General FAQs
Does Yella Terra make their own components?
Yes, all products are made in-house by our sister company Perfectune Engineering. We source all materials locally wherever possible.
Cylinder head FAQs
What are the advantages of Diamond honed valve guides and tuffrided valves aptly named “DOUBLE DIAMOND”?
The diamond honing process provides perfectly sized, accurate and straight valve guide bores with a cross hatch surface (as with cylinder bores) to provide the best oil retention and wear resistance. Valves are diamond hard and have incredible wear resistance, valve guides & stems don’t wear, increasing head life dramatically, possibly as much as four or five times that of a standard head.
How do Yella Terra heads improve performance?
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.
Will a Yella Terra head affect my fuel economy?
With the power improvement gained, you use less throttle for the same speed so the economy is generally improved. 10-15% is not uncommon.
Will Yella Terra heads shorten the life of my engine?
No, engine life generally increases as you no longer have to rev your engine as much to produce good useable power. Of course if you drag race from every stoplight, your engine life will be shortened and fuel consumption increase.
Quoted compression ratio appears to be about standard, wouldn’t it be better to have a higher compression ratio?
In road applications today’s fuels cannot tolerate higher compression than or original, knocking, pinging or severe engine damage can result from too high a 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.
Do I need a different or special tuning?
No, in most cases standard tuning specifications will give the best results, but it will depend on other modifications
Would roller rockers be a good idea to fit with my new head?
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 the vehicle. Cylinder head wear will be almost negligible. A smoother, quieter more responsive engine will be the result.
Do I need to change carburettors, manifolds, camshaft and exhaust system?
No, however each of these modifications if selected carefully, alone or in combination will yield increased performance and increased economy. It is important to seek professional advice before committing to such modifications. Poorly selected items will cause annoyance and frustration.
Do Yella Terra heads require special head gaskets?
Head gaskets should be suitable for the compression ratio being used. Alloy heads usually work best with Graphite or similar material.
Do Yella Terra heads require special head bolts or studs?
Aftermarket bolts or studs are highly recommended and hardened washers are essential for all alloy heads.
What is the warranty on cylinder heads?
Yella Terra cylinder heads and various derivatives of such product range are guaranteed for a period of 12 months or 20,000km – whatever comes first. Warranty commences from date of original sellers invoices. The warranty covers faulty workmanship and materials. It does not cover faulty installation and maintenance or subsequent damage whatsoever. Perfectune Engineering, the manufacturer, reserves the right to examine any goods under claim and shall be the sole judge of the validity of each and any claim and reject, repair or replace goods at our sole discretion. All freight charges are the responsibility of the claimant.
Why Yella Terra heads?
Because of their winning technology for street, road and strip. Proven for over a quarter of a century, Yella Terra 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.
Roller rocker FAQs
What are roller rockers?
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.
How are these constructed and what are the benefits?
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 operating 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, quite considerable horsepower gains are common over conventional rockers.
Are roller rockers a new invention?
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 motor sport or marine competition application using standard rocker arms.
How do roller rockers extend the life of cylinder heads?
The standard non roller rocker 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 rocker 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.
What is the difference between YELLA TERRA rockers and STREET TERRA rockers?
Both Yella Terra 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, they are vastly superior to original rockers and many aftermarket brands, at an affordable price. The even stronger Yella Terra rocker arms are machined from heat treated certified aircraft grade aluminium extrusion. This combined with their “beefy” but well balanced design, makes them the strongest aluminium rockers available and the only brand guaranteed for life. All steel components, bearings etc. are identical in both series of rockers, should replacement components or overhaul be required these are readily available.
Why are STREET TERRA and Yella Terra rockers not anodised to nice colours?
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.
Will standard rockers covers fit?
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.
What are the advantages of shaft mount rockers?
Shaft mounting makes the rockers more stable and reliable at high 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.
What rockers do I fit with a solid lifter camshaft?
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.
Should I run a higher than standard rocker ratio?
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 results.
I am fitting larger diameter valve springs. Will I have any problems?
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 .060″ (1.5mm) clearance. Most Yella Terra and STREET TERRA rockers have adequate clearance; those that don’t can be notched at the factory for a nominal charge.
Do roller rockers need special push rods?
Usually no, with the exceptions being:
- When screw-in studs and hardened guide plates are to be fitted (on engines not fitted with them originally). These need hardened pushrods.
- When extremely heavy valve springs are fitted a more robust push rod than standard may be required.
What tappet settings do I use when fitting roller rockers?
Whether using Roller Rockers or standard rockers, the tappet settings remain the same as specified for your camshaft.
My rockers are 1.7:1 for a BB chev, can they be used on another type of engine with a similar ratio, such as Cleveland?
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. Its very easy to overlook a slight difference that can cause serious problems.
Should I reduce the oil supply to the top end when using roller rockers?
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 spring can be critical, so the decision to reduce oil supply should not be taken lightly.
What is the warranty on rockers?
STREET TERRA rockers are guaranteed against faulty workmanship and materials for a period of 12 months from date of purchase, subject to conditions below. TELLA TERRA rockers are also guaranteed against faulty workmanship or materials for a period of 12 months from date of purchase. We have such confidence in the quality of Yella Terra rockers, we offer a limited lifetime guarantee against breakage of the extruded aluminium arms, precision alloy steel trunnions or shafts and posilok nuts, while you own them.
