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Transmission Swap - FMX, C6, or...?

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r9b2 View Drop Down
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    Posted: 24-November-2023 at 5:54AM
Just got the original I6/C4 out of my Torino. I have a mostly stock 351C CJ ready to go, but need a transmission. I do have a FMX transmission that could work, but can't find any shops willing to rebuild it because of parts availability. 

What are my best options here? Also keeping in mind clearance for my headers. It's a 1973 Torino. Thinking of the possibility of going with a built C4, or maybe even AOD or 4R70W, but I do have 3.00 gears in back so I don't really need overdrive. Thanks in advance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 24-November-2023 at 6:18AM
1st off, what size flexplate do you have from your C4 157 or 164 tooth?

either can work with a 351C but the 157 tooth bell locates the big original starter very close to / interfering with the oil pan rail. a newer style mini-starter solves the issue with a small wiring modification. unless you're ready to replace the driveshaft, dip / fill tube, possibly recal the speedo gear and rework the shifter / linkage assy i'd be inclined to upgrade the transmission you have there. variations within the C4 world are vast and overwhelming, bazillions of changes over the production span including the C5. some parts work together, more do not. it takes a literal expert to know what works & what don't, and to make matters simple much of what don't work together will fit together. above my pay grade man! it's hard enough to just upgrade a complete existing unit and have it work much less start from scratch with 100% unknowns

you said "mostly stock 351C CJ", what's been done to it that's not stock?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SEKCOBRA Quote  Post ReplyReply Direct Link To This Post Posted: 25-November-2023 at 1:30AM
i have a low mileage C6 if your interested.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 25-November-2023 at 1:39PM
Originally posted by SEKCOBRA SEKCOBRA wrote:

i have a low mileage C6 if your interested.


There you go, a nice strong C6 that is made for it, and it's not that far away. I have one too but I'm way too far. A C6 is a good choice being the original preferred trans, but then people like to think of something with an overdrive.
Don
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 26-November-2023 at 1:43AM
I agree with Don.  SEK has a C6 from a 351-CJ, that's what I would use.  That's the only transmission that the 351-CJ used from the factory.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote r9b2 Quote  Post ReplyReply Direct Link To This Post Posted: 26-November-2023 at 3:23AM
Thanks for the replies, everyone. Apparently the C4 might bolt up to the 351, so it's just an easy option I'm considering since it's already here. If I went that route, I'd beef up the C4 when it's rebuilt.

As for the engine, it's not 100% stock. It has a timing set, RV cam, and I'll be running longtube headers. Not a crazy amount of power more than stock, so that's why I would strengthen the C4 a bit if I was gonna run that. SEKCOBRA, I'll pm you shortly
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SEKCOBRA Quote  Post ReplyReply Direct Link To This Post Posted: 26-November-2023 at 7:29AM
Ok
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 26-November-2023 at 2:12PM
The C6 in the typical form you will find them, need nothing to work great behind a 351C. The C4 could use a little work, though they too can do fine behind a mild 351. The C6 would be great if you find one like SEKCOBRA has from his original CJ car, a nice condition example you should be able to trust the history of.

A lot of these old parts have so much age and various owners, usage, it's tough to buy some things. The FMX could be a huge PITA if some parts are really scarce and hard to find in decent shape.
Don
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Post Options Post Options   Thanks (0) Thanks(0)   Quote paj1965 Quote  Post ReplyReply Direct Link To This Post Posted: 27-November-2023 at 3:28AM
I swapped a C6 into mine to replace the stock FMX.  One downside of the C6 is that it is big.  I have had issues finding headers that would fit around it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 27-November-2023 at 4:34PM
The Hooker 6915's are supposed to fit the 351C in Q code C6 Gran Torino's. I have a set to use with a 4R70W, which is also a good size.


or coated;
https://www.holley.com/products/exhaust/headers_and_exhaust_manifolds/all_headers/parts/6915-1HKR
Don
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 27-November-2023 at 4:45PM
My big question is if there exists a header for a 351C with 2V heads and a C6. Or will 4V headers work with 2V heads? (I don't think so but I could be wrong.)
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 28-November-2023 at 1:44PM
Originally posted by Inkara1 Inkara1 wrote:

My big question is if there exists a header for a 351C with 2V heads and a C6. Or will 4V headers work with 2V heads? (I don't think so but I could be wrong.)


