55 -> 63L fuel tank swap - what all is needed?

[NigelStu]

Good write up - why use the 318i pump? Is there something different/better about the 318 pump vs the stock early-model 325i/e low-pressure pump?


And can you show a picture of where the return line hooks up to the siphon hose? That is one bit I'm still unclear on.


See you at the Glen!

[CorvallisBMW]

Lot's of good inputs above. Just wanted to relay what we did with our 86 325e ( sporting a 3.5L ). We race Chumps and Lemons and needed to try and reach the 2hr mark.

1. Pulled the factory 55L tank
2. Bought a good used 65L tanks
3. Installed a 318i low pressure pump (plugged the return tube) on the left side ( you will need to use a file and shorten one of the tabs on the tank so the locking ring locks in)
4. Installed a new 325i high pressure intank pump on the right side
5. Ran the output of the low pressure side to the return side of the high pressure pump ( this will keep pushing any fuel from the left side to the right). I just used fuel line and ran it across the top of the tank. I think there were a few spots (on the body) I had to hit with a hammer to make sure this hose wasn't pinched at all.
6. Connected the high pressure pump output to the line running to the fuel rail ( had to use a brass reducer I got from ACE hardware to match the fuel line sizes).
7. The return line from the fuel rail gets connected to the siphon line on the tank ( I'm guessing this helps push fuel to the right side as well).
8. Removed the high pressure pump from the frame rail
9. Extended the factory high pressure pump wiring and supplied power to both pumps.
10. The 325e only had one fuel pump cover under the back seat so I added another one above the low pressure pump so I could work on it. Went to the junk yard and got a cover from a 325i. Once I got it on it looks factory ( as long as the inspectors don't figure our this was a "e" car).
11. Replaced the filter

We have a done a 24hr race a VIR last year after I completed the conversion. Ran well - we got about 1hr 45min out of it before we got nervous and brought it in for fill up. Never starved. We just found out that the WOT on the TPS was bad so the car was never running on our WOT tune so our fuel mileage would have been worse because of that. Doing Watkins Glen in April - we will give it a new test then :)
65.

Fantastic! This is exactly what we're hoping to do on our '87 325e/m30 Chump/LeMons racer. We can do 1hr45min with the current 55L tank so a 63L should get us to the magic 2-hour mark just fine.

[porschelou]

Thanks for questioning the fuel pumps NigelStu - It has been a while since I did this..

You are correct - Since our car was an "e" we had two pumps - low pressure in the stock tank and high pressure on the frame rail.

Since our low pressure was new I put that on the left side of the new 65L tank.

I then bought a new 318i pump which is a high pressure pump and has a return nipple on top. The reason you must use the 318 is because the 325 pump only has the high pressure nipple not both the HP and Return.

Sorry for the confusion. I updated my write-up correcting the original mistakes.

The 65L tank has a nipple on the left side where your Fuel Rail returns connects to - easy. Once you get the new tank and 318 pump just lay everything out and it's not a real bid deal. Luckily the new tank bolts right in.. Feel free to email me if you have questions.

[RGCintha29073]

^ can ya post up some bigger pics?

[porschelou]

Larger Pic's

The cloth looking hose is one of the vent lines. You just unplug it when you lower the old tank and move the hose over when re-installing the 65L.

[evandael]

If I were to buy a new late model tank, cut it open, install baffles, and re-weld it, which would be a better pairing of fuel pumps:

1) early model transfer pump on drivers side > late model 318i high pressure pump on passenger > filter/FPR/rail > return to early transfer pump

2) dual late model 318i high pressure pumps > filter/FPR/rail > return split to both pumps

I'm running an S52 and plan to autocross and do HPDE's with DOT-R's at most.

[NigelStu]

Or option 3) 2 low-pressure lifter pumps into a surge tank with high-pressure external pump to rail, return line to surge tank and surge tank overflow back to tank.

[evandael]

Or option 3) 2 low-pressure lifter pumps into a surge tank with high-pressure external pump to rail, return line to surge tank and surge tank overflow back to tank.

i had thought of that (it would be the ultimate setup) but don't want to overload the fuel pump circuit.

plus there are packaging issues of fitting a pump, surge, and filter in the place where only a filter and pump exist now (i don't really want to put it in the trunk)

[makeetrott0700@gmail.com]

hello,
welcome to this forum site, here you can find lots of things, i suggest you for your friends or any expert, i am not able to give you answers right now, sorry for that.
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[IronFreak]

hello,
welcome to this forum site, here you can find lots of things, i suggest you for your friends or any expert, i am not able to give you answers right now, sorry for that.
------------------------------
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^^^How does stuff like this get on our forum?

[NigelStu]

Parts are starting to arrive for my fuel tank upgrade. Pic is of the right/passenger side of the new 63L late-model tank. There are 2 places to put hoses here (both still have the caps on from shipping). I know the large one is for the vent.

I just want to confirm if the small one is where the fuel return line is supposed to go.... (And if it isn't the normal return nipple, what is its intended purpose?)

[jlevie]

The small line is for the pump output. The fuel return fitting is on the left side of the tank.

[roguetoaster]

Does anyone think there would be issues running two high pressure pumps and feeding one into the others return line? It would be handy in the event of a pump failure, right, or would it do nothing?

[evandael]

^ it would likely just churn up the fuel around the second pump's pickup. i'd run both pump outputs to a Y fitting and on to your FPR/fuel rail. do the same for the return... single line to a Y and then back to both pump return fittings.


from this thread it seems it could be achieved using two late model 318i/is pump/sender housings. or some fabbing if you're cheap.

[jlevie]

Does anyone think there would be issues running two high pressure pumps and feeding one into the others return line? It would be handy in the event of a pump failure, right, or would it do nothing?

The life of the left side pump may be short. High pressure pumps don't like to run dry which will happen on the left side. Transfer pumps are far less sensitive and don't usually suffer damage from running dry.