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Discussion Starter · #1 ·
hi
2 months ago i purchased 71' mustang as a project car, oryginaly car came with 351c 2bbl, last owner changed it to 400 and fmx trans. (i think its not c4 and its not c6) engine is not installed in the car yet its just sitting in the engine bay . i got the engine mounts for 351c.
did someone swap 400 into 71 mustang do i have to change something or its just bolt on, i got also long tube headers for 351m/400 not sure yet if they will fit without modification. i have also 351m i was going to swap into my 68 mustang but decided to leave it # matching car, i can always put 351m into '71 if 400 wont fit
any advice?
 

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George1861 said:
last sentence 351M & 400 are the same engine. The '71s had the 429 in them,so a 351M/400 will fit.
Meaning they are built on the same block but have different internal parts. The transmission is an FMX if it has a cast iron body. They are very good transmissions.
 

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Sand1 said:
Meaning they are built on the same block but have different internal parts. The transmission is an FMX if it has a cast iron body. They are very good transmissions.
The crank & rods are the only difference between the M & the 400. Exept for some built in '73, the M/400 have the 429/460 bell pattern.
 

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Just checking, you are probably aware of the number of folks out there (even Ford folks) who dont believe there is such a thing as a 400 cid M block. I had the 400 out of my truck sitting on the floor. I was pointing out the decal that said 400 cid and a guy was still arguing that it was a 351. He kept pointing to the engine class, 351M/400. I finally had to kill him and bury him under the shop floor lol JK.
 

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George1861 said:
The crank & rods are the only difference between the M & the 400. Except for some built in '73, the M/400 have the 429/460 bell pattern.

The rods are the same between the 351m and the 400 ,the Pistons and crank are the difference.
Also the motor was built as the 400 but the stroke ,was changed to the 351,hence 351 Modified, from a 400, because the demand for the 351 cube engine was higher because of the dropped 351 cleveland motor.the Windsor plant couldn't keep up .The 351m crank is a 351windsor crank with different snout.
 

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Discussion Starter · #8 ·
next problem
first had some problems with engine mounts but welder came in handy...
i ordered full-length hedman headers(#HED-88220 ) from summit racing, passenger side fits fine but the problem is with driver side cant get clearance because of steering box ( car is with power steering) (headers should fit with power steering acording to summit racing) maybe diferent steering box that i can use or different headers, has anyone had this problem or know how to work around it? ( i can take pic if thats gonna help) really dont want to go with stock headers.

any advice
 

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Won't be a problem, my mates got a 400 in his 72 'Vert:hy:
I recently installed a 400 in my 71 Mustang, but I had to cobble together my motor mounts from the 400-engine-side combined with the 429 vehicle-side. Seems to work ok (engine hasn't fallen out yet), but I'm wondering: is there a "legitimate" 400/Mustang motor mount??
 

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I recently put a 400 in my 71 Mustang, but had to cobble together my motor mounts from the 400-engine-side with the 429-vehicle-side. The motor hasn't fallen out yet, but I'm wondering: is there a "legitimate" manufactured engine mount for a 71 400Mustang?
 

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You're not likely to get a response from these posters, they were in 2007. Also, the 400 was the same block as the 351M, neither engine offered in a Mustang. Not sure what the fit looks like, but I've seen oddball mix and matches before that worked just fine, how loose is the fit?
 

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Thanks for the response, Cat. No, I didn't expect a reply! The 400, it turns out, is exactly the same width as the 429 (also same deck height, 10.5 ", near as I could measure with a tape measure), so it fits in the 71 Stang real nice -- I swapped it out with my heavy 429, went whole-hog aluminum with it, and saved 200 pounds campared with my only-partially aluminunized 429 (465 pounds vs 680 pounds). I'm happy with it aside from my fears over my cobbled motor mounts. As an old geezer with a withered gas-pedal foot, and 55 mph speed limits, I don't really feel a power loss, in fact the 400 seems to bring in the torque at a lower rpm, the rear tires seem more prone to break loose on starting than the 429.
 

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The 351M and 400 were built for trucks, not cars, so they were designed more for low end torque rather than top end horse power. As I had said, if the motor mounts fit snugly, you shouldn't have any worries, as long as the engine is sitting properly.
 
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