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Got a question regarding fuel pumps and boosting

686 Views 3 Replies 3 Participants Last post by  Ol'Racer
When boosting the lotus a main issue is the fuel pump not being able to handle the additional need. Changing the pump is a MAJOR hassle and people like turbophil have even gone to the extent of building a inline tank to handle the short bursts of additional fuel need.

Question: Why would simply just adding another inline pump not work, basically running two pumps in series? Many car mfg do this, including my BMW 535is; one in the tank and the main one after the filter. The main under load just pulls the fuel through the smaller tank pump. As usual residual fuel is returned back to the tank after the press regulator.

Just curious as to why this would not work for the Lotus. Has anyone tried this?
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Yup - it'll work...

(search function) ;)
Not sure if Turbophil did add a additional inline pump, he built a surge tank for short bursts, which I suspect would provide low pressure to the injectors under extreme extended load conditions, as the engine is using more fuel than the pump can deliver so even though the resevour is empting to take care of the additional need as the pump is not up to capacity, the pressure will drop.

I have not read all of Phils post, but if a additional inline pump was added then the surge tank would not be needed.

A accusump (diaphram) system would also work, but a inline pump would be cheaper and simpler.

Maybe wrong...
In Phil's setup the surge tank pump becomes the main feeding pump. The in-tank pump becomes the filler of the surge tank. The surge is used to safeguard the main tank from sucking air and grenading the engine in case of a high g's turn. The pressure doesn't drop, that would defeat the purpose of the fuel in the small reserve tank. Don't forget that the big dog pump is doing the feeding and it's high pressure. That's why it's called a surge or pot pump...'cause the fuel is used for emergencies and no pressure loss. The tank should last for 15-25 seconds under high pressure...NOT low pressure. That should be way longer than a high G turn would last.

The problem with adding a pump in series is if the in-tank pump craps out, it then blocks the flow of the higher pressure pusher/puller pump. I had that same scenario happen to me. I had to go into the main tank and pull the pump and let the exterior mounted pump do the main job. Luckily, the exterior tank had the capacity to keep the pressure that was needed for the injectors and I never put an in tank pump back in.

Phil agreed that a pump in series would work the same as a surge tank setup...regarding blockage. With a surge tank, if both pumps are working, you should never have fuel starvation. Yet, if the in-tank pump buys it, it would create a blockage and would have to be changed or pulled to let the main pump do the job. Back to square one.
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