What stall converter do I need?

Transmission and Drivetrain Tech

  1. jboyd2

    jboyd2 68 cuda

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    Hello Fabo, Can you help me determine what stall converter i need? I've read that generally, you can take the rpm where the cam starts making power and add 500 rpm to that for your tc stall. I haven't read enough to see how the tire height and vehicle weight come into play. My car is a 1968 Plymouth Barracuda notchback that is fairly stock. It does not have any weight reducing upgrades. Engine is a 340 .06 over, flat top pistons, Lunati Voodoo Lun10200703 cam Duration 268/276, Lift .494/.513. I have 3.23 gears and the tires are 225/70/14 26.4" diameter. I currently have a stock converter. I'm about 200miles on a rebuilt engine so I have not floored it from a stop, but I can tell it's going to be a little sluggish. Your help is appreciated.
     
  2. 70aarcuda

    70aarcuda Master Hoader of SBM FABO Gold Member Legendary Member

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    Before you spend several hundreds of dollars on a converter...

    Fine tune your combination...get the timing set...initial and total timing..

    get the carb adjusted correctly...you will be surprise the different...
     
  3. EL5DEMON340

    EL5DEMON340 Well-Known Member

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    Something mild 3k from a good company.
     
  4. jboyd2

    jboyd2 68 cuda

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    A member(spl440) helped me set the timing and adjust the carb but I have a little more to do to get it right. The springs in the distributor are too light so the final timing is advancing too much. I hope to get the springs changed and put a light back on it in the next couple of weeks. I'll definitely wait to see what improvements that makes, before making a purchase.
     
  5. crackedback

    crackedback FABO Gold Member FABO Gold Member

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    This x1000

    That thing should KILL the tires.

    If it doesn't have 16-22 initial timing, it's not close to correct.

    Springs DO NOT limit the total timing. There is a way to mechanically limit it. Find out what's necessary to get it done and do it. It takes time and effort to get ignition timing correct!

    A good 2500-3000 converter would be a nice piece for that build.
     
  6. TimDart

    TimDart Well-Known Member

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    I'm surprised the car ran at all with that combo. I have a 340 Roadrunner with a very similar build that had the old Mopar Purpel shaft car in and as soon as I put it into drive it would die. Changed the cam for a 268 and a 2,000 convertor and all was good.
    PTC do a good priced entry level convertor 11" at around $280 which is bult to order one they know your build details
    Probably next on my list as I could use a little more stall.
     
  7. jboyd2

    jboyd2 68 cuda

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    It actually idles really well and does fine when put in gear. It never tries to die on me. I'm going to set TDC and redo the timing to make sure that's not the probably, then I'll look into a tc. Thanks for the info on PTC. I'll check them out.
     
  8. nm9stheham

    nm9stheham Well-Known Member

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    I would change the original statement to say '500 RPM above where the engine starts making TORQUE'.

    We have a very close to the same combo in a '65 'Cuda, except the rear gear is 3.55 with wider tires and the heads are 63 cc chambers to make 10:1 static CR. We have a 2200 stall Hughes and at just over 1/2 to 2/3 throttle from a dead stop and and closed throttle, it will spin the tires a bit. So we are up on the torque curve there for sure at 2000-2200 RPM or so. Initial is at 11 degrees at this point. (Still dialing it in...)

    I am guessing that you have the standard 340 or 360 open chamber heads? If so, your RPM of making good torque will indeed be higher than ours due to lower CR. In that case, going to a higher stall at 2500 or up would make sense. Just don't go too high if you are planning on a street driven car, or you will be spinning the TC a lot and heating up the trans and burning fuel for not good end. A lot of the recommendations for TC are for best ET's on the track....that is a different TC selection than a street cruiser.
     
  9. diymirage

    diymirage HP@idle > hondaHP@redline

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    care to elaborate on that statement?

    what do you mean by "starts making torque"?

    is there a percentage of peak torque we are looking for?
     
