964 Injector Flow Rates ?

[Frog76]

Hi,
I am trying to find out the flow rate for the fule injectors on a 964 engine. They are Bosch # 0 280 150 731. Does anyone have this info ? Have looked everywhere without success.

Thanks
Craig

[Bill Verburg]

194 cc/min 16 Ohms ~39hp ea.

[CamB]

Bill - that number looks right (I have info somewhere).

I have never understood why Porsche specified injectors which would run "at the limit" at the "standard" pressure setting.

[tbitz]

I recall asking Todd Knighton (Protomotive Turbos) about what the stock injectors are for the 3.2L Carrera and he said they were 21lbs/hr (~210cc/min).

Note 194cc/min (19lbs/hr) will give a max 234Hp at 100% duty cycle and only 200Hp at 85% duty cycle.

I think the 964 is rated for 250Hp so 19lbs/hr just don't add up.

Even 21lbs/hr only give 252Hp@100% duty cycle and injectors shouldn't be operated at more than 85%-90% duty cycle.

I looked in my database of injector numbers and the above number did not come up, but If I needed 250Hp with six injectors I use 25lbs/hr.

Note: I'm using 32lbs/hr on my 3.0SC EFI conversion project, but I have a turbo in the future plans.....

[Bill Verburg]

I am sorry that you feel that the #s are inadequate. You'll have to talk to Bosch, the source of the info.

The Bosch 0 280 150 158, 3.2 injectors, are rated at 229 cc/min, 46hp perhaps there is a mistake in their literature or perhaps the injectors were down graded.

[CamB]

Bill

I'm not arguing! It just seems strange. I hoped someone could shed a little light.

I recall asking Todd Knighton (Protomotive Turbos) about what the stock injectors are for the 3.2L Carrera and he said they were 21lbs/hr (~210cc/min).

Note 194cc/min (19lbs/hr) will give a max 234Hp at 100% duty cycle and only 200Hp at 85% duty cycle.

I had a set of Carrera injectors and they hit their limit trying to make over 250hp on my 3.2 (a short stroke SC), so it can happen. The fuel pump was undersize too though (replaced with a bigger one and 951 injectors).

Thing is, Merv (WydRyd) has a Carrera with one of Todd's turbo kits. Yes, the system pressure is wound up, but he has a dyno for 350+ hp!!!!

[Mike the mechanic]

The thing is, the injectors are rated at a certain pressure. They may be 19lb/hr at 45 psi, which is the standard for measuring injector flow, BUT, if you run more rail pressure, which Porsche may be doing, they will flow more. I can say that my stock Carrera injectors and pump let me get to high 300hp mark, turbocharged, with over 85psi rail pressure while under boost.

[CamB]

Yeah, but does a 964 have the facility for increasing pressure?? I know you use a rising-rate pressure thingy on the turbo cars.

Its all a little weird and there is clearly something I don't understand!!!

Cam

[Mike the mechanic]

Cam, every F.I. car has a fuel pressure regulator. On a naturally aspirated car, it isn't a rising rate regulator, instead it works on engine load. When the engine is idling, or low load driving, the vacuum signal at the regulator is high, which pulls the diaphram in the regulator, allowing the fuel to return to the tank, with little restriction. This in turn makes the fuel rail pressure relatively low, lets say 40 psi. When more throttle is applied, or under load conditions, the vacuum signal at the regulator diminishes, causing the diaphram in the regulator to close the passage somewhat for the fuel to return to the tank, which in turn raises the fuel rail pressure to it's highest setting, say 55 psi. Now an adjustable FPR can be adjusted to increase the pressure in the rail more, during load conditions. And a turbo car, with its vacuum turning into boost pressure at the regulator vacuum signal, pushes the diaphram, further restricting the fuel's return to the tank, making more pressure. Hope this helps!!

[Mike the mechanic]

Also, if the 964 injector is rated at 19lb/hr at 45 psi, it is possible Porsche is allowing more rail pressure, which would increase the injector's flow.

[CamB]

Yeah - makes sense - I'm just showing my ignorance. Thanks!

I need to go back and look at my own setup again. I suspect I have only a fixed fuel pressure regulator (the simplest way?). From my memory of the plumbing, I don't know that it has any sort of connection for load (I have throttle bodies).

So it makes sense I would run out of juice if there no facility existed to raise the pressure.

Here is what I've got:

Filter and the other thing (accumulator?) on the left wall of the engine bay:



Back view of regulator



Front view

[Mike the mechanic]

Cam, with throttle bodies, you don't have a proper vacuum signal for a regulator, because the lack of a plenum. You HAVE to use a fixed regulator,so, I would set the pressure high (it looks to me as though your pressure regulator is adjustable, and with your programmable engine management system, you can decrease the injector pulse width at lower rpms, and maybe play with the TPS signal settings and/or accelerator pump feature.

