Engine Swap Compatibility Questions

[Viking Ninja]

Hello Everyone,

My son and I have a 1986 F150 Lariat project that we would like some advice and recommendations on. It currently has a 302/5.0 EFI, however the engine is toast. I have recently found a a possible donor engine for sale with the following description:  


"351w HO factory 4bbl I pulled out of my 85 bronco. Motor runs like a dream I have videos just before I pulled, and guarantee a healthy strong motor. She’s been refreshed not that long ago and has roller timing chain. $1000 obo. Drop it in and go. For extra $500 I have an oil pan, oil pickup, and hooker headers that allow you to put a 351w into a 66-77 bronco with no modification."

How difficult a swap would this be? What would it entail? Would additional parts would I need to acquire?  Would the headers, oil pan and oil pickup be an option I should invest in?  I am currently working a lot of long hours so please forgive me if it takes a bit for me to answer. We really would appreciate any and all help and advice.

[Gary Lewis]

That's probably the easiest swap to a different engine that you could do.  Our page at Documentation/Engines/Engine Swaps has some info on things you need to consider, and I've copied some of that here so you can see what the differences might be to other engines, but have added info specific to your questions about the 351HO:

Engine stands: Also called perches or brackets, the engine stands are bolted and/or riveted to the frame.  This is covered in detail on the page called Engine Perches/Stands/Brackets, but generally there are different stands for each of these engine lines, so if you are converting from one engine line to another you'll have to change out the stands.  Fortunately for you the 5.0L is in the same engine family or line as the 351W and the current engine stands and mounts will work.

Oil Pan: The engines in these trucks have to have a rear-sump oil pan.  But, most Ford cars had front-sump oil pans.  So, if you are swapping an engine from a car into a truck you'll need a rear-sump pan as well as the longer oil pickup and main-bolt stud that holds the pickup.  However, in this case the engine you are buying should come with the right pan already installed.

Transmission: For the engines used in these trucks there were 3 bell housing bolt patterns, and transmissions from one pattern will not work with an engine from another pattern w/o adaptation.  But the "small-block" pattern includes the 3.8L V6, the 300 in-line six, and the 255, 302, and 351W V8's, so your current transmission will bolt up.  However, you didn't say what that is and it might be the AOD since it was offered behind the 5.0L.  But it wasn't offered behind the 351 as it didn't stand up to the torque of the bigger engine very well, so we need to have a further discussion about what you have.

Flywheels: Each engine series had its own flywheels, and even within the series there were differences.  I don't remember the differences between 5.0L and 351W for sure, but if the 351HO comes with its own flywheel or flexplate then you don't have to worry about that.  Otherwise we need to get others involved as there was a change on the 5.0L at some point where it was balanced differently from the 351.

Radiator: The 300 six radiator is the odd one out here as its inlet and outlet are swapped from all of the other engines.  But, the radiators for the V engines are similar enough that you can usually re-use the old radiator - if it has enough cooling capacity.  And in your case you should be fine with the 5.0L's radiator - assuming it is in good shape.

Exhaust system: Obviously an in-line engine has a different exhaust system than a V8, but there's a lot of variation w/in the V8 line as well since 255's and 302's are narrower than 351W's so their Y-pipes are different.  The 351M and 400's are the same block as each other so take the same exhaust.  The 460's are quite wide and the diesel engines are very different from the gas engines.  So, basically if you swap from one engine series to another you will have to change out at least part of the exhaust system.  But in the case of swapping from a 5.0L to a 351W I think the main difference is in the Y-pipe.  However, the headers he talked about appear to be to fit that engine in an early Bronco and probably won't fit your truck.

Throttle cable: Supposedly each engine line takes a different length throttle cable.  But the biggest difference is to the 300 six, and in your case the cable should be fine.

Fuel line: As with the throttle cable there are differences.  But for your swap the major difference is that you currently have EFI and that takes a high-pressure fuel system, which the carb on the HO engine is NOT going to like.  So you'll need to put a pressure regulator, or two, on the system to drop the pressure down to ~5 psi for the carb.  I've done that and it works well.

Wiring: All of the gas engines have roughly the same basic electrical requirements, so the engine wiring harnesses between different engines with the same ignition systems are electrically the same.  However, the alternators and sending units are in differing locations so the length of each wire may be quite different between the harnesses for different engines.  For instance, the oil pressure sending unit on a 351M or 400 is at the rear on top, but on a 351W its by the fuel pump, down low.  So, the wire to the oil pressure sending unit is a lot longer on an M than a W.  In other words, if you don't use the harness for the engine you are swapping to then you are very likely to have to adjust the length of the wires going to various things.  In addition, the wiring harnesses for an 8 cylinder engine has a ground to tell the tach to count 4 pulses per revolution, where the 6 cylinder harnesses don't have the ground so the tach counts 3 pulses per revolution.

However, in your case the EFI system's wiring is quite different than the one the HO had in his Bronco.  But, if you could get him to include the engine wiring harness then it would essentially be a plug & play situation - after you remove a lot of the 5.0L's wiring.

Springs: There is a wide range of weights between engines, and Ford put the correct springs in the truck to make it work with the engine it came with.  So, if you are changing engines you'll want to consider changing out the springs.  Here are the stock engine weights as best I can tell from Kelly Hotrod for the V-engine info, and BlueOvalTrucks for the diesel info.
3.8L V6: 402 lbs
300 in-line six
255 (460), 302 (460), and 351W (525)
351M & 400: 575 lbs
460: 720 lbs
Diesel: 860 lbs

In your case the 65 pound difference is probably not enough to worry about, but I included it so you can see what other swaps might do to your springs.

In other words, if you are going to swap to a different engine then the 351W is the easiest.  But there are things that will have to change, and one of those might be the transmission.  So let us know what tranny you have.

[mat in tn]

very good list of things to consider. one of the unique items about the aod that you mentioned is the flex plate. the one for the aod is specific due to its mounting bolt positions. the torque converter will bolt up to other flex plates but may hold the torque converter bound against the fluid pump inside the trans.
another is the tv cable. when going from efi to carb you will need to attach it to the carb properly. and adjust it properly.
and the carb engines use a shorter accelerator cable. there are many details to consider. yes, it is done often and can be done well. but what is the true desire here? project or problem solving? rebuilding the existing engine may be best if only problem solving because everything already fits.

[Rembrant]

I am assuming that the 302 to 351W swap would also mean EFI to carb swap? If you are by chance thinking of trying to swap in the 351W and retain the factory SD EFI, then I don't think that I would bother with it. Swapping to a complete 351w with carb though? Easy peazy, I'd say.

You'd likely have to change the flexplate or flywheel...unless the two vehicles happen to have the same transmissions. In other words, you can't put the 302 flywheel/flexplate on the 351w. Otherwise it will all swap in there pretty easily. You'd have to install a pre-EFI fuel tank and new fuel line, and gear up a DSII ignition or similar.

[StraightSix]

Ds2 ignition is simple, cost effective, native to the platform, and easily upgraded down the line (msd ignition controller/coil, etc).

I hoped I would have more to add, but Gary and the guys killed it. Good luck!