For a long time now there has been speculation that the tuning was different between TH, TJ, and TJ Sports/VRX.

After inspecting all of the roms (only just got a definition for the TH 3.5 - Thanks Wytwun) I can now confirm there is zero difference in both fuel and ignition maps.

What this means is in a TH model if you were to swap cams and exhaust - there is a 16kw at the fly gain (8kw from cams, 8kw from exhaust), for a TJ base model an 8kw flywheel gain from exhaust. Note this is based its mits quoted figures of 147, 155, and 163kw.

Ignition and fuel maps are the same across the board with the only difference being the TJ Ralliart ignition map which is more aggressive.

As for the 3lt ECU's running 3.5L engines, there has been a common speculation that the ECU will "adapt" - this is incorrect, the reason it still runs without damage is that the ECU is tuned for a 240cc injector and upgrading to a 275cc injector causes the fuel mixture to richen. The ignition map is way too aggressive for 91 fuel however the extra fuel balances this out (but at a cost, you will loose power and have a flat spot in the high load range).

It is possible to gain power from a 3lt ECU by swapping back to 3lt injectors as the scaling will line back up, however you will need to run a minimum 98ron as ignition advance is up to 41 degrees in places and with a lower octane fuel this can cause damage.

You talk about more fuel when using the larger injector, I don't believe this to be true on a stock engine. The duty cycle of the injector will simply reduce, right?

Duty cycle will decrease if the ECU knows there is a higher injector in place, when the ECU thinks the injector is smaller it is applying the same amount of power as it would to a 240cc injector and therefore injecting more fuel :)

Dean,
It is great that you are doing all of this research BUT please only make bold comments until when you have actually done this and tried this and tested this.....several times.

I have fitted somewhere in the order of 50 3.5 engines into 3.0 bays with the 3.0 ECU, I have done on many occasions testing with mixtures etc on some of the first ones I did to ensure that there would be no issues. We have not melted a single engine, we do not have ANY flat spots, we do not have excessive fuel consumption in fact the fuel consumptions has generally been better for most of the cars this has been done to. The power and torque has improved with most commenting that when over taking for instance they do not need to shift back out of OD, off the lights they had to adjust driving habbits as were getting a lot of wheel spin especially in the wet where the 3.0 did not do this.

So in summary, running a 3.0 ECU and a 3.5, for NORMAL driving is fine, if you are going to go hard 100% of the time then you will most likely want to do something, I did have the 3.5 running off a 3.0 ecu in my old sedan for some 8 months, it got a flogging on regular unleaded, did not melt any pistons, no knocking issues and I also do tow heavy loads as well as my boat very often, again no issues and this is where you will get issues

Also, the ECU has no frigging clue what injector is in there, do you really think it has a chat to the injector or has spy camera's in the engine bay to have a look lol The ecu will run initially a base fuel map, once the conditions are right it will then assess readings from the 02 sensor and trim from there. NO it does not have knock sensor as the older second gens do and this is unfortunate but either way, running the 3.5 injectors seems to have been the best compromise thus far for keeping the average TE/F/H on the road for the average person not wanting to scrap an otherwise perfectly good car

What I am saying here is due to the injector scaling, it is fine to run the 3.0 ecu on a 3.5, however it will run richer and lose power under high load. Don't take it the wrong way - On my research last time, I didn't account for injectors hence the ignition map would have been dangerous on 91ron with less fuel.

These are the injector scalings - They are used in conjunction with the fuel map, unfortunately we cannot alter them on TH ECU's yet, however we can on TJ-TW thanks to Wytwun :)

http://img8.imageshack.us/img8/871/injectorsize.jpg (http://imageshack.us/photo/my-images/8/injectorsize.jpg/)

The number is lesser to account for things like dirty injectors, as a result it will always run a little bit richer then possible even on a 3.5L tune.

Dean I think you need to factor in the low compression on these engines too. This allows for more leeway when it comes to all manner of things like the fuel that can safely be used in any given engine. Mix and matching injectors and ECUs between 3.0 and 3.5 engines should still be within safe tolerances laid out by mitsubishi. I think you are being too pedantic in the details here when essentially we are talking about stock engines.

Sure, if you race the things every weekend then it is certainly worth considering, but day to day driving is fine. I'm essentially agreeing to Mals comment above

Don't forget fuel trim will adjust over time as well to a certain degree.

could a 3.0L computer run a 6g75?
i have a piggyback too.