Fuel Rail sizing ?

[KWIKR 1]

is there some sort of chart or formula to determine fuel rail sizing ? trying to figure out what HP level -8an (11/16) fuel rails will support in a SBC boosted application . thanks

 

[Mike E]

There are a lot of variables to come in to play other than rail ID. But, I have personally converted intakes with -8 rails for turbo motors that make 2100 hp on the engine dyno. That is usually with a single 160lb. injector per cylinder on c16 and two weldon 2025 pumps on 400+ cid motors. I have a feeling you could go even higher as long as you have enough fuel pump.

 

[KWIKR 1]

There are a lot of variables to come in to play other than rail ID. But, I have personally converted intakes with -8 rails for turbo motors that make 2100 hp on the engine dyno. That is usually with a single 160lb. injector per cylinder on c16 and two weldon 2025 pumps on 400+ cid motors. I have a feeling you could go even higher as long as you have enough fuel pump.

wow !!! didn't think it would support that much HP regardless of the pump . I understand what your saying that pressure plays a critical role as well . MANY thanks for the info MeanMike .

 

[Louie L.]

The -8 Edelbrock fuel rails have been high 6s in the 1/4.

 

[KWIKR 1]

The -8 Edelbrock fuel rails have been high 6s in the 1/4.

yeah..I came across that on other forums alot of guys running fast or big HP numbers on those Edelbrock rails . I was also concerened if the fuel rails were to big in relation to injector sizing/pressure/volume . that the reg may not be able to bleed off enough volume/pressure at idle . the result being it would not be a true reading at or on the rail . am I thinking correctly on this , or would rail volume/sizing not play a critical role in this ?


Many thanks for your reply .

 

[Mike E]

yeah..I came across that on other forums alot of guys running fast or big HP numbers on those Edelbrock rails . I was also concerened if the fuel rails were to big in relation to injector sizing/pressure/volume . that the reg may not be able to bleed off enough volume/pressure at idle . the result being it would not be a true reading at or on the rail . am I thinking correctly on this , or would rail volume not play a critical role in this ?


Many thanks for your reply .

No, the rail size does nothing to the flow rate. What goes into the rails minus what goes out of the injectors equals what the regulator has to bypass. Theoretically The flow rate coming out of the rail is the same with a -6 or a -10 because with the same amount going in and the same amount leaving the injectors, nothing else changes. The only thing that is changed because of rail ID is the speed the fuel moves through. The same flow rate of fuel through a .5" rail has to move at a much faster speed than it does through a .75" rail.

The real advantage to a -10 rail is that the larger volume in the rail acts as a reservoir to keep pressure spikes down when injectors open and close. These pressure spikes aren't something that you can measure with a normal mechanical dial fuel pressure guage. I had a friend in college who did his masters thesis on fuel rail/ injector dynamics and that is what he spend most of his time studying.

 

[KWIKR 1]

What goes into the rails minus what goes out of the injectors equals what the regulator has to bypass.

That makes sense . Great Info MeanMike ! thanks so.... a -6 return theoretically should be able to do the job on a high HP rating ?

 

[Mike E]

That makes sense . Great Info MeanMike ! thanks so.... a -6 return theoretically should be able to do the job on a high HP rating ?

Theoretically yes. But in reality comparing the same flow rate in a -8 or -10 to the same in a -6, the friction losses are pretty high because of the speed that fuel has to travel, length of the hose, bends in the hose ,etc. A fuel rail is 2' long at most with no bends, so friction losses are minimal.

For reference. The weldon 2040 regulator that most people use up to 2000hp has a return orifice of .281" and a -6 hose is roughly .325" ID.

 

[KWIKR 1]

Theoretically yes. But in reality comparing the same flow rate in a -8 or -10 to the same in a -6, the friction losses are pretty high because of the speed that fuel has to travel, length of the hose, bends in the hose ,etc. A fuel rail is 2' long at most with no bends, so friction losses are minimal.

For reference. The weldon 2040 regulator that most people use up to 2000hp has a return orifice of .281" and a -6 hose is roughly .325" ID.

got it . many thanks meanmike
Any idea on how the Weldon 2040 reg stacks up against the MagnaFuel MP-9950-B ?

 

[Mike E]

No idea. I've never used anything other than the weldon.

 

[Dusty Bradford]

All I have ever used is the large Weldon reg. Even with a -6 return it's more than enough to return the full volume of a 2345 pump.

I use a -8 return with my mechanical weldon pump.

-8 rails will support well over 2000hp. I'm at around 2000-2100 and duty cycle is still 80% on a single set of 160's. The mechanical pump really helps though, base fuel psi is 65psi, that's not possible with an electric pump.