[CamB]

Thanks Mike

I bypassed that problem by spending a fortune on 951 injectors - at least now I could upgrade to any cam I want (I have S cams for 270hp, but pistons have cutouts for RSR cams for who knows how much - probably 320hp). I have injectors and a fuel pump to support 400-500hp!

Yeah, it all started making sense as soon as you said that all injected cars have a variable pressure regulator. Thanks for helping me sort it out

[tsuter]

Here is a link for determining what injector you need. Russ C. has been doing this a long time.
The link doesn't explain "duty cycle" too well. It just says plan for no more than 80% max.
Duty cycle is the "pulse width" of the injector divided by the available cycle time of the motor.
At 6000RPM that is 100RPS or one revolution per 10ms. Multiply by 2 for compression and exhaust and you got 20ms per injection cyle MAX to get your fuel in.
At 80% duty cycle at 6000RPM you got 16ms for the injector "on time" or pulse.
So if your ECM can't deliver the fuel in 16ms or faster then its flow is too small.
Of course planning at 2000-5000RPM, you got much more time so the injector sizing is also very dependent on how you plan to drive the car.
When the injector exceeds 80-85 percent or so for extended durations it is basically acting like CIS and will suffer early burnout - not to mention fuel blow down in the exhaust

Keep in mind injector flow increases as the square root of the increase in fuel pressure so it takes a bit of pressure to jack your flow up much.

http://www.rceng.com/technical.htm

[Bill Verburg]

I did a little more checking. The only # I can find for the 964 is the
194 cc/min from the Bosh literature which does appear low.

The only other reference I have is a cross reference from Accel which has the 993 injectors @
#150124 - catalog 24 lb/hr @39.7psi, static 23.1 lbs/hr @2.7bar(44psi) static 24.3 lbs/hr@ 3bar(44.1psi), static 236 cc/min@3bar(44.1psi), 14.4 ohm impedence

and a high perf upgrade @
#150126 catalog 26 lb/hr @39.7psi, static 24.3 lbs/hr @2.7bar(44psi), static 25.6 lbs/hr@ 3bar(44.1psi), static 249 cc/min@3bar(44.1psi), 14.4 ohm impedence

993 & 964 fuel pump pressure is 3.8bar &#177 0.2bar, fuel rail is 3.3bar &#177 0.2bar @idle

3.2 Carrera fuel rail is only 2 bar &#177 0.2 @ idle so it may not be so strange that the 3.2 Carrrera is rated at 229 cc/min

[Frog76]

Hi,
Thanks to everyone for the replies. I contacted Bosch Technical Support and they confirmed the 194cc/min flow rate, which does seem insufficient for the hp the 964 produces. So the only conclusion is that Porsche must be increasing the fuel pressure above the measuring pressure used by Bosch to get the desired hp.

In the meantime, I did a log on the car and found that the injectors were running at 103% !!!. They have now been replaced with larger ones - resulting in a max duty cycle of 58%.

Thanks
Craig

[ChrisBennet]

Originally posted by Frog76

In the meantime, I did a log on the car and found that the injectors were running at 103% !!!. They have now been replaced with larger ones - resulting in a max duty cycle of 58%.

Thanks
Craig

How do you get 103%? I thought 100% meant they were open all the time.
-Chris

[ischmitz]

I know the 964 engine has a vacuum connection to the fuel pressure regulator. Does anyone know its characteristics?

Something like a fuel pressure vs. engine speed plot would be nice to give us an idea where the fuel pressure at the rails really is under full load and 6000 RPM.

I would like to know where the 964 injectors max out.

Another concern is what happens when you go into open loop (WOT). Wouldn't larger 993 injectors alone through the mixture off without changing the mapping in the DME to account for them?

Ingo

[kojab]

ischmitz. If the vacuum connection to the fuel pressure regulator goes directly to the inlet manifold this would mean that the fuel pressure would be constant across the injector as the fuel pressure is referenced by the manifold vacuum.
If you wanted to know the max fuel pressure at full load all you have to do is find some way to continuously run the fuel pump/pumps and with the engine NOT running measure the fuel pressure at the fuel rail. The recorded pressure found should be the same at RPM 6000 at full load and if not, and it was less pressure you would likely have a fuel delivery problem. Yes any larger injectors would throw off the tune if the DME is not recalibrated to suit larger injectors.
Does anyone have a bin file for the standard DME 964 engine. I would like to find the fuel and spark tables.

Cheers kojab