cBigganz

I'm working on getting fuel setup with my ps1000 and a base map that was set to primary hold. One thing I'm confused about and cannot find useful info on is what primary hold.

I understand the basics of primary hold, but nobody says if the primary injectors will increase or decrease with rpm after staging. For example, if you pass staging threshold at 4000rpm, is the last block what the primaries stay at? Or will the primaries follow the last column based on rpm. If the primaries are stuck at 27% duty cycle that they were at 4000rpm, even though the engine is now at 6000rpm, it seems like there is a lot of potential injector wasted. Is anyone able to clarify this a little for me?

If the primaries indeed hold exactly what value they staged at, I'll change everything to common as I don't want to hit a wall with over 1000cc worth of usable injector remaining.

Thanks!

C. Ludwig

iTrader: (27)

The pulse width follows the last column before the staging load. Duty cycle is a function of RPM. So, if you're at 40% duty for a given pulse width at 4000 rpm, with the same pulse width at 8000 rpm, you're at 80% duty. So you need to account for that. You're correct that you can generally maximize an injector more with common mode. But primary hold is thought to be easier to get a smooth transition since the primary doesn't fall off at the transition.

cBigganz

Thanks for the quick response. I think I understand the process behind primary hold now. On my current map, staging is set to 7.2 psi, at 4000rpm pulse is 8.448ms. It seems i could continue to push my staging deeper into boost. My only worry with primary mode is i would have to transition as far right as possible to maximize primaries, and that could be as high as 14psi or more. Not sure how safe it would be mess with turning fuel on and off at that point.

Just to be clear, as long as the highest rpm pulse in the staging column won't exceed highest recommended duty cycle at maximum rpm, there is no issue with primary hold aside from some flow traded for stability? I'll continue to play with this a bit as i have plenty of injector to spare for now. (2x id1000 and 2x id2000)

I'll try common mode too, which would allow me to bring in the secondaries at 7.2psi on my current tune, with 2.8ms at 7.3psi by my rough calculations. Could bring them in a bit earlier still, but this pulse should be high enough to avoid issues. Will report back which I find to be more stable and any information that may be useful to people learning to tune in the future.

C. Ludwig

iTrader: (27)

You got it. I almost always use common mode for just this reason.

You're peak pulse width should be at peak torque with pulse width falling slightly in each column as RPM rises past peak torque. So that helps you in regard to duty cycle at higher revs.

cBigganz

Thanks for the tips, I will adjust accordingly. Going to need to get it on the dyno soon for the high load high rpm stuff!

cBigganz

Update for anyone searching in the future.

I am now using "Common mode". The PS1000 "Primary Hold mode" was not a good solution for my setup (1000cc primaries, 2000cc secondaries) as I wanted transition low for safety reasons. If i had smaller primary injectors that reached 90% duty cycle around 2 psi boost, it would have worked. The tune is still a work in progress, but it runs and drives pretty well.