Discussion
I fitted a Rocky Mountain Overdrive to my Defender 110 Station Wagon. It has a mixed life with green laning (not enough) and longish road journeys too. It has the 1.41 high-ratio which suits the 300 TDi engine (287,000 miles) but is a bit low geared for motorway cruising.
The options were:
Fit 1.2 high ratio transfer box
Fit Overdrive
I chose the latter because of the flexibility it gives, so far it seems to be a good choice. Cruising at an indicated 70mph in overdrive fifth is a lot quieter but it does need to be shifted out of overdrive for steeper inclines (e.g. the Lickey bank) to maintain 70. I think if anything the overdrive ratio of 0.78 : 1 is a bit on the steep side and 0.5ish would work better. The problem is that at 70mph the engine is doing about 1800 rpm which is peak torque - engine speeds slower than this are on the descending side of the torque curve. If higher road speeds were attempted I am sure it could hold 2200 to 2400 rpm with ease.
It's a high-mileage engine so I am reluctant to turn up the fuelling but will have a look at the intercooler to see how clean that is inside, maybe even fit an Allisport replacement.
100SRV
The options were:
Fit 1.2 high ratio transfer box
Fit Overdrive
I chose the latter because of the flexibility it gives, so far it seems to be a good choice. Cruising at an indicated 70mph in overdrive fifth is a lot quieter but it does need to be shifted out of overdrive for steeper inclines (e.g. the Lickey bank) to maintain 70. I think if anything the overdrive ratio of 0.78 : 1 is a bit on the steep side and 0.5ish would work better. The problem is that at 70mph the engine is doing about 1800 rpm which is peak torque - engine speeds slower than this are on the descending side of the torque curve. If higher road speeds were attempted I am sure it could hold 2200 to 2400 rpm with ease.
It's a high-mileage engine so I am reluctant to turn up the fuelling but will have a look at the intercooler to see how clean that is inside, maybe even fit an Allisport replacement.
100SRV
Two long trips completed in the past week, both 250 miles with Sankey trailer at indicated 65mph (actually 60) oh the M6. Journey time five hours on each occasion. After the motorway a couple of days local use taking the trip distance to 350 miles.
Fuel consumption worked out at 30 mpg which is 1 mpg better than before the overdrive was fitted. Biggest benefit is more relaxed cruising.
Fuel consumption worked out at 30 mpg which is 1 mpg better than before the overdrive was fitted. Biggest benefit is more relaxed cruising.
Another long trip, 400 miles mixed green laning, B and A roads then about 150 miles motorway.
56.7 litres used and just shy of 32mpg.
Very impressed.
Without overdrive it would be around 30 ish per gallon on that sort of trip.
Top up after a mix of local, A road and motorway, 116 miles and 14.9 litres gives about 35 mpg.
56.7 litres used and just shy of 32mpg.
Very impressed.
Without overdrive it would be around 30 ish per gallon on that sort of trip.
Top up after a mix of local, A road and motorway, 116 miles and 14.9 litres gives about 35 mpg.
Edited by 100SRV on Sunday 3rd June 20:16
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