6east

Hey,

Firstly allow me to say that I am new to these forums, I currently don't drive a LS powered car but have and will do again in the future.

The reason I joined up is because the amount of knowleadge on these forums is extremely high in my opinin and I hope I can ask questions and also provide answeres sometimes also.

Now about my question, as I stated in my intro thread I drive a 05 Audi C5 RS6 which I am in the process of upgrading performance wise with large turbos, coolers etc and the fuel system also o support the new setup plus allow me to run E85

I've pretty much worked out what flow my pump(s) will need to maintain for the target horsepower and I will provide this information later but the question I have is about reducing the base fuel pressure and if its viable?

The base pressure on this and I believe other FI Audis is 4.0Bar (58psi), as you may know when calculating fuel needs pressure plays a big part as the pumps must flow the required fuel at the base pressure plus any boost which in this case will be 1.5-1.8ar so I have rounded up to 2.0Bar as I have with all calculations to allow headroom.

The question I have is why is the bad pressure 4.0Bar instead of 3.0Bar? Most if not all efi parts are rated at 3.0Bar.

If I was able to reduce the base pressure to 3.0Bar by changing to a 3.0Bar FPR this would allow me to simply the fuel pumps greatly as the flow required would need to be achieved at 5Bar (72.5psi) instead of 6Bar (87psi) which my calculations and research have shown is right on the boarder.

Can anyone please advise if lowering the base fuel pressure will result in any problems? I understand the tune will need to be modified which is fine as it was going to be extensively tuned anyway but I am more concerned about any detrimental effects this would have in terms or power, reliability etc.

Based on the target horsepower of 750hp and 900bp while running E85 and the following specs:

4.2Lt 40V (5V Per)
7000rpm redline
Base FP 4.0Bar
Boost 2.0 (1.5-1.8 Avg)
880cc Siemens Injectors

I used the calculators here: http://www.deatschwerks.com/resources/fuel-calculators/ and came up with the following:

E85 Needed = 6400cc/min (20% Headroom)
injector = 800cc/min @3Bar (80% DC, 20% Headroom)
Fuel Pump = 360LPH @6Bar (20% Headroom, 4bar FP plus 2Bar boost)

Now looking at the flow chart for the Walbro 465 shown here: http://3.bp.blogspot.com/-NJWhwL9iIy...-465-13.5v.jpg

If I was to lower the base pressure this pump can supply more than enough fuel to satisfy my calculations, that is based on the assumption they are correct.

If I was to remain the base pressure this pump would fall short of satisfying my calculated flow requirements, I will be able to increas its flow by using a Fuel Pump Booster by running the pump at 17.5V.

So sorry for the long post but I was hoping that I would find some help and advise to determine if either of the following are viable:

1) Reduce base pressure to 3.0bar and install single Walbro DCSS465.
2) Retain base pressure at 4.0bar and install single a Walbro DCSS465 and voltage booster to increase flow.

I also assume I will need to upgrade the feed and return lines, I was planning to using a -6 (3/8") FEED and -8 (1/2") RETURN.

Thanks in advance!

stevieturbo

Flow chart for the 465 doesnt work.

The main reason they run a higher base pressure ( as do the LS engines ) is because injectors will spray better at higher pressures, which = better burn = cleaner emissions
The other may be because a fixed rail pressure setup is usually a dead end one, so may require slightly higher pressures to work efficiently.

Ive seen mention that the ratings when flowing E85 are actually lower than when using gasoline. So that 465 flows some 7-8% less with E85. ( in that fore innovations link )

Look at a chart online ( oddly googled in a thread you started lol ), at 70psi and 13.5v, the 465 would be around 380lph on gasoline, so potentially only around 350lph in real terms. IMO not enough for your needs.
All these new Walbro's also draw huge amounts of current too.

Here is a good test of a few pumps, although not the 465

http://radiumauto.com/media/blog-pag...l-Pump-Test-73

And I would be inclined to go with a 1/2" feed, and a 3/8" return. You want an unrestricted supply to the engine.

Single in-tank options will always be a struggle though.

Like them or loathe them, a pair of 044's will easily do what you need, they will flow almost the same up to around 100psi, and they are ultra reliable.
Fitting them in-tank may be difficult though.

If that isnt an option, you could opt for an external swirl tank for the 044's and just supply the swirl tank with a suitable in-tank lift pump.

Failing that, it might be easier to squeeze a couple of the smaller Walbos' in tank.

But again, do be aware of the huge current draw. Some of them can be around 20A each at moderate pressures !! with even higher at higher pressures.

Ive tested my own 044's and 2 of them draw around 22A amps my 52psi base pressure. Rising to at most 28A at close to 100psi ( during a test purely to check current draw ).
Under normal use on my car the pair never exceed 25A

6east

Can you advise if my calculations are correct? I'd also appreciate if you had the time to show the calculations or atleast the formula to work out the fuel needed for a given WDR output.

I don't want to run dual outside pumps due to space, even dual internal would be an issue as all the fuel will be flowing for when it will be used on E85 which will be 20% at most for the time.

I confident that the 465 with BAP will cover my needs especially is I am with a 3bar base pressure as this way I can dial out the BAP when running petrol and activate it when running E85.

Thanks again.

stevieturbo

The DW calculator does seem to be on the low side. The numbers they are claiming for E85 are about the same as other calculators are claiming for gasoline. Given E85 will require about 30-40% more flow, that really doesnt make sense.

http://www.injectorrx.com/fuel-injector-calculator/

Which would be closer to 1200cc per cylinder for your 900hp goal on E85 running at 90% duty and a fairly normal 43.5psi base pressure.

If that is correct, in simple terms that's more than 9600cc/min of fuel flow required ( ie 8 cyl x 1200 ). 576lph. Far far above any single pump on offer. And that isnt with any headroom for the fuel return which would be needed for the FPR to function properly.

6east

Sorry if I mistyped but the peer target is 700 I'm just using 750 for head room?

6east

I just googled some other fuel injector calculators and all provided different results! Now I am not expecting any miracles but I'd expect them to be within 10% variance of one another!

I think I need to find the formulas and try them myself, if you know them I'd appreciate them!

Also your calculations on needed 1000+cc injectors is wrong as I specifically chose these injectors to support 700-750hp on e85 with a safe amount of headroom but for the lift of me I cannot find he calculations etc!

I'll keep looking but any help as always will be appreciated.

stevieturbo

The DW calculator is the only one that seems miles off. All the rest seem similar.

And as I said, all of what I stated was in relation to 900hp that you mentioned in the first post.