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Replacing the original TBI engine with a carbureted engine

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JT88K5

JT88K5

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Made a deal to buy a built (by a reputable engine shop) 400sbc from a friend. Trying to come up with a list of things that will need addressed. The 400 is currently connected to an NV4500 and in a 86 single cab short bed. I plan on leaving the existing 700r4 in my K5.

Difference in accessories, he has no air, I need air, everything else looks like it’s in the same spot. Not too concerned about getting that straightened out. Hoping to move my TV cable bracket over as well. Plan on picking up a Holley 12-880 for regulating fuel pressure using the existing in tank tbi pump. Moving the stock fan to new engine, he runs an electric. I have an upgraded aluminum radiator so cooling should be good. Exhaust will need addressed. I did find some posts on here i want to replicate for exhaust. Planning on going from headers to 2.5” y pipe into 3” collector then running single 3” in the stock location.


At some point I would like to go back to an aftermarket EFI setup. I’m looking for advise on what to do with wiring. I don’t want to permanently eliminate anything I’ll need later and at the moment, I have no idea what that might be.

Thanks
JT
 
you'll need a new flex plate. 400 are external balance.

edit factory 400 are external balance I believe there are some after market internal balance cranks, better ask you buddy
 
Pretty much all wiring can be disconnected/de-pinned and/or tucked out of the way.

It's a good plan as it leaves options open. I don't recall what it looks like, but something that would allow you to run all the stock EFI wiring, but with upgraded programming/learning capability, would seem a better step than going through the work and expense of swapping to carb then back to EFI.

Embedded lockers https://www.dynamicefi.com/ is probably a good bet, but I don't know about the tuning aspect of it. That's really what gets everyone away from OBD1 EFI. Not the capabilities or limitations, just the pain in programming.
 
I was thinking the only cost involved in installing the carbureted motor was the fuel regulator and that it would be less work to get it back on the road. If the carb suites my needs, I may leave it that way. Not likely but you don’t know until you try. Plus it will give me a good reference point to know if efi install was worth the hassle (aka working well) once done.

Does that sound like a dumb way of looking at it?
400 bored40 over, liberty heads. Roller rockers. RV cam, don’t have the specs yet.
New crank, rods and pistons when built. Not positive but I think they did use an internal balanced crank.

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A TBI engine is basically a carbureted engine….with a few sensors added….I’d do as suggested and roll the harness up and tuck it away. You still distributor wiring, alternator wiring, and AC wiring….technically you could use your existing harness for those connections and just not use the TB sensor wiring.
 
I don't know. Have you DRIVEN a carbureted vehicle then an EFI vehicle? lol

Last I checked carbs were pretty stupid expensive, but if you get a carb with it, that isn't a cost to consider I suppose.

You'll need to adapt the TV cable to the carb, regulator, carb if you don't have one, somehow deal with fuel lines (which isn't trivial IMO) and then re-wire that which you need to, to run.

Me? I wouldn't do it. I'd spend the effort making EFI work, knowing full well how it performs. The tossup is the 400, as you can't just swap that engine and have it run right. Of course I have my own biases. Your truck your decision! :)
 
I am pretty sure the TBI computer controlled HEI distributor will not work with a carbureted engine. The distributor will have to be changed to a Vacuum advanced controlled HEI distributor, which means a little change in the wiring.
 
1-ton said:
I am pretty sure the TBI computer controlled HEI distributor will not work with a carbureted engine. The distributor will have to be changed to a Vacuum advanced controlled HEI distributor, which means a little change in the wiring.
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This is correct. The TBI controlled units have all of the timing control through the computer. Vacuum and weights for the carb unless a separate timing controller box is used
 
Heres another thread just for the rabbit hole on the regulator.
I always advise on having the regulator on the return side.
That leaves the feed to the fuel system under the pressure side behind the regulator, where the flow is not restricted but you can easily check the pressure and adjust accordingly

Where to place regulator

Was talking to a buddy of mine and discussing regulator position and he says it should be on the return side and I said feed side. It's a holley 12-886 regulator. Documentation I've read says it could go either way. What are y'alls thoughts on the placement?
ck5.com ck5.com
 
Wes Harden said:
Oh well shoot, always an exception isn't there.
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Probably more paradigm shift. Since the single rear seal change over, most all the weight is on the fly/flex

So the relieved damper means that one is external

But a solid damper doesnt mean it is an internal, even from the factory
 
Hope everyone had a good weekend. Thanks for the comments.

I haven’t driven a carb engine since I had my 76 cutlass supreme ~40 years ago. Wasn’t really looking to go back. After more thought, and thoughtful comments, I agree getting it to run with the carb is counter productive.

I have access to a free Holley sniper 2, known good. Looks like I should be able to use the existing vacuum advance distributor on the motor now and it has a location for the tv cable for the 700r4. Is there a fuel pump I can use to replace the existing in tank pump, not necessarily the entire sending unit, that will give me the 60 psi required. I plan on connecting a FP regulator as Holley recommends. That should get me spark and fuel.

Anyone use the Holley hyper spark distributor? Wondering if the digical timing and advance would be worth it.
 
JT88K5 said:
Hope everyone had a good weekend. Thanks for the comments.

I haven’t driven a carb engine since I had my 76 cutlass supreme ~40 years ago. Wasn’t really looking to go back. After more thought, and thoughtful comments, I agree getting it to run with the carb is counter productive.

I have access to a free Holley sniper 2, known good. Looks like I should be able to use the existing vacuum advance distributor on the motor now and it has a location for the tv cable for the 700r4. Is there a fuel pump I can use to replace the existing in tank pump, not necessarily the entire sending unit, that will give me the 60 psi required. I plan on connecting a FP regulator as Holley recommends. That should get me spark and fuel.

Anyone use the Holley hyper spark distributor? Wondering if the digical timing and advance would be worth it.
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Yes I believe it is ep381. (I would check going off memory) Thats what I got for my tbi to ls swap. Fits in the stock sending unit. I think using the sniper system is a much better idea.
 
If you need 60psi, the EP381 is what you seek. Walbro's whatever -255 also runs in that vicinity IIRC.
 
A year ago I bought a Holley pressure regulator and in-line gauge and ( both) were made in CHINA . I had to call Holley directly have them explain the funky directions included with in-line gauge adjustments. Just FYI.
 
MrHappy said:
A year ago I bought a Holley pressure regulator and in-line gauge and ( both) were made in CHINA . I had to call Holley directly have them explain the funky directions included with in-line gauge adjustments. Just FYI.
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Are those parts still working? I ordered the same.

Regarding the fuel pump. Is it acceptable to use heat shrink and solder for in tank pump? I used one of those heat shrink butt connectors with solder in it. Haven’t put the tank back in yet.

Can anyone tell me what this sensor is on the old tbi motor? Center screen to the right of the dipstick… in case it ain’t obvious.

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