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Hot Rods 400 turbo vs 350 turbo

Discussion in 'The Hokey Ass Message Board' started by bangngears, Aug 11, 2025 at 8:30 AM.

  1. bangngears
    Joined: Aug 30, 2007
    Posts: 1,289

    bangngears
    Member
    from ofallon mo

    I got into a discussion with a friend of mine over power loss from a 400 vs 350 turbo. He says on a chassis dyno a 400 is 75 hp less than a 350. I say bs. What say all you transmission guys?
     
  2. BJR
    Joined: Mar 11, 2005
    Posts: 11,061

    BJR
    Member

    I always heard 15 HP.
     
  3. TA DAD
    Joined: Mar 2, 2014
    Posts: 1,565

    TA DAD
    Member
    from NC

    Plus the 400 is heavier by 15 to 20 pounds
     
    Dan Hay and Just Gary like this.
  4. For simplicity of operation it's hard to beat the TH400. Good for hauling, towing and overall durability. Good choice if you're not worried about a little extra weight. If you're concerned with lighter weight and maybe shaving a tenth or a few hundredths off your 1/4 mile times a prepped TH350 might be a better choice.
     
  5. bangngears
    Joined: Aug 30, 2007
    Posts: 1,289

    bangngears
    Member
    from ofallon mo

    i was looking for either when the 4oo popped up, so went with it. i have had a bone stock 400 in my 39 for over 20 years. not one problem. they are a tough transmission.
     
    jaracer likes this.
  6. Bird man
    Joined: Dec 28, 2009
    Posts: 1,010

    Bird man
    Member
    from Milwaukee

    Would love to see how a Borg Warner Auto or a Hydromatic compare!
     
  7. 19Eddy30
    Joined: Mar 27, 2011
    Posts: 3,454

    19Eddy30
    Member
    from VA

    These Older Pg 350's & occasionally 400
    Stock Bells are getting Brittle ,
    Not from average torque though ,
    IMG_3791.png
     
    Kerrynzl, Fitty Toomuch and TA DAD like this.
  8. krylon32
    Joined: Jan 29, 2006
    Posts: 10,479

    krylon32
    ALLIANCE MEMBER
    from Nebraska
    1. Central Nebraska H.A.M.B.

    Did several deuces in the 70's with 400's then switched to 350's because of availability. Currently doing a new 32 roadster with a 400 to closely duplicate one I built in 1978-9. For got how big they were. I remember they seemed to be bulletproof.?
     
    saltflats likes this.
  9. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,618

    theHIGHLANDER
    Member

    I don't think there's a tougher more reliable auto than the 400. Want more? 34 element sprag, bearings vs bushings, all of which may just be ¾-1 ton truck internals. It'll last forever in a car, for years in a racer. I sold mine with a Hipster transbrake and the stuff above, had about 300+ rounds of racing. He said he was gonna freshen it up. A cpl months later I'd seen him and he said he didn't have to do anything to it. My convertor was a 5,000 stall Continental. My car weighed 3545 with me n fuel so if they hold up like that...? Can you tell I like em;)
     
    427 sleeper likes this.
  10. lostone
    Joined: Oct 13, 2013
    Posts: 3,461

    lostone
    Member
    from kansas

    Turbo 400 is my favorite Trans too.

    To me well worth anything that it might add over a 350 to the car (15 lbs ? 10 more horse loss) I'm fine with that.

    ....
     
  11. Pulled a th475 out of a motorhome.
    A HD 400 with thick case and straight cut gears
    Got it in my future build pile.
     
    saltflats likes this.
  12. I’ve got a TH400 in my coupe and it’s a great transmission that outlive us all, but… it’s not a good combo with the other driveline components. That tall first gear plus my 3.08 ring and pinion makes it a dog, but a good road car. I have a fresh 700r4 but that would require moving the trans mount several inches forward.

    motor is a mildly warmed over 9:1 327

    I’d rather do a 3.73 rear and a gear vendors with the TH400 but I doubt I’ll ever be able to afford that.
     
  13. Th475 with Doug Nash OD
    Test fit, used a regular th400 that was already in my ride.
    IMG_2979.jpeg
     
    Last edited: Aug 11, 2025 at 7:48 PM
  14. I’ve had my eyes peeled for one of those for years. Must be kinda rare.
     
  15. I guess. It popped up on FB. Drove 4 hours to pick it up.
    It’s a simple set up. I’m using a 2 speed rear end switch and wiring. Let off the gas and pull up the switch. Bang. It’s in OD
     
    Last edited: Aug 11, 2025 at 8:24 PM
    Roothawg and Dan Hay like this.
  16. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 15,247

    Bandit Billy
    ALLIANCE MEMBER

    As a general rule of thumb, I avoid things that "poop" up. Normally they are shit.
     
  17. :):):)
    Well I bout pooped my draws when I found it

    saved me from doing a 4l80 swap
     
    Sharpone, 1952henry and X-cpe like this.
  18. gimpyshotrods
    Joined: May 20, 2009
    Posts: 24,410

    gimpyshotrods
    ALLIANCE MEMBER

    I will keep my eyes open.

    I seem to find them all of the time, in both the overdrive and underdrive versions (+20%/-20%)

    The design was eventually sold to US Gear, so look for those, too
     
    Sharpone likes this.
  19. Tow Truck Tom
    Joined: Jul 3, 2018
    Posts: 3,223

    Tow Truck Tom
    Member
    from Clayton DE

    HMMM not the dream I had, running freight in vans with a lead foot and a 'beat the clock' attitude. My favorite trans guy never heard of me 'til I saddled up on the 400TH
    @anthony myrick Nice set up have there. I'm sure you'll do right by each other.
    I just was just a demon trying to make a wad of money for cheap pay.
     
    Sharpone likes this.
  20. squirrel
    Joined: Sep 23, 2004
    Posts: 59,253

    squirrel
    Member

    The guys who say you lose some number of HP in a transmission...how do you figure? Seems to me it's a percentage. Because I know that when I have my engine idling, making no HP at all, and put the TH400 into gear and the car starts moving, I'm not losing 75 hp in the transmission.
     
  21. J_J_
    Joined: Feb 8, 2007
    Posts: 132

    J_J_
    Member

    like the chart though ya just bummed me out with the C6 numbers.. I was planning on building roughly 600 hp for the F100 and figured on loosing 20-30% in drive line which would make the 65 look good but now I really want solid numbers to base the build on.. Now I'm gonna overthink this for way longer than I should..
     
    Sharpone likes this.
  22. Beanscoot
    Joined: May 14, 2008
    Posts: 3,546

    Beanscoot
    Member

    It's funny to hear about a "Heavy Duty" version of a TH400... as if they aren't already heavy duty!
     
  23. J_J_
    Joined: Feb 8, 2007
    Posts: 132

    J_J_
    Member

    haven't done that yet but have definitely cracked a few 400's right at the 2nd gear clutch pack breaking the teeth out at the snap ring . last two broke clear through leaving a little window on top the case
     
    SS327 and Sharpone like this.
  24. X2!!
     
    Sharpone likes this.
  25. Hollywood-East
    Joined: Mar 13, 2008
    Posts: 2,103

    Hollywood-East
    Member

    I've heard 40hp. On the 400..
     

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