Can injectors be too big?

[BlackViper]

I can get any size injectors for the same price and would like to know if theres any reason not to get the biggest cc ones?

The car looks at the O2 sensors to check the A/F doesn't it? So if it puts too much fuel in it would learn to turn the injectors off sooner wouldn't it?

Even if I need to get an a/f controller to make them run good I wouldn't mind. Its just if I get the biggest size so I will never need to upgrade them if I plan on doing more to my car.

I am merely trying to save money, like I would think all of you would too. So please try not to call me an idiot for asking this question.


BlackViper

 

[allwheelTSI]

well yeah.. there is certainly a such thign as too big. regardless of how big you go,if you're upgrading the injectors,you need some type of fuel control.. i'd reccomend the SAFC from APEX'i. you can go as large as 720cc with the SAFC.

 

[Groomz]

I see that you have a 2G DSM. Nice!!! Back on topic, sorry. I would recommend going out and getting a DSMlink V2. When you purchase it they will program the new EPROM chip for whatever injector you are running, so that the car will actually run if the ECU resets or anything like that. All you have to do is type in the injector size and it does most of the work, including making it idle correctly.
www.dsmlink.com

Its all there.

 

[Enigma_Man]

The quick explanation: yes, injectors can be too big.

Well. Our cars do use the O2 sensor while under light throttle to slightly adjust the a/f ratio, but not enough to compensate for even slightly bigger injectors, let alone the really big ones that are out there on the market.

You need some form of control (safc, etc) that makes the ECU see less air-flow, or an ecu replacement (dsmlink, aem ecs, etc). For example, if you buy injectors that are 900cc (2x the original 450's, and a quite large injector size), if you don't adjust the amount of air the car sees, the car will squirt 2x the amount of fuel into the engine, and you will run terribly rich, and even the O2 sensor data won't be enough to correct for it (in addition to the fact that at wide-open-throttle, the ECU completely ignores the O2 sensor, and relies on fuel maps and the airflow sensor to get the ratio right).

One of the problems with using a SAFC to correct for super-large injectors is that because you're fooling the ECU into seeing less airflow, the ECU also has maps that give more timing at less airflow levels (for better fuel mileage). But too much timing can cause lots of detonation, and wreck your engine. So the SAFCs and equivalents are only really safe for correcting for slightly uprated injectors.

If you want to go with really large injectors, the correct and safe way to do it is with a standalone, or replacement ECU (like the dsmlink, or AEM EMS). But that brings along a whole new set of challenges, and money to spend with it to buy all the other things you need to keep up with giant injectors.

Unfortunately, going fast is expensive, and there aren't too many ways around that fact. If you can't afford it, just be happy with what you have, and whatever reliability you hvae left.

-Jesse

Originally posted by BlackViper
I can get any size injectors for the same price and would like to know if theres any reason not to get the biggest cc ones?

The car looks at the O2 sensors to check the A/F doesn't it? So if it puts too much fuel in it would learn to turn the injectors off sooner wouldn't it?

Even if I need to get an a/f controller to make them run good I wouldn't mind. Its just if I get the biggest size so I will never need to upgrade them if I plan on doing more to my car.

I am merely trying to save money, like I would think all of you would too. So please try not to call me an idiot for asking this question.


BlackViper

 

[bosljeff]

Good answer.

 

[13secGST]

yep...basically like what I was going to say...Your injectors can be too big if you don't have something to tune them down with. You have to tune your injectors for your car and to me...anything bigger than 660s and I would want DSMLink or AEM EMS...I went with DSMlink for my 660s and it is really easy to tune them...just log your car cruising on the highway...just normal...then stop and let the car idle for 5-10minutes. Look at the High LTFT and the Low LTFT and to bring them closer together you adjust the injector dead time, then, to adjust everything as a whole, you adjust your global settings.

720s are hard with a AFC because they have such a long dead time. 660s/550s aren't to far off stock.

 

[out there]

i think it depends on what size injector and what type of fuel management. with the safc, i think it would be difficult to go above 900cc without going really rich at low rpms, because the most you can subtract is 50%. i'm having no real problem with my 680s, and i use the safc.

 

[allwheelTSI]

Originally posted by out there
i think it depends on what size injector and what type of fuel management. with the safc, i think it would be difficult to go above 900cc without going really rich at low rpms, because the most you can subtract is 50%. i'm having no real problem with my 680s, and i use the safc.

900cc? the SAFC can't tune bigger than 720s..

 

[theTuner]

SAFC cannot tune 660s totally either, i have 660s and i had to down the boost to 6-7 psi [ i know wastegate im sorry heh ] but it only goes to negative 50% leaned out, but if u never have lower your boost that much, then yes 660s can be totally tuned