81 step side dual tank help

Trevor Pool · Sep 6, 2020

I am about to start swapping in a 5.3 LS into my 1981 Chevy step side. My truck has factory dual tanks and I’d love to keep that option since I wanna use the truck for road trips to pick up parts for my other projects. I could really use some help with understanding the process of converting my stock fuel system up to run with the LS engine. I am currently looking into either running the Holley Mid rise intake, edelbrock intake w/ efi carb on top, or the stock LS intake. Could someone give me like a complete list of the parts I would need in order to convert my dual tanks over to run the LS motor. I want quality parts that aren’t going to crap out on me after a few years. I have read a lot online and I’m just lost with it all.

dvdswan · Sep 6, 2020

If you are going with in-tank pumps then you will need new tanks. Stock intake requires a return line from the regulator, not sure on the other intakes. You should already have the 6 port switching valve but depending on the size of the lines (3/8" and 5/16" for supply and return respectively) you may need to upgrade. If the intake does not have a return line you can use a corvette fuel filter that is inline.

Biggest thing is to not over think it. The fuel system is the easy part of the install.

Trevor Pool · Sep 6, 2020

dvdswan said:
If you are going with in-tank pumps then you will need new tanks. Stock intake requires a return line from the regulator, not sure on the other intakes. You should already have the 6 port switching valve but depending on the size of the lines (3/8" and 5/16" for supply and return respectively) you may need to upgrade. If the intake does not have a return line you can use a corvette fuel filter that is inline.

Biggest thing is to not over think it. The fuel system is the easy part of the install.

What new tanks would I need ? Is there a specific make and model I could look into ?

Slow build jim · Sep 6, 2020

87 tanks. they have baffles since they were eletric pumps. You will need the pickups too.

Trevor Pool · Sep 6, 2020

Slow build jim said:
87 tanks. they have baffles since they were eletric pumps. You will need the pickups too.

So basically the whole tank set up from a 87 truck?

Swearbody · Sep 6, 2020

If your selector setup works why not just install two inline pumps and an on off on switch for the pumps. Use the factory selector for swapping between tanks and switch pumps when you do.
The 3/8 feed is fine for a stock ls setup but you will want a matching return since the efi pump(s) will flow much more back to the tank.

I tried one pump after the selector and did not have any luck getting the fuel to flow well is why i say two pumps. This was with a mighty mite holley pump though. apparently electric pumps push well but not pull so good. the pump wouldnt pull from the driver side to passenger side to pump well enough. It was mounted beside the passenger tank and pulled from it just fine.
Perhaps a stronger efi pump would but i dont know

Trevor Pool · Sep 6, 2020

Swearbody said:
If your selector setup works why not just install two inline pumps and an on off on switch for the pumps. Use the factory selector for swapping between tanks and switch pumps when you do.
The 3/8 feed is fine for a stock ls setup but you will want a matching return since the efi pump(s) will flow much more back to the tank.

I tried one pump after the selector and did not have any luck getting the fuel to flow well is why i say two pumps. This was with a mighty mite holley pump though. apparently electric pumps push well but not pull so good. the pump wouldnt pull from the driver side to passenger side to pump well enough. It was mounted beside the passenger tank and pulled from it just fine.
Perhaps a stronger efi pump would but i dont know

I saw online that the stock tank switch isn’t rated for the psi that the efi system needs. Or something along those lines.

oldretiredafguy · Sep 6, 2020

Trevor Pool said:
So basically the whole tank set up from a 87 truck?

Trucks from 1973-1986 were carbureted, with a low pressure fuel pump. GM upgraded in the 1987 model year to TBI (Throttle Body Injection) fuel delivery system. The injection systems require a higher fuel pressure, and a return fuel line back to the tank(s). Square Body trucks from 1987 thru 1991 had this TBI as standard equipment on all gasoline models.

