I am currently planning a TBI setup for my slant six. So far, the biggest problem I'm seeing is the need for larger fuel line. I understand that I need a new sending unit so that I have a 3/8" line to the pump instead of the current 5/16", but I have been unable to find one with a return line larger than 1/4". I've read that I should have a minimum of 5/16" return line (and 3/8" is better).

So, I am wondering how others handled this problem. Is there a company that manufactures a sending unit with a larger return? Or have people been modifying their current sending units? I was unable to find any information on this through a search.

Also, I have been wondering how others have setup the kickdown linkage and throttle cable when using the Rochester 220 (GM 4.3L) throttle body? I seem to recall one person writing that they were able to make the 2bbl linkage work, but I can't remember what they had to do.

Any advice would be greatly appreciated!

Thanks!
-Jashen

Hey everyone,

I found the sending unit I need. It is a Spectra FG69B, and is available from RockAuto for $65 (in case anyone else had the same problem locating one). I finally came across that part number during a google search, on an archived page from the old slantsix.org message board.

Thanks to everyone who viewed the thread to try an help! And, if anyone has already done the kickdown linkage and throttle cable using a 4.3L GM throttle body, I'd be interested to know how you did it.

Thanks again!

-Jashen

Cool!...Keep us up to date

click to view full-version

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Not sure why you need a bigger fuel line - I used the stock line all the way around for my installation. Maybe you can post some more detail about how you are going about it.

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

Thanks for the replies!

I had read several posts on this site (and others) suggesting that the lines should be larger than stock to prevent the pump from working harder than it has to, thus expanding the pump's life. I can't really see why it would be that necessary for a TBI system running ~20psi, though. By the way, the information about the sending unit I mentioned above was incorrect. I ordered it, got it in the other day, and found that it has the stock 1/4" return line. I don't know why the other people said it was 5/16", but it is my fault for not reasearching it better. I think I'll still use it, though.

In regards to the setup, I am going to use an adapter plate to go from the GM 4.3L throttle body to my Super Six manifold. I have both a set of 40lb and 45lb injectors, but I think the 40lb will be sufficient. Mostly, I am wanting to do this to get familiar with the megasquirt system before trying multiport/sequential injection on my high performance engine). If I can get the linkage figured out, I'll probably start the swap in a couple of weeks. I'll try to post pics if I get it figured out.

Two 40 Lb injectors will support roughly 160 HP. the 45 Lb going to about 180 hp. Either size should work fine on a stock engine. For comparison I use 4 30-lb injectors in my throttle body, for a max of 240 hp, which I am nowhere near, and my stock engine idles very well.

I understand your fuel line thinking now. I used a different philosophy and placed my high pressure fuel pump under the hood. I used a completely stock fuel system including the mechanical pump to fill a surge tank (less than a quart) under the hood, and I pick up and return the high pressure fuel from that tank. Overflow is routed back to the rear tank via the former vapor return line. I have a total of about 18" of high pressure fuel in the whole system, and that's in a 3/8" fuel rail and EFI rated fuel line.

My pump is virtually silent under the hood, and you cannot hear it running when the engine is running.

I really didn't elaborate much on that system in my EFI thread (Kearney Thrash) but it worked perfectly first time, every time for me with my conversion. I really don't see the need to put the high pressure all the way back in the rear and run high pressure fuel the length of the car. I know the OEMs do it but they have their reasons I guess. I learned quite a bit from my first EFI build with my Ramcharger and did this one better.

-G

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

GunPilot,

Glad to hear that you haven't been having problems with the fuel pump in your setup (gives me hope that I won't)! If I remember correctly, it was recommended that the fuel pump be as close to the tank as possible to decrease its workload (something about being able to "push" fuel easier than "pull" it). I really don't know how accurate it is, but I thought it would be worth doing if I'm already changing fuel lines and the sending unit.

I haven't dyno'd this engine yet, but I'd estimate it to be in the 180-200 hp range. So, it might be a good idea to start with the 45lb injectors, and possibly go larger if necessary. This is a daily driver, so I generally keep it under 4500RPM (that's ~75mph with the 3.73 gears). Typing that last sentence made me remember how much I wish I had an overdrive transmission in my Dart.

I read the same thing about the HP pumps. With the surge tank as the source, my high pressure pump is about eight inches from it's fuel tank, so no issue there. I'll take some pics of my setup and diagram it so what I'm saying is clearer.

