I have a 1995 Defender 110 300 TDI and often tow an ex-Army Sankey MkIII trailer converted for camping.
Until late last year, I was averaging 26-27.5 MPG (see note 1)
My old steel military raised air intake (RAI – see note 2, Bearmach or Mantec brand I think) with 2.5 inch internal diameter tube was rusty and needed replacing; and I replaced it with a Mantec polyurethane 3 inch tube RAI (with Donaldson Air Ram head). This immediately increased my MPG to 27-28.5 MPG; I also noticed a small increase in power. This set me thinking, and I explored the airflow inside the engine bay.
On the inside, the Land Rover air duct box and hose appears to reduce the cross-sectional area through which air flows, yet the air cleaner box has a 3 inch inlet (this applies to both the standard Land Rover air cleaner, and the military Wolf / Donaldson air cleaner box which I use —without the second filter safety element on UK roads).
So I explored the question ‘what would happen if there was a 3 inch minimum cross-sectional area for air to flow from RAI head to air cleaner box intake?’
Before I could answer this question, I had to address the cause of an MOT failure (excessive emissions). The expensive solution to this was a new turbo (the wastegate had seized on the old one), new fuel injectors (the old ones were 20-25 % out), fuel injector pump reconditioning and new glow plugs. While I was at it, I also got my local garage to do an engine carbon clean!
Doing all this took my fuel consumption to 28.5 - 30.5 MPG, produced a very noticeable increase in power —especially when towing uphill— and negligible emissions.
I could now answer the airflow question!
I noticed that the air duct box for the 200TDI has a circular cross-section, as opposed to the rectangle of the 300TDI, and while the box is basically the same shape, it is a mirror image because the 200 TDI air duct is on the left hand side, whereas on the 300 TDI it is on the right hand side.
So I started looking for something similar to the 200 box which would fit a 300. My research led me to the Nugget Stuff sealed air intake box which was designed for the Puma TDCI with a 90 mm outlet. I had a chat over the telephone with Wayne Nielsen at Nugget Stuff, and he sent me a Puma sealed air intake box to try, with some 90mm hose, a stepdown ring and a length of 76mm/ 3 inch hose (superb quality hose!).
Last week, the system was installed into my Land Rover. I immediately noticed an increase in power and a lower tone in the engine sound; I could accelerate like a boy racer!
The day it was fitted, I called Wayne and said that I expected my fuel consumption to increase because my right foot was enjoying the ability to accelerate so much more quickly! After a day or two, I checked my fuel consumption (my local garage pump really does dispense exactly what it says; I have checked!), and sure enough I was doing 26.5 MPG (short school runs and local errands).
After a week, having now disciplined myself to be more ‘sensible' in how I drive —but I am still driving faster than I did —I am now doing 29.8 MPG. That’s very close to my best ever 30.5 MPG which was achieved with less speed and engine power.
Conclusion —the combination of a 3 inch RAI and minimum 3 inch air flow through to the air cleaner box on my Land Rover has increased power and engine efficiency very noticeably, and given me a sealed system.
1 On purchase in 2012 it was 18 MPG; the increase to 26 was achieved by fitting: full width intercooler (also increased power by 25%), full silicone hosing, EGR blanking plate, RAI and frequent tyre pressure checking.
2 In my view, an RAI only keeps the air intake out of the dust; and an RAI only becomes a snorkel when the air intake system is sealed for wading.