Powerhouse Automotive

Brakes | Nitrous | Superchargers

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Jaguar Supercharger 4.0 & 4.2 V8 Upper Pulleys

Jaguar Supercharger 4.0 & 4.2 V8 Upper Pulleys

The Eaton M112 superchargers fitted to 4.0 and 4.2 Jaguar and Range Rover models differ only slightly in their internal components, and use identical pulleys. Upgrading these pulleys to spin the supercharger faster, raising boost pressure, is a very straightforward conversion proven by long term success on thousands of cars.

On both the 4.0 and 4.2 models, there is a choice between 6% and 10% pulley upgrade.

6% 4.0/4.2 V8 Upper Pulleys

The 6% or “1.5lb” pulley is easier to fit, needing no material removal from the supercharger snout (except in rare cases where the snout has been factory machined off-centre in the casting, and a high spot may have to be trimmed slightly), and offers around 25bhp/ftlb midrange increase. That is a difference you can feel, especially as it gives a more instant response reducing the apparent ‘lag’ these engines are often criticised for. The majority of pulleys on the market, including those provided by other suppliers in the UK and worldwide, are the 6% variant. Our stainless steel 6% pulleys are £158.

10% 4.0/4.2 V8 Upper Pulleys

The 10% or “2.5lb” pulley does require aluminium removal from the supercharger snout to reduce diameter and allow clearance for this smaller pulley. The task is quite achievable with DIY skills for the keen home tinkerer (I changed my first one on the drive at home), though even some garages are wary to attempt it until they realise it’s actually quite straightforward, if still a bit of a pain! The extra work with a die grinder or mini belt sander pays off, as these pulleys give 35-40bhp/ftlb midrange increase. We have had more than one customer ring us when they return home from having this job done, and say “no way that is only 40bhp!”. The improvement is a black and white difference and gives these cars a new lease of life. Our stainless steel 10% pulleys are £158.

Belt Slippage

Concerns over belt slippage with smaller pulleys are a legacy of other manufacturers using aluminium for upper pulleys in the early days of modifying supercharged Jaguars. Aluminium has limited friction qualities when hot, which can be an issue on the small upper pulleys on these cars, but our upper pulleys are made from high grade stainless steel and do not suffer such issues. That said, if your belt is old & worn, we stock a range of high quality ‘Gates’ brand belts which are of superior quality to original fitment (if your pulley system has the drive ribs on both sides, you will need to source your belt from your main dealer).

Upper Pulley Installation

For DIY fitment or to trade customers, we supply all of our pulleys with a pictorial installation guide sheet, and for a small deposit we can provide a nylon pulley template to ease the trimming process on 10% conversions.

We can also provide installation service if required at our premises, which costs £165 for the 6% pulley and £285 for the 10% pulley. We would need your car for half a day.

For installation of 10% pulleys, we have developed a unique in-situ machining process to ensure neat, stress-raiser free machined finish reduction of the snout, and a cold puller fitment process to avoid any heat stress to the front oil seal (the latter applies to both 6% and 10% conversions).

Snout Machining By Mail

While snout trimming for fitment of 10% pulleys can be done in-situ using hand tools, a much tidier finish (to the ideal size retaining maximum strength and free of stress-raising flaws) is achieved when the snout is turned down in a lathe, giving a perfectly machined finish. If you need your snout upgrade with 10% pulley completed to the highest standards, send your snout or full supercharger to us to be machine finished for peace of mind.

More Information

Telephone us or email enquiries@powerhouse.uk to discuss or place an order.