Th400 2 speed or 3 speed

Discussion in 'PSI Superchargers Tech Questions' started by Hk_radial, Sep 12, 2020.

  1. Hk_radial

    Hk_radial New Member

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    Im working on my new car/project ... 2004 mustang small tire pro 275 with brad8 c rotor

    Still no Transmission ... some said 2 speed others say 3 speed ... any advice please ... and what is the best brand/builder TH400 or TG400 transmission can handle this power to push a 3100lb car into the 3 second club ...

    Thanks
     
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  2. f3r-camaro

    f3r-camaro Member

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    We ran a 2 speed Lockup 400 with 1.48 first and was very reliable. Tried a 1.51-1.25 3 speed and didn’t pick up any.

    But starting a new build i would consider a 4 or 5 speed Liberty. We switched to 5 speed and it’s definitely faster
     
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  3. Mike Canter

    Mike Canter Top Dragster
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    Here is something to think about. The more gears in the transmission allows you to keep the engine up higher during the run and this means more boost during the run. A two speed is just too much rpm drop on the shift so you lose rpm and therefore lose boost and the engine has to try and recover.
     
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    lucky devil and Zuhair like this.
  4. Ron C

    Ron C Jr. Dragster

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    Do you run mostly 1/8 in that class....
     
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  5. Hk_radial

    Hk_radial New Member

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    Thanks great idea for liberty
     
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  6. Hk_radial

    Hk_radial New Member

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    Thanks mike
     
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  7. Hk_radial

    Hk_radial New Member

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    Yes we run 1/8 only
     
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  8. Ron C

    Ron C Jr. Dragster

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    My son and I help run two big tire Street Outlaw cars. 1/8 mile. Both cars run 14-71 HH Blowers. One has always run a two speed and the other did run a lenco 3 speed. The 3 speed was killing us on the rpm drop and boost drop and not enough strip left to recover. We went to a 2 speed and times and speed picked up. So...pick your poison.
     
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  9. Mike Canter

    Mike Canter Top Dragster
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    That is why you want more gears with closer ratios to keep the rpms up and that is why so many Promods have switched to multi gear Liberty transmissions.
     
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  10. Ron C

    Ron C Jr. Dragster

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    I agree with what your saying. But sometimes ya gotta deal with what ya got....unfortunately .
     
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  11. Mike Canter

    Mike Canter Top Dragster
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    I agree, Liberty transmissions are not cheap and it is a lot of work and money keeping the dog clutches in shape.
     
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  12. Ron C

    Ron C Jr. Dragster

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    We gave up trying to find the right Lenco gears. How many gears ProMods going to?
     
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  13. jay70cuda

    jay70cuda Well-Known Member

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    I think some of this depends on your hp. I know a legal 3 speed car in Orlando this spring went 3.62 in the 1/8. Mineshaft conditions but ok. That same car has been 3.71@200 legal trim 2800ft air. But I see some pdra cars that aren't latest and greatest engine program run the 5 speed lockup and go 3.68@202. To me if your engine is making real power and not well it should make 3000hp.... then to me a Lenco is fine. I had 4.56 gear with 1.78 3 speed went 3.78@197 2600lbs. My poor attempt at real 1/8 setup with 5.0 gear and 1.60 trans has only been 3.88@194.
     
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  14. Mike Canter

    Mike Canter Top Dragster
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    3.78 is ok but not fast enough these days if you want to win. That’s why the Liberty transmissions are used to get every 100th of a second. The Liberty transmission is what works in NHRA Promod.
     
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  15. sammy christian

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    uh, yeah, NHRA PM still has most contenders running TH400 or like Mike J., a Quick-drive/BJ.
    When the 3sp Liberty let some down, it was not worth the trouble.
     
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  16. jay70cuda

    jay70cuda Well-Known Member

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    But do turbo 400s last in a blower car? My quickdrive and Lenco are bullet proof but the weight is too much.
     
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  17. TOL

    TOL Active Member

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    Curious, was the 1.78 too much of a problem or just about right in your opinion for yours?

    Mine, I have targeted 1.76/1.25/1.00, with a 4.57 gear and 34.5 or 36.0" tire going in.

    Don't know where I will go after that? Heavy, C-screw at 1.92:1. 509 cubes and 4.00 stroke. Big RPM.

    Wish I could lose some weight from the program. Hmmm, maybe the driver could shed a few pounds :)....
     
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  18. jay70cuda

    jay70cuda Well-Known Member

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    No it wasn't a problem at all. I seen all these 1/8 mile cars flying and was told mine would do the same if it was geared for the 1/8. Well it didn't. My 1/4 setup was easy on everything and would go down any track really. I'll be back to a 4.56 setup next year. I've already made my mind up.
     
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  19. TOL

    TOL Active Member

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    Thanks Jay!.........
     
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  20. sean70ss

    sean70ss Member

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    Liberty is nice but the damage and carnage it causes for one mishap is expensive. Especially with the ring and pinion and if you are not spot on 10k can down the poop quick. Your limited ratio wise and changeability with the turbo 400. Many have been real fast as well. A few cars have been in the .40's and low 50's with a lenco 2 speed. I would be interested to see how a 2 speed works with a lock-up. A 4-5 speed would be doable as well. I would do some experimenting with the rear gear and my ratios.
     
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