What Is The Best Manual Transmission for a 455 TH400 Conversion???

Discussion in 'U-shift em' started by haganlee, Jan 20, 2016.

  1. haganlee

    haganlee Well-Known Member

    What is the best manual transmission to for an auto to manual conversion?
    Currently have a 1970 Buick GS 350 that was converted to a 455 with TH400 with posi rear end with what I believe are 3.07 gears. Everything else is pretty much stock and good driver quality car. Currently when driving around 60-65mph I am running around 2400+rpms. My end goal is to update suspension, convert to a manual transmission, possibly brakes upgrades and some additional engine performance upgrades. Here are my questions:
    1. Would a Muncie 4 speed run lower highway rpms(65-70mph)?
    2. Would a 5 or 6 speed be a better option?(if so are there any used transmissions out there that would be good options)
    3. What would be the easiest and most cost effective conversion?

    Thanks for any help
     
  2. wkillgs

    wkillgs Gold Level Contributor

    If you want to reduce highway rpm, you either need to change the gears in your rear to a numerically lower set (2.78, 2.56), get a trans with an overdrive, or install an auxiliary overdrive unit like a Gear Vendors.

    A Muncie M21 or M22 close ratio would not work well with the 3.07 rear, you should use a 3.42 -up so you don't have to slip the clutch a lot to get the car moving.
    A Muncie M20 wide ratio would be better with the 3.07 gears. Still no overdrive tho.

    Taller rear tires would reduce your highway rpm a little.
     
  3. 69GS400s

    69GS400s ...my own amusement ride!

    Final drive ratio of th350/400= 1:1

    Final drive ratio of (stock) Muncie m20/m21/m22 = 1:1
     
  4. flynbuick

    flynbuick Guest


    We have calculated the cost to correctly convert to a manual transmission to be in excess of $3000.00. To go to a 6 speed TR 6060 will be 4-5k.

    I would stay with an automatic. Turning 2400 rpms on the road is nothing.
     
  5. bigjimmyl

    bigjimmyl Well-Known Member

    a 200r4 swap from a thm350 cost me 2500.00 ish. rpm at 80 mph 3500 with a 364.
    just sayin
     
  6. sriley531

    sriley531 M.M.O.G.

    If you want to add a man pedal, the easiest/most cost effective route is the Muncie. Autogear has so many custom gearsets now, you can actually get one with a .87 4th gear if you really wanted. With a 3.07 though, I don't know why you'd need to go lower than a 1:1. With alot of 5 and 6 speed swaps, you're going to need to perform some trans tunnel surgery to make them fit, so be prepared for some fab work if you really want to go that route. All things the same, if you wanna row gears, throw in a Muncie. I tach around 2850rpm at 65 with a 255 tire and 3.42 gears with mine. You should be golden with a 3.07.
     
  7. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    2,500rpm? I had 4.56 gears on a 27" tire turning 3,200'ish rpm at 80mph.

    A standard 4-speed would be the cheapest. I wouldn't go any lower than 3.23 gears and 3.42 is pretty ideal for street and some highway. Cruising at 3,000-3,500rpm doesn't bother me at all other than the fuel usage.

    If you want a manual transmission with an overdrive either a TKO-600 or T-56. Both require a fair amount of trans tunnel modifications. There is another OD manual transmission on the market that claimed no trans tunnel modifications and would take the torque, but they seem hard to come by and the parent company had some financial issues.
     
  8. STAGE III

    STAGE III Lost Experimental Block. Platinum Member.

    Great topic going to watch this one. Mine has a Muncie and BBB in it but all I know so far:3gears:
     
  9. crash

    crash Well-Known Member

    You could use a 2.88 first gear ST-10, would work good with the 3.07 rear gear, use a 904 iron main case, use your th 400 drive shaft...

    Hope this helps... Crash
     
  10. haganlee

    haganlee Well-Known Member

    Ok I guess since I am new to the Buick I didn't realize running high rpms on highway with a 455 is no big deal. Not like I am going to be driving a ton of highway anyway. I believe I agree with sriley that when it boils down to it I really want the man pedal and to row through gears!
    So, it sounds like if I went with a Muncie M20 I would need to change the gears as the 3.07 would be difficult to start off in first gear? Is that correct? What would be my best options for locating the tranny(new or used)? I have found A conversion kit on eBay with man pedals and all hardware. Will still need bell housing and clutch. Will I need a new driveshaft and a new steering column(currently have a column shift with tilt)? Would like to keep my column and just remove the shifter if possible since it has tilt.
    thanks again for everyone's input!
     
  11. STAGE III

    STAGE III Lost Experimental Block. Platinum Member.

    i think you need a new crossmember and rear end braces to Lee
     
  12. afracer

    afracer Well-Known Member

    I'm eventually converting my 71 Skylark to a manual trans. Was going to go T56, but think I'll go TKO 600 instead as its supposed to fit much better and uses most of the same parts as the 4 speed. I hate not having overdrive. My Sport Wagon has a 200-4r and with 3.42 gears it is awesome to drive, especially on the freeway. Snagged about 2-3 more mpg's and increased engine life considerably by dropping the revs so much.
     
  13. 1972 Stage 1

    1972 Stage 1 Well-Known Member

    If you end up going with a Muncie 4 speed, I'm only 20-30 minutes from Prosper and have a rebuilt M-20 trans, used bell housing, and a used flywheel. I possibly have a few other small items like a set of pedals, clutch fork, and shifter linkages. I can deliver to save you shipping charges. Send me a PM if interested.
     
  14. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    High rpm is a relative term. What some call high, other's may not, etc.

    I ran 3.08 gears with a 26" tall tire for a few months and to works just fine with the caviate that depending on your compression ratio, you may have some pinging concern. An 8.5:1 engine may never have an issue and feeling that broad torque curve in each gear is a pretty good feeling. On a 9.5:1 engine, on hot day's you may have an issue. Starting from a stop I just slipped the clutch more on hot days to get me by.
     
  15. 87GN_70GS

    87GN_70GS Well-Known Member

    Legend LGT-700 5 speed. No tunnel mods, no noisy gear whine, 700 ft-lb torque rating. But is expensive
     
  16. STAGE III

    STAGE III Lost Experimental Block. Platinum Member.

    How much?
     
  17. 87GN_70GS

    87GN_70GS Well-Known Member

    I think its around $3000
     
  18. STAGE III

    STAGE III Lost Experimental Block. Platinum Member.

    thre thre threeeeeeeee thouuuuuuuuusand:shock::dollar::dollar::dollar::dollar::dollar::eek2:

    I am thinking this Muncie is jussssssssssssst fine till i win the lottery but thanks for the info, sounds like a tremendously nice trans that could stand up to our BBB's
     
  19. sailbrd

    sailbrd Well-Known Member

    I have a 200r4 with a 3:73, 3500 rpm would get me arrested.
     
  20. stickshift

    stickshift Silver Level contributor

    With 3.07 gears, my opinion of the best stick tranny is the Doug Nash / Richmond 5 speed. 1st gear is so low you will never need to slip the clutch, and 5th is 1:1. It sounds like an M22 with an extra gear. I love mine, and would never go back to a 4 speed.
     

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