mjims

I'm currently organising the Mapping of my TT with a local tuner and Rolling Road. Whilst discussing the modifications to the car for a base map, he expressed some concern about the 5.0Bar Fuel Pressure Regular fitted.

He suggested that I use larger injectors rather than a higher pressure.

Does anyone have a recommended Injector type or is there a preferred method of choice to increasing the performance in this area?

If larger injectors are the way to go, what is the best type and how much should I expect to pay?

merry xmas

Woodster

My understanding is that everyone uses a 5 bar fuel pressure regulater when stepping up the
performance of the twin turbo. my shop chose the adjustable type, and their is also available
a non adjustable. call someone like steve @ rennsport systems or viper bob. I do not have
any knowledge of larger injectors, you will have to ask the higher powers (listed above).

Geoffrey

I don't like to run Bosch injectors past 75psi of fuel pressure. I use the same rule of thumb for Siemens and Rochesters tend to stick at pressures above 65psi. If you set your static fuel pressure at 5 bar (about 75psi) and run 1 bar of boost, you'll have a total of 90psi of fuel pressure. The stock 44lb/hr injectors are saturated injectors and the higher fuel pressure puts a higher load on the injector drivers since there is more pressure holding them closed. Obviously 5bar FPRs work, however, given a choice I'd use a properly sized inejctor and run a base fuel pressure of 55psi (3.8bar).

To understand how much more fuel you'll get by raising the fuel pressure, you can use the following formula - New Flow Rate = Old Flow Rate * sqr root of new pressure/old pressure. So, in the case of the stock fuel injectors, the 44lb/hr injectors are really 49lb/hr injectors at 3.8bar since fuel injectors are rated at 43.5psi. Raising the fuel pressure to 5bar will provide an injector with the equivelant of a 57lb/hr injector. In my experience, this flow rate is able to sustain about 500 - 525hp based on the relatively poor BSFC of a Turbo 911 engine.

mjims

Thanks for the clear explanation, it makes logical sense.

I agree that although the 5Bar FPR works it appears to be a 'cheat' instead of going to the expence of 6 new larger injectors.

With larger injectors, do I need to consider adding another fuel pump to keep up with the higher flow?

Does anyone know tht flow capacity of the standard pump? I understand it's just a standard 964/993 item. Not unique to the Turbo?

Is it simply a case of plumbing in a parrallel pump with the standard sized pipework, or will this require the complete pipework from tank to engine replacing?

Would it not be simpler to fit a larger more powerfull pump?

Geoffrey

The stock fuel pump is good to over 600hp and should be the same as the 930 rear fuel pump.

mjims

Wow...

You mean I've found something that isn't going require a small fortune to modify!

ngoldrich

Geoffrey,

Question on my 993 3.8 TT GT2 race car -

I am finishing freshening the engine right now.

I run dual Bosch race pumps and they are each capable of 5 Bar and 165 litrer per hour (based on the bosch spec chart for these pumps).

My question is that if I am running 5 bar fuel pumps, are the pumps safely capable of maintaining consistent fuel volume and pressure a bit above 5 bar?

So if my base psi currently is 57 and I am running max of 18 psi of boost then the fuel pressure at max will be 75 psi.

What if I want to richen it up slightly when I run it on the chassis dyno - I cannot adjust the ecu maps (Zytek - dont ask). If I need to raise the pressure 5 psi (62 base and 80 max), will these pumps be able to handle it? I am not sure.

Both of my pumps are the same bosch 5bar 165 lpr high pressure pumps in series. So the first pump output feeds the second pump input which means the second pump is getting fed fuel at 70+ psi. I would think this makes it more likely that I will be able to do it since the second pump is already getting fed at a high psi. But Will I be safe to raise it a bit or do I need to change my second pump that outputs to the fuel rail to the Bosh 10 Bar 200 lpr pump along with my adjustable fpr?

The car ran great for 14 races. I am just proactively freshening it. I did notice it running slightly lean, so I wanted to richen it a bit. I just want to know how much range you think I have before I need to change the pump.

It is a motorsport design 765 HP engine and runs fantastically.

BTW - it is a 6 high butterfly setup with 2 fuel injectors per cylinder.

