What kinda fuel is best for my setup? - Page 2 - Subaru WRX Forum
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post #16 of 24 Old 12-01-2011, 12:44 PM
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90% is as high as you want to go to be safe at WOT at redline. however since IDC is more of a guess using pulse width or whatever on all 4 injectors at once instead of each by them selves, most believe its off by 10-15% or so. thats why some insane tuners can tune up to 110% and the car still runs. obviously its impossible to run to 110% IDC but thats the way we read it off the ECU.

i dont see why running lower would hurt anything. i mean at idle your running about 1-2%, the cars not breaking down is it?? what would a higher yet lower demand (60%) do to cause harm?

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post #17 of 24 Old 12-01-2011, 01:07 PM
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Only thing I can think of is our fuel is garbage here in the states compared to other countries.

Maybe it was just with stock injectors ? I ran stocker and modded stocker only. Never aftermarket.

Then again, I feel safer running smaller injectors at 80'ish than scaling larger injectors down.

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post #18 of 24 Old 12-01-2011, 01:09 PM
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Only thing I could make sense is that all the nozzles and injector size, latency, etc are different at different pulses/volume. I would guess they have an "optimum" spray pattern, which is why typically bigger injectors don't idle quite as nice. Just a theory, as I would guess most of these thoughts are, unless we hear it from the horse's mouth; i.e. injector engineer.
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post #19 of 24 Old 12-01-2011, 01:35 PM
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Quote:
Originally Posted by pzr2874 View Post
Hey Chris, did your tuner/you decide that 61% IDC's is ok?

I have always read/been told that IDC's should be in the neighborhood or 80-85% Maybe even 90%

Just curious
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Originally Posted by newtothegame View Post
Paul, I have heard the exact opposite almost from my tuners and such. They said you shouldnt exceed or go past 90% pretty much. Now Im confused and wondering.
Yep, IDC's should be kept below 90% just for safety's sake. There isn't really an "ideal" IDC that your injectors will run the best at. The only issue you'll ever run into is when you have injectors that are too big for the ECU to run...

Case in point with the WRX/STI, you can only run down to xx ms IPW's. If you have a big injector needs to be open for 1ms to idle nicely, and the ecu only lets you go down to 2ms, then you're going to be running quite rich at idle.

The injector dynamics/five-o injectors can go as low as 2ms pulse width, so idle isn't really an issue, even with 1000-1200cc injectors. Mine idle better than stock I would say.

Oh, and 61% is just because I bought big injectors for the future turbo If I knew I was staying with the VF52 I would have stuck with 900 or 1000's.

-Chris
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post #20 of 24 Old 12-01-2011, 03:11 PM
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So it does have something to do with voltage/power delivered to the injectors... Awesome.... Thanks Chris... can't give you any more rep....

Mods need to fix this ancient system... lol

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post #21 of 24 Old 12-01-2011, 04:00 PM
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Yep, I guess the easiest way to think about it is:

Stock 565 cc's @ 5 ms will flow about .047 CC's of fuel... A 1200cc injector will flow about .1 cc's in the same 5ms. If you just throw the injectors in without adjusting, you'll be running pig rich. When you scale them down, it adjusts the IPW.

Scaled the ecu will give the injector a shorter IPW to adjust for the extra fuel coming out for the same opening period. E.g. the 1200cc injector needs IPW set up at 2.35ms to get the same fuel into the cylinder as the stock injectors at 5ms... If your ECU can't go down that low in IPW, then you're hosed.

These are all theoretical #'s for the OEM IPW's... I'm not sure what they're actually set at from the factory.

I know there is a lot more to tuning fuel and injectors than this, but you can get a general idea of why throwing injectors into the car without tuning doesn't work.

-Chris
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post #22 of 24 Old 12-01-2011, 06:57 PM
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Also depends on if your injectors are modded or if they are factory build injectors. Most manufactures supply some type of injector data sheet that shows the flow rates at various levels of pressure. It should also include a Latency(dead time) section. One thing to remember is that the voltage they use will be different than your cars, so you will have to fiddle around with the numbers a bit.

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post #23 of 24 Old 12-01-2011, 08:52 PM
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I ran my stock injectors over 100% IDC for a limited amount of time before I did my first turbo upgrade. My tuner said it'd be fine unless I planned on running it that way forever. Which I wasn't because I was already coming back in a few months to do the turbo upgrade amongst other things.

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post #24 of 24 Old 12-02-2011, 01:03 AM Thread Starter
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I bought 1000cc from advanced fuel injection...they flow match em within 1% most are 2 to 2.5%...seem like a legitimate company...they come with clips too. I have no idea what those are for maybe they fit multiple years or something I don't know. I figure I will be running about 65% on pump and about 80-85% on e85..plus If i ever go bigger turbo I can run those on pump gas with no problem. Same price as 850s so I hope my car doesn't idle like crap. Now I am just waiting on my damn header and fmic which is on back order then im ready for tune

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