Waterguy

Thanks Tony, that flow sheet confirms the size of the stock injectors. 262 cc/min equals 25 lb/hr at 80% and 2.5 bar pressure. At 100% duty cycle, that translates to 31 lb/hr at 2.5 bar, 34 lb/hr at 3 bar.

At Tony's 55-60 psi, the injectors should flow 38 to 40 lb/hr at 100%. I am surprised that he could fuel 330 rwhp safely. I would have estimated a bit lower, but I am assuming that Tony is speaking from actual past experience and not just calculation. Assuming 15% drive line losses, this would be 388-394 brake HP at 153 to 160 lb/hr fuel, or BSFC = 0.39 to 0.41 lb/hr/brake HP.

cpt_koolbeenz

I just got new Siemens 52 lb @ 3.8 bar injectors. My question is, is it alright to run them at the spec 3.8-4 bar pressure with the stock pump?

BTW Danno made me special DME map for them based on the 52 lb factor.

Thanks!

TonyG

Waterguy

You are correct about the past experience. We actualy removed the locking nut on the fuel puressure adjuster, and ran the adjustment about as far in as it would go :-)

This type of stuff was done long ago (going on 5 years ago)... when there wasn't much on the market.

We were able to properly fuel somewhere between 325RWHP and 335RWHP (I don't remember which its been so long), but it was maxed out for sure....

TonyG

TurboTommy

I was also wondering if the stock fuel pump can deal with high fuel pressures together with enough flow to make the big hp #s? I also heard that the injector drivers might not like excessive fuel pressures. How much would be excessive for the drivers and the pump?

Also, I'm a little surprised that Porsche would have designed the injection system in such a way that there would be poor fuel mixing at low RPM (if all the injectors are driven at the same time).

Also, I've got info that the stock injectors are rated at 37lb/hr at 2.5 bar. It's amazing isn't it; all the conflicting bits of information in this business. Drives ya crazy.

TonyG

TurboTommy

Running 55psi-60psi is a lot of static pressure. If you're running a 1:1 rising rate fuel pressure regulator, like we are (for the most part), you can easily be running close to a net 80psi+++ Way too much for sustained operation.

By far, it's better to go with larger injectors...

As far as batch fire being bad... Who knows why... But it's not really bad as the events are still occuring so fast even at low speed...

But concerning the flow of the stock injectors... Like anything else on this list... there's probably as much inaccurate information given (like the fact that the stock DME has one injector driver thus is a full batch fire setup... take apart a DME and look..), as there is accurate. The only accurate info, is the info that's been proven through testing... hence the reason I posted stock injector flow chart.

TonyG

cpt_koolbeenz

Does anyone know if it is acceptable to run my new 52 lb injectors (@55 psi or 3.8 bar) at that pressure????
That is what the 968 and all the 944 16 valvers use right???

Waterguy

Guru chips are tuned for 3 bar (43.5 psi.) This is what the 944 16 valve engines use, and Guru usually supplies a 3 bar fpr with their kits. Using higher static pressure will just cause you to run rich.

cpt_koolbeenz

Thanks Waterguy-
Danno made me new chips to work with 52 lb injectors. They were rated at 52 lbs @ 3.8 bar not at the usual 3 bar... Didn't know about that until I got them. This says the 16v's use 3.8 bar regulators.
http://www.clarks-garage.com/shop-manual/fuel-12.htm
I guess I should ask Danno?

Waterguy

Kool, you are right that the 16 valve engines use a 3.8 bar fpr (I checked the shop manuals to confirm it.) I think that the stock fuel pump should be good for your 52# injectors at that flow rate, especially if you don't go high horsepower (big turbo and/or extreme boost.) Since you have custom chips tuned for your injectors and 3.8 bar fuel pressure, you should be good to go.

cpt_koolbeenz

>>>I think that the stock fuel pump should be good for your 52# injectors at that flow rate, especially if you don't go high horsepower (big turbo and/or extreme boost.) Since you have custom chips tuned for your injectors and 3.8 bar fuel pressure, you should be good to go.<<<

330 too much? T04E MAP?
Hopefully the pump will support it...

Matt H

According to Lindsey the stock pump will be fine with your power output. Even so a new much larger one is like 75 bucks (must be the only reasonable upgrade on these cars!!)
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TurboTommy

koolbenz,
I asked that question and you seen what Tony's answer was (probably too much pressure) Now, I don't know if Tony knows this for sure and I don't know if he was referring that it was too much pressure for the pump or the injector drivers ( this is important to know). The fact that the 16 valvers use this fuel pressure doesn't mean anything because they don't have to deal with the rising rate of boost pressure.

TonyG

TurboTommy

You are correct (and I did know this...).

What I don't know for sure, is what the rate of rise is for a N/A regulator, and if they will react to positive pressure applied, like a turbo regulator. Maybe they will... or maybe they won't.

But if they do, and it's a 1:1 relationship, then you obviously have to add the static fuel pressure, to the quantity of boost being run, to end up with your final fuel pressure.

In the case of a turbo factory regulator, where the fuel pressure is 36psi (2.5bar approximate), and you are running, for example, 20psi of boost, the net fuel pressure at that boost level would be 56psi.

Now take that same example, and install a 3.8bar regulator (approx 56psi static) assuming a 1:1 rate of rise (which I don't know whether or not this is the correct rate of rise), then at that same 20psi boost, you would be at 76psi fuel pressure... which is too much.

B951S

So why does it have 2 separate outputs firing injectors 1&2 and 3&4 together? What You are talking about a single driver in group fire mode, the stock DME is batch fire mode firing SEPARATE pairs individually for every revolution. Run a search and there are numerous posts on this.

TonyG

>>>....firing each pair for every revolution<<<