Montreal Fuel Pump

[Doug Gould]

There is a good thread on the AlfaBB to which I have just added the following post. I'm leaning toward doing it myself with a Bosch FP165 pump and a commercial fuel regulator.

I had a fuel pump fail over Easter. While I'm waiting for time zones to align to catch Giorgio Pennatti, here is what I have learned.

My fuel pump failure (at least intermittently) seems to allow fuel pressure to bleed from the good pump through the bad one. It would have been good to disable the bad pump, but the fuses run the CDI packs too, so it doesn't run at all happily with one fuse out. This kind of says that having 2 pumps is a false sense of redundancy.

The Spica injection  in the Montreal requires a pump output of about 25psi, which is significantly more than a carburettor (which rules out the solid state pumps like Facet) but less than the modern fuel injection pumps at about 60psi. Therefore, a fuel regulator is required.

The original pumps have a capacity of 112 litres / hour (according to Bruce Taylor, who has, I suspect, measured his output). An od Bosch catalogue I found lists the 0 580 970 001/003 pumps as 100 litres / hour minimum and 2 bar pressure (approx 28 psi).

At cruise speeds the engine consumes (at a guess) 10 -12 litres / hour. My guess is that full power is maybe 4 times this. Lets say 60 litres / hour. Therefore the pump capacity is maybe 3 times that consumed by the engine. I think that there are 2 reasons for this: a) provide cooling via fuel flow to the Spica pump and b) create a high enough fuel flow so that the pressure change at different engine fuel consumption (ie idle to full power) is stable.

The choice of replacement pumps are basically Walbro or Bosch. Both have single pumps capable of replacing the original dual pump setup. Interestingly, the new pumps are described as roller pumps. I presume that modern manufacturing allows better tolerances that result in a more efficient pump.

Its also worth noting that there are many, many Bosch fuel pump part numbers floating around, but some years ago Bosch undertook a part rationalisation programme. So now there is effectively 3 choices. The FP100, FP 165 and FP 200 (the famous 044 pump).

The Bosch pumps are:
FP100 dia 54mm 185mm long 100 lph
FP165 dia 60mm 168m long 220 lph
FP200 dia 60mm 196mm long 270 lph

The Walbro pump is:
GSL 392 Dia 43mm  162mm long 250 lph

A significant difference between the Bosch & Walbro is the inlet & outlet sizes. The Walbro has an M10 thread for inlet & outlet wheras the Bosch ones are M12 outlets with 14 - 18mm inlets. Frankly, the larger inlet / outlets appeal to me. Remember that the ID of the spigot for the fuel line will be significantly smaller than the tread size.

For reference the standard Montreal pump is about Dia 60mm and about 140mm long. Clearance to the fuel tank will not allow a fuel pump of very much larger diameter, but there is room for the pump to be longer. The tray is about 190mm wide and the fuel pump could "hang out" maybe 20mm past the tray on the inboard side. So, the length of the pump including tubing could be maybe 210mm.

Note also, that Bruce Taylor suggests that the OE Bosch pumps draw 2.5 amps each. Both the Walbro and Bosch pumps draw something like 7 - 8 amps. Which raises the question of whether a replacement pump should have a relay rather than being wired to a single fuse intended for a 2.5A pump.

Returning to fuel pressures, The Montreal has an orifice in the fuel line to reduce the fuel line pressure to the 12-15 psi (is this correct??) required for the Spica injection. The pressure on the spica side of the orifice will  vary in relation with the pressure on the pump side (I forget the formulae and I'm not hitting the text books to refresh my memory). But we can take it that the pump side pressure is important. The Bosch reference I found says that the original Montreal had a pressure of 2 bar (29 psi). They have an inbuilt regulator (the 3rd line is the fuel return from this) which sets this pressure. Bruce Taylor refers to a pressure of 1.5 kg/cm2 (21 psi) but I think this refers to the input to the Spica (after the inline orifice) rather than the pump outlet pressure. 2 bar (29psi) seems like a good number to me.

Any replacement pump will require a fuel regulator to deliver a regulated 2 bar pressure. This should be a 3 line regulator with a fuel return line for excess fuel from the regulator. These are readily available commercially from race shops (Or Goirgio's kit has his own design inline unit, which packages nicely).

My conclusion? Forget originality and fit a modern pump. Its likely to be cheaper, more reliable and with better fuel pressure control. There are only 2 choices. Buy Giorgio's kit or do it yourself. I'm leaning toward the Bosch FP165 because its more readily available in Australia and I like the idea of the larger outlet fittings. But, expediency might still win the day and I'll buy Giorgios kit.

[ItalCarGuy]

Nice write-up Doug. Makes sense to me which says alot! It'll be a while before I get to my fuel pumps but Giorgio's kit looks very thoughtfully prepared, much like all his products. If I have problems with mine I won't have a problem swaying from original as it is out of sight anyway. If you do go the way of doing it yourself, please add some photos to this thread when you do it.

[Doug Gould]

I doing basically the same setup as George Bettiol. I came up with this plan independent of George, which I think is a nice confirmation that we both agree.   I will use the Bosch motorsport FP165 (P/no 0 580 464 979) pump with a Fuelab 535 fuel regulator. Its all on order. The pump is AUD$280 and the regulator about AUD$200 plus there will be maybe AUD$50 of fittings. I'll post once it gets here and I start.