Pauerman

For guys using the 57# injectors, which fixed regulator are you using?

What is the hp/tq ceiling for this size injector @ 80% duty cycle with a 2.5 bar or 3 bar regulator?

Waterguy

My calculation:

320 rwhp @ 2.5 bar and 12.5:1 afr
350 rwhp @ 3 bar and 12.5:1 afr

Injectors are not as stressed at the torque peak (lower rpm means less fuel required.) These could support 375 ft-lbs (rear wheel) at 2.5 bar at 4,500 rpm, 80% duty cycle.

Matt H

What about a 72 lb/hr at 2.5 bar (stock)
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote

porshhhh951

matt i would just think you would be running really rich......i mean how much can our stock dme adjust the fuel.......10% 15%???? i would think your air/fuel ratio would be pretty scewed.......isint tony running a simliar setup.....maybe he can shed some light on the subject.

TurboTommy

Laust,
I don't think that all the injectors are activated at the same time all the time. I believe at low RPMs the system is sequential and at a certain RPM (I don't know exactly what RPM) it actually switches over to batch, but it's two and two; so i've heard.

Matt H

He is running similar and I will be running MAF with ARC-2
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote

Waterguy

About 410 rwhp @ 2.5 bar and 12.5:1 afr, 80% duty cycle.

Russ Murphy

<<<Anyone else know of a good source for injectors besides Racetronix?>>>

Sean,
Try

Marren Injectors/Motorsport Great prices, and they do (did?) stock Siemans.

Laust Pedersen

TurboTommy,

There is a “washout of terms” here, normally true sequential means that the injector fires once per combustion (on that injector’s cylinder).
A 4-cyl (4-stroke) engine will have 1 combustion per 180º crank angle and with true sequential injection there will also be 1 injection per 180º crank angle. This will require a cam timing signal and is therefore a little more expensive to implement.
Batch or group firing can take many forms and the next step towards simplicity is firing the injectors in pairs so a 4- cyl engine will have 2 simultaneous injections per 360º crank angle. Some companies call this sequential injection. In this case a cam timing signal is almost necessary or else 2 injectors (half of the time) will inject into an open valve while the 2 others will never see an open valve, likely giving uneven mixture.
One further step towards simplicity is firing all at once each 180º crank angle, which is what I assumed.
Relying on TonyG’s statement that it is not true sequential, there still is the option that they switch between case 2 and 3.

Laust

Tomas L

It's batch firing all the time.
As Laust is saying, you need a cam timing signal to build a sequential (or semi sequential) system that's worth something and the 944 doesn't have one.
On the schematic of the DME that I have seen, connector #15 (injectors 1&2) is connected to connector #14 (injectors 3&4) on the circuit board and there is only one injector driver.

Tomas

Tomas L

Waterguy
I have also come up with something around 0.45 when I've tried to calculate BSFC based on the limits of the stock injectors. What puzzles me is that all sources that I have seen quote BSFC values around 0.55-0.60 for turbo cars. Are we sure of the rating of the stock injectors?
Has someone any 951 BSFC figures from a dyno test?
Has someone maxed out bigger than stock injectors on the dyno? Which size and fuel pressure? At what hp?

Tomas

Waterguy

Danno has done a lot of investigation on the stock injectors. He is convinced they are 34 lb at 3 bar, 31 lb at 2.5 bar iirc. They max out with the Guru chips and MAP kit at 1 bar boost (260-280 rwhp) using the 3 bar regulator.

I calculated the duty cycle for the stock boost curve and 220 hp. The stock injectors (31 lb at 2.5 bar) hit 80% duty cycle at 220 hp, so it seems they are well chosen for the stock 951. When I checked the 951S boost curve, they hit about 91% duty cycle at 250 hp. If anyone has a stock (non-chipped) 951 with a duty cycle meter, they could verify these calculations. It seems that Porsche decided that these injectors were close enough when they upgraded to the 951S, since they didn't go to bigger injectors.

I have heard people say that the stock injectors are good up to 300 or 320 rwhp. I don't think this is the case. I calculate they are good for 240 rwhp at 2.5 bar, 260 rwhp at 3 bar if you want to keep 12.5:1 AFR. This may be a bit conservative, since Jake951 hit 269 rwhp at 12.4:1 with the stock injectors at 12.4:1 AFR.

TonyG

The stock injectors are 260cc @ 2.5bar @ 80% duty cycle.

You can, with about 55psi - 60psi static fuel pressure, fuel 330RWHP - 335RWHP (but that's pushing it big time) properly.


The factory electronics have 1 injector driver. All injectors fire at the same time.

B951S

Just a note....My understanding is the factory DME is niether seqential nor does it fire all injectors at the same time, it is a batch fire system. The factory DME has 2 inejctor drives and runs 2 injectors at a time. There is a gray / gray& blk wire that comes out of the DME for each driver. Thats why you wire in 2 ballast resistors for low Z injectors (is you use them that is).

RajDatta

Not sure I would call running stock 951 injectors at 4 bar pushing it, as that is what the factory used for 968 turbo S. I am sure they were very conservative about 305hp as the performance of the car does not measure up to these low hp numbers. They could run 175mph with only 305hp? Doesn't make sense.