Injector Timing

[Caleditor]

I need help figuring out injector timing.

I have a car in the shop with a big cam. The owner has no information on the cam. I am not sure if he is the one that had it installed. When the car came to me it was idling at 71+ kpa and now I have it in the low 50's.

I am looking for a test procedure that would dial in the injector timing for the cam.

[delcowizzid]

the guys i know tweak it untill you get the richest a/f ratio on wideband

[EagleMark]

What would be the mathematical solution with known cam specs?

[mecanicman]

Easiast way to get close is know the cam events of the stock cam and adjust eoit by the differance of the new cam events. I have a spreadsheet somewhere someone created to figure it out. If you dont know the cam specs you have to tune your table reasonably close first at least in a given area. Then push the eoit values back until you can see a differance in how it runs, this will usually richen the fuel trims also. Can see results on dyno, pick up torque at lower rpms only in my experiance.

[delcowizzid]

one would wonder if it could be done with a spreadsheet with varying amounts of reversion depending on cam events

[mecanicman]

The theory is the fuel is sprayed against the back of the intake valve to use its heat to aid in evaporation. The idea of using the cam events to shift the timing just tries to maintain the injection relative to valve events. It only seems to make a differance at low rpms as when injector duty cycle climbs and therefore airflow increases(port velocities) it becomes a nonissue. I have used the spreadsheet with success, only when there has been evidence of an issue. It's surprising how different the engine runs below 2-2500 rpm when this change is required.

[Caleditor]

Please read these threads on cam timing with specs

http://www.hptuners.com/forum/showthread.php?18549-Please-Help-Define-Injector-Timing

http://www.hptuners.com/forum/showthread.php?12605-When-does-an-injector-quot-turn-on-quot&highlight=injection

http://www.hptuners.com/forum/showthread.php?23465-Cam-Overlap-vs-Injector-Timing

[Caleditor]

If you ever get a car in with a big cam, no cats, and it smells Very Lean or what most think is a Rich smell. This is actually raw fuel making in into the exhaust from both the intake and exhaust valves open when in overlap. Injector timing can help if not eliminate the smell and the cloud that follows the car like Pig Pen