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Thread: th400 or 350

  1. #1
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    th400 or 350

    Hi guys
    my 82 shortbox is currently stripped for some winter work but as ever i need some advice.
    Last year i had the 700r4 and the 350 and it all worked fine but ive now got a fresh built 350 and a th400 but believe the 400 will give me clearance issues.

    ive got the cab off at the moment and id also like to have a five link made.

    i have trouble getting parts over here due to cost so we need to fabricate as much as possible.

    any advice please.

  2. #2
    ghetto star Tukin15sLike20s's Avatar
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    a th400 will be stronger than you will ever need. I would stick with the 700r4 for the overdrive. Just srat putting the tranny in and hammer and massage the metal as needed till it fits
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    i like your thinking and its not for highway or as we call it motorway driving. will i have to cut the floor out or just massage it as you suggest.

  4. #4
    ls1+t56+01=love low86blazer's Avatar
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    th400 uses more hp to run.
    just make your own x member
    Your gonna need to cut the ears off the tranny for exhaust to clear it

    the only massageing I had to do was spot weld seam on the fire wall. and i didnt really have to do that

    as said before its one of gms strongest transmissions
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  5. #5
    will work for food! phatfarmer2's Avatar
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    so how bad is the th400 on the highway? i really wanna put it in my truck rather then my 700r4, becuase its bullet proof...
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  6. #6
    ls1+t56+01=love low86blazer's Avatar
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    whats your rear gears? and your overal tire diameter?

    with that i can find speed and what rpm youll be at.
    Quote Originally Posted by bayhustle81 View Post
    can i add the vortec to this 4.3 if it didnt come with one?
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  7. #7
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    ive got a 308 rear end and about 18 inch diameter tire.

  8. #8
    ls1+t56+01=love low86blazer's Avatar
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    Im having trouble beleiveing your running an overall diameter of 18" thats about 145/30/15.

    To get the most acurate give me the tire width in MM aspect ratio, and rim diameter. Then i can figure out your over diameter, and then get your speed and rpm's.

    But for shits and giggles with a 145/30/15 18" overall, 3.08 rear gear and in 3rd gear :

    at 65 mph its 4000rpm
    Quote Originally Posted by bayhustle81 View Post
    can i add the vortec to this 4.3 if it didnt come with one?
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  9. #9
    ls1+t56+01=love low86blazer's Avatar
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    Im runnning 3.73 with a 27inch diameter tire in 3rd gear:

    i reach 65 mph at about 3000rpm


    lol i think its time for a gear venders over drive!

    if anyone wants the whole rpm range to mph i can list it as well.
    Quote Originally Posted by bayhustle81 View Post
    can i add the vortec to this 4.3 if it didnt come with one?
    Quote Originally Posted by Superbee View Post

  10. #10
    It's all about to change winditup57's Avatar
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    In mine..with 3.42 gears, 26"tall tire, I was running about 3-3100 rmps at 65-70mph. I have a TH400...no trans tunnel mods other than the body lip, which I do on every car I put a motor in. I had to move the crossmember back a good 8 inches..but that was no big deal.
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  11. #11
    Registered User 91350s10blazer's Avatar
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    I have a TH350 with a 3.73 rear end and 235/60/16 tires. The TH400 takes alot more HP to turn than the TH350. The TH350 will be fine unless you're packing major HP and then the stock rearend won't last. I turn about 3500 at 70mph.

  12. #12
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    sorry guys i might have screwed up on the tire size , i think its a 235 60 15

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    Originally posted by uk85blazer
    sorry guys i might have screwed up on the tire size , i think its a 235 60 15
    @ 65MPH revs = 2380Rpm
    damn i wish i had a 3.08 gear...... no wait; no i dont;)

  14. #14
    Senior Member bigjsp's Avatar
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    I love T400 for racing and towing

    For practical street usage a 700R4 4l60E is much better, If you are making enough power to hurt them, it really isn't a streetable daily driver.


    but in terms of gear ratios and comparison a T400 with 2.87s = a 700R4 in OD with 4.10s 4.1 X0.7 well almost because the T400 will stil have convertor slip.

    T 400 first gear is 2.48 but a 700 R4 has a 3.25 ............................. so a huge advantage to the 700R4


    you will need to add another tranny cooler as modern radaitors / tranny coolers are expecting to be in lock up and generating less heat.



    T400 is supposed to eat 15 horse compared to a T350 or 700R4.

    but with a average rebuild T400s are good to 800 HP with slicks

  15. #15
    It's all about to change winditup57's Avatar
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    I think I will sacrifice 15 hp to have peace of mind.
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