The Eaton M112 superchargers fitted to 4.2 Range Rover models can be easily upgraded by changing the pulley, increasing the driven speed of the supercharger.
This is a very popular conversion proven by long term success on thousands of cars.
For the Range Rover and Range Rover Sport M112 supercharger there is a choice of 6% and or 10% supercharger upper pulley upgrade. Both work well, but the extra benefit of the 10% pulley needs a little more installation work.
The 6% or “1.5lb” M112 supercharger 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, in which case 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% supercharger upper pulleys are machined to the highest standards with ISO standard groove profiles for maximum belt grip and are availabe in our shop.
The 10% or “2.5lb” M112 supercharger pulley does require aluminium removal from the supercharger snout to reduce diameter of the supercharger snout casting, allowing clearance for the smaller pulley. The trimming task is quite achievable with DIY skills for the keen home tinkerer, and many of our customers have done this at home. Some garages can be wary to attempt the job 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 clearly noticeable difference and gives these cars a new lease of life, best described as ‘just making the engine feel bigger’. Our stainless steel 10% supercharger upper pulleys are £185.
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 Range Rovers. Aluminium has limited friction qualities when hot, which can be an issue on the small upper pulleys on these cars, but we manufacture our M112 supercharger pulleys using high grade stainless steel, with precisely machined correct ISO standard groove profile to avoid such issues. That said, if your belt is old & worn, it is always best to change it.
While snout trimming for fitment of 10% pulleys can be done in-situ using hand tools, it is a tedious job and a much tidier finish (to the ideal size retaining maximum strength and free of stress-raising flaws) is achieved when the snout is machined down in a lathe, giving a perfect finish to the exact ideal dimensions. If you need your Range Rover M112 snout upgrade with 10% pulley completed to the highest standards, send can your snout or full supercharger to us to be upgraded for peace of mind, which is one of our busiest services.
We can also provide upgraded and rebuilt Range Rover M112 supercharger snouts on core exchange basis to minimise the time your car is held up in the garage. Please email us at enquiries@powerhouse.uk or call on 01246 260665 – Option 3 to discuss.