Thanks,
Norm

Geoffrey

Without the pump part numbers it is hard to tell exactly what they are, however, from what you describe, it sounds like you have the equivelant of a 930 rear pump which is listed as a 150/hr pump. Basically there are two Bosch pumps, the 150/hr 046 930 pump and the 220/hr 044 962 pump. The former is a very stout pump and the later is the same, just more. While not being an expert in fuel system design, I do know there can be issues when two equally output pumps are put in series, the high pressure from the first pump causes the second pump to not work as well. This is why the prepump is generally much smaller (ex. 930 front/rear pumps). I know a single 930 pump is Ok up to about 600hp. I've not tested it much higher than that, so it may be Ok, I just don't know but based on injector flow rate, etc. the math does not look very good. I would however, suggest running the two pumps in parallel to a single line. I know this design works up to over 850hp with a base fuel pressure of 55psi and 20psi of boost. I would install the two pumps in the front trunk and you would want to install a 1 way valve at each of the pumps so if one fails, the functioning pump won't run fuel backwards through the failed pump and back to the tank (fuel will take the path of least resistance).

So for your question about raising the fuel pressure, I'd not hesitate to raise the fuel pressure 5psi. My comments were generalalities not absolutes. Several thoughts here, since you are running 2 inejctors per cylinder, I'd think that they are probably Bosch of some type, probably in the 37-44lb/hr range. If they are 0280150803 they will have a green top and are 37lb/hr injectors, if they are 44lb/hr injectors they could be one of two Bosch. If they are not Bosch, I don't know then. It is very likely they are peak and hold injectors which give better performance than saturated injector becuase they require more current to drive them and therefore, are less affected by high fuel pressure. This means there is less injector dead time and it is a faster reacting injector. What AFR are you targeting? At 1bar, I'd suggest no leaner than 12.2:1 and at higher boost levels, 11.9:1-12.2:1 should be fine. If you have access to cylinder head temps, I'd monitor those, particularly during an enduro. If the cylinder heads were getting much above 210 degrees C, I'd richen up the mixture to reduce the cylinder head temps. I know from experience that an AFR in the 12.5:1-12.7:1 range is too lean and will melt an engine during prolonged running such as during an enduro.

Come on, tell my the Zytek story...

Jussi

My Motronic tuner also adviced to use bigger injectors rather than 5 Bar FPR!
mjims:
What size injectors did you use and were they good for your setup?
I noticed that in newer topic you mentioned about doubling up your fuel pump, why is that? Injectors weren't good enough or did you tune your car more?
What hp/Nm level you have?

Geoffrey:
You seem to know very much from these things.
Could you give me help is that injectors/FPR/more fuel pumps question?
My hp/Nm target is +520/700
with 3.8 P/C, upgraded turbos, 1.0-1.2bar, flame rings, flowed heads, RS Cams, ARPs, Carrillos
but with original IC and cats/exhausts.

Thanks
-Juha

K24madness

Stock injectors are 57lbs at 5bar. They are rated at 44lbs at 3 bar. You need to see whats available in the pressure range you are looking for. I currently run 60lb injectors at 40psi with protomotive software designed for stock injectors at 5 bar.

I think what you will want is a 50lb-60lb injector. Here is a link to help you understand how pressure affects flow.

http://www.partswhse.com/fuelinjecto...fiflowcalc.htm

Jussi

Thanks. Could you tell what is partnumber and manufacturer of your injectors?
The link didn't work but I tried google and found following (which might be same)
http://www.fuelinjectorwhse.com/fiflowcalc.htm

K24madness

semens deka 4's. They cost $55.00 each from http://www.racetronix.com/ they are also flow matched. You want the high Z version.

Jussi

Do you recommend these
http://www.racetronix.com/L107FM.html
or are next ones good enough for max.550hp without changing fuel pump or FPR?
http://www.racetronix.com/3172FM.html
Thanks for knowledge.

K24madness

Yes the first ones.

Those will support 700+ HP at 4.5 bar.

You will need to run an adjustable FPR

rmrmd1956

Do you know the BFSC of the 996 water cooled turbo??