Description
Jaguar 4.2 Upper Supercharger Pulley – AJ33S / AJ34S / 428PS
Jaguar 4.2 upper supercharger pulley upgrades are one of the simplest ways to increase Eaton M112 supercharger speed on compatible Jaguar, Land Rover and Range Rover 4.2L Supercharged V8 applications. A smaller upper pulley increases the supercharger drive ratio, producing more boost and stronger midrange performance without replacing the factory supercharger.
Alpha Jag offers a basic 6% press-fit pulley as well as a modular anti-slip pulley system available in 6% and 10% configurations.
Standard vs Modular Anti-Slip Design
6% Standard Press-Fit – $285
The standard 6% pulley is a conventional one-piece press-fit upgrade. It increases supercharger speed by approximately 6% and normally does not require material removal from the supercharger snout. This version does not use the Alpha Jag anti-slip surface and is not modular.
6% Anti-Slip Modular – $365 Press-Fit / $385 Heat-Shrink
The 6% Anti-Slip version uses Alpha Jag’s modular two-piece design. A reusable hub mounts to the supercharger shaft and the 6% anti-slip pulley ring bolts to that hub. The belt-contact surface is designed to improve belt engagement and reduce the likelihood of belt slip under higher supercharger load.
Choose either Press-Fit installation for $365 or the Heat-Shrink installation version for $385.
10% Anti-Slip Modular – $365 Press-Fit / $385 Heat-Shrink
The 10% Anti-Slip version uses the same modular hub concept but with a smaller 10% pulley ring for the greatest supercharger-speed increase and the highest performance potential of the available upper-pulley options.
Choose either Press-Fit installation for $365 or the Heat-Shrink installation version for $385.
Important: the 10% pulley requires clearance modification to the aluminum supercharger snout. The snout must be carefully shaved or machined to provide adequate clearance for the smaller pulley ring. Professional machining is recommended when practical.
Reusable Modular Hub – Upgrade from 6% to 10% Later
One of the main advantages of the Alpha Jag modular anti-slip pulley is that the hub does not have to be removed every time the pulley ratio is changed. The hub is installed on the supercharger shaft once, while the outer pulley ring is bolted to the hub.
This means a customer can begin with the 6% anti-slip pulley and later move to the 10% anti-slip pulley by unbolting the 6% ring and installing the 10% ring on the existing hub. There is no need to pull the hub from the supercharger shaft and install a new hub.
The required snout-clearance modification must still be performed before installing the smaller 10% pulley ring.
Why Choose an Anti-Slip M112 Pulley?
As upper-pulley diameter decreases, belt grip becomes increasingly important. Each anti-slip Jaguar 4.2 upper supercharger pulley is designed to provide more positive belt engagement under load and help reduce belt slip as supercharger speed, engine speed and temperature increase.
The anti-slip surface itself is not advertised as creating additional boost. The additional boost from the 6% or 10% configuration comes from the pulley ratio. The anti-slip design is intended to help the belt maintain more consistent engagement with that pulley.
4.2L Supercharged Engine Codes: AJ33S, AJ34S & 428PS
The Jaguar 4.2L Supercharged AJ-V8 was introduced as the AJ33S and was later updated to AJ34S specification. Additional background is available in the Jaguar AJ-V8 4.2L engine overview on Wikipedia.
Compatible Land Rover and Range Rover 4.2L Supercharged applications are commonly identified by the 428PS engine code. Engine and accessory details differ by application, so exact vehicle fitment should be verified if there is any uncertainty.
Compatible Jaguar 4.2L Supercharged Applications
- Jaguar S-TYPE R 4.2 Supercharged
- Jaguar XKR 4.2 Supercharged — X100 and X150
- Jaguar XJR / Super V8 / Daimler Super Eight 4.2 Supercharged
- Jaguar XF SV8 4.2 Supercharged
Range Rover 4.2 Supercharged – 428PS
- Range Rover L322 4.2 Supercharged
- Range Rover Sport L320 4.2 Supercharged
Earlier 4.0L Supercharged Compatibility – AJ26S / AJ27S
Selected earlier Jaguar 4.0L Supercharged AJ26S / AJ27S Eaton M112 applications use the same upper-pulley architecture. More background on the earlier engine family is available in the Jaguar AJ-V8 4.0L engine overview on Wikipedia.
Owners of earlier 4.0L vehicles should contact Alpha Jag with the year, model and supercharger configuration before ordering.
Installation Notes
- 6% Standard $285: conventional one-piece press-fit installation.
- 6% / 10% Modular Press-Fit $365: reusable modular hub installed by press-fit method.
- 6% / 10% Modular Heat-Shrink $385: reusable modular hub configured for heat-shrink installation.
- The 6% versions normally require no supercharger-snout material removal, although rare casting variations can require minor local clearance work.
- The 10% pulley ring requires supercharger snout clearance machining/shaving.
- Inspect the supercharger belt, idlers and tensioner during installation and replace worn components as needed.
ECU Tuning & Supporting Upgrades
The pulley can be installed as a mechanical upgrade on many compatible M112 applications, but custom calibration can further optimize the vehicle around the increased airflow and boost. For modified builds, consider pairing the pulley with Alpha Jag custom ECU tuning and a compatible performance intake system.
Jaguar 4.2 Upper Supercharger Pulley FAQ
What is the difference between the $285 and $365/$385 pulleys?
The $285 6% pulley is a conventional one-piece press-fit pulley without the Alpha Jag anti-slip surface. All $365 and $385 options use the modular Alpha Jag anti-slip design with a reusable hub and removable pulley ring.
What is the difference between the $365 and $385 modular versions?
The pulley ratio and modular anti-slip design are the same. The $365 option uses a press-fit hub installation, while the $385 option uses the heat-shrink installation configuration.
Can I install the 6% pulley now and upgrade to 10% later?
Yes. With either modular anti-slip version, the hub remains installed on the supercharger shaft. The 6% pulley ring can later be unbolted and replaced with the 10% ring without removing and reinstalling the hub. The snout must be modified for proper clearance before the 10% ring is installed.
Does the 6% pulley require shaving the supercharger snout?
Normally, no. The 6% pulley generally clears the factory M112 snout without material removal. Rare casting variations can require minor local clearance work.
Does the 10% pulley require snout modification?
Yes. The 10% pulley ring requires careful removal of aluminum from the supercharger snout for proper clearance.
Which option provides the largest performance increase?
The 10% Anti-Slip modular pulley provides the greatest supercharger-speed increase and therefore the highest potential boost and midrange performance gain of the available upper-pulley configurations.
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