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Old 05-20-2012, 12:50 PM   #1
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Default Big boost and returnless fuel system

Currently I have ID1000s and Walbro 255 on my 99 Miater. Understand it runs a constant RAIL pressure of ~60psi. So we're looking at around 70psi effective fuel pressure at idle, 60 at atm pressure, and then less in boost.

My question is, at what point (boost wise) does fuel pressure become an issue with the stock fpr on the returnless system. Or to word it another way, what's the minimum effective fuel pressure (rail pressure - manifold pressure) for most injectors/ID1000s?

I'll probably be running about 20psi here soon, 25psi max. That puts me around 60-25= 35 psi effective pressure.... that too low is my concern? I know these ID1000s 'like' 70-90psi if possible.

What are the best alternatives for the money? OEM return setup swap? I've read that the Walbro 255 can overwhelm the stock fpr a bit in that setup, making fuel pressure non-linear at idle/low load, but I don't see that being a huge issue, that's something you're already dealing with on the returnless setup anyways. This seems like it would be a pretty easy and cheap route, and this way I'll maintain 43.5psi effective fuel pressure at whatever boost I may run.

Other thing I've seen on TSEs site is the fuellab adjustable FPR. Setting that to around 70-90psi seems like it would be nice, and give my injectors lots of headroom, but running that much, or more at idle could be an issue jah?

If I missed some big discussion thread on this already, show me the way...

Thanks
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Old 05-20-2012, 02:49 PM   #2
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Been looking around a bunch on this still. I guess my biggest question is- what is the "minimum fuel pressure" needed for proper atomization. Flow wise I should be good to go, even at ~35psi fuel pressure.
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Old 05-20-2012, 06:50 PM   #3
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Running more pressure at idle shouldn't be an issue if you have enough resolution, which you should with MS2
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Old 05-20-2012, 06:59 PM   #4
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Looking at the 255 HP plot of flow vs pressure... looks like you can only afford about 10psi increase (on the conservative side) for enough flow for ~400whp. Wonder if there's some sort of drop in regulator for these returnless systems to give me ~70psi static pressure. Searching has brought up nothing so far.

Either way I'm gonna be just leaving everything as-is initially.... I'm just waiting on motor build to finish, getting bored and looking for stuff to do/think about in the meantime, lol.
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Old 05-22-2012, 09:07 PM   #5
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You won't have enough fuel to do 20psi from anything at 35psi of fuel pressure, even from ID1000s. It's time to upgrade to a return system, or add a 1:1 boost-referenced FPR to your current system.
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Old 05-22-2012, 09:54 PM   #6
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Aaron, I have been wanting to make the switch to return style for a while now. It really isn't that difficult either, just a matter of finding the time to do it.

From what I've gathered here and at m.net, the na lines will drop right in on both the fp sending unit and the 99 rail. I have also searched for a drop in 70psi in tank regulator, but like you, have come up empty.

I toyed around with the idea of increasing voltage to the fuel pump as a way to bump up the pressure as well.

Let me know if you decide to run return lines, I'd like to know how it turns out.
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