advice needed for arduino as diesel injection brain...

PaulS:
If the uC is to be used, that variable relationship needs to be maintained, or the performance of your engine is going to change. And, probably not for the better.

That's for sure Paul.
The fun part is that we don't do it this way because it will gain power but mostly because others don't do it this way at all.
Will order a Mega tomorrow and gonna have some fun...