Injector flow characteristics: Hesitation explained?
Posted: Fri Jan 24, 2003 5:40 pm
I copied and pasted this from a post on www.nasioc.com. Do you think that's how all of subaru injectors work? Are my 380cc injectors actually 190cc? Could this also explain some hesitation issues?:
"Just thought I'd post some info here on the actual flow rates for the STi injectors and the flow balance of new STi injectors.
I just got a brand new set of STi injectors which I sent out to RC engineering to be flow tested. The results are interesting (at least to me)
First of all they each were rated as having excellent spray patterns (anyone else who has done this please chime in so we can get a feel for quality)
The individual injectors were flow tested at 43 psi, static and came back with the following flow rates.
1 ---- 270.0 cc/min
2 ---- 273.0 cc/min
3 ---- 268.0 cc/min
4 ---- 268.0 cc/min
(edit) okay I posted this right after I got up (work night shift) and I made the not necessarily rational assumption that RC engineering numbers were correct and brain storming how that could be ----
Now this is the interesting part. Everyone knows these are rated as 550 cc/min injectors whats up with that. After scratching my head for a moment I realized that the advertized flow rate of 550 is 2x the actual flow rate at the stock fuel pressure/manifold pressure differential.
This can only mean one thing. Subru uses a batch fire strategy at high fuel demands firing each injector on each engine revolution, or 2x per power stroke. The net flow rate would be equivalent to an injector of twice the flow rate, only firing once at the same pulse width.
This fits several sources I've found that mention that this stategy allows better control of idle fuel air mixtures (means lower emissions). They would then be able to run the smaller injectors with longer total pulse times / power stroke at high fuel demands and dropping to smaller pulse times on injecting only once per power stroke at small fuel demands.
The thing that popped into my head was this would be a possible explantion for two things folks have noticed.
1) Several folks have seen small dips in power output on dyno runs that seemed un-explainable ---- could these mark the rpm where the ECU transitions from 1x to 2x per
power stroke triggering of the injectors ?
2) If that is the case, this is another possible explaination for those folks who have seen power losses in mid upper rpm ranges when they install after market solid crank pulleys.
It is possible that on those particular engines the torsional harmonics that occur due to the lack of damping cause rpm confusion for the ECU at the point where it must transition from single fire to batch fire modes on the injectors. In that case it would repeatedly be switching back and forth between the modes because it is not getting consistant rpm values.
Just some food for thought.
Larry
Last edited by hotrod on 01-24-2003 at 02"
"Just thought I'd post some info here on the actual flow rates for the STi injectors and the flow balance of new STi injectors.
I just got a brand new set of STi injectors which I sent out to RC engineering to be flow tested. The results are interesting (at least to me)
First of all they each were rated as having excellent spray patterns (anyone else who has done this please chime in so we can get a feel for quality)
The individual injectors were flow tested at 43 psi, static and came back with the following flow rates.
1 ---- 270.0 cc/min
2 ---- 273.0 cc/min
3 ---- 268.0 cc/min
4 ---- 268.0 cc/min
(edit) okay I posted this right after I got up (work night shift) and I made the not necessarily rational assumption that RC engineering numbers were correct and brain storming how that could be ----
Now this is the interesting part. Everyone knows these are rated as 550 cc/min injectors whats up with that. After scratching my head for a moment I realized that the advertized flow rate of 550 is 2x the actual flow rate at the stock fuel pressure/manifold pressure differential.
This can only mean one thing. Subru uses a batch fire strategy at high fuel demands firing each injector on each engine revolution, or 2x per power stroke. The net flow rate would be equivalent to an injector of twice the flow rate, only firing once at the same pulse width.
This fits several sources I've found that mention that this stategy allows better control of idle fuel air mixtures (means lower emissions). They would then be able to run the smaller injectors with longer total pulse times / power stroke at high fuel demands and dropping to smaller pulse times on injecting only once per power stroke at small fuel demands.
The thing that popped into my head was this would be a possible explantion for two things folks have noticed.
1) Several folks have seen small dips in power output on dyno runs that seemed un-explainable ---- could these mark the rpm where the ECU transitions from 1x to 2x per
power stroke triggering of the injectors ?
2) If that is the case, this is another possible explaination for those folks who have seen power losses in mid upper rpm ranges when they install after market solid crank pulleys.
It is possible that on those particular engines the torsional harmonics that occur due to the lack of damping cause rpm confusion for the ECU at the point where it must transition from single fire to batch fire modes on the injectors. In that case it would repeatedly be switching back and forth between the modes because it is not getting consistant rpm values.
Just some food for thought.
Larry
Last edited by hotrod on 01-24-2003 at 02"
