Thread: 300 TDi inlet air pressure test

Pressure reading of 300 Tdi air inlet system.


Project. To measure the pressure range across the air inlet system on a Land Rover Discovery 1 from snorkel inlet to turbo inlet.


Test vehicle. 1997 Land Rover Discovery 300 Tdi with VNT turbo and Safari snorkel.


Test equipment. Digital manometer ( about $30 ebay ), 2.0 M 3mm tubing, Pope or similar 4mm threaded both ends joiner, paper and biro.


Reason. To find out by how much the pressure increased across the inlet system, where the greatest increases were so as to see what actions could be taken to eliminate the restrictions. Less restrictions mean increased air flow and more air into the engine which coupled with more fuel would mean more power.


Points measured.

1. Off the 90 bend at the inlet of the snorkel.
2. At the inlet to the air box.
3. In the inlet side of the air box, prior to the filter.
4. In the outlet side of the air box after the filter.
5. On the outlet hose from the air box about 50mm along.
6. On the outlet hose just prior to the inlet of the turbo ( not read at this stage )

All measurements were taken in 3rd gear (auto) at 3,000 rpm up a small incline so the engine was under some load.




Reading Point
Reading / inH2O
Difference
Percentage


1
Snorkel inlet
1.2










7.5
50
2
Air box inlet
8.7










0.7
4.6
3
Prior to filter
9.4










2.2
14.7
4
After filter
11.6










2.3
15.3
5
Exit of filter
13.9










2.3 estimated
15.3
6
Inlet to turbo
16.2 estimated






Total
16.2
15




As you can see from this the biggest restriction is the snorkel. Part of this is the size of the snorkel and part is the fact that the snorkel has three 90 bends at the engine end. The first turns through the guard into the engine bay, the second turns before the ABS system and the third around the ABS and into the air box.
The air filter on it's own does not cause a large restriction ( well used filter tested ). The air box total has a larger restriction.


Improvements.
The snorkel could be removed but this negates the purpose of it being there so is not an option. A purpose built snorkel could be made that is of larger diameter (one of the tubular types) and goes further forward down the guard then turns directly into the air filter. This would eliminate two 90 bends in the test vehicle.


Another option would be to fit a tubular style air box with the inlet end over the outside of the filter. The outlet would be the other end from the centre of the filter, a K&N tubular or tapered style filter could be used. From the readings above the outlet from the filter is an issue more than the inlet.


Seeing that a good standard car has a total reading of 10 inH2O and a bad one 20 inH2O, the disco with snorkel is not too bad.


Read this article AutoSpeed - Ultimate DIY Automotive Modification Tool-Kit, Part 1

Been away, size is about 3" although not round, shape and size changes as it travels down the truck. I thought they were all fairly standard