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Old 09-08-2008, 02:26 PM
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TBI to carb swap

Hey guys i was helping my father with his truck this weekend. It it and 87' GMC sierra 1500 305 TBI. The truck hasn't beed running for some time now because of a bad fuel pump.
This weekend we put an in-line electric pump on it and were able to get fuel up to the T/B. It started up and ran for mabey 30 seconds then fuel quit spraying from the injectors into the T/B. He said that he'd rather just put a carb on it and do away with the computer and TBI.
We first looked around to see if there were an adapter to go from the TBI to a 4bbl carb using the same intake manifold with no luck. So we decided to just change the manifold to a 4bbl stock carb manifold. Pretty simple plan, but it won't work. The bolt holes it the center of the TBI manifold are made so the bolt threads straight down into the heads rather than going at an angle. None if the intakes i have will fit on these cylinder heads, i have 2 weiand accelerators, 3 performer rpm's, and 6 stock style SBC manifolds, some early model, and some late model, all have the same results. Even one from another 87' 305 won't work cuz its an HO with double hump heads.

I guess my question is do they make a manifold to do this swap or will he have to either change the heads or stay with the TBI. If so what should i look for at a salvage yard to get the right on for a carb. I didn't know that just because a 305 was TBI it would have different heads than other SBC's but they do, i guess you learn somethin new everyday.

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Old 09-08-2008, 02:36 PM
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Your kinda getting spendy with this swap, as compared to changing the original fuel pump. They are inexpensive, and not too hard to change. My gues is that the in line pump doesn't have the pressure needed to run the injectors. Also, if the injectors are giving grief, they aren't expensive. Somewhere around $40-$60 each. The pump shouldn't be more than $75-$100. Drop the tank, and the pump comes out the same way as the old style senders.
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Old 09-08-2008, 02:49 PM
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Quote:
Originally Posted by eatonde
Hey guys i was helping my father with his truck this weekend. It it and 87' GMC sierra 1500 305 TBI. The truck hasn't beed running for some time now because of a bad fuel pump.
This weekend we put an in-line electric pump on it and were able to get fuel up to the T/B. It started up and ran for mabey 30 seconds then fuel quit spraying from the injectors into the T/B. He said that he'd rather just put a carb on it and do away with the computer and TBI.
We first looked around to see if there were an adapter to go from the TBI to a 4bbl carb using the same intake manifold with no luck. So we decided to just change the manifold to a 4bbl stock carb manifold. Pretty simple plan, but it won't work. The bolt holes it the center of the TBI manifold are made so the bolt threads straight down into the heads rather than going at an angle. None if the intakes i have will fit on these cylinder heads, i have 2 weiand accelerators, 3 performer rpm's, and 6 stock style SBC manifolds, some early model, and some late model, all have the same results. Even one from another 87' 305 won't work cuz its an HO with double hump heads.

I guess my question is do they make a manifold to do this swap or will he have to either change the heads or stay with the TBI. If so what should i look for at a salvage yard to get the right on for a carb. I didn't know that just because a 305 was TBI it would have different heads than other SBC's but they do, i guess you learn somethin new everyday.
There is no junkyard solution unless you go back further than 86 and also take the heads. The hot rod solution is a new intake with the proper bolt angles. The cheap solution is to take one of your old manifolds and egg the center holes to fit the bolt angle, then make an angle adapter from tube or billet to match the bolt head and manifold or carve a new pad into the manifold so the bolt head meets it at the proper angle.

The fuel pump solution is to put the proper pump into the tank. The TBI needs a 15 psi pump give or take a couple psi. An ordinary 6 psi pump can't do the job. While you're in the tank, you'll probably discover the intake filter screen is plugged with 21 years of gunk and junk, but a new filter comes with the new pump, so your in luck.

Bogie
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Old 09-08-2008, 03:25 PM
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TBI to carb

So there are no carb manifolds made for the style head on this engine? right? I wanna be sure before we walk around the junkyard all day and come up empty handed.

Either way, i think he is pretty set on switching it to a carburetor. So the cheapest solution would be to just drill the holes out so the bolt will go straight down?
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Old 09-08-2008, 03:27 PM
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Quote:
Originally Posted by eatonde
So there are no carb manifolds made for the style head on this engine? right? I wanna be sure before we walk around the junkyard all day and come up empty handed.

Either way, i think he is pretty set on switching it to a carburetor. So the cheapest solution would be to just drill the holes out so the bolt will go straight down?
Nothing from the factory on production vehicles.

