Working out restrictor size for an Audi RS4

[rs4steve]

Hi

I'm trying to work out the correct jet and restrictor size but the figures I'm getting dont seem right. The car is a 2.7 v6 twin turbo running standard 380bhp, the injectors are 480cc standard. I have to run two jets as it has two intercoolers. Do they both need to be .7mm? Or both jet sizes totalling .7mm?

The wording in the HFS-3 fitting guide states "First work out the total fuel flow by adding up the capacity of the fuel injectors. Multiply the result by the prefered %." Is that all 6 injectors?

Any help working out the jet size would be appreciated.

Cheers

Steve

[Howerton Engineering]

We have a page below that lays out the calculations:

http://www.howertonengineering.com/Jet_Calc.html

480cc x 6 inj. = 2880cc

2880 x .2 (for 50/50 assume 15-20%) = 576cc

Since you need two jets, 576cc / 2 = 288cc per jet. Assuming 20psi peak boost you would need two .5mm jets. Other variables might push you up or down a jet size.

Another general rule of thumb is 150cc per 100hp, which happens to be 570cc, nearly the same as the 576 we got earlier.

Again, many variables can change the numbers, hopefully this helps you out a bit.

[rs4steve]

finally i see the light thank you very much.
ow and one more thing will i need to put in a restrictor if the flow is say 600cc as it is 400bhp i will need to put in a .7 restrictor ? hope this is correct.

[rs4steve]

ok one more restrictor jet question i hate not fully understanding anything, apart from women i dont want to understand about them any more.
how come a .7 restriictor flows up to 680cc/min
and a .7 jet flows 410cc/min acording to the user manual surely .7 is .7 wether its a jet or a restrictor in the fav .
sorry about the anal questions i cant stand the un none

[Howerton Engineering]

You are noticing the fine points of the system. There are some differences in what you are comparing. The restrictors are a fixed hole size and can actually vary in flow by how long the restrictor orifice is. A .7mm hole 1mm long will flow differently than a .7mm hole 5mm long.

Also, the jet has spinner behind the jet orifice itself that also regulates and controls flow.

So it's not quite an apple to apples comparison by just the nomenclature of the name.