Supply flow needed for twin EFI pumps

[30psi 4agte]

hey guys.

Now that i have finally beenable to drive this car of mine i have noticed that my bosch motorsport fuel pump is noisy ( just my luck ) not all the time just every now and again. I have removed it to have a look to see if anything could be found lodged in it but nothing.

It is one of those things. Is the pump on it way out or is it just noisy ??? - I have had noisy pumps with no fuel flow / pressure probs in the past last for ages. Like i said its just one of those things do you spend the money to replace it or wait for it to shit itself and you to become stranded at the same time.

I vote for the first one !

Anyway i have decided to tackle this prob slightly different im gonna keep the noisy pump in it for now but im also gonna put another bosch pump in it as well and run to pumps into the one supply line via a Y piece.
This will not only give me a backup pump should one die on me and allow me to still drive the car home but will also make sure this little animal is never short on fuel.


My question is this : The bosch pumps have a 1/2 inch inlet supply . Now for two pumps you would think that to run a single fuel line from my surge tank to both pumps it would need to be a 1 inch dia line but i dont think it works like this IE the supply doesnt need to be that big.

What is the method to calculate flow through a pipe or hose????

Im sure we have covered this before in regards to IC pipes but i cant find the thread im looking for.


Cheers guys !

[STR8 2.8]

a 0.7in pipe would be roughly the equivalent of the two 1/2 pipes

[30psi 4agte]

how do you work that out ??

[STR8 2.8]

using the same volumetric flow rate and velocites for both pipes its just based on cross sectional area.
the cross sectional area for two 0.5in pipes is the same as one 0.7in pipe

[LeeRoy]

not Pie x R squared?

- LeeRoy

[ace]

not Pie x R squared?

- LeeRoy

Yeah i agree, you can find out the radius of the hoses (half of the internal diamter) and then their cross sectional area...

[STR8 2.8]

pi*r^2 is the cross sectional area...

[STR8 2.8]

just not feeling the rep love

[nick.parker]

pi*r^2 is the cross sectional area...

Since measuring the radius is harder than measuring the (D)iameter you might want to measure the diameter and then the same equation yields :-

CROSS SECTIONAL AREA = (3.142 x D x D) / 4

so D = SQRT ((4 x AREA) / 3.142 )

hence if area doubles (x2) the relative diameter will be SQRT(2) = 1.414 times bigger.
So double the cross section of the 0.5 inch would be 0.5 x 1.414 = 0.707 inch diameter pipe.

Cheers, Nick

[STR8 2.8]

ok ill take on the lead and explain myself a bit better.
volumteric flow rate Q = area*velocity
you'd want the flow rate to be equal if not better for your single pipe off the twins. so Q1=Q2 hence A1*v1=A2*v2
i jsut assumed the velocity to be constant, so therefore A1=A2
A1=combined cross sectional area of the two pipes
A2=area of singe pipe
and as mentioned area=pi*d^2/4

you could have any size pipe theoretically, but the pump can only push so much and it can't pump the fuel fast enough to maintain the same flow.

[30psi 4agte]

im talking about the fuel supply to the pump so it is basicly a gravity feed to the pumps

[STR8 2.8]

ah, well in that case anything 0.7 or bigger