engine change
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Junior User
Joined: Sep 2002
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From: Charleston USA
engine change
i have a 79 bronco and it has a 351m. the engine is pretty tired and old now, i was wondering. would i be able to swap in a 351 cobra jet and would it mount up to my c-6? or will i have to change transmissions also?
Posting Guru
Joined: Aug 2000
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From: PacNW
engine change
>i have a 79 bronco and it has a 351m. the engine is pretty
>tired and old now, i was wondering. would i be able to swap
>in a 351 cobra jet and would it mount up to my c-6? or will
>i have to change transmissions also?
A 351CJ is just a low compression 351C-4V which has the same bellhousing bolt pattern as a 351W or 302 so the answer is yes you could swap it in and yes you would need a new trans.
>tired and old now, i was wondering. would i be able to swap
>in a 351 cobra jet and would it mount up to my c-6? or will
>i have to change transmissions also?
A 351CJ is just a low compression 351C-4V which has the same bellhousing bolt pattern as a 351W or 302 so the answer is yes you could swap it in and yes you would need a new trans.
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Junior User
Joined: Sep 2002
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From: Charleston USA
engine change
since it is like a 351C would i be able to use any parts on my 351M? cause i really don't want to have to change my tranny. or is the engine just really a beefed up 351W?
Tuned
Joined: Jun 2001
Posts: 266
Likes: 0
engine change
>since it is like a 351C would i be able to use any parts on
>my 351M? cause i really don't want to have to change my
>tranny. or is the engine just really a beefed up 351W?
A lot of parts would swap but the only one you might possibly want would be the heads - but as someone else hinted, the 2V heads you already have are best for low-end torque. Also you would need intake spacers.
Your best bet is to overhaul the 351M and while you are at it, replace the crank and pistons with 400 parts, turning it into a torque monster 400. Add a 4V carb and intake, an RV cam, straight up timing gears, 9:1 pistons (if you can find them), and a decent set of small tube headers and dual exhaust. This will kick the crap out of a 351CJ, particularly at low to mid RPM...
>my 351M? cause i really don't want to have to change my
>tranny. or is the engine just really a beefed up 351W?
A lot of parts would swap but the only one you might possibly want would be the heads - but as someone else hinted, the 2V heads you already have are best for low-end torque. Also you would need intake spacers.
Your best bet is to overhaul the 351M and while you are at it, replace the crank and pistons with 400 parts, turning it into a torque monster 400. Add a 4V carb and intake, an RV cam, straight up timing gears, 9:1 pistons (if you can find them), and a decent set of small tube headers and dual exhaust. This will kick the crap out of a 351CJ, particularly at low to mid RPM...
Posting Guru
Joined: Aug 2000
Posts: 2,416
Likes: 4
From: PacNW
engine change
>since it is like a 351C would i be able to use any parts on
>my 351M? cause i really don't want to have to change my
>tranny. or is the engine just really a beefed up 351W?
The 351C CJ is a basic 351C with open chamber (+/- 75cc) 4V heads. These heads have large intake runners which don't develop much torque in the low end which is not really good for a truck since you need the torque down low to move all of that weight. You could swap the heads onto your 351M but you will face the same lack of torque issue you did with the 351C. If you were to make the 351M into a 400 then the loss of torque might not be as bad because of the increased displacement.
>my 351M? cause i really don't want to have to change my
>tranny. or is the engine just really a beefed up 351W?
The 351C CJ is a basic 351C with open chamber (+/- 75cc) 4V heads. These heads have large intake runners which don't develop much torque in the low end which is not really good for a truck since you need the torque down low to move all of that weight. You could swap the heads onto your 351M but you will face the same lack of torque issue you did with the 351C. If you were to make the 351M into a 400 then the loss of torque might not be as bad because of the increased displacement.
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Junior User
Joined: Sep 2002
Posts: 67
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From: Charleston USA
engine change
thanks for all the info guys, it really made me think twice now. i am not going to use the cj engine or parts now. shoot for that fact, i might not even use my 351m now. i got a phone call the other day and a friend of mine is selling a block and crank for a 429 for $50 i am going to get that and buld it up and replace my 351m cause the best part of the 429, it is in pieces so i can do a brand new build up and my other buddy is giving me a set of heads for it. now i will have some big block torgue. so thanks again for all the help guys.
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Posting Guru
Joined: Jun 2002
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engine change
There are many more parts needed to complete the 429 engine. Swapping it into your truck will require different motor mounts, exhaust, oil pan, intake manifold, timing cover, water pump, flywheel, starter, etc. The list is very long so make sure you research thoroughly before commiting to the swap.
Consider rebuilding your 351M as a 400 similar to this build up. It makes as much or more power than a stock 429.
http://home.earthlink.net/~tcrocker/400.html
Consider rebuilding your 351M as a 400 similar to this build up. It makes as much or more power than a stock 429.
http://home.earthlink.net/~tcrocker/400.html
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