Blowtus

Hi guys. I've just got the rtek 1.5 chip working in my moderately standard s4 turbo. I understand that the fuel system starts running into it's limits somewhere around the 10psi mark. Can anyone confirm what duty cycle the injectors are comfortable at with the rtek chip in? I'm planning on building an electronic boost control kit that bases it's responses on duty cycle. ie, 70% duty cycle I can tell it I want 12psi, 75% have 9psi, and 80% have the wastegate totally open, reverting to stock pressure. Not real clear on those figures obviously, but currently this sounds like a great way for me to safely maximise the cars output.

Basically, what is the hard limit for injector duty cycle, and where would be a good point (I don't want to stuff the injectors) to start dropping boost?

NZConvertible

If you mean the AutoSpeed/Labtronics IEBC from Jaycar, you can't use it. It's an excellent boost controller, but because it uses injector duty cycle as it's load input it can't be used with the Mazda rotary's staged injection system. When the secondary injectors come on the duty cycle halves (since total injector flow would otherwise double). This would be interpreted by the IEBC as a halving of engine load, and would effect the boost accordingly. I was disappointed to find this out, as I was quite looking forward to bulding that kit.

Blowtus

ack! Didn't consider that one.
If I were to specify a certain psi for everything between 10 and 80% it should work though, shouldn't it? Hence the idea of it regulating max duty cycle would still work? I just wouldn't get the nifty ability to make it all smooth and happy...

NZConvertible

You're not setting a certain boost level, you're setting a certain solenoid duty cycle. To maintain a flat boost level the solenoid duty cycle needs to change as rpm and airflow change. That's why if you look at the tuning curves published in AutoSpeed the solenoid duty cycle changes considerably as load changes to keep boost level.

The whole system is based on the fact that load is normally proportional to injector duty cycle, but we have a huge step in that relationship. I think that no matter what you do with the tuning you'll get a huge boost dip as the secondaries come on. Sucks I know.

I was going to email AutoSpeed to get their opinion, but I'm pretty sure they'll just confirm what I think will happen. To make this doubly worse, the staged injection also means you can't use their cool Digital Fuel Adjuster with different sized primary and secondary injectors. It'll work fine with stock injectors, but if you need to upgrade the injectors you have to do all four. Great projects, wrong car...


BTW, for anyone wondering what we're talking about, it's these DIY kits:

Independent Electronic Boost Controller
Digital Fuel Adjuster

Blowtus

yeah, did some more thinking and realised I had it around wrong in my head
I wonder if there'd be any sort of simple electronic contraption that could somehow average them together. Maybe I'll email and see if they've got anything useful to say.

A closed wastegate until the secondary's fired would be too much... and I imagine the car would lose too much response to make having it permanently open a small amount any good... hmm