Determining safe timing limits ?

[someguy]

Short of installing a cylinder pressure sensor and/or blowing up an engine, how does one determine the limit of safe timing advancement at various RPMs ?

Is engine rattle a reliable indicator ?

Are there any rules of thumb as a starting place ?

Thanks

[2007 5.9]

I have a peak value that I use...which most would think is low...but I WILL NOT go over this value unless it's on a dyno..to verify that increasing timing over this value is necessary.

My value is 25* overall. No pilot or post

[DoghouseDiesel]

Like Les, said, without the truck on the dyno there are certain limits that I stay within.

Some of those limits are determined by nozzles spray pattern, piston bowl design, engine RPM, piston clearance, etc....

What is a limit on one truck, is not necessarily a limit on another truck.

The limits I use on an '06 - '07 5.9 are NOT the limits I use on a 6.7.

[2007 5.9]

Agreed rich...my 6.7 numbers aren't the same as 5.9...didn't see the title area...

[someguy]

I have a peak value that I use...which most would think is low...but I WILL NOT go over this value unless it's on a dyno..to verify that increasing timing over this value is necessary.

My value is 25* overall. No pilot or post

How does this change with a pilot shot ?

What is the start of timing in EFI Live ?

Is it where the main injection starts ? Or where the pilot starts ? And so if there is no pilot then its where the main injection starts ? Time to get out the oscilloscope ? :laughs:

Thanks !

[2007 5.9]

Main is the basis for all timing...pilot is x degrees before main, and post 1 and post 2, are x degrees after main.

All timing, pilot/post are referenced from main.

[someguy]

25* at low RPMs is earlier than 25* at high RPMs because the injection ignition time is about the same but the piston is moving slower at low RPMs and fast at high RPMs.

Are you accounting for that somehow ?

I wasn't really looking for a fixed number, I was more looking for what the NON DESTRUCTIVE signs were or how people were arriving at what was good and what was bad.

[someguy]

Main is the basis for all timing...pilot is x degrees before main, and post 1 and post 2, are x degrees after main.

All timing, pilot/post are referenced from main.

Are the post injections started relative to the start of main or from the end of main ?

If you make the pilot long and close to the main, will the ECM allow it to run into the main, creating one long injection ?

[someguy]

Thanks for all of this, btw.

[2007 5.9]

25* at low RPMs is earlier than 25* at high RPMs because the injection ignition time is about the same but the piston is moving slower at low RPMs and fast at high RPMs.

Are you accounting for that somehow ?

I wasn't really looking for a fixed number, I was more looking for what the NON DESTRUCTIVE signs were or how people were arriving at what was good and what was bad.

One word to answer your question definitively...

Dyno

[2007 5.9]

Are the post injections started relative to the start of main or from the end of main ?

If you make the pilot long and close to the main, will the ECM allow it to run into the main, creating one long injection ?

There are minimum delays set from end of pilot to beginning of main and end of main to beginning of post.

As long as those values are never changed, you can't have one big event.

[someguy]

One word to answer your question definitively...

Dyno I don't think a dyno will indicate when you've reached a safe timing limit. A dyno will show (at full throttle) when adding timing stops adding power. The timing at max power may still have cylinder pressures in excess of what the engine will take.

[2007 5.9]

So then back to your original post...you'd need to install pressure gauges in all cylinders.

Hp curves, sounds, and all around engine attitude will let you know.

If your not sure...I'd suggest a private tuning session with somebody who knows how to tune appropriately.

[2007 5.9]

How does one know what the "Safe" pressure limit is??

Cummins won't release this info...

[DoghouseDiesel]

I don't think a dyno will indicate when you've reached a safe timing limit. A dyno will show (at full throttle) when adding timing stops adding power. The timing at max power may still have cylinder pressures in excess of what the engine will take.

Nope, you can see exactly when you've reached the saturation point for timing on the dyno, you just have to know what you're looking for.

You'll see it on the dyno before you hear it in the motor.

And no, the dyno is not just for WOT / Max Power.

Tunes are built based on the engines build, not one size fits all. What I have my engine timed at would blow a stock engines head gasket on the first pull.

Safe pressures are, again, based on the engines build. A stock motor vs a motor with a 12V crank, Carrillo rods, .100" taken off the top of the pistons, heavy duty rod bolts, etc., will handle different pressures.

And yes, timing values vary with RPM's.

No need for a scope, the values are right there......unless you're tuning Smarty style.