Fuel System Upgrade

Last updated: February 3, 2003


Date: Thu, 27 Jan 2000 12:47:20 -0500
From: "Ryan Schlagheck" (ryan.schlagheck@worldnet.att.net)

I've though/discussed this out loud before. What I came up with is the following: There's no sense in having a high-flow pump and huge injectors if you can't get it through the "spaghetti" (read: way too small) fuel lines fast enough, so increase the capacity of the fuel lines.

Eventually, you'll get to the point where you'll want big 'ole fuel lines running from the tank to a distribution block for the enlarged primaries, larger secondaries, and any additional injectors you want to run off the intake plenum. A nice add'l injector plumb was done on one of Mostly Mazda's cars, and it is in one of the first pictures on my Laguna Seca image gallery at http://schlagheck.com/rx7/gallery/.

Run -6 or -8AN braided lines _outside_ the car from tank to engine bay and then a fuel distribution block there.

Add'l pump at the tank, and fuel pressure regulator after the distribution block. Looks like the rest will follow for fuel delivery (injector selection, FPR).

While you're at it, bypass the stock fuel filter and put an inline SX or something like that with a removeable element in the trunk with the fuel pump. I talked a lot about this with Roger Mandeville, and it's something I plan to do in the distant future. I believe I also spoke with Ray Lochhead about the same setup, as well as Carlos Iglesias.


Date: Thu, 27 Jan 2000 17:27:53 GMT
From: skan@ticnet.com

As far as fuel upgrade is concern, you'll need an upgrade fuel pump (I use the RP fuel pump), custom made fuel rail, SX fuel pressure regulator, two 170lbs injectors (you can order them from motec website).

The fuel rail can be a pain but RP sells them as a kit including the rail, brackets, injectors..etc.. As far as I know, I get about 86% duty cycle running all four injectors at 18.5psi of boost. That means I'll probably maxed out at around 22psi of boost if I want to maintain the same A/F ratio.

I would also recommend upgrading the primary injectors (you can get them bore out (probably around 850cc) or you can get another custom rail/injectors setup). This will help to improve your switchover point from primaries to primaries+secondaries a little smoother. It'll also allow you to run around 24-26psi of boost safely.

So far with my setup with the wet kit N2O, I don't see any fuel pressure drop from the fuel pump which tells me it can handle the loads at over 18psi of boost. I'm not sure about the fuel lines but I'm not planning to mess with it (not until I notice a difference). I do and have been running 17psi (1.2bar on the boost controller) on pump gas for the past 1.5 yrs so I don't see a problem with hurting the motor with pump gas as long as you have the a/f ratio setup conservatively.


Carlos Iglesias' diagram:

Fuel System Diagram

Fuel Rail

Date: Tue, 11 Apr 2000 09:01:59 -0400
From: "Karagiannis, Demetrios Mr ODCSINT/GD" (Demetrios.Karagiannis@hqda.army.mil)

>Those who have upgraded your fuel systems... do I need to keep the
>dampener that is attached to the primary rail?

I didn't keep mine but it maybe a good idea to revisit this. When using large injectors this is very necesary for pulse dampening. But to answer your question I don't use one currently and have no problems a good way to test this is to use one of the extra channels on the Haltech to monitor fuel pressure (sounds like I came up with a new project)


Date: Wed, 12 Apr 2000 07:35:29 +0200 From: "Bernd Kluesener" (bklues@syskonnect.pp.se)

> I'm not sure if we are talking about the same part but if you are talking
> about those things below the injectors (below the injector gasket), they're
> bad news.  I suggest anybody with aftermarket injectors to take them off
> since they do break off with bigger injectors spraying them and can damage
> your rotor and rotor housing.  Both of mine for the secondary injectors were
> broken and they were new two years ago. 

The things you are describing are the so called air bleed sockets which help in fuel atomization.

The pulsation damper on the other hand is located at the entrance to the primary fuel rail. It helps to smoothen the pulsations (pressure fluctuations) caused by large injectors 'emptying' the fuel rails/lines.

Fuel Lines

Date: Wed, 12 Apr 2000 14:19:34 -0400 From: "Karagiannis, Demetrios Mr ODCSINT/GD" Subject: RE: (rx7) [3] fuel system line size

>What is the stock ID of the fuel hose, and what is the ID of -6 AN
>Looking at the stock lines, I would think they are large enough even
>for very high horsepower cars.  Can someone do some computations to
>determine the max flow through the stock system at 55-65 psi?  I'm trying to
>determine if there is a benefit to using -8 AN instead of -6 AN, and if
>there is a benefit, how much of a practical benefit.

I'm currently still using the stock fuel lines. Even if you were pushing upwards of 600hp you would not need anything bigger then a -6


Date: Wed, 12 Apr 2000 18:21:25 +0000
From: ryan.schlagheck@att.net

-8AN is overkill. -6AN will get you plenty of fuel flow. -8AN and up might require you to run a big@ss aftermarket fuel pump to keep the pressure up without burning out something like the stock or Cosmo pump - or you could run two pumps in-line like I think Kevin Wyum did in his car. It's been a while, so I don't recall for certain.

Put it another way...I asked Ari about upgraded fuel lines and he's still able to run 9's with the "spaghetti" stock fuel lines the length of the car to the engine bay. Plus, -6AN is easier to route and can take a smaller turning radius than -8AN (by a small but significant margin) when you run the lines from back to front to back.


Date: Wed, 12 Apr 2000 17:10:57 -0400
From: "\(Mr\) Sandy Linthicum" (sandy-linthicum@nc.rr.com)

Stock hard fuel lines are smaller than AN4. AN6 should handle you up to 500+ hp. After that you might want to plumb the primaries and secondaries separately with independent AN6 lines.


Date: Fri, 14 Apr 2000 20:16:59 +0200
From: "Bernd Kluesener" (bklues@syskonnect.pp.se)

> I am by no expert either but I do have the catalog from Earl's Perfomance
> Products handy which explains the AN thread sizes.  The following are direct
> quotations from the technical section of the catalog. ( By the way, it's a
> fairly informative catalog.  It also explains how to put together the
> aluminum fittings and the stainless steel braided hoses together.  The
> catalog is free from 310 609-1602)
> " 'AN' ( Army-Navy) Sizes were established by the Aerospace industry years
> ago and were designated O.D.(outside diameter) of the rigid metal tube that
> each size fitting is used with.
> The numbers assigned equate to the O.D. of the tubing in 1/16 inch.  Since
> tubing and hoses are found with assorted wall thickness we can now
> understand that the designated size number does not necessarily tell you how
> large the inside diameter will be. (For example, the inside diameter of an
> Earl's size 6 hose end is nearly as large as the inside diameter of some
> other manufacturer's -8 hose ends.)
> Each AN size number has its own standard thread size."
> The technical section then goes on to explain the standard SAE thread sizes
> of each AN size.  There is also an explanation of NPT thread sizes.

You are right, the AN numbers are pipe OD in 1/16 inch. I measured my AN6 fuel stuff today and found the following

Goodridge aluminum pipe running from the tank to the firewall:
OD = 10mm (6/16 inch would be 9.5mm)
ID = 8mm

Goodridge braided hose ID = 8.7mm

Fuel Cell

Date: Thu, 6 Feb 2003 13:46:26 -0800
From: "Jeff Foster" (jeff@step4.com)

HinsonSuperCars.com is working on an alum. fuel cell replacement for our cars. They specialize on LS1 swaps, but of course it would work with either engine. They are supposed to have more info available on their website by march I believe as they are doing final fitment/development right now.

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