What gears are everybody running with TH200-4R?

Discussion in 'Got gears?' started by Piston_Freddy, Sep 10, 2011.

  1. Piston_Freddy

    Piston_Freddy Well-Known Member

    I'm thinking TH350 to TH200-4R and open 2.73 to posi 3.something???

    I like the higway gears I have right now, but the car is slow as snail.I'd like lowest gears and still cruise at the higway.I have 295/50R15 tires at the back right now.
     
  2. Mark Demko

    Mark Demko Well-Known Member

    I'd say 3.42 to 3.73
     
  3. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    If you like the gears you have now, go with a 4.10. In OD, it will put you almost exactly where you are right now. A 3.73 will drop you down to about a2.50 in OD. I have a 4.10 in mine and I think it's perfect.
     
  4. techg8

    techg8 The BS GS

    I have run everything from 3.08 to 4.10 with a 200-4r

    I liked 3.73 best
     
  5. Sir Speedy

    Sir Speedy Well-Known Member

    I run a 3.73 with 275/60/15 tires. Works well but can not put the lock up convertor on until the engine will be above 2100 rpm due to the camshaft I'm running.
     
  6. knucklebusted

    knucklebusted Well-Known Member

    Of course tire size comes into play as well. If you are running short 225-60/14 tire, it makes a big difference over say 275-60/15.

    I'm running 275-60/15s on my turbo 200-4R with 3.73s. That makes it 2200 @ 70MPH. I like it there.

    You should pick your cruise speed and decide what RPM you desire. You can work backwards from there. Also, the lower first gear in the 200-4R makes whatever gear you pick much nicer from a dead stop. 3.73's act like 4.10s in first but feel like 2.50s on the open road!
     
  7. sailbrd

    sailbrd Well-Known Member

    I run 3:73 with a 28" tall tire with the 455. On the GN I think it is a 3:42 with a shorter tire.

    I can run lock up down to about 1500 rpm. My cam is 244/260 with .580 lift. Not real happy there but it will do it. Working on a rpm activated switch for the lockout, right now have it set up on a manual switch.
     
  8. knucklebusted

    knucklebusted Well-Known Member

    Yes, I would like that as well. I was thinking of trying to rig a circuit based on a very low RPM rev limiter. If below the rev limiter, no lockup, above the limiter, lockup.

    I also have the TCI vacuum switch but I had to set it so that it pretty much locks up in 4th about 2 seconds after the shift or it hunted in and out forever. I even tried a restricting disc to reduce the signal speed but that didn't seem to help at all. I've thought of a small canister to make it have to build up some vacuum before it would engage or even use ported vacuum over manifold vacuum. Maybe I'll start another thread.

    At any rate, at WOT, it will drop out of lockup and not go back in until I let off a bit but frankly I've not had the nerve to MPH it out in top gear since that might be somewhere north of 150!
     
  9. Piston_Freddy

    Piston_Freddy Well-Known Member

    Thanks for the input everyone! I think my current gears are 2.73??? I have a '71 Skylark Custom with a 350-4 auto.Those got the 2.73 gears, right? Those gears are OK at 60mph but at 70mhp they are little to slow, so I think 3.73 with TH200-4R would be best?

    This rear end is 8.5 ?
    [​IMG]

    Can I order posi and gear set without taking the rear end apart? What kind a posi and gear set would everybody recommend at Summit? I don't want to order any wrong parts.
     
  10. knucklebusted

    knucklebusted Well-Known Member

    What tire are you running. If you plan to leave it alone with shorter tires, I'd consider 3.42s. Taller tires will be fine with 3.73s.

    Your rear end looks like the stock '71 Buick 8.5 rear with bolt in axles. I don't know what your definition of "apart" is but you'll have to drain the grease, pull the axles, remove the differential, remove the pinion, setup and install new gears and posi differential. You don't necessarily have to remove the housing from the car or mess with the brakes but it can make life a little easier.

    I expect Jim (Monzaz) to give you some good info shortly. I got a rear end off of him and it works great with a TrueTrac and 3.73 gears. He can probably set you up with all the parts you need and he supports the community. Not sure about shipping to Estonia though.
     
  11. 73-462GS

    73-462GS GS Mike

    I am running a 3.73 rear with my 700R4 with a 27" tire. I think a lower ratio (numerically) would be better on the highway and if I did it again I would go 3.42. I have a manual switch on my lockup and lockit up at anything over 1500 RPM. Below that it bucks like sailbrds.
     
  12. speedtigger

    speedtigger 9 Second Club

    There are a couple things that you can consider when choosing a gear. The first is cruise RPM, the 2nd is maximizing your engines RPM range for performance. Cruise RPM is typically all about engine wear and fuel economy, while performance gearing can be evaluated by using quarter mile information if applicable.

