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Recommended torque converter for 400i TH400?

Discussion in '365 GT4 2+2/400/412' started by sebackman, May 31, 2019.

  1. sebackman

    sebackman Karting

    May 19, 2010
    62
    Dear all

    Can somebody here please elaborate on exactly what turbin/torque converter with higher stall speed (2200-2400 rpm) would fit the 400i TH400 auto box? Also, which one would be a good choice and why?

    Aftermarket converters seem to differ in size, bolt pattern and potentially other things. After reading up a little on TH400’s the converters seem to have different performace dependant on car (weight) and motor (hp and torque at different revs). I looked at Summit Racing and they offer a number of converters for the TH400.

    I have seen that member "raemin" mentioned in a different thread that it should be bigger than a 9” converter. Higher stall speed converters has also been mentioned as successful upgrades in other threads but I can’t find a link or reference to required specs.

    I have a 1980 Straman convertible with the additional sub-frame to stiffen the chassis and hence I don’t think the box has ever been serviced except for filter. The car has only covered 30k miles from new so that is probably fine but I plan to take down the sub frame and service the box with a higher rpm converter and a shift kit that many say is a real improvement.

    All input much appreciated

    Kind regards

    //Rob
     
  2. Newman

    Newman F1 World Champ
    Professional Ferrari Technician Owner Consultant

    Dec 26, 2001
    13,447
    Canada
    Full Name:
    Newman
  3. sebackman

    sebackman Karting

    May 19, 2010
    62
    Hi Newman,

    I did see that thread but there is no data or specs there.
     
  4. raemin

    raemin Formula Junior

    Jan 16, 2007
    385
    Lyon (FR)
    Full Name:
    R. Emin
    As we do not have transbreak, the actual "slipage" of the converter is approx 600 rpm lower than the claimed stall rpm.

    With a 1800 stall converter, the actual flash speed would be 1200, so 3600 rpm on the output shaft of the engine would mean 2400 rpm (3600-1200) after the converter. That's like having a 1rst gear that is 1/3 shorter. You need a bit more than that in order to compete against a manual gearbox, but that's more than acceptable. With a 2400 stall converter you end up with a 1/2 shorter ratio (3800 > 1600 rpm).

    Once the engine revs higher than peak torque, the torque is reduced so the slipage becomes less important. if the converter is too small, the slipage may remain even at high rpm wich is bad for top speed.

    So we are looking for maximum slipage at low rpm and minimal loss at high rpm.

    I have a switch pitch converter so can switch betwen low and high stall. I played with a protorque 1200/2400 converter and really liked it on 2400. After 180km/h, 2400 stall feels a bit loose, but I really like it otherwise. Imitially had a PAE 1000/4000 converter that did not even last 1000km. I've ordered a third converter (1800/3200), but not tested this one yet.

    One of our fellow club members had a 9inch converter fitted by Teddy'sPerformance in France (3000rpm stall). Works great but he does not like it.

    Lessons learned:
    1) the sweet spot is between 1800 and 2400, 10 inches.
    2) you'd better buy a strong converter ("furnaced" or whatever they call it)
    3) stall speed does not mean a lot, a good vendor will let you know the actual flash speed of his converter based on your engine specs, wich is important in order to figure out the torque multiplication factor.
    4) Jhon Kilgore told me one day that any converter would be better than the stock one...
     
    Ak Jim likes this.
  5. raemin

    raemin Formula Junior

    Jan 16, 2007
    385
    Lyon (FR)
    Full Name:
    R. Emin
    To fully amswer your questions:
    1) bolt pattern is a non issue as we have a flat flex plate, so you just have to drill new holes in order to accomodate the smaller pattern (eg: 9'' converter). I asked a machinist to do it in order to have them acurately centered. Took him 5minutes, did it for free.
    2) with more slipage the shifts do feel a bit soft, so you may go for a few modifications in the hydraulic plumbing of the gearbox, so as to make the gearbox shift a bit faster and harder. Not too hard as it damages the rear axle, but sufficiently to suit the prancing horse. On top of it this (reportedly) reduces the transition when there is friction in the gearbox, so saves the friction bands. That's what the shift kits are about. No real performance gain, but feels better.
     
  6. sebackman

    sebackman Karting

    May 19, 2010
    62
    Hi raemin,

    Thank you for all the information.

    A 2400rpm converter seem to be the solution.

    Is a "switch pitch converter" still available and would that be an advantage. If so, is it worth it compared to a good standard converter? What other changes is needed to run such converter?

    You mention that you friend does not like his 3000rpm converter even if it works just fine. Why?

    I have a shift kit so that will go in at the same time. What other upgrades would you recommend? Pump?

    There are still questions on the converter choice as when I check at Summit Racing with all the parameters you kindly provided. There are two bolt diameters available (what is the original bolt circle?) and several different brand/class options. Based upon your experience which one would you recommend for casual driving and occasional spirited driving?

    https://www.summitracing.com/int/search/department/transmission-drivetrain/section/transmissions/furnace-brazed/yes/diameter-in/10-000-in?N=4294949522%2B4294949521%2B4294949305%2B4294422599%2B4294910467%2B4294949301%2B4294949302&SortBy=Default&SortOrder=Ascending

    Kind regards
    //Rob
     
  7. Ak Jim

    Ak Jim F1 Rookie
    Rossa Subscribed Owner

    Dec 23, 2007
    4,790
    North Pole AK
    Is it possible to use a locking torque converter? You could run a higher stall for initial acceleration then have it lock up for steady state. Use a vacuum switch to lock and unlock.
     
