Gt40p Spring Rate With Flat Tappet Cam

Discussion in 'Fox 5.0 Mustang Tech' started by DTARS, Sep 1, 2013.

  1. im sure this has been asked on this forum already, but i cant find a post on it.

    im not sure what springs/spring rates to use on my gt40p heads with a hydraulic flat tappet cam.

    im also using 1.6 roller rockers. any help info would be great thanks.
  2. i havnt picked a cam out yet, was thinking about goin with a lunati or comp cams xe256, waiting till tues to give lunati a call
  3. That's not an overly aggressive grind and flat tappet camshafts don't generally require as much spring as roller. Grab a set of these, they should do you fine and won't break the bank....

    Heres a good read to provide you with a general perspective on the subject... Spring Tech.htm

    #4 Gearbanger 101, Sep 1, 2013
    Last edited: Sep 2, 2013
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  4. Those are quite a bit cheaper than the Trick Flow ones.. has anyone ran them yet? I don't want to cheap out on something like that so just wondering what experiences people have had.
  5. Many have used Dave's spring kits with great success. My buddy runs them in his roller 5.0l with more cam than you plan on running and he has zero issues.
  6. Hmm good to know. Us tight budget people enjoy finds like these :) lol. Ill just be using a TFS1 cam so nothing drastic.
  7. ya so i ended up goin with a lunati voodo cam with the 351 firing order .
    i forget what duration tho.
    i ended up ordering the springs from alexes . but i accidentaly ordered 7/16 roller rockers instead of 5/16 , so im just gona drill n retap to 7/16ths , looks like the mounts have plenty of meat for that. ill see what the machine shop recomends
  8. finished drilling and tapping my heads for the 7/16 studs.


  9. What kind of rockers are they?
  10. 7/16ths roller rockers forgot what brand tho
  11. You sure they aren't stud mounted rockers? Those heads were designed to accept pedestal mounted rocker arms.
  12. yes they are stud mounted rockers, im going to be using guide plates with them, why am i doing this, no clue figure id be different and not use pedestal rockers lol well that and i didnt want to spend 200+ on them either lol
  13. In that case, you'd better get them to the machine shop. It's not as easy as just drilling and tapping the holes and screwing the studs. You have to machine down the pedestals approx 0.25-0.30 as well. You'll also need to run hardened pushrods not too.

    That's why most don't bother. For the cost and trouble involved in the conversion, you're better off running pedestal mounted rocker arms from the get go.

    ....but, you're this far now. :D
  14. oops lol. oh well ill just have my friend mill them , but first ill see how it fits up with the pushrod gauge . what is the reason for milling off 0.25-0.30
  15. To retain the proper installed height. I just did a quick search. I was off with my numbers a tad. .230- .250 is what most cut. I'd shoot for right in the middle.

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  16. im wondering what will happen if i dont mill off .230-250.

    is it just for clearence to the valve cover, or for it to function properly

    ill see how it compares to the stock pedestal rocker .

    if not a angle grinder and caliper and some fine line tape should suffice lmao j/k
  17. If you don't mill down the pedestal, your pushrods are going to be way too short and you'll most certainly make contact with the valve covers.