budd

iTrader: (5)

That diagram looks the exact same as every other swirl pot diagram I've seen. Some pots very with where they put the fittings but they all run in the same configuration.

When you say you already have a high pressure pump do you mean in tank?

Re 1 or 2 pumps; usually one external pump is enough to supply the rail, I'm using a single Bosch Motorsport item that will be more than enough (over kill in fact) for circuit racing, I'm limited to 286bhp by Subaru Cup production class regs, at this low HP the engine won't be demanding massive amounts of fuel.
My reason for fitting a swirl pot is to combat fuel starvation, due to the design of the Impreza tank once the fuel level starts to drop fuel starvation is a very real problem on long / high G corners, the swirl pots solves this issue.
However if real big HP is planned or drifting /drag racing then a simple system my not be up to it, a larger capacity pot, multiple pumps, revised fuel line bore size etc etc may be required, if this the case then best approach would be to re-design the whole fuel system from tank to rail, build a no compromise system with enough 'headroom' to cope.

re swirl pot size; I found this on NASIOC it uses Nissans as examples but the principles are the same for any car and the math can be used to work out Impreza fuel usage.

There seems to be a lot of debate regarding how big you should make a fuel surge tank. Everybody will give you a diffrent answer from no surge tank at all to 3L. Some people even claim you need a 5L one for drifting

So I'll try and clear it up for you (the way I see it, if you think I'm wrong please abuse me!)

The size of your fuel surge tank really depends on your engines fuel system. You can use maths to work out how big it needs to be:

Take for example a RB30/25. It runs 6 fuel injectors that flow 270cc (270ml) of fuel per minute at 43psi (2.96 bar) at 100% duty cycle

Therefore your total maximum fuel flow is 1.620L per minute. This figure is calcuted by multiplying your number of fuel injectors by the size of your injectors.

So in a surge condition in your fuel tank when your lift pump is sucking nothing but air a 1.620L fuel tank will give me a whole minute of surge "protection"

But really the sort of turn that would create a condition like that would have to be a big one. I mean how many places are there where you can pull a high G turn like that for over a minute (beside the donut pad!) I doubt that drifters can hold a high G drift without changeing direction for over a minute. So what I do is half that figure.

So now I'm down to a 810cc (.81L) surge tank. Its small and compact and gives me a whole 30 seconds.

Now before somebody shoots me down this only applies to a N/A EFI engine. To apply it to a boost engine (be it turbo or supercharger) you'll need to factor in how your fuel pressure regulator works.

To clear a few things up, the fuel pressure regulator changes the fuel pressure depending on the pressure conditions in the inlet manifold. For example on a N/A engine at full throttle you will get zero manifold vacume. For every PSI of inletmanifold air pressure you put into that the Regulator will add a extra PSI of fuel pressure to your injectors. This will increase your injector flow by a few CC a min.

Say if I was going to throw 10psi of boost into my N/A RB30/25. The fuel pressure regulator would "see" 10psi of manifold pressure and increase the fuel pressure by the same amount. My 270cc injectors are now 332.79cc injectors.

To get this figure you divide your injector size by its base fuel pressure (43psi for most Nissans) So my 270cc injector will flow a extra 6.279cc of fuel for every extra PSI of fuel rail pressure. So 10psi of boost will cause the regulator to add 10psi of rail pressure which adds a extra 62.79cc of injector flow.

Now we times this figure by the number of fuel injectors I have and then divide it by 2. We get a result of 188.37

Simply add 188.37 to our prevously calculated surge tank volume (810ml in this case) and we have our surge tank volume -- 998.37cc -- 998.37ml -- Almost a Litre in english!

See so simple As a example I'll work it out for a SR20DET that runs 7psi of boost pressure stock

370cc (injector size) x 4 (number of injectors/cylinders) = 1480cc <-- Fuel used at 100% cycle

1480cc / 2 = 740cc <-- divide by 2 to give you 30 seconds of "protection"

370cc (injector size) / 43psi (base fuel pressure) = 8.6 <-- Extra cc of fuel flowed from injector when another psi of fuel pressure is added to the rail

8.6cc (extra fue when adding 1psil) x 7psi (boost pressure) = 60.23cc <-- extra fuel flowed through 1 injector at 7psi of boost

60.23 (extra fuel when adding 7psi) x 4 (number of injectors/cylinders) = 240.93cc <-- Extra fuel flowed at 7psi of boost

240.93cc (extra fuel) / 2 = 120.465cc <-- 30 seconds of "protection"

120.465mm (extra fuel from 7psi of boost) + 740cc (calculated surge tank size) = 860ml

Now as you can see depending on how much boost you run, and how big your inectors are (not to mention fuel pressure) all play a part in saying how big your tank will need to be. I have not taken into account riseing rate fuel pressure regulators. They alter the rail pressure at a diffrent rate to your boost pressure eg 1:1.5 make sure you include this in your calculations.

You also have to realise that not many EFI tuners like to run injectors at 100% duty cycle. And its very rare to run a motors injectors at 100% duty cycle. The fuel surge tank takes care of a "worst case" scenario.

Some people also like to over size their tanks to accomadate more boost etc. Thats fine the problem is you can go tooooo big and have the same problems with your fuel pickup like in your stock tanks. The tank should be tall and narrow, to get as little fuel "slosh" as possible. It *must* be mounted vertically.

Hope this helps.