Hi
This is my first post on this forum.
From what I have read fuel pressure in the fuel rail should be around 45 to 50 psi At idle but I wanted to know if anyone knew what the stock return line fuel pressure down stream of the fuel pressure regulator should be at idle.
Regards
Peter

 

Its relatively low, why are you asking?

 

I would assume to get a handle on when they need to upgrade.

Stock return lines on Evo's do fairly well into the 500-600+ whp range.

 

The HP level really doesn't have much to do with it. It's more related how many and what fuel pumps you're running. I've seen people over do their fuel system (dual walbro 450's) requiring them to make unnecessary upgrades (like the return line and an FPR) when a single 450 or dual 255's would've done fine and not needed the other upgrades.

 

Hi
Im planning on upgrading fuel pump to a DW65 before having the car retuned.
I have read various threads that recommend drilling out the return orifice in the fuel pump module.
However I have read other threads that say not to drill it out.
I want to do some calculations and try and quantify what the increase in return line pressure is likely to be with a new pump and knowing what the stock return line pressure is to begin with will allow me to do my calculations.

 

If you plan on keeping the pump resistor circuit there’s no need to drill the orifice.

 

The DW65 is essentially a compact, direct fit, walbro 255. No need to mod any of the fuel system, just drop it in and go.

However, I do recommend going with an ASNU 330 pump over the DW if you haven't already made your purchase. They're more reliable and flow more for future upgrades, they generally support 500-550whp on E85.

 

I suppose I over speculated that people know how to size a setup for their HP level. That's my fault.

 

Thanks every one for their input.
looks like all I need to do is fit a new pump.
Regards Peter.

 

As an update I fitted a pressure gauge downstream of the FPR.
With the engine idling and the vac line connected I recorded.
20 psi with the stock fuel pump and
24 psi with a new DW65c fuel pump.

I also did a flow rate test by timing how long it took to fill a 1 litre container.
Note. For this test I connected a hose to the output of the FPR so there was no back pressure down stream of the FPR.
The stock fuel pump flow rate was 1 litre in 28.05 seconds or 128 l per hr.
However under the same conditions the DW 65 took 33.6 seconds which is only 107 l per hr which is not what I expected.
With the FPR connected to tank and back pressure on the FPR the return pressure was measured at 24 psi which indicates that the flow rate had increased with the DW65 but with no back pressure the the flow rate looks to decrease?

 

Are you doing this test in full voltage / high power mode or in low voltage idle/cruise mode? If its the latter then I would try the test again in full voltage mode.

That being said if you haven't upgraded your fuel pump wiring yet then that could also be an issue. Bigger pumps draw more current and on stock wiring this will cause voltage drop at the pump if not upgraded. Voltage drop will directly effect the performance of the pump.

 

The only pressure that matters is pressure in the fuel rail. Its either the correct pressure and the return line is enough. Or its too high and the return or regulator are being over ran.. Not sure why you're measuring pressure in the return line.

 

Hi guys.
I ran the tests at low voltage.
I am not so much interested in the maximum flow rate at full voltage.
The reason I did these tests is to try and determine the loss coefficient for the small orifice in the fuel pump housing.
I have read several threads were guys drill out this orifice to reduce high pressure in the fuel system.
However in all the threads I have read it looks like the size of hole being drilled is done by trial and error.
By measuring the flow rate, pressure drop and diameter of the orifice it is possible to calculate the loss coefficient for the orifice which can then be used to calculate the size of the orifice to be drilled it also allows me to better understand how the system works.
It also gives me a baseline for checking if the small filter in the return line is getting clogged in the future.
Regards Peter