For certain things a factory replacement is just fine. Fuel pumps. Well.... Now I am unsure where I am going with my xkr but a twin screw may be in the future. I also have a 4.2 on a stand out of an xkr as well. For now it just has basic bolt ons. New coated rotors with later model blower, exhaust, ported tb, 3.5 intake/94mm maf. The current fuel pumps have about 150,000 miles on it.


In tank fuel pump technology has come a long way since 2001. So is it worth upgrading to a higher lph primary pump>? Can that be done and can the secondary be deactivated. I have made over 400 supercharged rwhp with a single 255 HP LPH pump and over 500 supercharged RWHP with a 340 lph pump. Bottomline is I know they have never been changed and with the miles I don't feel comfortable. Thanks all!@

 

no input?

 

I think Andre has upgraded his pumps in his twin screw setup. Not sure of that, but I believe he mentioned it somewhere along the way.

Not sure it would be necessary to disable the 2nd pump, even if you did put a larger primary. Flow at the pressure you want is the name of the game.

 

Im thinking I could definitely get away with one pump. I also don't want to much flow where I may heat the fuel up. Being im not getting into this till summer its just a bit of research for now

 

I don't think it's a good idea to disable the secondary pump and install a higher flow primary pump. I have tried the 255 lph pump in my XK8 supercharging project (the XK8 has no secondary pump), but such a high flow enlarged the fuel pressure and created very much heat in the fuel system, the fuel tank was difficult to touch after 1 hour of driving. Not sure what exactly created this heat (either the flow itself, or the heat from the engine being transferred and accumulated in the tank faster, or higher heat generation of the powerful pump).
In your case I would try the high flow pump in place of the secondary pump. This should create enough fuel supply to the engine when you floor it, but there will not be excessive useless fuel flow at idle and cruising.

 

The stock FPR can only handle a certain amount of flow, so if you increase the flow to much, it can cause the mixture to be very rich in closed loop, but in open loop you could get a lean condition. So be careful here, of buy a larger flow FPR.

I have never used 255 or larger (i.e. aeromotive 340) fuel pumps, so I have no experience with heating issues, nor have I heard anyone about it (except from JagxkFan).

Walbros 255 may have been used a lot (I don’t know of any though), but you also need to be careful with the noise generation. A pump that is just as small as the original probably needs to turn faster to have a higher flow at higher pressures. That at least causes extra noises. Next to that these pumps also draw more current, which was for me a reason to pass on these.

I choose the Bosch 040 pumps, these are large beasts, and are made to run already at high pressures. They flow lower fuel as the 255’s at lower pressures, but again more at high pressures where the 255’s collapse. They also consume less current than the 255’s, so this was for me the perfect combination. They do produce more noise, it’s a low hum which you can hear at idle, but over time you get used to it, so I don’t hear it anymore, unless I try to listen to it. If you go for these I recommend isolating them well, I used fuel tank foam which I put into the bucket with two holes in which I place the pumps, so they are cushioned to the bottom and sides. This isolation maybe a good idea as well if you go for 255’s though.

Just make sure you check the end fuel pressure you require and the required boost, add some spare (i.e. 15 psi) and check the flow chart of the pump if they can deliver still enough fuel (especially if you only go for 1 pump!)

Another option is to go for stock pumps and if you require more power later go for KenneBells boost a pump.

If you go for a 4.2 block, and the 4.2 injectors and increase the power (so boost pressure) I would advise you should go to a new FPR so you can run them on the stock 55 psi (compared to the stock 43 psi of the 4.0 injectors), and also upgrade the pumps or go for the boost a pump.

 

Thanks Avos. Years ago I had a dual bosch 040 pump setup that I ran externally on one of my cars. That was before the 255lph came out. They were a bit noisy even when isolating the mounting points. The Aeromotive Stealth pump at 340lph allegedly runs cooler than the smaller pumps.


