A while back while logging my 550/1200 injector statistics with my DL, I observed that my Settings 5 Pri/Sec Transition (%) of 40% was really logging at 48% and even though I had changed Sec Transition (ms) to (850/1200) * 1.5 = 1.0625 the transition was coming on too strong. Reducing % to 30 and ms to .1000 helped the logged duty cycle transition down to 38% (close to 40) and the transistion was smoother. The car ran better. This was all posted back then and is in my tuning notes. I still run the same values with my current 550/1600 setup.

Now lets go one step further for those of use who have removed the vacuum secondary butterfly valves. This might also apply to those who haven't but I can't verify that.

Consider that most of our driving is at a low duty cycle and only on the primary injectors. That means that all the fuel and air are coming through only the primary ports which is on one side of the chamber and has to mix not only into but across to the other side where the secondary ports are not yet working. Yes, it works fine. But at what point do the secondary ports become active (admiting air), and when do their injectors also start working.

I measured the TPS VTA1 at the point that my mechanical secondaries start to open and it was at 1.20 volts. Cruising in 5th gear at 1.20 VTA1 volts was at about 62mph/2700 rpm and the duty cycle was at about 19.5%. ( I have the .806 short JDM 5th gear) From logging, I know that cruisng around 95mph/4100rpm the secondary injectors start working.

That means that between 62 and 95 mph, the secondary ports are admitting air but no no fuel is mixing with it. All the fuel is still coming from the primaries. This might/should cause uneven air/fuel mixing in the chamber. I always wondered why at around 60mph the engine sometimes feels lean even though the AFRs are the same before, at, and after that speed. Unfortunately, I have know way of knowing what percentage of air comes through both ports at those speeds.

I have not been able to play around with having the secondary injectors coming active sooner to see if engine responce is better at those speeds. My single turbo exhaust manifold is out for repair.

Has anyone tested this? Yes I know the answer is NO but I had to ask!

 

Interesting find!

One thing I do know - I plumbed my boost gauge into the double throttle vacuum line for the secondary butterfly valves. I saw vacuum (closed valves) up until about 40-50 degrees C water temp, then atmospheric pressure (open valves). Once they were open, that was it - they didn't close, move, anything at that point. This was a LONG time ago, and I can't remember if it was with the PFC or stock ECU.

Point being your theory should hold true regardless if those butterflies are there or not.

A bit from my FC days - from working on numerous FC engines, it's obvious that the secondary intake runners are usually caked with carbon buildup. From what I've gathered, it's from reversion when the secondaries are not in use - stuff blows into the unused runners. This is true non-turbo or turbo as well. Almost makes you wonder if it would have been useful to have the secondary ports with some sort of valve that will let it close the port at the engine interface, then the port opens with the secondary throttle plates. But, there may be more to it than meets the eye - the "dead" port may aid efficiency somehow, this gets into the black stuff of airflow.

Anyhow, enough rambling. Dunno if the problem you're seeing could be tuned out, or if it would require a major engineering change.

Dale

 

I am not worried about the slight intermittant leaness feel at around 60 mph. It does not occur that often. I am just trying to push the envelope of responsiveness of our engines.

Have wondered how our engines would run if the throttles were in the base of the LIM which would prevent that posible secondary back flow.