Swearbody · Sep 6, 2020

oldretiredafguy said:
Trucks from 1973-1986 were carbureted, with a low pressure fuel pump. GM upgraded in the 1987 model year to TBI (Throttle Body Injection) fuel delivery system. The injection systems require a higher fuel pressure, and a return fuel line back to the tank(s). Square Body trucks from 1987 thru 1991 had this TBI as standard equipment on all gasoline models.

Yep! tbi is 14psi pump in tank vs carb at 8psi pump on block. Return lines on both are the same!!
An ls is gonna need 55-60psi

Trevor Pool said:
I saw online that the stock tank switch isn’t rated for the psi that the efi system needs. Or something along those lines.

That may very well be the case. I was using a 7psi holley inline pump that pulled from the selector. I was unaware that the selector couldn't handle much pressure above that.

Trevor Pool · Sep 6, 2020

oldretiredafguy said:
Trucks from 1973-1986 were carbureted, with a low pressure fuel pump. GM upgraded in the 1987 model year to TBI (Throttle Body Injection) fuel delivery system. The injection systems require a higher fuel pressure, and a return fuel line back to the tank(s). Square Body trucks from 1987 thru 1991 had this TBI as standard equipment on all gasoline models.

will an 87 tank fit right into the 81 step-side tank location ?

Trevor Pool · Sep 6, 2020

Swearbody said:
Yep! tbi is 14psi pump in tank vs carb at 8psi pump on block. Return lines on both are the same!!
An ls is gonna need 55-60psi

That may very well be the case. I was using a 7psi holley inline pump that pulled from the selector. I was unaware that the selector couldn't handle much pressure above that.

So, even with the Tbi set up it still wouldn’t be enough pressure for the LS engine ?

eskimomann209 · Sep 7, 2020

Trevor Pool said:
So, even with the Tbi set up it still wouldn’t be enough pressure for the LS engine ?

The TBI setup alone is not enough to run an LS engine. You need to mount a Walboro 255 style pump onto the TBI sender. It’s easy peasy. Then You’ll have the 65ish psi you need. Also I’m running one of those delphi tank selectors on the same pump up to 65 psi and it handles it just fine.

Trevor Pool · Sep 7, 2020

eskimomann209 said:
The TBI setup alone is not enough to run an LS engine. You need to mount a Walboro 255 style pump onto the TBI sender. It’s easy peasy. Then You’ll have the 65ish psi you need. Also I’m running one of those delphi tank selectors on the same pump up to 65 psi and it handles it just fine.

Okay, I’m starting to understand the process. Is it at all possible to install the walboro 255 pump into my stock tank and sending unit eliminating the need to purchase two new tanks and sending units?

Swearbody · Sep 7, 2020

Trevor Pool said:
So, even with the Tbi set up it still wouldn’t be enough pressure for the LS engine ?

correct!!

eskimomann209 said:
The TBI setup alone is not enough to run an LS engine. You need to mount a Walboro 255 style pump onto the TBI sender. It’s easy peasy. Then You’ll have the 65ish psi you need. Also I’m running one of those delphi tank selectors on the same pump up to 65 psi and it handles it just fine.

I thought the selector would be fine but wasnt sure at all

Trevor Pool said:
Okay, I’m starting to understand the process. Is it at all possible to install the walboro 255 pump into my stock tank and sending unit eliminating the need to purchase two new tanks and sending units?

Not sure about the wal255 in our tanks with our senders but Ive used them that way on mazda turbo builds
You can find pumps that will retro fit like this though for our trucks all day and can probabaly do the wal255 that way. You will need two pumps though like i was saying if you want to keep the stock selector.

Dave M · Sep 7, 2020

What about retaining the standard tanks, using an electric pump per tank, to supply fuel to a surge tank set up, which has the high pressure pump feeding the EFI rail.

81 step side dual tank help

Which intake to choose ?

Holley mid rise

Edelbrock w/ efi carb

Stock LS intake

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