Now I wasn't aware the factory regulator was restrictive like that. I've never had an issue with a 255 in other applications but if I had a 255 then a secondary pump kicking in well that could be an issue. Do the lines tend to be a restriction or just the regulator? And what did you do regulator wise? Here is where I start to collect more stock parts to see whats going on before I pull this thing apart....Think used gas tanks go cheap around here:O) I am not completely comfortable playing with certain things such as injector changes as I have no way to tune this thing. And although some play with this car performance wise. There isn't much out there

 

The 040 is for intank use, are you sure you didn’t have the 044 ones? These are for outside mounting and are of a higher capacity, so also noisier then the 040's.

The lines can take much more flow, I haven’t reach a maximum there yet, though I am using the 040’s of course.

There are many FPRs on the market, just make sure you buy one that is also able to hold the pressure once you turn off the engine for at least 1 or 2 hours. Some high performance ones (i.e. Aeromotive) are not able to, they are designed for perfect steady flow at high volumes.

I use a Kinsler K-140 (best I know of, though expensive), but also have good experience with the Tomei L (stands for Large) version.

Here an example of flow/current for the different pumps:


Just to note, this all isn't applicable for the 4.2 x103 cars, they only have 1 fuel pump, not easy to change...

 

I have had 2*Walbro 255 High Pressure pumps last two years. No issues. Just the metal parts at return line needed bore out bigger since otherwise fuel pressure went up too much and was not under full control of the FPR.
They have been so quite ones that can hear just by opening the trunk. Beware Chinese copies. They are just noisy and fail after short period.

 

Just added a Walbro as well to the list

It could be that the XJR's tank is a bit more isolated from the cabin.

Good that you mention the cheap Chinese copies, that also goes for the Bosch 040 pumps. At least when I bought them, you could check it very easy, Chinese copies had Made in Germany on the box, but they are actually made in Czech republic ...

 

Yes it was two 044's not 040. I remember also using a pump from a vr4 3000gt at some point in the past.


So the return line in the pickup at the tank is too small? And you ran two 255lph pumps? Id say that's overkill for me but perhaps a 255 and then a factory sized secondary? Ive never had a noise issue even in my mustang convertibles. I barely hear the 255 make a peep. All I know is that Id prefer not to remove the tank twice. Seems its not such a fun thing to do on this car

 

Oh and yes. The Chinese replicas are awful. I learned the hard way via a blown head gasket on my supercharged v6

 

There was a bottleneck near the orig FPR. Min base pressure was over 60PSI after Walbros installation. Making the few mm hole bigger resolved the problem.

 

Couldn't edit my previous post, but there was a typo there, the Bosch 040 pump does about 200 lph at 43 psi instead of 100.

The stock pumps go a long way, and if you ever get to a point that you require more fuel, you can always go for a KB Boost a Pump.

 

Just to complete the info about the 040 pumps for reference, as some are asking how I have fitted them.

Attached a picture comparing the original and the Bosch one, and a picture of the new ones in the tank.

I have use special fuel foam to fill up the inner part of the tank, and made 2 smaller holes in it to squeeze the pumps in so they sit tight, yet loose enough to minimize vibrations. I also leave a little bit of foam on the bottom so they don’t hit the tank itself, but not to much so they don't sit to high.

 

What is safe HP limit for stock pumps in 4.0 cars?

 

For good working pumps, and pending on what you find safe of course, I have had them at around 470rwhp. But that was with my kit/setup, for any other TS setup it might already be lower in rwhp pending on the overall efficiency.

 

Andre. Ive tried figuring this out but have gotten mixed data. What exactly is the flow of the stock pumps? I don't see myself fever getting the HP you have unless you start making a kit for the 2004 and up xjr's:O)

 

See post number #8 and 1st column, there is the stock flow for a 4.0 XKR pump, at least this was the flow tested on a used pump which was in good working condition.

PS The kit is as ready as can be for the 4.2 XJR, I just need to wait for a dyno to confirm all is working as expected.

 

Can you send some photos of that 4.2 xjr kit installed?