Lean out fuel with larger injectors?

[2000SiR]

This might be really dumb question, but i'm learning. when you run larger injectors with boost (say 440cc and supercharged) are you suppose to lean the fuel since the injectors are larger than stock? or leave them the way they are currently set? I have a s300 ecu, and i'm trying to figure out how to get the best hp with driveability out of my set up.

Thanks

[rage2]

I would suggest calling someone to tune your S300 ecu.

[ca18det240sx]

you are supposed to tune it to maintain a consistent, non detonating mixture of fuel. When tuning a supercharged/turbocharged car, 12:1 and under is a good ratio to start at. You would want to have around a 14:1 ratio when not on boost to get better mileage, and then have it get rich as the boost comes on.

[stevo 27]

yes id say bring it to a dyno and have it tunned by a pro :thumbsup:

[barmanjay]

Originally posted by ca18det240sx
you are supposed to tune it to maintain a consistent, non detonating mixture of fuel. When tuning a supercharged/turbocharged car, 12:1 and under is a good ratio to start at. You would want to have around a 14:1 ratio when not on boost to get better mileage, and then have it get rich as the boost comes on.

Listen to him ^^^

you don't want to automatically lean out your injectors,.. you want to get it tuned professionally

you NEED to know what your a/f is coming out of your exhaust to tune properly,.. so unless you have a WIDE BAND O2 sensor,.. not one of those gay 2 wire O2's, there's no point trying to do it yourself,.. you'll probably kill your motor.

[doublepostwhore]

you should NEVER be running 14:1 14.7:1 is under perfect atmospheric condtions... 14:1 is WAY to lean. One little surge, or kick back and then your EGT's go through the roof.

start at 12:1 and APPROACH 13.5:1.

this is ofcourse if you want to keep your block in good running order... Those who lean out their map that much risk serious melt down... all for a 6-10% increase in power at the cost of your block?

Keep in mind AF changes per gear aswell.

Honnestly tuning is an art not a science... take it to an og tuner... LIKE RAGE2

[Annoyingrob]

Originally posted by doublepostwhore
you should NEVER be running 14:1 14.7:1 is under perfect atmospheric condtions... 14:1 is WAY to lean. One little surge, or kick back and then your EGT's go through the roof.

So, howcome every single car made in the last 20+ years has a narrowband O2 sensor SPECIFICALY DESIGNED to cruise the car at 14.7:1?

Yes, ideal power is achieved around 12.5:1, but you do not want to be running that rich unless you're on the throttle. part throttle maps are usually around 14.7:1. IN FACT, your EGTs will actually be LOWEST around this point. As soon as you start going richer or leaner from his point, your EGTs start going up. How do you you think airplanes trim their fuel for cruising? They rely on the EGTs.

[gpomp]

Originally posted by doublepostwhore
you should NEVER be running 14:1 14.7:1 is under perfect atmospheric condtions...
that's just wrong.

[doublepostwhore]

I was under the impression 14:1 consituted lean.

He said that he was adding a supercharger, he is asking under boost conditions. so you sir are wrong.

A bigger injector doesnt mean it WILL dump more fuel, it means it has the CAPACITY to dump more fuel... the ecu will tell it how much to dump ( a set number) so the size of the injector is invariable aslong as it does not impede the min/max flow.

I am no tuning god... so enlighten me as to what constitutes lean/rich under any condition.

Dont tell me to search... i would have already read it ;)

[Annoyingrob]

the larger your ratio, the leaner it is. So, 14:1 is leaner then 12:1.

With no other modifications, simply installing larger injectors will cause the motor to run richer (because it's dumping in more fuel per duty cycle percentage), unless the car is in closed loop mode (cruise and idle).

Basically, yes, you need to re-tune your fuel tables with larger injectors, or else the vehicle will be running way richer then it was. If your ECU is outputting the saem signal to the injector, but the injector is bigger, it will dump mmore fuel. The signal needs to be scaled back to compensate for the larger injector.

doublepostwhore: no, you are wrong. He specifically said that you want to run 14:1 when NOT on boost. He never ever mentioned running that ON boost.

[Jason Lange]

Originally posted by doublepostwhore

A bigger injector doesnt mean it WILL dump more fuel, it means it has the CAPACITY to dump more fuel... the ecu will tell it how much to dump ( a set number) so the size of the injector is invariable aslong as it does not impede the min/max flow.

I am no tuning god...

An injector only opens when it is told it doesnt open a litlle bit or alot, it just opens when told. The number of times it opens and closes and length of time is how you control fuel. The computer knows to open x amount etc. If you change the injectors and don't change the duty cycle, etc... on the ecu it will just add the + or - the % of size difference of the injector. Anyways...:)

[doublepostwhore]

:)

i concied defeat... time to re-learn how my car works.

doublepostwhore out.