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Technical The great C4 debate

Discussion in 'The Hokey Ass Message Board' started by topher5150, May 22, 2020.

  1. topher5150
    Joined: Feb 10, 2017
    Posts: 1,912


    If this has already been addressed by the great and powerful Ford gods then kindly point me in the right direction. If not I humbly present to the benevolent Ford gods a sacrifice of my first born.
    In my 47 Ford coupe I am putting in a 351W from an 80s truck. The transmission is from a 71-72 302 Mustang (PEE AC4 D 27PDAJ25). I have determined that the transmission is a 157 tooth bellhousing (5.875" BH depth, and 10.50" T/C)
    What I need to know is can I use a 157 tooth flexplate on a 351W? Can I retain the 351W's current harmonic balancer? Or do I have to get a new bellhousing/torque converter?
    Thor1 likes this.
  2. No issues... All 289/302 used the 28oz balance until the early '80s, and the 351W did all along until the end of production. It only gets weird when you try mixing 28 and 50oz stuff. A C4 to a 50oz motor, you need a aftermarket flexplate. AOD to a 28oz motor, same story. In this case, if you have all the matching OEM parts for that trans it's a bolt-on.
  3. One last comment. Ford didn't factory install the C4 behind the 351 because they didn't feel it could take the torque and meet their reliability standards. OK, there was some exceptions; some of the last of the car-use 351s starting in the late '70s used the C4, but by this time the power was smogged down to 302 levels. You might consider 'freshening' the C4 with some upgraded bits for the increased torque, particularly if you lean on the motor.
    Hnstray and loudbang like this.
  4. topher5150
    Joined: Feb 10, 2017
    Posts: 1,912


    Ok that wasn't as painful as I thought it was going to be.
    Sent from my moto z4 using The H.A.M.B. mobile app
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  5. doyoulikesleds
    Joined: Jul 12, 2014
    Posts: 254


    the 351 went to 50 oz in 84 or so so you need to know what 351 you have
  6. Nope, it didn't. The reason for the change on the 302 was because they seriously lightened the crankshaft and needed the extra external weight to offset the lighter crank counter weights. The 351W used the same crank all the way through.
    Truckdoctor Andy and topher5150 like this.
  7. BamaMav
    Joined: Jun 19, 2011
    Posts: 4,163

    from Berry, AL

    I had one of those exceptions---1978 Granada 351W C4. Had the deep bell like the C5 lock up converters with the large converter bolt pattern, same as the AOD. Definitely not a performance engine, 2 barrel, but torquey. I used the engine in a 4x4 pickup, it did fine, trans was later used behind a late model 5.0 flat tappet engine with an AOD flexplate.
  8. topher5150
    Joined: Feb 10, 2017
    Posts: 1,912


    Two more questions. When I got the transmission a while back I pulled the valve body of to take a look inside. I run through all the gears but when I get to 1st it seems to want to want to pop back into 2nd without much effort. Did I install something wrong on the valve body?

    Is there a way to replace the kickdown lever with out disassembleing the trans?

    Sent from my moto z4 using The H.A.M.B. mobile app
  9. Crazy thing now is those C4’s are behind plenty of fast Fords running some impressive et’s....
    Gammz likes this.
  10. buzz4041
    Joined: Nov 14, 2008
    Posts: 278

    from Texas

    My nephew runs a C4 behind his 408CI 600HP. I had his tranny guy build mine up for me but I will only have 400HP.
  11. deucemac
    Joined: Aug 31, 2008
    Posts: 1,055


    Another C-4 horsepower story. The daughter of a friend of mine was given an 84 T-bird with a very healthy 351c and C-4 because she wanted to learn to drag race. Her grandfather gave her the car and had a fresh C-4 from a well known nationally know builder installed for her. She made about 6 passes and the trans let go. My friend called and asked if I would look at it. I tore it down and found a snap ring installed backwards on the output shaft for the low/reverse drum. I looked at what had been done to the trans and was surprised at what I found. Outside of a full manual valve body and Kevlar clutches and bands, it had all the things I normally do to a C-4 for performance upgrades. I called my friend and asked him how much his dad paid for the trans and he told me $2700! I told him that maybe I should start doing C-4s again for a living because outside of the two items mentioned, it was the same as I always did for far less money. That was 4 years ago and they moved back to Texas and his daughter is still drag racing the car with only fluid changes and band adjustments. A properly built C-4 can handle far more power than most people believe.
  12. The key word here is 'properly'... The C4 is a very good trans as built by Ford and used as intended. But it was their entry-level trans, and as such Ford didn't spend more on it than they needed to to meet their quality and longevity standards. Properly upgraded, it'll take punishing amounts of power that would grenade a stock one.
  13. RmK57
    Joined: Dec 31, 2008
    Posts: 1,464


    If your leaving it in drive then yes, from a dead stop and lightly accelerate it will shift into second at 4-5-6 mph. The kickdown lever bolts to the outside of the trans, so yes.

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