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Old 06-26-2015, 10:50 PM
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tbi to carb fuel lines, need advice please.

Hello all, as the title says, I'm having a few issues. I have a 1990 454ss and the poor engine has had enough so that being said I built a new one, just had it dynoed today! Anyways, it's an early 80s 454 and carbureted. I'm gonna be running a mechanical fuel pump, I'm wondering if I could use the existing pressure line and return line that originally went into the rear of the tbi throttle body but how I could make that work with the mechanical fuel pump. Thanks for any suggestions, this is my first build.

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Old 06-27-2015, 06:57 AM
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Inorder to use the TBI lines you'll need to get the correct fittings for them. I assume they have the step at the end that requires an o-ring. If that's the case, then you'll need to adapt them at your pump and/or regulator. I have done exactly what you're trying to do. but was for an EFI setup. I found a place that can make just about any line and has about every fitting available. It was pretty easy once I found someone to make them.

What are you planning to do with the in tank pump? I think that you'll have to either run it to a regualtor or remove it.
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Old 06-27-2015, 07:36 AM
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run a new line from the filter to the carb. parts stores sell repair sections that fit the filter ends.
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Old 06-27-2015, 08:38 AM
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Why not just use the in tank pump and regulate the fuel. The return line is already there
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Old 06-27-2015, 01:04 PM
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It makes 554 hp, so I'm thinking you're right. The stock lines will probably be to much of a restriction. So I'll just have to run all new bigger line.
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Old 06-27-2015, 09:03 PM
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Quote:
Originally Posted by chevy454ss View Post
It makes 554 hp, so I'm thinking you're right. The stock lines will probably be to much of a restriction. So I'll just have to run all new bigger line.
To quote TechInspector - bzzzzt - wrong.

When looking at fuel line sizing you need to consider pressure (Boyle's Law - PV=nRT). The stock fuel lines are nowhere big enough if you are running the mechanical pump at 5-8 psi, but at 30-50 psi they are more than large enough for 500 HP. Look at an EVO, Eclipse, etc, making 500-700 on 8mm lines. Now crank the pressure upto 80psi and they'll be more than large enough.

Run the stock pump (or higher pressure) to you're regulator and then run a 3/8-1/2 line from the regulator to your carb - no problem IMO. Crussell85 is right on the money.
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Old 06-27-2015, 10:01 PM
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Quote:
Originally Posted by hcompton View Post
Isnt the stock tbi pump only like 18 psi or something really low. Its not a high pressure pump. You also have to figure distance in that equation. I know for sure the stock tpi pump will not put out anywhere close to 500 hp. And most regulators wont convert 80 psi to 6 psi at a reasonable flow rate. That is where you need a 300 dollar regulater. All the vette guys have to swap over the pumps usally below 400 hp with the tpi to carb swap. Skinny lines are ok for a bit above stock power levels but at 500 your way over the lines and pumps capacity. Even if it was open it might not flow that much fuel without the regulator in place. Even the honda guys have to swap them out at modest power levels for a big block there not going to cut it.
The stock regulator cuts the fuel pressure to 15-18 psi, but the pump is making more than that. Not seeing the OP's original setup, I'd check the pump pressure and verify the line size. I'm not sure of the BB line size, but the SB is 8mm. Also, he could always err on the side of caution and increase his line size just to make sure the line size isn't the weakest link in the fuel supply chain, but I'm sure that he can get this thing running with the stock pump and lines and determine later if he needs to upgrade. For that fact he could do away with the stock pump setup and just run a 1/2" line for a mechanical pump. It really depends on what he wants to do and when he wants to do it. He is going to to have spend some money on the fuel system whether it is a new regulator, lines, pump, etc. at some point, it's matter of when and how much money he wants to spend. I always think on the cheap (it might be a bad habit)
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Old 06-27-2015, 11:05 PM
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I decided to use the stock in-tank electric pump, mainly because I'm being told on the 454ss forum that the mechanical pump won't clear the frame. Now I'm sure I could make it work but I'll stick to electric. I will run bigger lines though just to be on the safe side.
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Old 06-28-2015, 09:08 AM
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Solid advice! I might do the twin pump or just pull the tank, remove the pump and put a piece of hose in place then get a higher flow pump and mount outside the tank, undecided right now haha.
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Old 06-28-2015, 09:31 AM
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Ya I'll buy an after market one for sure if that's the case. Right now I'm running a 750 cfm quick fuel carb, gets the job done I suppose. Do you or anyone know much about tbi? Does the ecm tell the fuel pump to turn on or is it hooked to key power? Thanks
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Old 06-28-2015, 04:21 PM
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tbi to carb fuel lines,need advise please

This harness is necessary for wiring the electric fuel pump. JEGS Performance Products 10564, JEGS Electric Fuel Pump Harness and Relay Kit | JEGS Performance Products. I would get a fuel pump like the Holley 12-890. http://www.summitracing.com/parts/hly-12-890. Return regulator. http://www.summitracing.com/parts/hly-12-845. I don't think the Holley 12-802-1 will put out enough using a return regulator. For the fuel line from tank to front check out Summit Racing for a 20' roll of aluminum tubing.

Last edited by cdminter59; 06-28-2015 at 04:35 PM.
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Old 06-28-2015, 06:19 PM
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tbi to carb fuel lines, need advice please.

Man, finish reading the complete TECH RESOURCES. It says for street and strip. This pump is compatible with pump gas, but is not recommended for street driven vehicles where the ambient temperature is regularly above 90 degrees. I sent an email to Holley to see how much driving can be done on the street in temperatures 90 and above. if I receive an email back saying not at all then you would have to go to the 12-800 pump.
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