  10. Abodybomber

    Abodybomber Breaking street machines , since 1983.....:) Legendary Member

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    This...
     
  11. Abodybomber

    Abodybomber Breaking street machines , since 1983.....:) Legendary Member

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    And this... These two guys , kinda know a lot..
     
  12. nm9stheham

    nm9stheham Well-Known Member

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    OP..... you could just go by the Lunati recommendation.....2400 RPM stall. The cam mfr's generally give a range of RPM's and that cam is rated for 1800-6200 RPM. 1800 + 500 = 2300.....

    The only reservation I would have on that is that at 55 mph in 3rd gear, cruising, the RPM's will be in the 2200-2300 range with that 3.23 rear gear. The gear and cam combo put you right in a grey area of operation for a 2500 stall TC, at that speed, a 2500 TC may be spinning a bit and heating. You can either:
    - live with that and don't do a lot of cruising at 55 mph
    - drop down to a 2200 RPM stall TC and maybe live with a slightly less than best 'enthusiastic' launch
    - or go to a 3.55 rear gear

    Kinda depends on your goals and use for the car... street or drag race?

    Also, what heads and pistons do you have on this engine? Any idea on the compression ratio?
     
  13. nm9stheham

    nm9stheham Well-Known Member

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    A darned good question... the point I was trying to make to the OP was that you want to be well up on the torque curve of the cam when the TC stalls, not well up on the HP curve.

    For 'up on the torque curve', I go by mfr's RPM ranges; they are generally spec'd for the lower RPM end of the range where the torque is well 'up on the curve', and for a 'typical build'. And I then think of how the engine will vary from a 'typical build', and maybe modify their range ends.

    It would be educational to see if there are curves on cams and see where the lower end of the mfr's RPM range is on a 'typical engine' build torque curve..... but I suspect that data is hard to find. (I see a few for Comp cams but the torque graphs tend to start above the lower end or their RPM range...so that's no use.)
     
  14. jboyd2

    jboyd2 68 cuda

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    Thanks for the responses. This will be a street driven car that I'll play around in from time to time when someone pulls on side of me. It has x-heads and flat top pistons, but I'm not sure what brand pistons. C/R is 10:1
     
  15. jboyd2

    jboyd2 68 cuda

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    I'll be working on the tuning some more next week to ensure that is correct. I verified tdc was set correctly, but I have not checked to be sure the cam is properly degreed.
     
  16. nm9stheham

    nm9stheham Well-Known Member

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    OK so a fun street car, it sounds like. For me, I would go as low as I could on the TC stall, just to keep the thing from spinning a lot of unnecessary RPM's to be moving along.

    And the reason I ask about the CR is that a low CR is going to need some help for a crisp launch, but a higher CR is one where I would be willing to shade a step lower on the TC stall for a fun street use car; the higher CR will be 'up on the torque curve' better. Your real CR is likely in the low to mid 9 range, which is pretty decent for a street car. As CB said, that ought to be spinning those 'not too tall' tires with that cam and setup.

    As you have perceived, cam timing can have a dramatic effect. That Lunati cam comes with a 4 degree ground-in cam advance. So with things installed straight-up, the cam should be timed at 4 degrees advance.
     
  17. thesiren74

    thesiren74 Well-Known Member

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    I have a t.c.i. 3500 stall conv and from a dead stop 1st and 2nd are useless.
     
  18. jboyd2

    jboyd2 68 cuda

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    nm9stheham thanks. I'll see if I can get the tuning issues figured out, then see how the stock torque converter is performing.

    Thesirens that sounds awesome. It'll bring many smiles to my face once it's running correctly
     
  19. krazykuda

    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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    Now you're stalling.... LOL!
     
  20. nm9stheham

    nm9stheham Well-Known Member

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    OK; your cam would not be expected to be 'happy' with a stock converter. I have used a stock converter OK... but only with a torque cam with 15 degrees less duration.
     
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