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Hi there I'm looking at getting a new engine for my '66 coupe. I'm looking at a 351W or a 390. I'm not sure if the 390 will fit in the stock engine bay. I'm saving up the money and wanting to get the engine all ready to go before I go on my deployment next year with the Navy and when I get back I will redo the drivetrain for the car to handle the new engine. What would be the better of the two in the long run? I'm wanting to do this right and do it the first time. The last time I rebuilt the 6 cylinder but now I want to but the big V8 into it. Any input would be great.
 

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In order to get a 390 in the 66, you'll have to go to a different front suspension like the ones that use coilovers or the Mustang II conversions. The stock shock towers won't allow the 390 to fit. I'm doing a strut conversion on a Meteor and it's giving me lots of room for the 390, but it's also a tall engine which is why the Thunderbolts in the mid 60s had the bubble hood scoops. You might be better off with a 351, or better yet build a 347 stroker that will bolt in like it was stock.
 

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The 390 in the mustang was different that other 390's, I think the exhaust manifolds were different and possibly the heads, I would do some more checking, switching from a I6 to V8 requires several changes besides suspension, several of the mustang sites have done the conversion, I would recommend checking them out, the mustangs are a little heavy up front already, so putting a big block up there just makes it worse. Good Luck.
 

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In a '66' I would stay away from the 390 and go straight for the 347 or 351. So many cheap and available parts for the Winsor, less weight on the front end, stock exhaust and mounts. As far as the Mustang 390's being different than others, not really after '67'. Ford did have to revised the bolt mounting pattern on the heads for the different manifolds required to fit in the chassis.
Dave
 

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In a '66' I would stay away from the 390 and go straight for the 347 or 351. So many cheap and available parts for the Winsor, less weight on the front end, stock exhaust and mounts. As far as the Mustang 390's being different than others, not really after '67'. Ford did have to revised the bolt mounting pattern on the heads for the different manifolds required to fit in the chassis.
Dave
+1 absolutely right on Dave.:bigthumbsup
 

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The 351W will fit in the 66 BUT you are going to have a hard time finding headers to fit your application - especially if you use a top-loader four speed.
If I were to do it over I would build a 347 and leave it at that.
 

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A 390 would give a really big fight before sitting in the 66 engine bay, the shock towers mostly, but also its a lot of weight for an already heavy nosed car, its, considerably taller too, so you would also need to change/modify the hood, improve suspension, brakes, drivetrain, etc. i would recommend to not go any further than a 351 on that car, unless you be planning to do Pro-Drag racing, you don't need mor than the 351 power. :bigthumbsup
 
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