How much can you tune a 4.6 Disco?
Please forgive the blatant sales plug, even though I'm a paid-up trader on this site. I thought you may enjoy a little clip of a Disco II I set up last year. It's well worth turning the volume up for this:
[ame]https://www.youtube.com/watch?v=UTtexZGLeIA[/ame]
North American Specification (NAS) 4.6 Discovery 2 MAF
The 4.6 Litre version of the Discovery was only sold in North America, Canada, and Mexico. It was fitted with a larger Mass Air Flow (MAF) sensor, as used on all versions of the P38 Range Rover.
It is possible to fit this sensor to the 4.0 Litre vehicles at the same time they are reprogrammed with a Tornado upgrade, as the MAF characteristics are programmed in the software. It will not work properly otherwise.
Using a larger MAF will cause the system to see less air flow than the engine is actually consuming, so it will never add enough fuel. On top of this, there will probably be too much ignition advance at high loads for the same reason.
As yet I haven't had a chance to test the different MAF sensors back-to-back on the dyno, but my clients tell me it is worth around 10 BHP.
Since these are all parts from a standard vehicle, the correct air filter box lid and inlet trunk are available from the Land Rover parts catalogue. Alternatively they can be easily sourced from one of the many good USA vehicle breakers.
PHC000110 Air Filter Box Lid 4.6
PDH000480 Hose - MAF to Inlet Manifold 4.6
Why re-program for a larger engine and MAF?
Quote:
Originally Posted by
ozscott
So to summarise....is it the case that a 4.6 converted thor d2 with original 4.0 intake, injectors, maf and ecu will run as hard as a north American 4.6 stocker? And is there any need to change ECU for a 4.6 hi comp?
Cheers
Using a larger MAF will cause the system to see less air flow than the engine is actually consuming, so it will never add enough fuel. On top of this, there will probably be too much ignition advance at high loads for the same reason.
Motronic actually performs a very sophisticated measurement of the exact quantity of air the engine is consuming, which is the basis of all the fuelling and ignition calculations. In order to do this it needs to know the exact characteristics of the MAF meter, which are hard-programmed into the software.
Whilst the Motronic system will run a 4.6 engine even with a 4.0 Litre tune and standard MAF, you certainly won't be getting the best out of it. As your motor has Oxygen sensors in the exhaust, the fuelling runs in closed-loop which gives it the ability to trim the fuelling to suit the engine. Of course it will only be using the preset factory targets for this function. The ignition has knock detection to prevent detonation, which will also trim back any dangerous levels of ignition advance.
A couple of years ago when nobody could do anything with these systems, the stark choice with a capacity upgrade was to drop it in the hole and see what happened. As you can see from the last paragraph, Motronic will have a good shot at making the best of it. Indeed there are hundreds of these vehicles running around with 4.6 engines operating on 4.0 Litre tunes.
The fact that they work has lead to the general opinion that the conversion works, which is evidently true. However I will explain why you can get a very big improvement by reprogramming the ECM to suit the new larger engine.
As a bit of background, there are over 150 versions of the software for the Disco and it is important that you have the correct one. Earlier systems such as GEMS had software that would cope with pretty well any configuration of the vehicle, with just a few software switches. Although there are four types of Motronic ECM, the software is unique to each possible configuration of the vehicle.
The ECU mapping will need revision to accommodate the larger capacity, and here are the reasons why you would get a bad result from a 4.6 engine on a 4.0 map. The engine's fuel and ignition requirements are determined by engine speed and load. Engine load is determined by measuring the true mass of air that the engine is consuming at any particular speed, using the "Hot Film" Mass Air Flow (MAF) meter.
Mass airflow is proportional to the torque that the engine is producing (for this type of engine), and hence it is closely related to the engine capacity. This is also heavily influenced by atmospheric conditions such as barometric pressure, temperature, etc.
Therefore it is vital that the software is programmed with the correct maximum mass air consumption of the engine, known as airflow meter scaling. This is vital for good driveability and fuel economy especially on large capacity engines, and allows correct control of part throttle fuelling. Note that airflow meter scaling determines when the top of the fuel map is reached. When using an engine of larger capacity than the software was designed for, the top of the map will be reached too soon. This leads to over-fuelling at part throttle, and under-fuelling at full throttle.
A re-profiled Fuel Map which provides good fuel economy on part throttle, and allows engine to rev more freely (standard profile reduces fuelling heavily after 4000RPM). This produces quicker, more progressive throttle response and better mid range torque.
Although the ECU can work around large errors in the fuelling where Oxygen sensors are present where the map is significantly incorrect, when it reaches the limits of adjustment it will upset the entire fuelling learning process.
When re-calibrating the Motronic ECM for a larger capacity engine, there are actually over 38 maps that need re-scaling for both engine load and speed. This level of detail is one of the reasons why the Tornado upgrades are not cheap, although I do believe that the quality is unmatched.
