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What's the largest injectors?

General questions and chit-chat about the ECU+.

What's the largest injectors?

Postby justin0469 » Mon Jan 23, 2006 2:48 pm

So I am having a discussion with someone about the capabilites of ECU+. They were wondering about its ability to control 1400cc injectors. (little overkill I think but whatever) I know that you can type in your injector size now, but does it really control any size injectors by just doing calculations to determine what to do with them? Even if that is so, what is the largest injectors that someone has been successful with?
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Postby honki24 » Wed Jan 25, 2006 12:48 pm

you are very best off getting whatever injectors you want, sending the ecu in to your favorite flash tuner (ex: dynoflash) and having him tune for the injectors and do the fine tuning w/ the ecu+. All because of the inherent piggyback nature of injectors. W/o getting too complicated in the detail, the fuel and timing adjustments are vaguely linked, so it becomes exponentially more difficult to tune for larger injectors via the piggyback.
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Re: What's the largest injectors?

Postby tlcoll1 » Thu Jan 26, 2006 8:30 pm

justin0469 wrote:They were wondering about its ability to control 1400cc injectors.

You'd have to do what konki24 said and get your stock ECU re-tuned for those (if it's even possible). So let's see - if the stock injectors on the EVO (550's) are good for 320 or so HP, then the 1400's should be good for 8-900 HP. Yea, that's gonna happen.

Tom
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Postby dsevo » Tue Jan 31, 2006 11:03 am

I just ordered 780's, will I be ok just tuning on the ECU+? I have read that some people get the best results by not scaling the injectors and just running it on the 550 setting. Is this true, and is there a math calculation that I can do to figure out my initial tune, like 550/780, or 780/550? I guess what I'm asking is how do I figure out what would be equivalent to 0% on 550's, or basically the stock tune (as a starting point). I might just be confused, so let me know if I am. Thanks
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Postby 992gnt » Wed Feb 01, 2006 11:11 pm

I just put in 660's, and if I set the injector scaling to 660, the car when cold will start and stall immediately. Restart it and everything is fine. If I set the scaling back to 550, it starts up just like it used to. :shock:
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Postby tlcoll1 » Wed Feb 08, 2006 9:34 pm

Most people end up richening the mixture towards idle when they set the injector scaling to match their injectors.

Tom
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Postby 992gnt » Wed Feb 08, 2006 9:38 pm

By switching the scaling back to 550's in effect I'm leaning it back out, right? I've had it set this way for a week now and the car hasn't stalled once. Even the idle is better that it was when it was set to 660's.
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Postby tlcoll1 » Wed Feb 08, 2006 9:50 pm

992gnt wrote:By switching the scaling back to 550's in effect I'm leaning it back out, right? I've had it set this way for a week now and the car hasn't stalled once. Even the idle is better that it was when it was set to 660's.

With the 550 setting you're richening it across the board.

It's a long, involved story, but with larger injectors you can't quite use the straight injector scaling and have the car run exactly right. The problem is worse the larger the injector, but what you want to do is to have the fuel curve rich in the low ranges (load load and low RPM) and progressively less rich as you go down and to the right in the maps. For 660's, you have two choices:

1. Use the 660 setting, and do something like this:

+20% +19% +18% +17%
+19% +18% +17% +16%
...
+1% 0% 0% 0%

2. Use the 550 setting, and do something like this:

+3% +2% +1% 0%
+2% +1% 0% -1%
+1% 0% -1% -2%
...
-16% -17% -18% -19%

See how the curve gets leaner as you move down and to the right? Make your curve that way. Both approaches sorta get you to the same end but in different ways.

Tom
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Postby 992gnt » Wed Feb 08, 2006 10:21 pm

What you have there makes sense, and matches what I am currently running with the 660's scaled at 550. I guess I was expecting to change the scaling and make a few tweaks, not make such a drastic change to the previous maps. I would have never gone that way on my own, since in my mind a larger injector at the same pw should drop more fuel not less. Thanks for the info, I've still got a lot to learn. :lol:
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Postby tlcoll1 » Thu Feb 09, 2006 8:37 pm

Yea - so the deal with bigger injectors is that they do flow more for a given pulse width, but they don't flow linearly more, and the ECU+'s injector scaling compensates linearly. So what happens is that the ECU+ ends up overcompensating at low loads, so you need to richen it at the bottom end.

Yea, there's a lot to learn. I sure don't know it all, either!

Tom
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Postby 992gnt » Fri Feb 10, 2006 6:49 pm

tlcoll1 wrote:... but they don't flow linearly more, and the ECU+'s injector scaling compensates linearly.
Tom


That statement goes a long way as far as my understanding is concerned. I wasn't aware that the increased flow wasn't linear. Thanks again.
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Re: What's the largest injectors?

Postby da1sexmonk83 » Tue Jun 24, 2008 11:35 am

This is a great informational thread. It is exactly what I need. But could you give me that

+__% ,+__% ,+__% ,+__%
+__% ,+__% ,+__% ,+__%
+__% ,+__% ,+__% ,+__%

Quick table for what I should put for 750cc injectors? (at least a general starting point like you did for him)
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Re: What's the largest injectors?

Postby tlcoll1 » Wed Jun 25, 2008 9:37 pm

750's are way big. Same idea as I posted above for the 660's above, but maybe start at +30-40% at idle and 0% to start at WOT and 8000 RPM. This is assuming you have your ECU+ injector scaling set for 750's. You can use the v2.10 software's 2D interpolation to build this table easily.

Tom
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Re: What's the largest injectors?

Postby da1sexmonk83 » Wed Jun 25, 2008 10:08 pm

Thats all I needed thank you, that is very helpful! And I know those are a little big. I was planning on 660's but Slowboy said that the mods on my car might even over shoot these.
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Re: What's the largest injectors?

Postby tlcoll1 » Fri Jun 27, 2008 12:34 am

I'd be careful about getting mondo injectors - they're hard to tune and make your idle crummy. I usually advise people to get the smallest injectors that they *really* need. 550's are good for low 12's in the 1/4 mile, and low 12's are about the fastest you'll see on pump gas. You'll need to be looking for 11's, running race gas, and 25+ PSI before needing more than 660's IMO. I think people sometimes over-do injectors in order to avoid buying larger ones in the future, and also it's easy to over estimate how fast your car is. In the grand scheme of things, almost no DSMs can run in the 11's, but some folks buy injectors assuming they'll be running 10's.

One man's opinion.

Tom
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