Interesting info on B3702 Injection timing

[LS1_Dragster]

I messed with this value on my 454 and it seemed to make it run a little better at idle so I figured I would mess with it on my wife's dragster.

The dragster has a 2001 LS1 with PRC 2.5 Heads and MS3 cam, all else is stock and has 80K miles on it.

First run at the track was with no changes from prior runs for the past year, corrected altitude was 7123 and the times were typical for the D/A:

60 -> 1.338
1/8 -> 5.899
MPH -> 116.65
1/4 -> 9.270
MPH -> 145.02

Did nothing but add 20% to B3702 across the board. The next run the D/A was 7380 which is little worse then the first run:

60 ->1.305
1/8 ->5.822
MPH ->117.73
1/4 -> 9.164
MPH ->146.38

It was a pleasant surprise to see such a huge reduction in ET. At this point the WB02 was reading rich so I leaned it 2% and it ran:

60 -> 1.311
1/8 ->5.801
MPH -> 119.01
1/4 -> 9.103
MPH -> 148.44

We're talking .17 reduction because I changed the injector timing which in turn show it running too rich. Keep in mind that the program I have has been running since last year and being a dragster what extremely consistent, so this is a true reduction.

Next time out I will get the WB02 correct then add some more to B3702 and see if there is even more to be gained. It's amazing how the air/fuel mixture changed so much....

Food for thought.

Lee

[5.7ute]

Thanks for posting that info Lee.
Just to complicate things a bit, what injectors are being used in this combo? & what duty cycle are they maxxing at?
I have lost a couple of mph since upping the injectors for a dry nitrous shot, all other things being equal & was going to be looking at this table. I believe the smaller pulsewidth for the larger injectors is not getting a decent mix in the cylinder. Hopefully I should be getting back on the dyno before the 1320x meet here & will post any thing I can add to your findings.
Cheers Mick

[LS1_Dragster]

The injectors are accel 36#, fuel pressure is 50# max duty cycle is 71% and max 13ms.

I can only assume that since the cam is larger then stock it's going to be opening way sooner so by adding to the table it sprays closer to when the valve is closed so it gets better atomization.

It also makes sense why it shows running richer afterwords. If the fuel wasnt atomizing and some raw fuel was was leaving the head it would tend to cool the O2 and give a false lean condition. I estimate that it's probably around 5% too rich after this change.

Cant wait to make more changes next time out!

Lee

[joecar]

Very interesting, thanks for posting.

[LS1_Dragster]

Just an update:

Took the dragster out last night and played with injector timing on one run. I increased the value 15% more and reduced the et by .070.

I wanted to experiment more but it was only the last two runs for that setting to verify the next run wasnt a fluke. Both runs picked up .07 with the identical DA.

Here's the data for B3702:

LABELS Injection Timing (mS)
ECT °F {link: SAE.ECT} Value
-40 3.523438
-18 3.523438
3 3.523438
25 3.523438
46 3.523438
68 3.523438
90 4.902344
111 6.281250
133 6.281250
154 7.660156
176 7.660156
198 7.660156
219 7.660156
241 7.660156
262 7.660156
284 7.660156

And B3703:

LABELS Injection Timing Trim (mS)
ECT °F {link: SAE.ECT} Value
-40 7.660156
-18 7.660156
3 7.660156
25 7.660156
46 7.660156
68 7.660156
90 7.660156
111 7.660156
133 7.660156
154 7.660156
176 7.660156
198 7.660156
219 7.660156
241 7.660156
262 7.660156
284 7.660156


Next time out I will increase it more and see what happens.....

Lee

[joecar]

Some of us are trying to figure out what crank/cam/valve event the injector timing tables are relative to (e.g. time BBDC...?)...

We appreciate your efforts in experimenting with this...

5.7ute (Mick) is very interested in this.

[Gelf VXR]

Some of us are trying to figure out what crank/cam/valve event the injector timing tables are relative to (e.g. time BBDC...?)...

We appreciate your efforts in experimenting with this...

5.7ute (Mick) is very interested in this.

Hi Joe

I believe the injector timing is in crank regress and relative to TDC on the compression stroke?

Foe example on the LS2 the advance is 490 degrees when cold and 220 degrees at normal running temps, so the timing events for the LS2 are as follows:


Engine cold

Inj fires. 130 BTDC. CLOSED INLET VALVE
IVO. 16 ATDC
ICL. 118 ATDC
IVC. 40 ABDC


Engine hot

IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC

[joecar]

Hi Joe

I believe the injector timing is in crank regress and relative to TDC on the compression stroke?

Foe example on the LS2 the advance is 490 degrees when cold and 220 degrees at normal running temps, so the timing events for the LS2 are as follows:


Engine cold

Inj fires. 130 BTDC. CLOSED INLET VALVE
IVO. 16 ATDC
ICL. 118 ATDC
IVC. 40 ABDC


Engine hot

IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC

Hi Gelf,

That does make sense (relative to TDC compression stroke)...

The LS2 injector timing is directly in degrees... makes visualization easier...

The LS1 injector timing is in milliseconds, so I have to convert that to degrees based on rpm:

offset[°BTDC] = 720 * Toffset * RPM/120000

where Toffset is in ms,

range of Toffset B3702 is 0° to 8°, so offset[°BTDC] range is 0° to 288° (at 6000 rpm)... does this make sense...?



BTW: oh, your IVO would be 16° BTDC (to give you ICL 118°).

[Gelf VXR]

BTW: oh, your IVO would be 16° BTDC (to give you ICL 118°).

Are you sure? 118 centre line, intake duration 204 degrees @ 0.05

118 ATDC - 102 = 16 ATDC

[Goldfinger911]

Hi Joe

I believe the injector timing is in crank regress and relative to TDC on the compression stroke?

Foe example on the LS2 the advance is 490 degrees when cold and 220 degrees at normal running temps, so the timing events for the LS2 are as follows:


Engine cold

Inj fires. 130 BTDC. CLOSED INLET VALVE
IVO. 16 ATDC
ICL. 118 ATDC
IVC. 40 ABDC


Engine hot

IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC

The injector firing event of #1 cylinder is based off the crank trigger at TDC on #1. Also known as tooth #0 (on a 48 tooth crank trigger; 7.5 deg per tooth).

I have been playing with "a brand-x stand-alone EMS" on my LS1 and you can set the ignition and injector firing events of each cylinder by degree or tooth. More importantly you can see exactly when the injector is firing in both ways as well.

The reason I bring this up is I was amazed to see how a slight movement of the injector firing event affects idle, AFR, idle load, and throttle response. You also immediately notice things like, your AFR getting leaner on the gauge, but the exhaust smelling like unburnt fuel. So far, adjusting the event so as to yield the richest idle mixture (the most burnt fuel at a fixed pulse width) seems to get me closest to optimal with everything else.