  8. raemin

    raemin Formula Junior

    Jan 16, 2007
    385
    Lyon (FR)
    Full Name:
    R. Emin
    Locking torque converter were never reliable on the TH400. A switch pitch converter requires some modifications in the internal of the gearbox: the input shaft has an internal passage that allows for an additional flow of fluid that changes the pitch of the converter. A switch pitch converter is slightly less powerful than a fixed pitch on the same pitch but it is extremely versatile. That's the best upgrade I could find for my car. These are now hard to find, as the gearbox was only manufactured for 2 years in the 60s. Some conversion kits are available from time to time.

    The 3000 stall converter works nicely, but it is too slippery at high speed. So Ok if you want to perform the best quarter mile acceleration, and accept to sacrifice top speed. This particular car is fitted with a mild shift kit, with such slippage the gear shift feels "mushy" . I think this is really Francisco's main concern: the feeling is not appropriate.

    For the converter, something in the $500 price range is usually more than acceptable. No need to worry about the bold pattern, the original converter is huge, so chances are that you will have to drill holes in the flex-plate anyway.Will try to send you a pic of my flexplate.

    I you've got a bit more cash I would suggest to "rollerize" the gearbox, that's basically adding ball bearings, pressure bearings everywhere and getting rid of all the teflon bits that melt under high temperature. Using parts from the 4L80 is also a good idea as they made stronger parts for these later variants of the TH400 (the sprag for instance). That's an upgrade that I would consider as your car is hard to service and such gearbox are more reliable. I know some mods were made to my valve body, pumps etc... I was promised a bit of boost when shifting gears, and indeed there is a bit of additional punch for half a second or so. Not sure if there is any performance increase, but here again the feeling is nice. That's like having a better exhaust sounds: no significant performance gain, but nice to have. If you are really looking for performance "ultralight" gears and drums (not tested yet).

    In such purchasing process it is important to discuss with the seller and listen to his advices, if the seller only submits the product catalogue you'd better look somewhere else. Here are the specialists I've been dealing with.

    • Jim Weise (TriShield Performance) is the only one who could make a custom switch pitch converter for me. Not sure if he has the other parts for the variable pitch conversion. He is kind of old-fashioned, but knows his business.
    • ProTorque have been very helpfull, and at least provided me with a reliable converter. Not as much slippage as I wanted, but well made and strong. Plus they respond to emails enquiries, and give good advices.They have some nice fixed pitch converters, no more variable pitch though.
    • Jakes Performance was very helpful.That's when things go wrong that you can see the sort of commitment a seller is up to: he provided excellent service when my second converter blew-up in my brand new gearbox... On the plus side he also documents all the modifications made to the gearbox, and even explain how to do these on your own.
    • John Kilgore is by far the most knowledgeable person I've been discussing with. Back then I did not want to spend the additional 5k on the ultralight gears, but I kind regret it know. He was(is?) able to source switch pitch gearboxes and parts.
    • In Europe: Teddy's perfomance (Jacques Monier).
    I presume many other vendors are available on your side of the Atlantic, the point is to invest our money on someone who explains and documents what he does on our cars.
     
    Ak Jim likes this.
  9. sebackman

    sebackman Karting

    May 19, 2010
    62
    Hi raemin,

    Brilliant information. I do know a vey good transmission person up here in the Nordics that can do the gearbox. I will follow your suggestion to upgrade bearings, add a new pump and I already have the shift kit (B&M). I will probably ask them for a recommendation for a 2400rpm stall converter and see of they potentially do have some ideas about a switch pitch conversion.

    With the info from you and the fact that there is lot of info on the box in general (albeit not in the Ferrari application) I think that may be a job for next winter.

    Do you have the bolt patter of the flex plate in the Ferrari application available? If I can get a converter that has the correct pattern it will fit without drilling, which would be nice.

    Mine is a convertible so I need to figure out if I want to take the box out myself or get help with that. On the convertibles there is a big sub-frame that needs to be taken down before you can get to remove the rear axle, toque tube and the finally the gearbox. No sure about doing that on my own....

    Kind regards
    //Rob
     
  10. raemin

    raemin Formula Junior

    Jan 16, 2007
    385
    Lyon (FR)
    Full Name:
    R. Emin
    For a fixed pitch transmission, bear in mind the 2400 converter will feel a bit loose above 180km/h. This is probably acceptable for a cab, but if you do not want to sacrifice top end a 2200 would be a good compromise.

    As far as the swap is concerned, this is a "doable" job as long as you have the appropriate tools (which I do not have...). I did replace a Renault Alpine gearbox on my own a few years ago, each individual parts are easy to handle and align (lightweight), this was an horrendous job (6 days) but could be achieved in my "amateur" backyard. By contrast the Ferrari is a well designed car and removing the gearbox is a straight process (but no way to do it in your backyard). On my first gearbox swap my mechanic was late and I was expected to have diner with members of the club (i.e with the car...) 400 miles away from Lyon. I just did whatever he asked me to do to help him finish the job; the gearbox was installed in less than 5 hours. (I am not talking about the full swap, just re-installing the new gear box). So this can be considered as a simple job. This being said, compared to the alpine gearbox swap, parts are so much heavier that there is no way I could have done it on my own. Convenient car-lift, gearbox jack, etc. : without these tools it's quite difficult to work on the transmission. I presume this will be all the more true with the "Pavesi plumbing".

    Will try to take a picture of the flex-plate.
     
  11. raemin

    raemin Formula Junior

    Jan 16, 2007
    385
    Lyon (FR)
    Full Name:
    R. Emin
    Image Unavailable, Please Login
    Here is the flex plate drilled to accomodate for the new bolt patern.

    As you can see there is quite a bit of work pending on my engine..
    .
     

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