question on A/F ratios and injectors
 

I finally put in my wideband to help tune a bit with my SAFC but I cant seem to get the car rich enough at high RPMs under full boost.

I'm reading right around 11.3 A/F til about 4K RPM then my car spikes to almost 15 lbs of boost. I turned the boost down and "tried" to add more fuel but at 10 lbs around 4k RPM I get up the 14+ A/F readings. I'm pretty much at the richest I can get the car so for now I wont drive it hard.

MODS:
-S5 J-spec T2 motor
-Monster street port
-S4 turbo
-3" turbo-back exhaust
-255 lph Walbro fuel pump
-stock injectors
-Racing Beat FCD
-No emissions stuff


I figured now I will invest in an FPR and some bigger secondaries.
QUESTION: What will be a good size injector and do I use low or high inpedence?

WILL THIS HELP FIX MY PROBLEM?


Thx for any help in advance :icon_tup:

Eddie

15lb of boost on a s4 turbo thats not good.
infact after about 10lb you maxing out on that turbo

that might your problem

i would agree thats alot of psi for that turbo. it maxes @ 12 tops. also i would highly recomend upgrading to 720 or 750 secondaries and get your 550 primaries cleaned and blueprinted(whichdoctor, marren fuel inj, RC enj, etc...). you are using a s5 harness i take it so they would be high imp injectors also.

You MUST rewire the fuel pump. Injectors aren't enough. I've had the problem you are describing with 1680cc secondary injectors.

Ok so having the walbro in tank with stock connections isnt enough? What are you referring to when you say rewire?


The 15 lbs of boost was on the first pull so I wont let it happen again. I will def get bigger high impedence inj.

Search fuel pump rewire. There are two ways to do it: one is to retain the stock resistor relay (which lowers pump voltage under low loads for better efficiency at idle mostly), and one is to remove it. I personally chose to remove it because IMO it is simpler and more reliable to take it out.

Ok so you're basically stating to run direct power to it with a switch for ON/OFF functions for a better volt current?

I have a new dry cell battery putting out a lot of CCA and volts stay at 14 but I'll ask about it


Thanks for your words of wisdom

I don't want to jack the thread, but that got me thinking. I used to have s4 motor with s5 turbo/ported wastegate. I would also get like almost 15lbs spikes and my boost would level off around 10 or 12lbs. I know this is turbo's limits, but what do mean by it maxing out after 10? Do you mean it's harmful to the turbo itself?

I think the s4 turbo has a reliable limit of 10PSI as opposed to an S5 turbo which could safely do 12-14 if I'm not mistaking?

yes s4 turbo maxes out EFFICENCY @11.5-12psi and s5 is around 14. after that amount of boost the turbo fades off drastically in power because its spinning to fast therefore resulting in failure just an amount of time the seals hold and the cam stays in position. if your going to run more than the set limits on either turbo plan on replacing it soon

A more important reason to not go above the efficiency range of the compressor is the higher intake air temps as noted by the people that have dyno tuned with EMS's monitoring IATs. 12psi is where the turbo is still making power, above that it turns into a hair dryer and hot air = detonation and preignition especially mixed with leaner AFRs.

No, I am telling you to install a relay that will switch power directly to the pump. But the pump will still be triggered by the ignition switch and circuit opening relay. You will be increasing voltage without the hassle of a separate switch. That is exactly how I have my car.

Search for the thread I made on this.