Doing an engine swap from a 289 to a 351 - what do I need?

BB67FB · Jul 22, 2008

So I found a 1986 351 out of a truck with low miles, and am going to swap it into my 1967 mustang, what parts do I need? As I understand it, everything will bolt up, but I am unsure about the ignition and the flywheel. Any one have experience on this? The engine is complete, but was hooked up to an automatic. thanks!

rbohm · Jul 22, 2008

you will need a flywheel from the 351w as the 302 is balanced differently.

you will also need the accessory brackets from the 351 as there are a couple of holes far enough apart that the 302 brackets wont fit.

you may need a swap header since the 351w is wider than the 302, but there is more room under the hood of the 67-70 stangs, so that isnt as important as it is on the 65-66 cars.

mounts are the same as with the 302, as is the bell housing.

you are going to find that some wiring will need to be extended, as well as the throttle linkage, but not much.

you may have to use a drop over style air cleaner for hood clearance, but check first.

you will need to change either the radiator or the water pump so the outlets line up.

you will need a 351w distributor as the 302 one is too small on the shaft, and uses a different oil pump drive shaft.

brianj5600 · Jul 23, 2008

rbohm said:
you will need a flywheel from the 351w as the 302 is balanced differently.

?????? I thought all 351's were 28oz.

D.Hearne · Jul 23, 2008

The imbalance weights are the same. No change there. No swap header either, just use a header for a 69-70 with a 351W. As far as the accessory brackets, Ford used an adapter bracket on the heads to compensate for the taller deck/wider head spacing. I don't believe the 86 Windsor will have that on it. You'll also need a front sump 351W oilpan.

BB67FB · Jul 23, 2008

So as I understand it, the flywheel will work along with the bellhousing and all the clutch parts. Can i use the 289 oilpan? How hard will it be to use the 1986 distributor in my car? Any change in wiring?

rbohm · Jul 23, 2008

DH you are right, for some reason i was thinking that he was using an 86 302 yes you can use the flywheel from the 289 with no problem. as long as the distributor on the 351w is for a carbed engine there is no issue. it is easy to install a duraspark ignition box in your mustang. check out mustangsteve.com as he has the wiring diagram on his site. as for using the 289 oil pan on the 351w, sorry no way. the rear main cap on the 351 is larger than the one on the 289 and there would be about a 1/2 gap between the pan and the cap. there are also subtle differences in the pan rails. there are however plenty of oil pans available for the 351w, and most mustang parts vendors carry them. in fact summit racing has numerous pans from stock type pans that are inexpensive, to high capacity aftermarket pans.

BB67FB · Jul 23, 2008

Thanks for the info! Yes the engine is carbed, and its even a four barrel from the factory, which I was suprised to see. I guess it was a HO option for trucks that year, but from what little i have found on researching the engine, sounds like factory numbers were nothing too special. Any one have any idea what the compression ratio is in this engine? I have a set of 61cc trick flow heads that i am debating on putting on this engine, but if it yields a very low copression then its just not worth it. Sounds like ignition should be pretty easy too, thank goodness!

SadbutTrue · Jul 23, 2008

BB67FB said:
Thanks for the info! Yes the engine is carbed, and its even a four barrel from the factory, which I was suprised to see. I guess it was a HO option for trucks that year, but from what little i have found on researching the engine, sounds like factory numbers were nothing too special. Any one have any idea what the compression ratio is in this engine? I have a set of 61cc trick flow heads that i am debating on putting on this engine, but if it yields a very low copression then its just not worth it. Sounds like ignition should be pretty easy too, thank goodness!

I used Trick Flows on my 351w, spent about $80 to have them milled down .030 to drop the combustion chamber size down about 5 ccs. Compression should go up about 3-5 tenths of a point with .030, and you could go a little more aggressive on the milling than I did.

Definitely use the Trick Flows if they're just laying around. What was the 86's compression stock?

SadbutTrue · Jul 23, 2008

BB67FB said:
Thanks for the info! Yes the engine is carbed, and its even a four barrel from the factory, which I was suprised to see. I guess it was a HO option for trucks that year, but from what little i have found on researching the engine, sounds like factory numbers were nothing too special. Any one have any idea what the compression ratio is in this engine? I have a set of 61cc trick flow heads that i am debating on putting on this engine, but if it yields a very low copression then its just not worth it. Sounds like ignition should be pretty easy too, thank goodness!

Do note that you'll have to take the Trick Flows to a machinist anyway if they have the 7/16" head bolts (standard for 289/302, 351w have 1/2" bolts). I got lucky, my Trick Flows were a (relatively) rare model that came with the 1/2" bolt holes anyway.

If you have to have a machinist tap the holes a bit bigger might as well have him mill the heads down a smidge while he's at it.

BB67FB · Jul 23, 2008

I am not sure on what the compression ratio on the 86 is stock - I looked around a bit but found no info on it. Not sure on my head bolt size, I will have to check, but if I go with my trick flow heads I will need different pushrods too, right?

SadbutTrue · Jul 23, 2008

BB67FB said:
I am not sure on what the compression ratio on the 86 is stock - I looked around a bit but found no info on it. Not sure on my head bolt size, I will have to check, but if I go with my trick flow heads I will need different pushrods too, right?

Yeah. Trick Flow says the correct pushrod size with their heads should be 8.6" +/- .15", I determined I needed 8.7" long ones. Driven around 40 miles so far and it hasn't exploded, I guess thats a good sign. Checking the length isn't as big a deal as I thought it would be, once I figured it out it only took half an hour or so.

If you have (or can find) the original part number for the heads that'll tell you. I had TFS-51400005s, which come stock with 1/2" head bolt. The more common heads (51400002, 51400003, and 51400004, i believe) all come with 7/16" holes, since they're mostly installed on 302s.

BB67FB · Jul 23, 2008

Just checked out my heads, and if im gonna use em, I have to get em drilled out... Not the end of the world though, and I just might have to shave a bit off of em to gain some compression ratio while I am at it.

SadbutTrue · Jul 23, 2008

BB67FB said:
Just checked out my heads, and if im gonna use em, I have to get em drilled out... Not the end of the world though, and I just might have to shave a bit off of em to gain some compression ratio while I am at it.

Its not a big deal at all. It'll cost $50 at most and should be a good excuse to get the heads to a machinist to mill them some and maybe a valve job if they're used, which would be a smart idea anyway.

And be happy, the extra head bolt thickness means the stock 1/2"ers are plenty strong enough to handle all kinds of hp, whereas the 302s start reaching their limit somewhere between 400 and 500 (absolute max, most people I talked to didn't say they'd ever run anything less than ARPs after 450). So you save that money back elsewhere.

D.Hearne · Jul 23, 2008

The 351W flywheel won't work with the 289 bell. The 289 bell will be a 157 tooth bell. the Windsor flywheel will be a 164 tooth. That said, the 289 flywheel will work, but the stock clutch will not handle the torque from the 351, unless you upgrade to something like a Centerforce Dual friction clutch/pressure plate. Probably be best too, to upgrade the flywheel to a new one,(for safety's sake) if the 289 wheel is the original. That 351's comp ratio will be in the neighborhood of 8.5 to 9 to 1.

BB67FB · Jul 27, 2008

Dropped the heads off at the machinists yesterday but because its the weekend they wont check them until monday. My clutch is almost brand new so I dont think I will be replacing it. I was able to use the oil pickup from the 289, now I am just waiting on my oilpan.

Doing an engine swap from a 289 to a 351 - what do I need?

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