Interesting info on B3702 Injection timing

[joecar]

Oh, your duration is 204...?

Then you're right, your IVO is 16 ATDC (usually it's BTDC)...


(I thought it was 236, but maybe I'm thinking of someone else's cam).

What are your cam specs again...?

[Goldfinger911]

This is great info.

So... what about when you have a cam that has a lot of overlap? The LS1 and LS2 cams have none (negative overlap); so moving the injector firing event back and forth can be done within a pretty wide window. My cam is a custom grind for the track, and has a lot of duration, a 110 deg ICL and 21 degrees of overlap... so now the EVO event comes into play a whole lot more. Would you want the injector firing even earlier to take advantage of the pull-through effect of the exhaust? Or later, to minimize unburnt fuel passing through the cylinder?

[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.

[Gelf VXR]

Oh, your duration is 204...?

Then you're right, your IVO is 16 ATDC (usually it's BTDC)...

(I thought it was 236, but maybe I'm thinking of someone else's cam).

What are your cam specs again...?

Yes, i was reffering to the stock calibration and cam - 204/211 118ICL and 216LSA


My cam is 216/229 113ICL and 113LSA

Intake opens ~ 11-13 degrees earlier, ICL is 5 degrees earlier, inlet closes around the same time.

I propose to advance the B3702 5 degrees @ normal running temps in relation to the ICL.

I'm thinkin the optimum injector timing event is after the ICL event where intake velocity is highest and optimum for evapourating all the fuel.

[Gelf VXR]

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.

I was considering the the exhaust valve timing when cold, if the valve is open later, then perhaps the timing should be retarded in line with the difference from the stock cam. For example the stock cam closes 6 BTDC, my cam closes 1.5 ATDC, so I might need to retard 7 or 8 degreeswhen cold??

[Goldfinger911]

I was considering the the exhaust valve timing when cold, if the valve is open later, then perhaps the timing should be retarded in line with the difference from the stock cam. For example the stock cam closes 6 BTDC, my cam closes 1.5 ATDC, so I might need to retard 7 or 8 degreeswhen cold??

Hmm. Thats what I was thinking. Regarding cold running... when my car starts up... the tune does retard timing and it sounds very mean out the tail pipe. The AFR is rich, but very stable. I have always wondered about this when cold.

Wait... what stock cam has the EVC at 6 deg BTDC? I thought the stock LS1 EVC was 10.5 deg and the stock LS2 was 8.5 deg BTDC?

Mine is a bit more challenging to tune for; 242/248 .612"/.617" 112+2 LSA 110 ICL.

[Gelf VXR]

Stock cam specs attached

[Goldfinger911]

I dont want to sidetrack the thread.. but an LS2 cam has an LSA of 116 right? It would have to to give you an ECL of 114. Even though... the math doesnt work out right on the open and close events.

For example, isnt IVO = ID/2-ICL ? I think those numbers are incorrect.

[Gelf VXR]

I dont want to sidetrack the thread.. but an LS2 cam has an LSA of 116 right? It would have to to give you an ECL of 114. Even though... the math doesnt work out right on the open and close events.

For example, isnt IVO = ID/2-ICL ? I think those numbers are incorrect.

Your assuming the cam is assymetric?

[eficalibrator]

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.

In the context of tuning large overlap cams, with an emphasis on throttle response and idle control, this should work fine. (It may negatively effect emissions) Keep in mind that any previous VE or MAF mapping done in the reversion sensitive region will probably need to be revisited now that you have a cleaner wideband signal.