300 6cyl swap

Mr. Bob

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I have a 1986 Ford F350 with a remanufactured carbureted 6-cylinder 300 in it about 10 to 12 thousand miles on it and I have a 1991 Ford F-150 fuel injected 6-cylinder 300 that has a bad cylinder so I was wanting to take the one out of the F350 which is carbureted and put it in the F-150 which is fuel injected can anyone tell me how I can work this properly
 

pmuller9

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The 1991 fuel injection system's ignition timing is calibrated for the EFI fast burn cylinder head and 8.8 compression ratio.
The 1986 engine will not run properly with the 1991 EFI system
 

Mr. Bob

Active member
The 1991 fuel injection system's ignition timing is calibrated for the EFI fast burn cylinder head and 8.8 compression ratio.
The 1986 engine will not run properly with the 1991 EFI system
So how do I make it work? take the head off of the fuel injection and put it on the other or can I just set the block and head together in the truck and put the fuel injection stuff on it
 

Pontus

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So how do I make it work? take the head off of the fuel injection and put it on the other or can I just set the block and head together in the truck and put the fuel injection stuff on it
The block should be similar enough afaik, so you'd have to keep the EFI stuff including the head from the 91 and install it on the 86 block. You'll probably have to block off the fuel pump port. but I'm a bit confused because, if it's an original '86 motor, it should already have an EFI head, especially if you ordered a reman for an '86. Are you sure it wasn't converted to carb on the EFI motor? Does it have blocked off smog pump holes in the head just above the exhaust manifold runners, or is it still using the smog pump?
 
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Mr. Bob

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The 1986 F 350 came with a 6-cylinder 300 carbureted and I put a remanufactured in it 3 1/2 years ago and it's only got about 10 to 12 thousand miles on it because a 27 year old kid rear-ended me while I was doing 55 miles an hour down the highway and bent the frame on the truck broke the bed loose smacked into the cab $6,500 worth of parts and my labor in about 10 to 12 thousand miles on everything I'll go out and take some pictures of the engine and the truck here in a minute oh yes I meant to say that either way it goes the head on the 1986 is going to have to come off anyway because it's leaking antifreeze around the head gasket either they didn't torque it down properly or the head gasket wasn't worth a crap to start with I got the engine from O'Reilly's Auto
 

Mr. Bob

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The block should be similar enough afaik, so you'd have to keep the EFI stuff including the head from the 91 and install it on the 86 block. You'll probably have to block off the fuel pump port... but I'm a bit confused because, if it's an original '86 motor, it should already have an EFI head, especially if you ordered a reman for an '86. Are you sure it wasn't converted to carb on the EFI motor? Does it have blocked off smog pump holes in the head just above the exhaust manifold runners, or is it still using the smog pump?
20210715_115616.jpg
 

Pontus

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The 1986 engine is still a carburetor engine.
!987 was the first EFI 4.9
Ah, I had my years wrong and was looking at the valves on Rock Auto for reference to check my assumptions, sorry. I wonder why they went shorter 2 years prior.
 

Mr. Bob

Active member
20210715_115643.jpg
This is what the whole truck looks like it has a Borg Warner T30 four speed granny Gear transmission in it I put $6,500 worth of parts including the engine only thing that wasn't rebuilt or replaced on the truck was the internal transmission and the internal rear end except for I put new bearings the rear axle I'm keeping the engine but I'll part the rest of it out or trade or sell it as a whole
 

Pontus

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Those bolts that you were referring to aren't those for the injectors if you go with fuel injection?
No, those are the head bolts. As for which is better carb or EFI... that depends on a lot of factors, but generally EFI. But the EFI head is prone to cracking at the #5 exhaust valve iirc due to the smog pump blowing cold air at a hot, thin casting. The new Promaxx heads reportedly resolve this issue with a thicker casting. Yours may already be cracked so you'll want to get it checked unless you know that the bad cylinder wasn't related and it didn't have issues before... even so, not a bad idea to check. But personally, I'd keep the 91 as EFI if everything else about the truck makes it worth doing the work.

If you just want something that works, replace the head gasket and swap the motor. Donezo. You'll have to figure out the throttle linkage, bypass the fuel pump, and your cat may become clogged quickly, and of course you'll probably get worse gas mileage, but if it's what you need to get running, so be it.

But, if you're planning to sell the 86, why not just sell it with a running motor in it and use the extra money to get a reman motor for the 96?

As for the head gasket, Felpro 1024.
 

