Well I've had a Holley In-line pump (190L/Hr) to help out with the 175 shot so far along with the stock in-tank pump and it's worked out great, but I'm about to put in a set of ported heads and a 224/236 cam so I just put in a Walbro 255 in the tank and was wondering since the in-line pump flows less will it choke the Walbro? I've heard of the "boost-a-pump" in-line pump but I don't know if that's different than other in-lines...

 

anyone?

 

ive heard that if the inline goes out it will take out the in tank pump also, so if i were you id prolly take it out regardless

 

Most of us on the blown list remove the inline helper pumps once we go with a larger intank. I didn't do it for the restriction possibility, but to make the system simpler.

 

The inline pump is useful if you need a high fuel pressure... examples would be the NOS 5176 dry kit (80-90psi) or a blower with an FMU that boosts fuel pressure with reference to manifold boost. If you just need high volume at near-stock pressure, all you need is the larger pump, or dual pumps running in parallel, rather than in series. I run dual Bosch 205 lph pumps in parallel, 58psi operating pressure, and the fuel system is good for 1,000HP.

A fuel pump typically has an operating curve (flow vs. pressure) which causes flow volume to decrease as system pressure increases, and flow volume to increase as the pressure the pump needs to develop decreases. The pumps you mentioned are flow rated at a specific pressure, probably about 45psi. Reduce the pressure that each pump needs to contribute, and (within reason) the flow capacity of the "system" can exceed the rated flow capacity of the smaller pump, because each pump only needs to contribute a portion of the total system pressure.

When you put two pumps in series, the two pumps will reach an equilibirium point where they are operating at the points on their flow curves where they are both flowing the same volume, and the delta pressure developed by each pump is whatever it takes for the two pumps together to add up to the total pressure in the fuel system, while remaining "on the curve".

 

I used a T-rex in conjuntion with a stock 144k mile pump to make close to 500rwhp last weekend.

I would rather have put a intank pump in but didn't feel like dropping the suspension, tank, and exhaust at the time.

Looking back I would have made a really trick access panel to get to it from inside the car.