Intake Manifold Volume

[DOHCTOR_32V]

Hi, it appears that changing the Intake Manifold Volume value from 4.38 to 4.5 made me have to increase FN035 values. Peak load was 96 vs 92. Has anyone experienced this?

What else does this setting alter?

I read a post where it was said to be a global multiplier and recommended to leave this stock or always use a value of 4. What is the most recent recommendation?

[decipha]

nah thats unrelated

manifold volume is a global transient fuel modifier

you dial it in to get tip in situated

[DOHCTOR_32V]

Thanks. So just give it the manifold volume it likes on tip in? Not sure yet why the peak load at all RPM changed. Other than manifold volume, I was playing with injector timing in a reasonable range, but large swings. 4.38 manifold volume revs like a champ with this engine.

[decipha]

yep

nah that wont do it either

odd indeed

[Blocmi]

I find the peak load values seem to change with weather. I found if I dial FN035 in at home on a cool spring day, I have to adjust it again in warmer weather.

I've had a larger difference than what you're seeing just from weather conditions.

[DOHCTOR_32V]

Looking more into a few iterations of my tune with the difference tool, I did make a small change in the top of the MAF transfer curve along with the other things mentioned above.

[Blocmi]

In your case, the MAF changes were probably the cause.

The way I understand it... Load = Volumetric Efficiency

ECU calculates how much air the engine can pump and compares the expected value to actual flow the MAF is measuring. Change the MAF calibration and the calculated load is going to change.

[DOHCTOR_32V]

Thanks folks. The percentage change in MAF curve does correlate fairy close to the load shift in this case.