3500 LX9 RWD Swap - Fuel System Options and Guide?

[shapeshaver]

I have spent time reading and searching forums as to how to setup my 3500 LX9's fuel system. But differing opinions (as I understand them) have left me more than a little unclear as to what to do. I would like to use the injectors that came with the engine, (as well as the OBDII and Harness that came with the engine, but it seems that is not a good option? A topic for another thread...) but I also want as simple a setup as I can so long as it performs well and leaves me some headroom for future mods. I have purchased an OBD1 computer for spark and fuel management. The engine is being swapped into a 1962 Sunbeam Alpine with a Ford T5 trans as seen here: http://lx9alpine.com I'm using the TCE crank trigger kit and will install an upgraded cam and valve springs based on these other factors.

1. I purchased a 65 mm TB from a 02 Oldsmobile Intrigue. At what point would I want a bigger TB? (eg 75mm Northstar)
2. I am confused if I can use the stock Injectors that came with the engine or if I have to swap to 3400 system? Can I use the 3500 injector and rail system by incorporating a regulator or something like that???
3. Depending on the answer to Q#2, what type of fuel line(s) do I need to run to the tank? Single, dual, diameter?
4. Correct fuel pump?
5. If I want to turbo the engine in the future, what effect does that have on the above questions?

If there is a great article regarding these question that you know about please let me know and I'll do some more reading. But I am really interested in what has worked for the others of you who have done a similar swap. Thanks in advance for sharing your experiences and knowledge!

[Superdave]

This is how mine was set up... but my car was originally EFI so some things were a little easier. ('89 Camaro)

Fuel pump: Stock replacement for a Syclone/Typhoon (255 LPH) Fit in the stock Camaro tank with no mods
Fuel filter: Stock Camaro replacement, relocated for exhaust clearance
Fuel feed line: I used a fuel line kit from Summit, all braided stainless with AN fittings and adapters (My original steel line was rusted out and blew up when I ran the car for the first time)
Fuel return line: Stock 5/16" GM hard line
Fuel rails: Stock 3400 rail with a 55 PSI FPR
Rail fittings: TCE's AN fitting on the feed side, stock type on the return, (low pressure) fuel hose just clamped to the stock hard line.
Injectors: Ford Supercharged 3.8 "Super Coup" red top Multech 1's. IIRC they were 33lb/hr

This was on a 3500 that made close to 350 HP, you can scale the injectors down for something more tame.

1. 65mm is fine, somewhere north of 300 HP is where i'd start thinking about upgrading. You'll have to watch a vacuum gauge at WOT to see if the engine draws a vacuum at WOT. If so it's time for an upgrade.
2. In my experience, I would recommend using the 3400 rail with either the stock 3400 injectors or 3.4 DOHC injectors. This way you have an easier route for a pressure regulator and you can use a standard return line.
3. 2 lines, 3/8" feed and 5/16" return is fine
4. If you can go in-tank do it... otherwise find one that can make 55 PSI and flows 160-255 LPH. LS swaps in muscle cars are using external pumps so that shouldn't be a problem
5. just get a pump that will handle the fuel flow you need, and keep in mind that you'll have to get bigger injectors depending on how much boost you plan on running.

[caffeine]

Throw away all the OBDII stuff, as it isn't tuneable and it will be expecting communication from a BCM and from the factory auto trans.


On my firebird I run the stock rail with the schrader valve core removed and a -4AN to -6AN fitting on it, then a line goes from there to an external fuel pressure regulator.

Keep in mind that if you keep the stock rail your injector options will be more limited in the future (you would need 48mm o-ring to o-ring as opposed to the usual 60mm)

For fuel hard lines 3/8" for feed and 5/16" for return, AN size would be -6. You can also get fuel rail quick connect fittings to use with AN braided lines.

I have an engine with a big cam and a 65mm TB. It starts pulling a slight vacuum at WOT around 5000-5500 RPM but it still made over 250 whp.

[shapeshaver]

Thanks! What effect do oversized injectors have on the system? If I go NA now with the Forced Induction setup in the near future, I would rather use the bigger injector from the start.

[shapeshaver]

And, is there a way to set up the FI system as a non returnable system? If there is, what is the disadvantage? If not I have to figure out how to modify my stock tank....

[robertisaar]

And, is there a way to set up the FI system as a non returnable system? If there is, what is the disadvantage? If not I have to figure out how to modify my stock tank....

could..... a few ways with various advantages and disadvantages at that. i'm kind of curious to know how well a ~10 foot vacuum line going from the engine to a tank mounted regulator would work. if that works well, you would have a vacuum(and boost) referenced regulator. otherwise, exposing a regulator to atmospheric pressure will deliver full fuel pressure to the rails at all times, it wouldn't be boost or vacuum referenced though, so tuning would be a little more interesting.

maybe nAst1 would benefit from a table that modifies the injector BPC based on manifold vacuum/pressure for vehicles that run a constant pressure system?

[caffeine]

Usually retrofitting a returnless rail involves adding a regulator and return line somewhere, even if it's not in the engine bay. If you can easily source a 3400 fuel rail that's the best option.

[shapeshaver]

OK, I'll go get a 3400 fuel rail. What should I get the injectors from? The stock LX9 injectors are a smaller diameter and wont work with this rail then? Would injectors from a northstar Caddi work? There's one in the yard and I wanted to get the N* TB while it is easy to get, could grab injectors as well. What should I get a fuel pressure regulator from?

[caffeine]

A typical injector upgrade is 28# from a trailblazer inline-6. Diameter of the LX9 injectors isn't the issue; it's the length from o-ring to o-ring.

[robertisaar]

IIRC, the northstar injectors were right on the edge of workable in their stock application..... something like 20lb/hr?

[shapeshaver]

A typical injector upgrade is 28# from a trailblazer inline-6. Diameter of the LX9 injectors isn't the issue; it's the length from o-ring to o-ring.

I see, thanks for that info caffeine! Is there a range of years I have to look for in a trail blazer? Or, will any trailblazer (or other vehicle) with the inline 4.2L 6 work?

[1988GTU]

The LQ1 injectors work.

[shapeshaver]

I am purchasing a used set of these 3.8 red top injectors. I assume they have the same connector and clip as the cavalier wire harness and 3400 fuel rail? Does the 3400 fuel rail come with a 55 PSI FPR? Or, did you upgrade that from stock?

[Guest]

If those are the Ford 3.8 SC injectors, yes they will fit fine.