Duramax Diesels Forum Truck of the Week
  #16  
Old 09-14-2018, 05:40 PM
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Originally Posted by 2004LB7 View Post
As mentioned above, the gear pump on the back has a 0.108" opening for fuel. That is less then 1/8"

Also the feed fitting for the pump is also quite small, maybe smaller, as shown in this photo. Stock on left, ported on right
That's if you use that fitting, I just put a AN fitting on the back. Even ported that fitting is the big restriction
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  #17  
Old 09-14-2018, 06:00 PM
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Originally Posted by LBZ View Post
Just keep in mind the smallest orfice no matter where it is in that line is your highest restriction. You could put 3 line on but that restriction will only allow so much flow through at X pressure. Hence the reason some people port the orfice in the fuel rails or the fpr.
This is incorrect. You care about the sum total of all restrictions.
An 1/8" orifice that is 1/4" long is way different than 10 feet of 1/8" line as an example.

Any small opening (such as a fitting) that is a restriction causes the fluid to speed up to pass through at a given flow, this causes higher frictional losses due to velocity. It takes pressure to overcome the restriction. Line loss is a function of distance. If 1 foot of line loses 1 psi at a given flow, then 5 feet would result in approximately a 5 psi loss.
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  #18  
Old 09-14-2018, 06:33 PM
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Quote:
Originally Posted by 2004LB7 View Post
As mentioned above, the gear pump on the back has a 0.108" opening for fuel. That is less then 1/8"

Also the feed fitting for the pump is also quite small, maybe smaller, as shown in this photo. Stock on left, ported on right
That fitting is for the high pressure side
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  #19  
Old 09-14-2018, 08:00 PM
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Originally Posted by Lonnie View Post
This is incorrect. You care about the sum total of all restrictions.
An 1/8" orifice that is 1/4" long is way different than 10 feet of 1/8" line as an example.

Any small opening (such as a fitting) that is a restriction causes the fluid to speed up to pass through at a given flow, this causes higher frictional losses due to velocity. It takes pressure to overcome the restriction. Line loss is a function of distance. If 1 foot of line loses 1 psi at a given flow, then 5 feet would result in approximately a 5 psi loss.
I think both of you are correct. If you look at what he wrote he stated the smallest opening would be the highest restriction. He wasn't stating that the remaining line had no contribution to the overall pressure drop, just the highest restriction was the smallest opening.

Ultimately it is the smallest/highest restriction that will determine your max flow vs pressure. As an example, if a 1/2" line provides say 3 gallons per minute at X pressure and a 1/8" port restricts it to 0.5 gallons then upgrading to 5/8" line would not gain you anything

Of course a 1/8" line the whole way woud net you less the just a port at 1/8" but there is a steep diminishing returns on larger feed lines
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  #20  
Old 09-14-2018, 08:05 PM
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Originally Posted by PureHybrid View Post
That fitting is for the high pressure side
My bad if it is. There doesn't seem to be many images of the feed side showing the inside. I've seen them in person and it is considerably smaller than the feed hose
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  #21  
Old 09-14-2018, 09:32 PM
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Originally Posted by 2004LB7 View Post
My bad if it is. There doesn't seem to be many images of the feed side showing the inside. I've seen them in person and it is considerably smaller than the feed hose
If youre talking about the inlet fitting that supply hose connects to, here are a few pictures I took of a stock fitting and the 1/2 fitting I drilled out. I was afraid to go any bigger because I didnt want to get the metal too thin where it steps down at the top of the threads for the o-ring seal. I also used a bigger drill bit to put a chamfer on the end so the fuel would be somewhat funneled into the opening rather than hitting a square edge.







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  #22  
Old 09-14-2018, 09:53 PM
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Default 6an feed line too small?

Quote:
Originally Posted by 2004LB7 View Post
I think both of you are correct. If you look at what he wrote he stated the smallest opening would be the highest restriction. He wasn't stating that the remaining line had no contribution to the overall pressure drop, just the highest restriction was the smallest opening.



Ultimately it is the smallest/highest restriction that will determine your max flow vs pressure. As an example, if a 1/2" line provides say 3 gallons per minute at X pressure and a 1/8" port restricts it to 0.5 gallons then upgrading to 5/8" line would not gain you anything



Of course a 1/8" line the whole way woud net you less the just a port at 1/8" but there is a steep diminishing returns on larger feed lines


Exactly.
If the restriction at the end of the line is fixed and pressure is controlled by a regulator of sorts to maintain steady pressure, providing the pump can maintain the flow to achieve said pressure, larger line size will gain you nothing. Going 1/2 to 5/8 but still putting it through a 1/8 orfice at the end of the line over say 10 of hose will not change the flow rate through the orfice. This in terms is speaking of an application in a vehicle where friction loses are almost negligible. In 100 of hose, hose size matters more as you would lose flow to friction although this can be overcome by a higher volume pump but also increases heat into the system.

However if you increase the orfice size or add a second orfice in parallel to the first i.e. dual cp3 then yes a larger line size may benefit you as would running two lines from the outlet of the pump.

Keep in mind you are still limited by the smallest restriction-which in some cases may even be the pump outlet. Hence why a -12 pump outlet in most of our trucks is ideal to allow for increased flow requirements downstream as desired.
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  #23  
Old 10-10-2018, 12:28 PM
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Originally Posted by Bbuchanan11 View Post
Not sure where to put this but its for a drag truck. Im trying to clean everything up I want to make the feed lines for the cp3s an line. I got 8an going in to 2 6an lines for the feed lines. Looking inside the 6an fittings they look pretty small will they work or no? Thanks in advance
6AN will be fine to the CP's. The fitting on a stroker CP is 6AN. My line is 10AN from the 250 FASS, splitting to 2-6AN's to the pumps. Top pump is a big stroker, bottom is stock......125% injectors get plenty of fuel.
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