351M to Inline six swap
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Senior User
Joined: Jul 2009
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351M to Inline six swap
I found someone wanting to sell an Inline six cylinder complete. It is a 250ci. I have been considering swapping the 351M out for the inline 300ci. What would be involved in making the 250 a 300? Just increasing the stroke? Also, are these engines compatible with my transmission? 1977 F150 Custom 4x4 351M auto.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The 250 and 300 are different generations of inline 6; the engine in the picture would have never come in a 73-79 pickup. The 240, however, is the engine you might be thinking of - it's the same block as a 300. The 240/300 will not bolt up to your transmission as it uses a "small block" bellhousing, while your 351M uses a "big block" bellhousing. I imagine your truck has a C6, which has an integral bellhousing that cannot be swapped. I'm almost certain that a 250 would not bolt up either, but given that you seem to be looking for a 240/300, it's a moot point.
Moderator
Joined: Jan 2006
Posts: 1,779
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From: Waterloo IL
I wouldn't do it, just seems like a lot of money and work, a 460 would be a lot easier. When I bought my 1977 the 351m was sick. I had a 2wd 1977 F-150 with a 300 so I thought I'd just swap the 300 over to keep cost down. Well I had the 300 lowered into the engine bay. The motor mount perches are in totally different locations. So to remedy this you'd have to maybe find a conversion mount or make one. Or you could cut the perches off the frame and move them up. I wasn't going to put this much effort into a 6 cylinder so I built a 460.
