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Old 03-21-2006, 10:01 AM   #1
dexterous
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Default Modded injectors - Help me pick which injector to install into which cyl




I just got my results form Witch Hunter last night. I have done some searching and I cant decide where I want to install these injectors. Some say that 2 and 4 should get the highest others say 3 and 4. Can anybody recommend how I should install them?

I assume that Cyl 4 will get the highest flowing injector and Cyl 1 will get the lowest flowing injector but nothing is set in stone. From there I really dont know what to believe.
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Old 03-21-2006, 10:19 AM   #2
hotrod
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804 in #4, (drivers side rear) 798 in #3 (passenger side rear)
790 and 792 in the front holes.

Larry
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Old 03-21-2006, 10:37 AM   #3
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Thats exactly what I would do.
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Old 03-21-2006, 11:18 AM   #4
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Quote:
Originally Posted by hotrod
804 in #4, (drivers side rear) 798 in #3 (passenger side rear)
790 and 792 in the front holes.

Larry
Not trying to an ass.
But I don't understand why you would do this.
3 and 2 are the cyl with the dogleg exhaust ports. Wouldn't you want the highest flowing there?

TMS
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Old 03-21-2006, 11:23 AM   #5
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I have been under the impression that 3 and 4 ran the hottest and were typically the ones that failed.
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Old 03-21-2006, 11:40 AM   #6
Jon [in CT]
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I think most here believe that Cyl #4 runs leanest (based on EGT measurements) and is most prone to knock. It seems strange that FHI engineers haven't ever noticed that and fixed it by now. Unless it's intentional.

Subaru's modern ECUs certainly have the processing power and memory to detect knock and adjust spark advance on an individual cylinder basis. Yet they don't do this. Instead, they still seem to use the process laid out in FHI's patent US 4,726,339, which essentially says:
  • identify which cylinder is most likely to knock and mount a knock sensor close to its combustion chamber
  • only pay attention to that cylinder's knock
  • adjust timing advance to control knock in that one cylinder
  • apply that same timing advance to the other cylinders
I'm not sure it'd be wise to do something which results in Cyl #4 no longer being the one most prone to knock.
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Old 03-21-2006, 11:48 AM   #7
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4 is the closest on the fuel bank. it gets the MOST fuel, more fuel, higher egt's

3 is the leanest, thats why it fails.

1-2 fall in the middle i think.

Corrrect me if im wrong, but I think thats correct.
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Old 03-21-2006, 11:59 AM   #8
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more fuel = lower EGTs.
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Old 03-21-2006, 12:14 PM   #9
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Quote:
Originally Posted by Rokkit
4 is the closest on the fuel bank. it gets the MOST fuel, more fuel, higher egt's

3 is the leanest, thats why it fails.

1-2 fall in the middle i think.

Corrrect me if im wrong, but I think thats correct.
#4 fails 99/100. Less fuel = higher EGTs.



Quote:
Originally Posted by hotrod
804 in #4, (drivers side rear) 798 in #3 (passenger side rear)
790 and 792 in the front holes.

Larry
That's what I did: put biggest in #4, then 3, then 2, then 1.


Quote:
Originally Posted by Jon [in CT]
Subaru's modern ECUs certainly have the processing power and memory to detect knock and adjust spark advance on an individual cylinder basis. Yet they don't do this. Instead, they still seem to use the process laid out in FHI's patent US 4,726,339, which essentially says:
  • identify which cylinder is most likely to knock and mount a knock sensor close to its combustion chamber
  • only pay attention to that cylinder's knock
  • adjust timing advance to control knock in that one cylinder
  • apply that same timing advance to the other cylinders
I'm not sure it'd be wise to do something which results in Cyl #4 no longer being the one most prone to knock.
That's a damn good point Jon. I don't know which approach is better. I guess the ideal thing is the get them all as close as possible.
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Old 03-21-2006, 12:18 PM   #10
dexterous
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Guys,

First, keep in mind that this is on an STI NOT a WRX. I know that there are a number of differences between the two.

Second, are we all on the same page as far as cyl numbers go:

____ Bulk head ____

3-----------------4

top center of motor

1-----------------2
___ Front of car ___

IS THIS CORRECT?

Jon [in CT],

Are you saying that the factory knock sensor is monitoring Cyl 4? Hmmm...
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Old 03-21-2006, 12:21 PM   #11
hotrod
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The subaru is not that much different than most V8's it is very common for engines to run hotter in the rear most cylinders due to coolant flow considerations. If you study the layout of the subaru flat 4 you will see that rear of engine block does not get as much cooling as the front cylinders.

As far as the knock detection, Jon, you make an interesting point there, but if properly biased you would get all 4 cylinders having the same sensitivity to knock so I'm not sure it would change knock correction significantly unless #4 was so far off the mark that it would not knock at all when the others were in serious trouble.

Larry
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Old 03-21-2006, 12:25 PM   #12
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It would appear that I am hearing this:

804cc in Cyl 4
798cc in Cyl 3
792cc in Cyl 2
790cc in Cyl 1

Would a 1.7% difference really mean a whole lot on a car thats not tuned anywhere near the ragged edge?
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Old 03-21-2006, 12:53 PM   #13
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Old 03-21-2006, 12:54 PM   #14
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