This guarantee is subject to the following conditions. You must be the original purchaser and produce an acceptable original sellers invoice. These warranties do not extend to cover faulty installation or maintenance or to subsequent damage whatsoever. Perfectune engineering, the manufacturer, reserves the right to examine any goods under claim and shall be the sole judge of the validity of each and any claim and repair, replace goods at our sole discretion. All freight charges are the responsibility of the claimant.
Supercharger FAQs
How does the Terra Charger supercharger work?
The Terra charger is a positive displacement pump. Its purpose is to increase air pressure and density in the intake manifold. It does this by pumping more air than the engine would use without a supercharger. The Terra Charger is matched to the engine by its displacement and belt ratio, and can provide excess airflow at any engine speed. This concentrated charge of air provided by the Terra Charger results in a more powerful combustion stroke in the engine’s cylinders.
How is a supercharger different from a turbocharger?
A supercharger is connected directly to the crankshaft by a belt unlike a turbocharger which is driven by exhaust gases. The improved horsepower and torque, at lower engine rpm’s, is obtained by pumping extra air into the engine in direct relationship to crankshaft speed. The positive connection yields instant response, in contrast to tubochargers, which must overcome inertia and spin up to speed as the flow of exhaust gas increases. The supercharger has self contained oil whereas the turbocharger requires engine oil.
What’s different about centrifugal / impellor tyre blowers?
A centrifugal belt driven blower (sometimes called a “Hair Dryer”) is very similar to a turbocharger. Both require high engine speeds to spin an impellor up to extremely high speeds, frequently in excess of 100,000 RPM, before they generate useful manifold pressure to increase power. Compared to a Terra charger, turbochargers and impellor type blowers have poor low engine RPM efficiency. For practical purposes increased torque and power at low to medium engine RPM is more useful for a wider range of vehicle applications and service conditions.
The roots supercharger has been around for a long time, how is the Terra Charger supercharger different?
The Terra Charger supercharger is essentially a Roots blower pump, with one substantial design wrinkle: Each rotor has been twisted 60 degrees to form a helix. The two counter rotating rotors have three lobes, which intermesh during operation. These twisted rotors, along with specially designed inlet and outlet port geometry, help to reduce pressure variations resulting in a smooth discharge of air and a low level of noise during operation. This arrangement also improves efficiency over traditional Roots superchargers. With helical rotors and an axial inlet the Terra Charger supercharger can spin up to 14,000rpm, thereby reducing package size.
What are the benefits of the Terra Charger supercharger?
- Instant power response when needed
- Reduced exhaust emissions
- Patented technology to reduce noise
- Proven manufacturing capability
- Packaging flexibility, ie reduced package size
- Self-contained lubrication, ie no external oil connections to the engine.
How much power does the supercharger add?
This is dependent on the size of the supercharger and also the size of the engine. Typical improvements in the range of 25% to 50% are not uncommon.
How efficient is the Terra Charger?
Typically, the volumetric efficiencies are around 90%. See performance curves, including Volumetric efficiency.
What type of fuel is required? What about fuel economy?
Supercharging is compatible with all types of fuels. Fuel economy is totally dependent on driving style.
Can all engines be supercharged?
Yes, supercharging is very compatible with all engines whether the engine will be two or four valves/ cylinder, petrol, diesel, LPG, CNG, or 2-stroke.
Are special engine modifications required for installing the supercharger?
This is dependant on the level of power increase desired and the given engine design.
Is the Terra Charger supercharger easy to service?
The supercharger is serviced only as an assembly by Perfectune Engineering. Disassembly of the supercharger is not recommended. As previously mentioned, the supercharger has a self contained oiling system that does not require a fluid change for the life of the vehicle.
Is the product durable, safe?
The durability was the first criteria addressed during the design of the supercharger. Dedicated engineers with backgrounds in compressor, gearing , tribology and metallurgy, as well as thermal and structural analysis found solutions to many durability concerns. In addition, strict 500 hour customer durability tests have established a durable product. Numerous vehicles have successfully completed 160,00km. OEM vehicle durability tests. Improvements in bearing and seal designs incorporated in the product meet all OEM durability criteria. Safety, in turn, follows suit once durability is achieved.
Are superchargers noisy?
During typical driving conditions, the engine is under boost around 5% of the time, which means the remaining 95% of the time the engine is under vacuum, allowing for better fuel economy and a quieter ride. In addition, the helix angled rotors, along with specially designed inlet and outlet port geometry, also reduce pressure variations resulting in a smooth discharge flow and a lower level of noise during operation. The associated ducting and mounting used in installing the supercharger can play a major role in reducing the noise emitted by the supercharger.
Does Yella Terra see supercharging in the future?
With the continued interest in performance and the desire to maintain fuel economy, supercharging is the ideal product for the future. Using a supercharger to increase power on a smaller displacement engine, in turn achieving the performance of a larger engine, but not compromising fuel economy seems too good to be true – but that is what the Terra Charger supercharger provides.
Who uses superchargers in production vehicles?
The Terra Charger design is based on products from the world’s largest producer of superchargers and they can claim to have OEM supercharger applications for Buick, Pontiac, Oldsmobile, Mercedes, Aston Martin and Jaguar.
What’s the warranty?
Each Terra charger is warranted against faulty workmanship and materials for 12 months or 20,000 km from date of purchase – installation is outside of the manufacturer’s warranty and should be covered by the installers own warranty. Competition application of any type whatsoever are specifically excluded from warranty.