasket is fine.


Q10. Do YELLA TERRA heads require special head bolts or studs?

A. As with head gaskets, the standard bolts are usually fine provided they are in good serviceable condition, except when changing from iron to alloy cylinder heads where studs and nuts with hardened washers are more suited. In any case GMH stud sealer or similar should be used to seal the threads into blocks.


Q11. What sparkplugs should I use with my new YELLA TERRA cylinder head.

 ABH 308-3

  • NGK: BP5 FS
  • NGK: BP6 FS (suit high comp)


ABH 5000-9


AVH 33C56



A. Because of their winning technology for street, road and strip. Proven for over half a century, YELLA TERRA manufactured heads have been at the cutting edge of Australian motorsport.

The original XU1, a design developed by Perfectune and subsequently the manufacture of thousands of heads for the Bathurst XU1, L34, A9X and SLR5000 V8 Toranas.

All Brock Commodores and Police interceptor heads and the Walkinshaw PFI Group A heads.

The Hi Torque Control "Commodore Cup" and Alloy Heads used in Holden Auscars are all products of our extensive experience. 

The results speak for themselves! 




Q1. Should I consider intercooling my new supercharger/upgrade kit?

A. With supercharging, heat is a natural by-product of air compression. The Higher the boost pressure, the higher the associated air temperature, so intercooling becomes increasingly important. Passing heated charge air through a heat exchanger (intercooler) dramatically reduces the air temperature and any risk of harmful detonation.

Our Whipple supercharger kits utilise an air-to-water intercooler core positioned directly below the discharge of the supercharger. 

Our YELLA TERRA boost upgrade kits may or may not require intercooling, dependant on your pulley size and boost pressure . Our 100% Australian designed, engineered and manufactured intercooler kits efficiently transfer heat away from the intake charge with minimum interference to airflow.


Q2. Should I consider getting my car tuned after installing a boost upgrade kit or swapping pulley diameters?

A. The short answer is YES! We recommend tuning with the installation of any aftermarket performance product, particularly superchargers and boost upgrades. Tuning will ensure you are maximizing the performance of your engine and take full advantage of your new YELLA TERRA products. 

It is not uncommon for customers to carry several boost pulleys of varying sizes, from mild to wild for extra "bolt on boost". In these instances it is best to approach your tuner/engine specialist when finding the sweet spot (for those that you carry) and to safeguard your engine from harm.