Interesting info on B3702 Injection timing

[aaronc7]

reminder to self: brush up on eoit calc.

EOIT = 90 * (boundary + B3702) - 784

[joecar]

EOIT = 90 * (boundary + B3702) - 784

That's referenced from TDC at top of compression (spark plug would have just fired), right...?

I'm out of town so I can't easily look in a tune file or in my notes...

where boundary does come from (I'm not going to like the answer)...?

( I'm going to reread this thread and the HPT thread )

[aaronc7]

That's referenced from TDC at top of compression (spark plug would have just fired), right...?

I'm out of town so I can't easily look in a tune file or in my notes...

where boundary does come from (I'm not going to like the answer)...?

( I'm going to reread this thread and the HPT thread )

I simplified the equation, but if you 'write it out' I think it makes more sense. At least it did for me in trying to figure out what the math meant.

EOIT = -784 + 90 * boundary + 90 * B3702

360* would be end of exhaust stroke / start of intake stroke in the valve overlap area.

From what I understand boundary is just a known reference/starting point, separate from the 'injection timing' table. The table is not visible by default on EFI and there isn't a CAX posted on here, but it's out there, apparently. It's in the HPT tables, but obviously you can see that any change to boundary will directly affect the timing, just as B3702 would. I don't think you really need to alter boundary unless you're trying to change the timing significantly.

-784 was just observed to the starting reference point for the calculations (previously linked bluecat thread). So you just start there and work your way back from there based on those 2 values. I don't claim to be an expert or anything on this, just a guy who recently dug into it.

[joecar]

That's referenced from TDC at top of compression (spark plug would have just fired), right...?

360* would be end of exhaust stroke / start of intake stroke in the valve overlap area.

Ah, ok, I see.

[joecar]

...

From what I understand boundary is just a known reference/starting point, separate from the 'injection timing' table. The table is not visible by default on EFI and there isn't a CAX posted on here, but it's out there, apparently. It's in the HPT tables, but obviously you can see that any change to boundary will directly affect the timing, just as B3702 would. I don't think you really need to alter boundary unless you're trying to change the timing significantly.

...

Ok, that's the part I was not going to like...

ok, I guess we can play with table B3702 and not need to edit boundary.

[joecar]

I simplified the equation, but if you 'write it out' I think it makes more sense. At least it did for me in trying to figure out what the math meant.

EOIT = -784 + 90 * boundary + 90 * B3702

360* would be end of exhaust stroke / start of intake stroke in the valve overlap area.

...

-784 was just observed to the starting reference point for the calculations (previously linked bluecat thread). So you just start there and work your way back from there based on those 2 values. I don't claim to be an expert or anything on this, just a guy who recently dug into it.

Sometimes what is needed is a different perspective, then things make sense again... thanks

( I just started a new job, so I'm flat out learning all the new systems and code... the faster I go the further behind I get... lol )

[joecar]

I'm rereading the HPT and EFILive threads on EOIT.

[statesman]

I'm rereading the HPT and EFILive threads on EOIT.

Why does it even matter when your car is in pieces?

[joecar]

I'm tuning (playing with) another car (at night, after work), cam has some overlap, I want to see how EOIT change affects anything... someone said VE changes, but I don't see how it can.

Yeah... my car is in pieces, I'm slowly making progress... will post some pics soon as get suspension all back together (bushings (1LE), lowering springs (500 lb/in vs 360 lb/in), swaybars, swaybar mounts)... also new fuel pump (while rear axle is droped), new exhaust, new shorty CARB compliant headers...)

hmmm, I'm looking at the FAST 102 LSXR (has CARB EO) but this needs messing around with new fuel rails and new 100 mm TB.

[aaronc7]

What are the cam specs? It doesn't change VE in the actual sense of the meaning of VE, but best setting should yield lowest VE value/lowest injector pw. More 'efficient' / no wasted fuel I guess. If it's super aggressive cam and EOIT does indeed make a difference, then I would anticipate the low load/rpm VE table would need re-adjusted.