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

No need for larger fuel lines unless you are over 350 HP - good luck with that naturally aspirated.

I have 250 HP Slant with 2bbl TBI and stock fuel lines.

Lou

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Home of Slant6-powered fun machines since 1988

GunPilot,

I'd greatly appreciate the pics/diagram!


Dart270,

Glad to see another person did okay with the stock fuel lines! I've only seen or heard of one NA slant that dyno'd at over 350hp, and I'm sure I'll never get either of mine running like that. Are you using the Super Six manifold with your TBI setup? If so, could you post a pic showing how you did the linkage?



Thanks for your help, both of you!

-Jashen

I am not using the supersix manifold, but a Clifford 4bbl with adapter plate. All custom linkage cable (Lokar). Stick tranny so no kickdown either... Here's the car:

http://www.flickr.com/photos/16910097@N ... 013976355/

Lou

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Home of Slant6-powered fun machines since 1988

Here is my dorky attempt at a diagram using Paint:


You can see the fuel system has very little high pressure in it. Most of the stock components are used including stock tank, fuel line, stock pump. I used the vapor return as a fuel return. I have read online not to do that. I found there was a 1-way valve in the line at the engine compartment end. I cut that out and just had a straight steel line back to the tank. Seems to work fine.



Here's my original configuration not quite all hooked up but it shows the layout well. I originally used a tee to accomplish the regulator return and overflow to tank, but I found the surge tank (big filter canister) did not fill well. I figured out that the incoming fuel blocked the air trying to leave via the tee. I reconfigured it by drilling a hole in the location shown and JB welding in a vent tube. That did the trick.



Here is the system as configured. What you can't see is that I JB welded a large tube inside the filter adapter as per the diagram above so the high pressure fuel pump could pick fuel up from the bottom of the surge tank. You can see the new vent tube location and the tee is removed from the return, simplifying that connection.

The way it all works -

The stock mechanical pump lifts fuel up to the surge tank, filling it. The HP electric pump draws fuel out, pressurizes it through the fuel rail, and the return goes back in the top of the surge tank. Overflow (and air) leaves the top of the surge tank through the vent tube, and returns to the fuel tank.

To me, the advantages of doing it this way were in having the fuel system all in one place. I don't have to get under the car and mess with the fuel tank. I have very little pressurized fuel and a short pickup for the pump. I have a reserve of fuel for the pump so it won't suck air. I utilize the reliable stock pump as a lift pump, and a momentary demand for more fuel than it can flow (not likely) will come out of the surge tank, to be refilled as soon as the demand relaxes. I can change pump or fuel lines easily from under the hood, and it is all easy to inspect. Everything in the pictures came from NAPA. And I only need a short run of injection ho$e.

The only disadvantage I can see is if I get hit hard in the right front, I have about a pint and a half of fuel there to fly around. However, it's not much more than a double pumper carb holds, and it's in a steel can. It is a fuel filter.

Your mileage may vary, use at your own risk, I don't recommend anything, and no animals were harmed much by this fuel system. Hope this helps.

-G

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

Oh, and PS: in your mind's eye, replace all those rubber hoses with steel braided ones, and all the brass fittings with AN ones. Yes, that's what I meant.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

GunPilot,

Thanks for taking the time to do the pictures and give that explaination! The diagram helped quite a bit. I am now thinking of doing something similar. It does make sense that putting the mechanical pump before the high pressure pump would reduce the load on the high pressure pump. And, since I hadn't planned on removing the mechanical one anyways (was just going to put a short line connecting the inlet/outlet), I don't see what it could hurt to try it. I had been wondering about the need for a surge tank (since the stock tank doesn't have baffles), so I appreciate you letting me know the problem I might run into.

LOL at your last post . And, I probably don't have too worry much about the fire/explosion possibility after a bad wreck: I'll probably be dead from injuries sustained as a result of flying through the windshield (at 22, I'm still too stupid to wear a seatbelt).

Thanks again for the help!



Dart 270,

Thanks for the reply. I had considered the possibility of having to use the Lokar cable, but it is looking like the 2bbl linkage/cable setup is close enough that I might be able to make it work somehow. I'll know more when I mount the throttle body.

If you do a google on surge tanks and fords, you will find the full size bronco web site sells a surge tank like gunpilot shows. The Ford guys swear by it and it doesn't require a #2 Ford wrench to install.