Why so large of fuel lines?
10-11-2008, 05:01 PM
#1
Teching In
Thread Starter
Join Date: Nov 2006
Posts: 37
Likes: 0
Received 0 Likes
on
0 Posts
Why so large of fuel lines? I have read that most of the people running a walbro 255lph are using -8an fuel lines and i was curious why so big. I just recieved my walbro fuel pump and i noticed that it only has a 1/4" nipple so i can see using 3/8 fuel lines to have a 1/4 ID but that is only -6an. So can someone explain the advantages or is it not needed to go that large? I am hoping for around 450hp which i was told is sufficent for a single walbro 255lph high pressure. Any comments would be much appreciated. Thanks
Josh
Josh
10-11-2008, 08:47 PM
#2
FYI
a -4 is 1/4"
a -6 is 3/8"
a -8 id 1/2"
The -8 is not required with a single pump. A -6 will work fine with 1 pump.
You already have the equivalent of a -6 under there now.
The reason to use a larger line is because it flows better & will offer less pressure drop, helping the engine to get more fuel pressure than a more restrictive line.
True the pump has a 5/16" OD outlet & still flows a lot of fuel.... but 15 feet of 5/16" line would cause a substantial drop at high fuel flows. It is not the smallest part of the system that limits the maximum flow, but the actual sum total of all restrictions within the system. Therefore the long fuel line typically causes more restriction because of the extensive quantity instead of 1 fitting or connection limiting the total flow.
a -4 is 1/4"
a -6 is 3/8"
a -8 id 1/2"
The -8 is not required with a single pump. A -6 will work fine with 1 pump.
You already have the equivalent of a -6 under there now.
The reason to use a larger line is because it flows better & will offer less pressure drop, helping the engine to get more fuel pressure than a more restrictive line.
True the pump has a 5/16" OD outlet & still flows a lot of fuel.... but 15 feet of 5/16" line would cause a substantial drop at high fuel flows. It is not the smallest part of the system that limits the maximum flow, but the actual sum total of all restrictions within the system. Therefore the long fuel line typically causes more restriction because of the extensive quantity instead of 1 fitting or connection limiting the total flow.
10-11-2008, 09:12 PM
#3
Teching In
Thread Starter
Join Date: Nov 2006
Posts: 37
Likes: 0
Received 0 Likes
on
0 Posts
FYI
a -4 is 1/4"
a -6 is 3/8"
a -8 id 1/2"
The -8 is not required with a single pump. A -6 will work fine with 1 pump.
You already have the equivalent of a -6 under there now.
The reason to use a larger line is because it flows better & will offer less pressure drop, helping the engine to get more fuel pressure than a more restrictive line.
True the pump has a 5/16" OD outlet & still flows a lot of fuel.... but 15 feet of 5/16" line would cause a substantial drop at high fuel flows. It is not the smallest part of the system that limits the maximum flow, but the actual sum total of all restrictions within the system. Therefore the long fuel line typically causes more restriction because of the extensive quantity instead of 1 fitting or connection limiting the total flow.
a -4 is 1/4"
a -6 is 3/8"
a -8 id 1/2"
The -8 is not required with a single pump. A -6 will work fine with 1 pump.
You already have the equivalent of a -6 under there now.
The reason to use a larger line is because it flows better & will offer less pressure drop, helping the engine to get more fuel pressure than a more restrictive line.
True the pump has a 5/16" OD outlet & still flows a lot of fuel.... but 15 feet of 5/16" line would cause a substantial drop at high fuel flows. It is not the smallest part of the system that limits the maximum flow, but the actual sum total of all restrictions within the system. Therefore the long fuel line typically causes more restriction because of the extensive quantity instead of 1 fitting or connection limiting the total flow.
10-12-2008, 09:09 AM
#4
You have 2 choices....
A -6 will likely provide all the flow you need for a single pump application.
A -8 will not cost much more if you are buying everything anyway & will support your needs if you go crazy on the engine build later.
I see you are doing a swap so you likely are starting from scratch.
A -6 will likely provide all the flow you need for a single pump application.
A -8 will not cost much more if you are buying everything anyway & will support your needs if you go crazy on the engine build later.
I see you are doing a swap so you likely are starting from scratch.