Bogie
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Old 09-08-2008, 03:31 PM
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i just did this swap a couple of weeks ago on my 88 1500 350, i used a old style intake and reemed the center bolt holes to use it. works fine. with the fuel pump quiting your going to need to splice in fuel pump relay with a switched power wire. mine was grey and white striped. its located under the plastic cover on the passenger side of the firewall. (farrest to your right) -remember this is on a 1988 it might be different- with the computer it will pump then shut off for some reason with out running a hot wire to it. you will also need a fuel regulater, people say you need a return style regulater thats not true. you just tee off the fuel line one from the gas hose and the other to your return and the third to your regulater. mine is set at 6psi. you will also need a hei dist. and if you have a lock up tranny you will need to buy a lock up kit, or i heard you can wire it with a toggle. i dont know since i put a th350 in mine. im not the best at explaining things but i tried. it cost alot if you dont have parts laying around. switching it to carb was the best i have done with the truck. has way more power and no 3 inch thick wiring harness nomore i love it!
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Old 09-08-2008, 05:21 PM
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holes

So if he just opens the holes on the rpm manifold to let it line up with the holes in the heads it will still seal up ok? I thought about doing this, (wallering the holes out) to make the bolt line up, but i was afraid that the intake would not seal properly and i'd ruin a good manifold for no reason. If it will seal i'm gonna give it a shot.
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Old 09-08-2008, 05:32 PM
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Why not just lift the bed and replace the factory pump? I did this 3 weeks ago on my fathers pickup, it only took 2 guys to lift the bed and it don`t have to go far back. 3 hours total time the bed was off, fuel pump replaced, bed back on, up and running. The bed is held on by 8 bolts and they are easy to remove. Disconnect the rear lights at the connector by the rear bumper, remove the lights ground on the frame, remove the filler neck bolts and ground and it`s ready to lift.
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Old 09-08-2008, 06:24 PM
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there is an intake for that

there is an intake for that swap just buy a rpm intake for vortec heads and the bolt holes are right to make the swap easy as pie rpm intake for vortec heads
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Old 09-08-2008, 06:34 PM
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Quote:
Originally Posted by tommy85
there is an intake for that swap just buy a rpm intake for vortec heads and the bolt holes are right to make the swap easy as pie rpm intake for vortec heads
This engine doesn't have Vortec heads, it's equipped with Swirl Ports which are the same as older head manifold bolt patterns except for the center bolts angle which is changed from 90 degrees to the manifold face on the head to 72 degrees.

Bogie
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Old 09-08-2008, 06:40 PM
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Vortech heads dont have the center two bolt holes and the ports are diffrerent.

Shane
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Old 09-08-2008, 07:13 PM
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pump

Well guys the pump isn't the problem. we already have the tanks out and replaced them. They still didn't work. I don't know if the problem is in the computer or it the switch that lets you switch tanks, but that really dosn't matter to me.
It's his truck and he is one of the most pig headed, closed minded 50 year old men i've ever met. So when he gets it in his head that he's gonna do something a certain way there is no changing his mind. He wanted to go with the OTC electric fuel pump so i let him. He wants to put a carb on it so i'll help him. I'm not calling the shots on this one. I'm just doing what he wants me to do cuz he recently had back surgery and can't do all the bending to do it himself. This is a man that there is NO arguing with, so i just assume he is right and the rest of the world is wrong, its easier that way, if you know what i mean. If i spend all day telling him the right way to do something, it is just a waste of both of our time so he just do what he asks me to.

I'm sure you guys all know someone like this too. It just saves time and agurvation to let them be right and do it the way they want. so i'll try to drill the holes so a bolt can go straight through them and call this project done enough.
Thanks guys, Danny
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Old 09-08-2008, 07:18 PM
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You'll need an old hei distributor too. The one you have uses information from the confuser to work properly.




Larry
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Old 09-08-2008, 08:24 PM
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Quote:
Originally Posted by eatonde
he is one of the most pig headed, closed minded 50 year old men i've ever met. So when he gets it in his head that he's gonna do something a certain way there is no changing his mind. Thanks guys, Danny
Hey Danny, I think we're brothers.

Bogie
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Old 09-08-2008, 08:27 PM
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confuser=computer???

I think you were talkin about the computer when u said the confuser, but i can go with that cuz its def. good at confusing me. What is it that would change and not allow it to get info from the computer just because your using a carb?? If the computer is still hooked up and the coil is still hot shouldn't the dist still fire properly?? I've never really understood all this computer stuff so please feel free to enlighten me on how it works.
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