Tuning fuel, how do the calculations work?

[troy]

Currently my fuel map is a bit all over the place and I want to tidy it up. Currently setup as map vs rpm.

Example:

I have tuned 4500 rpm 80kpa to desired AFR, and resulting pulse width is 4.2ms.
Is setting 4.2ms for the rest of the rpm load sites for 80kpa going to result in a similar AFR? Or does the pulsewidth need to increase with rpm, or is rpm part of the calculation?

[stevieturbo]

In simple terms, PW will increase with engine load as long as airflow through the engine increases. So fuel demand will need to increase to match airflow.

You'll need to tune more than one site though.

[troy]

Yep, I understand that PW will increase as engine load does (KPA).

But what about at the same KPA and increasing RPM.

ie, will the pulsewidth at 80kpa 2000rpm be similar to 80kpa 5000rpm?

[Rob Stevens]

The injectors fire every engine cycle, generally the PW is at its maximum at peek torque and drops down either side of this on the rpm scale.

So to answer your last question, yes but consider my statement above.

[stevieturbo]

Yep, I understand that PW will increase as engine load does (KPA).

But what about at the same KPA and increasing RPM.

ie, will the pulsewidth at 80kpa 2000rpm be similar to 80kpa 5000rpm?

I already explained clearly.

Engine load is not KPA. That is simply air pressure.

I said fuel demand will increase with engine load, ie airflow.

Obviously an engine will consume more air at 5000rpm than it will at 2000rpm.

[ignitionautosport]

for a given rpm, pulse-width wil increase as torque (ie engine efficiency) increases.

So it will increase to peak torque at which you will have max pulse-width, then drop again as torque drops after that.