Quote:
Originally Posted by mid_life_crisis
I haven't seen it put as plainly as this (maybe it was stated in technical terms and I missed it) but if you boost this motor you need to add more fuel. If the DI is effectively maxxed out due to restrictions of the mechanical pump, you can only increase the amount of fuel coming through PI. In that case, a boosted engine has to have the ratio shifted a bit towards PI compared to stock, doesn't it?
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As @
moto-mike said, its not so much the percentage as the IPW or injection time. On my SC car I run a lower percent PI than stock yet my PI injection time is higher than stock. Think of it like this, 20% of the fuel at 12:1 AFR will be using the injectors less than 20% for 11:1 AFR. Now, let's put aside boost and needing both sets of injectors to fulfill the actual fuelling requirements, if we assume that a certain amount of PI may be required to give a homogeneous mixture, does that sit as a percentage of the mix or as a certain volume of fuel? Again, I understand that this may be over simplifying
Having gone an re-read all the old posts on here, there must be a reason why running a 20:80 split was chosen. I have seen little benefit of leaning heavily on the DI on a NA car. I have taken Mike's advice though on my car, running up to 6ms DI and then having it pegged there until redline seems to.work nicely.