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      11-30-2012, 01:52 AM   #19
Second Lieutenant

Drives: 335i e92
Join Date: Nov 2012
Location: CA

iTrader: (3)

Originally Posted by Wedge1967 View Post
Well, considering I didn't do the testing I can't provide you all the details regarding BMS's testing, but I did talk with Terry at Shift S3ctor. I was under the assumption that they were still seeing fueling issues with e85 at higher power levels, but you seem to be very knowledgeable regarding this so please feel free to correct me if I'm wrong.

The ability of a fuel delivery system to maintain a specific pressure (in PSI) is an important factor when analyzing a fuel system. It should not be confused with volumetric or ability to deliver a specific amount (in Gal. per minute or Litters per minute) of fuel. As a rule of thumb, when a system can not maintain a specific pressure, the vehicle will probably run very bad or not run at all. On the other hand, it is quite common to see vehicles with good fuel pressure and have performance problems due to a lack of fuel volume. Good fuel volume is the system’s ability to maintain a specific quantity or volume regardless of vehicle operation and that is the key point that everyone seems to overlook.

When two (or more) pumps are arranged in serial their resulting pump performance curve is obtained by adding their heads at the same flow rate as indicated in the figure below.

Pumps in series are used to overcome larger system head loss than one pump can handle alone.

* For two identical pumps in series the head will be twice the head of a single pump at the same flow rate - as indicated in point 2.

With a constant flowrate the combined head moves from 1 to 2.

Note! In practice the combined head and flow rate moves along the system curve to point 3.

* Point 3 is where the system operates with both pumps running
* Point 1 is where the system operates with one pump running

So I'm not saying that for most the replacement of the LPFP will fix the issue if the volume of fuel is increased by the replacement of the old pump. But when your system demands more volume that a single pump can deliver, adding a booster pump will increase the flow rate required to sustain the HPFP at peak demand.
Refer to either of the threads on the other two forums regarding the E85 pump. The data is right there. I cannot cross post it or I could get banned.

The info you copied somewhere from the internet is correct. What that stipulates is that running pumps in series jacks up the pressure and thus only flows more if you are losing pressure. The upgraded LPFP is NOT losing pressure. Are you suggesting we raise the stock pressure limit (I am not necessarily opposed, just genuinely curious)?

Btw, if you go back to the website you were just on and look at the schematic right below it, you will see that two pumps in parallel is a much more effective method of increasing flow rather than pressure... Kind of surprised you didn't post that.

Originally Posted by OECMG View Post
I think I finally got this. There is a high pressure fuel pump and a low fuel pressure pump. The low fuel pressure pump brings fuel to the high fuel pressure pump. The idea of the booster pump is to help the low fuel pressure pump bring more fuel to the high fuel pressure pump while keeping the orignal low fuel pressure pump in the tank. The other solution is to install a stronger low fuel pressure pump in the tank and not have an extra booster pump at all. So what is better???
Correct. We have yet to see which is better. They both get the job done, it really just comes down to price, ease of install, etc. Imho replacing the low capacity pump is preferable to slapping another pump on after it.

Originally Posted by Wedge1967 View Post
Replacing the LPFP could increase the pressure and volume, but eventually you will exceed the volume required to supply the HPFP with a single pump.
This statement is patently false. Are you seriously saying there isn't a single pump in the world that can flow enough to feed our HPFP??? There is and its already out there running. Its the pump Walbro designed for running E85 on which there are DIYs for... Even if its not that pump, to say there isn't a single pump that can flow enough is just plain wrong.

Last edited by ign335i; 11-30-2012 at 02:00 AM.