    For an ideal cruise for fuel economy and minimizing engine wear on a stock cammed engine, I think you will find a cruise RPM of 1800 to 2200 RPM to be ideal. As you get above that, you sacrifice the above proportionately. Below it, the engine will likely not be as efficient. So for an 1800 RPM cruise with the torque converter locked up you would need a 3.08 gear with a 27" tall tire in overdrive. For a 2200 RPM Cruise you would need a 3.73 gear with a 27" tall tire in overdrive.

    For performance use, lets look at your maximum ideal RPM range at the end of the quarter mile. To do this correctly, we need to establish your engines max RPM range and the cars estimated MPH at the end of the quarter mile. If I assume correctly and your car has a stock camshaft and a stock or near stock engine. With these assumptions we will say your max realistic RPMs are 4800 and your quarter mile terminal speed will be about 90 to 92. So we will use 92 MPH to be safe. So, to achieve 92 MPH at 4800 RPM at the end of the quarter mile you end up getting a 3.9 gear ratio which will put you at 4700 RPM on a 27 inch tall tire and about 5% converter slip which is a good number for a stock torque converter.

    What we find is that your ideal performance gearing (3.90) is slightly higher than your ideal cruise gear ratios (3.08 to 3.73). If all of the above parameters are assumed correctly, you have to make a little decision on what takes president: Performance or optimum cruise.

    With the 3.73 gears your cruise RPM with the converter locked in overdrive on a 27" tall tire would be 2178 RPM at 70 MPH. Your terminal quarter mile RPM would be 4486 RPM at 92 MPH with a 27" tall tire using 5% converter slip.

    With the 3.90 gears your cruise RPM with the converter locked in overdrive on a 27" tall tire would be 2277 RPM at 70 MPH. Your terminal quarter mile RPM would be 4690 RPM at 92 MPH with a 27" tall tire using 5% converter slip.

    If you are more cruise minded you can certainly move toward 3.08 gears as long as you are cool with loosing a little acceleration performance.

    Here is the handy tool you can use to explore the numbers:
    http://www.hotrodpitstop.com/tools.html#7
     
  13. Piston_Freddy

    Piston_Freddy Well-Known Member

    Right now it has 295/50-15 at the back and 235/60-15 in front.Wount the RPM's be too low with 3.42's, if I later plan on putting a "cam" in it, with a higer stall speed?

    So it will have a 28 spline axles? Or I should pull one of the axles just to be sure?

    I might need to PM him then.

    TH200-4R has a little better overdrive ratio(yes I know, very little).What tires are you running?Stock cam?converter?

    Big thanks speedtigger! Great post! :beer

    I installed a tach, so I will try and see what my RPM's are at certan speed and then dicide.I want lowest gears but still drive on the higway.

    Later on I'm putting a "cam" in it and convertor with a higher stall.
     
  14. 70 gsconvt

    70 gsconvt Silver Level contributor

    Another 3.73 here with a 28" tall tire, 325/50R15. I love it.
     
  15. knucklebusted

    knucklebusted Well-Known Member

    As long as you are aiming for an improvement, I'd go with at least 3.73s. RPM will be good with the tires you have.

    Yes, is should be a 28 spline bolt in axle.
     
  16. monzaz

    monzaz Jim

    You say the car is slow as a snail. You might want to first make certain your engine is doing all it can to put out power and torque.

    Timing and carb tuning will play HUGE factor in this. You may ONLY be band aiding the real problem... I can tell you for freeway with a normal aspirated motor not over camed (too much duration usually over 230 duration at .050) you can run 3.42 and 3.73 just fine on a 2004R. If you have complete stock can do the 3.42 and if you have a step or two over stock run the 3.73 as the came wil lneed more RPM to run better in over drive . Hope that helps. Jim

    J D
     
  17. Piston_Freddy

    Piston_Freddy Well-Known Member

    Here's a 0-60 video: http://www.youtube.com/watch?v=tUNKB5ZBejU&NR=1

    I'd like the car go faster to 0-60 then 9sec.I already ordered Crane recurve kit for the HEI and rebuilt Q-jet from Tri Shield Pereformance.Other then HEI, the engine is stock.
    Yes, I'll fine tune the engine when I have the recurve kit and rebuilt carb installed.After the trans and gears, I'll start to soup up the engine.

    Any recommandations on the posi and gear set brand?
     
  18. Torsdalen

    Torsdalen Well-Known Member

    I use a 3:36 chevelle 1965 8,2" 10 bolt rear. Almost perfect ratio, i guess 3:55 or 3:73 would be perfect.
     
  19. knucklebusted

    knucklebusted Well-Known Member

    Yeah, gears will help a lot as will the lower gear in the turbo 200-4R. Looks like you were doing nearly 50MPH before it shifted into second!

    Do you know your speedo is correct? Have you verified it with a GPS to be sure?
     
  20. Torsdalen

    Torsdalen Well-Known Member

    Hi Freddy !
    This is my trans from BTO (Bowtoe Overdrives )
    See attached picture.
     

    Attached Files:

Share This Page