I have a 66 F100 with a 390 and a 4 speed toploader. It is a 390 and not a 352. I just got a 81 F100 with an inline 6. I want to swap the engines and sell the 66. I read somewhere about putting a 460 in an 81 and it said you had to change the engine perches. Is this correct?

 

I'd just sell the 66 F100 like it is and find a 351 Windsor to bolt in in place of the 300-6.

This is for a number of reasons.

The 390 is a HEAVY motor. Much heavier than a 300. You'd have to find a different bell housing if you have a manual transmission, or you'd have to swap in the other transmission WITH the 390 to put it in the 81 as the 390 won't bolt up to the 300/302/351W/351C pattern bell housings.

Then you've got to look at fitment.

To swap from a 300 to a 390 will require moving the engine perches back towards the firewall a hair, if I remember right, then you'll need to get the correct motor mounts. Then you'll need to see if your stock radiator is going to work or if you'll have to get a different radiator. If you have to swap transmissions it may require fabbing up a cross-member or finding one to put under the truck.

The 390 being much heavier than the 300 will also require a different set of front-end springs. A 300 weighs around 525 lbs with the manifolds and flywheel, and a 390 fully dressed is closer to 700 if I remember right. This will make your front end droop and probably pull your tires in at the top.

On the other hand, with a 351...

You can build it to have the same power as the 390. It'll get better mileage. You can find a bolt-in radiator that will work for it easily. The 351W and the 300 have the same bell-housing patterns which means you can keep your stock transmission/bell housing.

The nice part about the whole deal?

With the 351, all you'll need to get are the flywheel/flex plate to match the motor, you'll need the motor perches, and the motor mounts. Depending on whether or not the radiators are the same or different, you may or may not need a radiator.

Compared to the 390 swap, the 351 Windsor swap would be plug and play.

 

The 390 is already built. I was going to keep the toploader hooked to it. I understand all that you're saying but I was only concerned with the perches. I also read that if the 81 came out with a 300, you would have to switch perches just to go with any V8

 

Checkout the engine swap kits at www.broncograveyard.com and/or google the L&L engine swap kits.

 

A 390 is a FE engine, and was never offered in a 80-up truck. So it's not a bolt in proposition. It has been done, but it takes a lot of head scratching to do it, much more than "just moving perches back". Do a search in this forum on 390 swap, there was a guy who just wrote in a couple of months ago about not how to do it, but how he did it, and tells some of the things he went through to get it in there.

 

I can't find the thread about the 390 swap.

 

I think it's this:

https://www.ford-trucks.com/forums/1...-390-swap.html

I went to Advanced Search... searched only this forum... used "390 swap" WITH QUOTES as the search term... had it show me threads and not posts... it's the 8th entry down in the list of results. (Actually, there are a bunch of posts from that thread listed in the results, could use any of them to get to the thread.)