Been noticing a lot of people/manufacturers using inline pumps to make up for higher pressures/fuel demand in power adder situations. Setups like the vortech TPI setup (cut the flex lines by the frame rail, install the inline pump), seem like a very simple approach.

I’m sure that you get more pressure and volume then either pump individually, but how much?

Anyone know where (HP/pressure…) these setups give out? How big a pump can you put inline before the pump in the tank becomes a restriction?

 

Can't give you exact numbers on volume, but pressure capabillity (maximum head pressure) directly adds up when running pumps in series. If you have one pump that has a maximum head pressure of 100 PSI, then add a second pump (also with a maximum head pressure of 100 PSI) in series with it the ultimate max head pressure after the second pump would be 200 PSI.
The gain in maximum volume depends on the flow (volume) curve of the pump VS pressure. For any pump, its max volume decreases as head pressure increases. By reducing the Pressure load on the intank pump you increase its volume. A nitrous application appreciates the extra volume from a booster pump but booster pumps really shine on a forced induction system, because the increased head pressure capabillity really comes into play when trying to supply high volume against high manifold and fuel pressure, particularly so when an FMU is used.
I'm sure there is a point of diminishing returns reguarding booster pump size, but the higher the volume capacity of the booster pump, the harder it "sucks" from the intank pump, and thus the intank pump flows more due to less restriction on its outlet side.

Since a pump supplies higher volume when pumping against less pressure differential, the booster pump can also flow higher maximum volume at a given fuel pressure than if it where used alone (without an intank pump). This is because the intank pump shares part of the total fuel pressure and the inline pump makes up the rest, so the inline pump isn't seeng the total fuel pressure differential between the fuel tank and fuel injectors. It is only seeing the pressure differential between its own inlet and outlet.


I know of a high 9 second Vortech supercharged TPI car running a stock intank and an SX inline pump, and countless 10 and 11 second cars running booster pumps so that should cover most street cars needs.

 

Hum, you sure about that?

Seems like in the mustang world (not that I've got one but I spend a lot of time around them since I spend a lot of time working on my brother's LTD) it's pretty common for people to install an aeromotive or larger inline pump (weldon, paxton...) and have them fail because the stock pump was too much of a restriction (or at least that's the conclusion drawn and what the pump manufacturor said).

I know that the stock ford intake pumps are a little smaller...

Any other thoughts/experiences?

 

You may be correct about the stang guys having problems, and you may have hit on why, their intank pumps are definetly smaller (flow and physical dimensions) than GMs and the stock fuel feed tubing diameter is smaller (5/16" I think).
All I can tell you is that I have been running a car with the stock GM pump in the tank and an SX pump inline since around '92 or '93 or so with no problems, and another with a Holley (walbro) 255 lt/hr intank and aeromotive inline for about 3 years now also with no problems, and I've got buddies that have run similar setups as well with no troubs.

 

Yea, you're lucky if all of your feed lines are 5/16 on a ford. I've seen them use the stock plastic lines off a 4th gen f-body as an upgrade, and my brother had me modifiy a turbocoupe regulator to make it adjustable and I swear that all the internal passages were less then 1/8" and the inlet was about 3/16...

Thanks Irock... sounds like it's worth giving a shot. should be a hell of a lot easier then putting a double pump assembly in the tank or sumping it (doing the math it looks like a 255 will be just too small)

 

One thing that I have heard of people having problems with on GM (and others) systems when using an inline with intank, is if the intank is not working before installing the inline (trying to get by a broke pump the easy way) or the intank fails during use wth an inline. In either case there would be a severe restriction and a major suction (causes gasses to sort of "boil" out of the fuel) load placed on the inline pumps inlet side which is bad for it and a severe reduction in flow, both of which heats the fuel and reduces the fuels ability to cool the pump.

 

Exactly.


I was trying to avoid replacing my intank walbro 255 when it was dying, so I installed an inline Vortech T-rex 255. Well, that worked for about 3 weeks.... Then all of a sudden on a ride home.. WHEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEENNNN the vortech started screaming!!!! I mean, so loud it gave me a headache.. Then the car started bucking, and my FP was bouncing from 5psi to 53psi... Needless to say I replaced the intank with a Granatelli 255 (reboxed Walbro) and put a new inline Vortech T-rex in. The original inline was TOAST after that experience..

Lesson learned- Trying to take the easy way out leaves you with a nice 2 mile walk home.