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Old 10-17-2013, 06:04 PM   #34
Maxwell Power
Former Vendor
 
Member#: 190729
Join Date: Oct 2008
Chapter/Region: NWIC
Location: Marysville, WA
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Pressure differential is moot and frankly I'm surprised anyone thinks it exists.

Here's why:

1. From the first injector to the last, the amount of fuel being used is less and less in steps. So from the beginning, you have less flow which lowers any potential for pressure drop. The largest demand on the fuel system is the line in the frame rail. Once it hits the first injector, the demand is less, which means flow rate is less, which means pressure drop is less.
2. The fuel system does not flow ONE flow rate through the whole system evenly.
3. The fuel pressure regulator is at the end. So if it sees a drop in fuel pressure at the last injector, it's going to bypass LESS fuel, which therefor keeps the pressure more balanced from beginning to end.


Lastly:
Nobody has ever had misfire issues from Series lines.
Many people have had misfire issues with Parallel lines.
Nobody has been able to prove any benefit with Parallel.
Many people have experienced uneven fueling from cylinder to cylinder with parallel.
The first year subaru implemented parallel rails, TONS of misfire issues. Just look up any 08+ STi.

Parallel fuel rails result in large differences in rail temperature and fuel temperature. Fuel temperature is a very important part of fueling (how important? 50C is over 6% fueling. 6% is a lot when we're concerned over 1 or 2% see the last article http://www.injectordynamics.com/NewsletterFeb2013.html). Someone mentioned that by going parallel you lower the speed of the fuel in the rail by half. This is true, in fact in extreme cases it's more than half. HOWEVER, that's not ideal. You want the highest velocity you can get away with without creating a back pressure and pressure drops. Higher velocity means you do a better job of balancing rail temps. Balanced rail temps means balanced fueling. Nice fat rails with a large quantity of fuel going through them would be nice too, but too big and fuel have such a slow fuel flow that you'd once again establish large changes in fuel temp from rail to rail.

So what you guys are doing is creating a problem while trying to prevent a problem that doesn't exist.

If you go series with injectors in the wrong order, you could have issues. However, our firing order is linear down the fuel rail. Subaru H4 is the only engine ever created to do this. The order of fuel feed should be opposite of engine firing order. This means that the fuel injectors are always firing towards the source of fuel. That means that you aren't going to get any lack of fuel from the load on the rail.

In V8's, I4, I6 etc, the firing order is not in a linear fashion down the rail and it is absolutely important and correct to go parallel with your fueling. Subaru isn't like any other engine out there.


Any lack of fuel is from a pump that is too small or from a rail system that is too small to handle the flow rate. It isn't from being series.
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Last edited by Maxwell Power; 10-17-2013 at 06:10 PM.
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