The primary reason for the selection of the Prima engine for duty in your Land Rover will be fuel economy. The Montego is well known for being frugal, 55mpg averages are common, but its also one of the cheapest engines to buy at the moment due to the ten plus year old cars failing their MOTs. The prima is also fairly well know for a long service life as well as its e?ciency and it is a high reving diesel with very similar power delivery to the Land Rover petrol engine. It is not unusual to pay $50 – $150 for a car with a good engine, in fact many people are given the carsm. So they have an edge over a lot of the other possibilities. The engine doesn’t ?t on a Land Rover gearbox, so an adapter plate is needed to ?t between the two, I supply these. The other problems are flywheel size and starter rotation, these are solved by the use of parts from a van supplied with the normaly aspirated version of the engine. The conversion doesn’t require any chassis or bulkhead modifications, you will have to make or adapt an exhaust, alter the wiring and fabricate a throttle cable other than that it’s all a bolt in job. The conversion should make a swb do between 34-40mpg, I manage both figures, its drivable at motorway speeds and will generally keeps up with traffic that a 2.25 Land Rover diesel wouldn’t.
The Montegos claimed consumption figures of upto 60mpg certainly makes it a suitable candidate for improving the consumption of your Land Rover. I do 34-40mpg, depending on driving conditions and speed. With 34 mpg being motorway driving and 40 mpg pottering around the lanes where I live; this makes sense as the drag at 80mph on the motorway is a lot more than the drag when pottering around at 30-40 mph. I have a 36 mpg average over the last few months, this is a long enough period to use this ?gure as an statistical average. Cost of Conversion. The major cost will be the custom parts, adapter and mounts. Unlike some other conversion where the engines will be the large part of the cost. I can speculate on the cost and I would expect it to be of the order of ¿500 that’s assuming you pay ¿100 for the flywheel and starter motor1 . I haven’t included things like a clutch as you would of needed a clutch anyway. You will also recover some of the cost by selling your old engine2 .
Return on your money can be seen in Figure1, this is based on current diesel and petrol costs and assuming 35mpg prima, 20 mpg petrol, which is being generous as some people only get 15-17mpg from the 2.25 petrol. The cost of conversion to LPG will in all liklihood make running lpg plus the cost of conversion very similar to the total for the Prima.

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