Fuel system parts

Here is a picture of most of the fuel system parts. You can see the 044 pump, new filter, deka 4 630cc injectors, aeromotive AFPR, and other associated parts. Not pictured is the fuel rail (still waiting for it to be made), tank filter (already installed), and some hoses and fittings (waiting on the rail so I get the right parts). You can see the AN 120 degree elbow on the end of the pump that adapts the pump to the tanks line size.

Fuel Tank

I pulled the fuel tank down yesterday to look for a leak. The car has always seemed to have a fuel smell inside. It ended up that at some point in the past a sub-woofer was mounted to the back deck with screws that went into the gas tank. When I got the car, I cleaned out everything that I didn't like, to include the sub mounts. I can remember that those screws were about 2 and a half inches long. So anyway I fixed the holes, checked all the lines and reinstalled the tank. I got a great deal on a 044 pump so I went with it instead of the HV pump that I discussed earlier. When taking the old pump off the hose clamp that connects the tank line to the pump just fell off. It was completely consumed by corrosion.... glad I found that! Now I am missing a piece of plumbing though, because the 044 doesn't have the same type of outlet port that the stock and HV pumps do. That's alright as I needed to order a new filter, new tank pick up, and compression fittings to convert the hard lines to AN lines up front. I'm still waiting for the new fuel rail to become available from EFI Express. That should be the last piece of the fuel system to acquire and then I can check that one off of the to-do list. Well I think that I will head back to the garage and find some more trouble to get into, maybe some wiring.

Fuel pump solution

Finally I have come to a decision in this area. I know that somebody will say that this is overkill for this project, but I will have room to grow. After a lot of digging around on different sites and reading a lot of flow information I came up with the following. Keep in mind that as pressure rises in a fuel system that the flow rate of your pump will decrease. The inverse is also true. To make matters worse there is no standard that manufacturers use to test their pump output.

The stock Bosch replacement pump for a 944 is p/n 0 580 464 069. It is rated for 98 L/hr @ 4 bar.

The stock Bosch replacement pump for the S6 is p/n 0 580 31 068. It is rated for 120 L/hr @ 3 bar.

With the difference in tested pressure I would assume that these pumps are about equal in flow at the same pressure. That would be for a stock application.

Since my 944's pump is of an unknown age and I hope to eventually be at a level of about 400bhp I decided to err on the side of caution and replace it with Bosch p/n 0 580 254 044. This unit is rated for 200 L/hr @ 5 bar or approximately 270 L/hr @ 3 bar. It's currently very popular in cars making at least 500 bhp so I have every confidence that it will supply enough fuel for my needs. It is also almost a direct fit for the 944 application. Just for your information there are several other Bosch units that fall in between the 069 and 044 models, but to tell you the truth I got tired of trying to figure out how small is too small.

Side note: As far as just using the s6 pump on the 944 until I start raising power levels...well you can't. The s6 is in tank and the 944 is in line.

Another note: After writing this info I have continued to receive information from different people. They have informed me that there are a lot of people with modded 951's making 400-500hp that are using the stock pump. That may be true, but it makes me uneasy. That being the case I may rethink my decision on using the 044 and try to find out the part number for the Bosch HV pump. It has upgraded performance over the stock pump, but not as much as the 044. I could live with that.

There are three main reasons to not go too big when selecting a fuel pump.

1: A larger pump requires more power to operate. This is going to take hp to produce, plus your wiring may not be up to the task of the increased current requirements.

2: Something I was not aware of until researching this topic, but it makes sense. If you circulate way more fuel than you need it will begin to actually act like a cooling system and transfer heat from your engine bay into your fuel tank. That is not a good thing.

3: Oh and this one is important to everyone. A larger pump costs more.

Final thoughts:

Alright the mystery is solved. I'm now going to choose a different pump. This is the mysterious Bosch HV pump. I located someone who read the numbers off the box for me so that I could look up the flow rate and current draw. Supposedly it is good for 450 rwhp sustained. That certainly will supply what I need without getting overly large. Here is the number break down on the three models for this car.

0 580 464 069 - 98 L/hr @ 4 bars - max 7 amp draw - stock replacement
0 580 254 910 - 130L/hr @ 5 bars - max 10 amp draw - this is the HV
0 580 254 044 - 200L/hr @ 5 bars - max 15.5 amp draw - this is the 044

On to the next problem.

Monday morning

Well I haven't done a single thing to the swap project over the last weekend, but I did get one of the home improvement projects done. One more to go and I can get started on the swap. I got a hold of an Audi service manual late last week. It looks to cover just about the whole car, so I hope it will allow me to make sense out of the wiring harness. I also picked up an HD camcorder to use for documentation of the swap. Hopefully in the next couple of weeks we will be able to get Nina to a dyno that is here in town and find out what she is good for in the stock configuration. I figure that will be a fun comparison to the finished project. I also found that Sokol (the Ukrainian guy with 20vt swapped 924) is using a walbro 255 liters/hr fuel pump in his car. I'll compare that to the S6 pumps flow rates to see how it stacks up.