Recommendations on when to enter PE with cams and stall converters.

[ASX29]

I have run into the this question myself a bunch of times on different vehicles I have owned. The stock tunes always seem delay the PE RPM and it seems that from a standstill with a stock calibration and you stab the throttle, the time from idle to 2500rpm feels quick to rev up from off idle even with stock stalls. With cams and stall converters, I have always removed the delay and set the enable rpm much lower (which just about every modified tune does) especially on a modified engine. My question would be, is there a rule of thumb to follow on when you should enter power enrichment. On an engine with a larger cam that moves the power band up to say for example 2500-6500rpm. Would it make sense to not enable PE until at least 2500rpm or when the engine is more efficient since the airflow below 2500rpm on a bigger cam is slower so by entering PE when you stab the throttle at idle there will be slight bog? Because even with a stall, there still is a period of time it take for any engine to rev to the stall speed and that is the time I want to clean up and cut down.

I do a lot of drag racing and where I notice where this is most noticeable is in the first 60ft. If I hold the RPM at say 1800rpm with the foot break and enter PE as soon as I stab the throttle its not as quick even if it feels quick. The AFR matches the commanded AFR of 12.8ish, so I know its not because of an over rich event. The more I delay the PE from the hit, the ever so slightly the 60ft times have improved. But its not something I can feel from a dig. I only notice it on the time slips by a tenth.

What are some recommendations?
- Should I just set the PE until the RPM matches the power band of the combination?
- Should I slow the enrichment rate so its not commanding PE so quick? (I always use 1.0)
- Or gradually enrich the PE tables in steps until you reach the power band?

[cobaltssoverbooster]

there are three states to fueling
normal operation (stoich), pe transition, and pe.
enrichment rate controls the pe transition zone fueling. by increasing the value you are increasing the transition fuel supply. some call this a pump shot or from carburetors this is what the accelerator pump cams in holley carburetors control.
you monitor this by watching the zone in which pe becomes active. during the transition you can monitor the afr in this very small zone before pe is in full effect and make adjustments to the afr via enrichment rate control.

pe transition begins based on the settings of pe rpm, pe tps, pe map, and sometimes pe torque. you typically adjust the enrichment based on load and where the engine seems to operate the smoothest (without dyno proof). somewhere around 65-70 kpa, 55-75 tps, and whatever rpm feels smooth. i personally start at 2500 rpm and make test pulls from there. the map activation prevents the pe from enriching during cruise or minor acceleration. set it too low and pe will stay active in cruise or come on too soon during minor acceleration and cause a sluggish feeling from over fueling.

its really hard to say what every setup likes because they behave differently. your time slips are good indicators of pe control performance, definitely keep using those as a tuning aid.

[IARLLC]

It seems likely that an enrichment rate of 2.0 might get you a better 60 foot time with a bigger cam.

[ASX29]

there are three states to fueling
normal operation (stoich), pe transition, and pe.
enrichment rate controls the pe transition zone fueling. by increasing the value you are increasing the transition fuel supply. some call this a pump shot or from carburetors this is what the accelerator pump cams in holley carburetors control.
you monitor this by watching the zone in which pe becomes active. during the transition you can monitor the afr in this very small zone before pe is in full effect and make adjustments to the afr via enrichment rate control.

pe transition begins based on the settings of pe rpm, pe tps, pe map, and sometimes pe torque. you typically adjust the enrichment based on load and where the engine seems to operate the smoothest (without dyno proof). somewhere around 65-70 kpa, 55-75 tps, and whatever rpm feels smooth. i personally start at 2500 rpm and make test pulls from there. the map activation prevents the pe from enriching during cruise or minor acceleration. set it too low and pe will stay active in cruise or come on too soon during minor acceleration and cause a sluggish feeling from over fueling.

its really hard to say what every setup likes because they behave differently. your time slips are good indicators of pe control performance, definitely keep using those as a tuning aid.

I know I feel like I am trying to fine tune such a small window of fueling that doesn't matter to most on the street because you will never notice. However, drag racing is an easy way to exploit tuning holes as I can actually see in real time how by simply changing the afr at the hit of the throttle from a quick lean spike to a commanded rich condition over (X) amount of time. And just preventing the lean spike then applying the enrichment later until the stall has flashed and the engine speed has started to accelerate into the power band has made big differences. And again I am working in a 1-2 second window of when this all happens. But If I can cut my 60ft time from my slowest 2.3 to a 2.1 or still getting faster, that is a huge difference. Like you noted all engines respond differently to when and where they want fuel and I was just trying to get a general starting point to start with since full PE at WOT and 1600 rpm does not work for me.

[cobaltssoverbooster]

I know I feel like I am trying to fine tune such a small window of fueling that doesn't matter to most on the street because you will never notice. However, drag racing is an easy way to exploit tuning holes as I can actually see in real time how by simply changing the afr at the hit of the throttle from a quick lean spike to a commanded rich condition over (X) amount of time. And just preventing the lean spike then applying the enrichment later until the stall has flashed and the engine speed has started to accelerate into the power band has made big differences. And again I am working in a 1-2 second window of when this all happens. But If I can cut my 60ft time from my slowest 2.3 to a 2.1 or still getting faster, that is a huge difference. Like you noted all engines respond differently to when and where they want fuel and I was just trying to get a general starting point to start with since full PE at WOT and 1600 rpm does not work for me.

i dont blame you i tune for all of this as well. Its just hard to throw you a perfect value so i made an attempt at a rough starting point and clearing up the controls so you could target the zones properly.

[ASX29]

i dont blame you i tune for all of this as well. Its just hard to throw you a perfect value so i made an attempt at a rough starting point and clearing up the controls so you could target the zones properly.

Well you helped clear up the fact that I am not crazy! I thought about putting it on the dyno but then again its not practical to start a dyno pull at 1500rpm. I guess a loose stall to quickly flash through that transition is the easiest route.