Mr. Bob

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No, those are the head bolts. As for which is better carb or EFI... that depends on a lot of factors, but generally EFI. But the EFI head is prone to cracking at the #5 exhaust valve iirc due to the smog pump blowing cold air at a hot, thin casting. The new Promaxx heads reportedly resolve this issue with a thicker casting. Yours may already be cracked so you'll want to get it checked unless you know that the bad cylinder wasn't related and it didn't have issues before... even so, not a bad idea to check. But personally, I'd keep the 91 as EFI if everything else about the truck makes it worth doing the work.

If you just want something that works, replace the head gasket and swap the motor. Donezo. You'll have to figure out the throttle linkage, bypass the fuel pump, and your cat may become clogged quickly, and of course you'll probably get worse gas mileage, but if it's what you need to get running, so be it.

But, if you're planning to sell the 86, why not just sell it with a running motor in it and use the extra money to get a reman motor for the 96?

As for the head gasket, Felpro 1024.
The frame is bent on the 86 F350 you cannot get the passenger side door open the back window is completely gone when the guy rear-ended me the bed used to sit at a distance from the cab he shoved it all the way into the back of the cab and it bounced back only thing that kept the bed on the truck was of U- Bolt shackles bad is sitting down on the frame now used to be some wood between the bed and the frame and that's all busted out that's why can't get the passenger door open I'm not for sure but it looks like they already cut the catalytic converter off on the 91 before I bought it isn't the Block & the head on these two Motors the same without the carburetor or fuel injection? That's not a bad idea if I could sell the whole truck like it is and have enough money to get another engine for the 91
 
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bubba22349

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No unfortunately the EFI engines (1987 to 1997) the heads were compleatly redesigned and then fuel injection intake added, different ignition, all top end parts and even the front dress parts (Water pump plus a serpentine belt drive system) they are all very different from your 1986 carb engine. There was a lot of changes from one year to the next. Best of luck
 

Mr. Bob

Active member
No unfortunately the EFI engines (1987 to 1997) the heads were completely redesigned and then fuel injection intake added different ignition, all top end parts and even the front dress parts (Water pump plus a serpentine belt drive) are all very different from your 1986 carb engine. Was a lot of changes from one year to the next. Best of luck
Is it possible to get a head for a 91 engine and put it on the 86 block put the front dressing from the 91 on the 86 and go that route with it?
 

bubba22349

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Yes that probably could work. The only thing I wouldn’t be sure of is if the piston dishes would match (all depends on what the rebuilder used in the 1986 short block) if they would be the same, but you woukd see that as soon as you pulled the heads off.
 

Mr. Bob

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Yes that probably could work. The only thing I wouldn’t be sure of is if the piston dishes would match (all depends on what the rebuilder used in the 1986 short block) if they would be the same, but you woukd see that as soon as you pulled the heads off.
I don't know what the Pistons dish is I've done everything on an engine just about except for the valve job and rebuilding internally I was told I could get a fuel injection kit to go on the 86 and convert it so I was hoping I would just be able to take the fuel injection off of the 91 and put it on the 86 just drop the motor from the 86 into the 91 and convert it to EFI using parts from the 91
 

Pontus

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You never know what the rebuilder did, but if they stuck with stock type pistons, it should look like the pic below. I'm not sure if Ford used the same EXACT pistons over the years, but the same parts are listed for every motor from 1975-1995. It's going to be a lot more work than it sounds like just swapping the block over, because as Bubba pointed out, you will need to swap over all the front bits, but they should all bolt on the same... I think. I'm no expert, and this may be uncharted territory, but I'm fairly certain that the only change in the actual block was to cast in a plate to cover the fuel pump hole. You'll need to cover that if you use the 86 motor, but they make plates specifically for that purpose (or you could easily make your own).
1626389217835.png
 

Frank

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Good afternoon Mr. Bob, and welcome. I have a 1990 F-150 that I converted FROM factory EFI to carburetor. The project was much more arduous than I anticipated. If you want to convert the 91 to carburetor, you will have to reconfigure the entire fuel pump system. The EFI pressure is 10x more than a carburetor can withstand. Also, if you have an automatic transmission in the 91, it will not shift correctly without the signal the EFI ignition system generates. There are other issues, like throttle linkage, etc. This is NOT a plug and play deal. I have many years of experience, but that project kicked my butt, and I regret I did it. As one who has gone that route, I strongly recommend you keep the 91 as EFI. As others suggested, put the EFI head on the 86 block, and put it back in as it was originally. Yes you can swap your accessories from the 91 to the 86 block. Two things not to overlook: You will have to get a block-off plate for the 86 mechanical fuel pump. Also, you will need to put a 91 water pump on the 86. The serpentine belt drives the water pump in the opposite direction as the V belt pumps.
 
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