proper way to tune the B0720 table

[ShawnM]

From what i can tell the B0720 table determines how much fuel the ecm thinks it is getting from the inectors based off of fuel rail pressure and injector on time. It would seem that all of the engine fueling is based off of this table. I would consider this a pretty important table to make sure it's correct. Being that these numbers should change for different size injectors, how do you figure out these numbers accurately?

[LB72004]

these numbers are not as important as you may think. the original figures where likely derived from bench testing the injectors and finding out how much fuel flow was occurring. they where then adjusted based on how the engine ran/how they wanted it to run.

when you know the orifice size you can figure out the flow. doubling the flow requires the injectors to be open twice as long or have four time as much pressure.

now i have never tuned for larger injectors but i believe it is based more on experience and some guess work.

off course you dont want to go crazy with adjustments, so start small and play it safe

[killerbee]

If using larger capacity injectors, it stands to reason that pulse time should be lower for a desired constant power delivery.

[ShawnM]

these numbers are not as important as you may think. the original figures where likely derived from bench testing the injectors and finding out how much fuel flow was occurring. they where then adjusted based on how the engine ran/how they wanted it to run.

when you know the orifice size you can figure out the flow. doubling the flow requires the injectors to be open twice as long or have four time as much pressure.

now i have never tuned for larger injectors but i believe it is based more on experience and some guess work.

off course you dont want to go crazy with adjustments, so start small and play it safe

not to argue but you really couldn't be further from the truth-most of the fueling tables in the ecm are based off of fuel quantity. if the ecm doesn't know the proper fuel quantity the injectors are putting out all of your tables will be off. We are buiding some 550-600 hp marine engines so guess work is out the window.

[LB72004]

i am pretty sure i could be further. check out this thread: http://www.dieselplace.com/forum/sho...d.php?t=388802

if the ecm doesn't know the proper fuel quantity the injectors are putting out all of your tables will be off

this is correct. all of the tables ARE off. BUT they are all off the same percent, so it all lines back up in the end.

if you want to have the most accurate tables then you must adjust for the injector lag. it looks as if GM didn't account for this and put in calculated values with zero lag. just remember if this is for high HP engines then you wont be able to make more HP then stock with the "correct" table. they have to be incorrect in order trick the ecm into delivering more fuel. but i am sure you already know this if you are making 600HP engines.

what i am trying to say is that the B0720 table does not need to be accurate for the engine to run properly, in fact the reverse is probably more true

no hard feelings
Jason

[THEFERMANATOR]

GM DID account for lag in there tables(or at least they did for LB7's). You can see it in the pilot tables pretty predominately, but it is there in all of them. I spent quite a bit of time finding the lag, and what actual flow times were what when I did my first tune for oversize injectors. Once you find the lag and have a basic understanding of how much oversize equivelates to what, you can set one up pretty close right out of the box.