Jussi

few calculations..
if stock injectors are 44lb/3bar, it makes that 57 lb with 5 bar which is good for example FVD 540hp kit.
So I think even less should be enough for 520-550hp, like these 57lb http://www.racetronix.com/3172FM.html, these makes 64lb with 3.8 bar.
I have heard that too big injectors are difficult to program to run nicely with low rpm and idle. Am I right?

K24madness

Yes it is true that to big of an injector is a bad thing. There is more to the story though. You need to understand the injectors stabilty in low flow situations. That 60lb deka 4 is a much better injector than the 57 you mentioned. If you set the 60lb deka4 at 39 PSI (2.7 bar) you will have the exact same flow as stock injectors at 5 bar. The pressure range for injectors is 2.5 to 5 bar.

These deka 60's have stabilty far better than anything else you will find in a high impedance injector.

Trust me when I say I have done the homework!

FWIW my car idles better with these than before. Low speed performance improved as well.

Red9

Madness,
can you give examples of what you would use where and why? Does this apply to 993 as well as 996?

K24madness

Red9,

Lets say that you need more injector flow. This is determined by logging the duty cycle and making sure it is under 80%. Now you need to increase injector size. In the case of the 993tt the stock injector is 44lb at 3 bar. It is 57lb at 5 bar.

If you are at 100% duty cycle and you want to get back under 80% then you go with a injector that is 20% larger or 68lbs. The 60lb injector at 56psi (3.8 bar) will achive that. The lower fuel pressure the more the fuel pump flows. The fuel pumps work is split between pressure and flow. The less work it does to create pressure the more headroom it has for flow.

I went with these 60lb injectors because they are far better than the stock ones. Spray pattern and stabilty of the solinoid are light years better than the bosch ones.

You will need to get the DME retuned to calibrate it for the larger injectors. I am working with protomotive to achive that. You don't want to have the injectors larger than needed. If you do idle suffers. Remember that an injector is sized with a range. You can adjust fuel pressure to fine tune within different sizes. Because we need to run high impeadance injectors we have limited choices. The Deka4's are the best choice of all the injectors I have found.

Once I get things dialed in I will share the results. So far things look very promising.

Jussi

Thanks for information.
I think I will choose these 60lb deka4 as also Racetronic recommended these when I asked help from there.
K24: how do I get this 2.7bar or 3.0bar from original fuel pump(3.8bar?), is it adjustable or should I change it to different one, what do you recommend?

K24madness

js-911,

you will need a adjustable FPR and attach a gauge to the fuel line and set to 39 psi for starters. Then you need to install a wide band o2 meter and confirm that the fuel ratios are correct. Then fine tune from there. If this is beyond your scope of understanding you should leave it to those that understand what I am saying.

Tom

sfl993t4

I run larger injectors (fitted by 9m) with a standard FPR and currently don't have any issues with idle etc.

Jussi

Could you tell what are flow rates of these injectors and what power level you have?
Thanks!

Jussi

If I stay with stock FPR and bigger injectors, like sfl993t4, do I need these wide band lambdas or are stock ones good when reprogramming Motronic ECU in dyno?

sfl993t4

Sorry, I don't know anything about the injectors.
Power level is 490bhp at 1 bar with Kevin's Stage 2.
Possibly didn't need the injectors with this power level, but didn't know how much power we could get out of the turbos (and may go for more power in the future).

K24madness

Regardless of what programming or injectors you run the fuel ratios should always be vairfied. The easiest and safest way is to check it on a dyno. I prefer the mustang AWD dyno but others will do in a pinch if you disconnect the VC.

Fuel ratios should not be leaner than 12:2 to 1 when full boost. I personally like it even richer than that. My ideal safe target is 11:8 to 1

Install an adjustable FPR and set it to the pressure recommended by the tuner as a base setting. Leave your heater fan box off to allow easy access to the FPR (temporary). Do some 4th gear dyno pulls and adjust FPR as needed. After the session disconnect the battery. This will reset long term fuel trims so the DME will readjust the fuel ratios for part throttle ratios.

Jussi

Any suggestions for this adjustable FPR, model, price, where to buy?
Range should be that 2.5-5 Bar.
Thanks

K24madness

I like this one. Scroll down the page.

http://www.tyrolsport.com/audiperformance.htm