The 4V headers and 2V headers will only work with the matching heads, the port sizes are so different they never made parts to fit both. Then way later on Edelbrock made the RPM Air Gap intake, which has large mounting flanges, lots of metal to cover either type of head(they are 2V port sizes that have the large mounting size). In general you can't mix 2V and 4V old type intakes or headers, much later there were a couple of exceptions.

BTW, I do have a NOS 2V header set I got in 1989 to build a 2V 351C, that plan changed long ago. They are Hedman headers, still in the box, rough shape with being stored so long.
Don
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Post Options Post Options   Thanks (0) Thanks(0)   Quote r9b2 Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2023 at 1:29AM
Originally posted by 72 RS 351 72 RS 351 wrote:

The Hooker 6915's are supposed to fit the 351C in Q code C6 Gran Torino's. I have a set to use with a 4R70W, which is also a good size.


or coated;
https://www.holley.com/products/exhaust/headers_and_exhaust_manifolds/all_headers/parts/6915-1HKR


Those are the headers I purchased for this car, they're sitting right next to it. Good to know they will for sure work. Also, I did consider a 4R70W for the sheer efficiency, but would need to mess with a controller and such. 

Still researching interchange for the C4.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2023 at 8:23AM
FPA also makes headers that will fit, listed for either 2V or 4V heads.


I still think the C6 is the best swap, especially when SEK has one from a Torino and may even have the little extras required for the swap.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SEKCOBRA Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2023 at 10:28AM
Have everything. Flywheel plate bolts
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2023 at 10:42AM
Originally posted by 72 RS 351 72 RS 351 wrote:

The 4V headers and 2V headers will only work with the matching heads, the port sizes are so different they never made parts to fit both. Then way later on Edelbrock made the RPM Air Gap intake, which has large mounting flanges, lots of metal to cover either type of head(they are 2V port sizes that have the large mounting size). In general you can't mix 2V and 4V old type intakes or headers, much later there were a couple of exceptions.

To this point, a previous owner put a stock Ford cast iron 4V intake on my 2V engine. Would it be worthwhile to put on an Edelbrock Performer 351-2V instead? Would I notice any difference in peak power or low-end torque or fuel economy or anything else? I'd want to stick with my Holley 600CFM vacuum secondary carb.
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 29-November-2023 at 11:35AM
Originally posted by Inkara1 Inkara1 wrote:

My big question is if there exists a header for a 351C with 2V heads and a C6. Or will 4V headers work with 2V heads? (I don't think so but I could be wrong.)


there's not enough material around the 2V exhaust port to seal a 4V header on US heads but they say the Aus 302C heads will seal the 4V header, there's a little more meat on them. cheap work-around if you have a set of 4V headers what i did was fabricobble myself a set of adapter plates. i traced around the outside of a 4V gasket then overlaid a 2V gasket centered on the bolt holes and traced the inside. it verked!


in the early days of the 351C before Edelbrock released the F351 #2750, sourcing a take-off factory cast iron 4V manifold and fitting it to the 2V engine was fairly popular. an old magazine article claimed the swap was good for 30-35 hp. whether or not you'd notice any difference i can't say, but in Cali i'd go with the Airgap manifold rather than the std performer. a lot of are disappointed by the smaller than port sized runners in the std performer, some guys make the alloy swap just for the weight savings alone. if keeping it stock appearing is important an Aus 302C manifold is an option (they have the 2V port size internally) but they're not extremely available and the choke stove piece (different from the US counterpart) is harder to find than the manifold itself. FYI there are at least 3 different 302C intakes, 2 spreadbores and a square flange that would suit your carb.




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