WOWEEEEEE, 3.90's are nasty

Discussion in 'Got gears?' started by Beamer, Oct 24, 2004.

  1. Beamer

    Beamer Suncoupes Rule !!!

    OMG !!!

    I put my 3.90 posi in this morning. The motor I have (with a TA413 cam) really likes it vs. the 2.56 that I had. It sure is fun to drive this way, but I am thinking I will still try to find me a 3.42 setup for my origonal rear end. Maybe I will keep this rear in the garage when I want to do some 1/8th mile runs.


    Took my neighbor out a little while ago I turned left on the main road and slowly got on it. When she hit second gear, I was not straightened out from turning, and she started to get sideways. Needless to say, he was laughing like a little boy. I can't wait to get my exhaust done up to comfortably run the RPM's up.

  2. BuickLeSabre1960

    BuickLeSabre1960 Hot Dogs Anyone?

    How much of a difference did it make? My brothers '66 Catalina has a 2.56 in it and he's wanting to change it out. What do you think it'll do to your gas mileage?
  3. Beamer

    Beamer Suncoupes Rule !!!

    World of difference it made. It is so responsive and will snap your neck back tremendously. I think it is too much gearing for me right now at least, but am living with it for the fun right now.

    As far as gas mileage, I know I am sucking down considerable more with these gears, but the fun is weighing in as worth it.

    What does he have for a motor? If it is torqy, then go for some 3.08's and he will like the difference, withouot hurting his mileage much at all. If it is a small block and he is looking for some snappy take-offs and not worried too much about mileage, then for for 3.73 to 4.11 gears. They really make a difference.


  4. BuickLeSabre1960

    BuickLeSabre1960 Hot Dogs Anyone?

    it's a 389 big block. we were thinking about either a 3.08 or a 3.3? in it
  5. Beamer

    Beamer Suncoupes Rule !!!

    3.08's or 3.23's would be an exciting difference for him, I am sure. Let me know what you end up doing and how much he likes it. Sounds interesting for sure.


  6. BuickLeSabre1960

    BuickLeSabre1960 Hot Dogs Anyone?

    I'll be sure to :TU:
  7. GStage1

    GStage1 Always looking for parts!

    For a full size car use 3.42-3.73

    Scott, if you want 3.42 gears, hit some local u-pull-it yards. Almost
    all Suburbans/Blazers came with them. Sometimes you will find 3.73-4.11.

    For the posi, you can get one from full size GM wagons from 80-87.

    The 3.73 you have now is great for city use, you will not like them on the hwy unless you install an OD trans.
  8. 70 gsconvt

    70 gsconvt Silver Level contributor

    I'm running 3.73's in my car now, and it's getting annoying on the highway as I'm buzzing along at almost 3300 rpm's at 70 mph. This is with a TH400 and 28" tall tires out back.

    I actually have a 2.73 rear I was going to put in my car. New everything and even a girdle. But now I'm looking into getting a Gear Vendor's overdrive unit like was said above. It should drop my rpm's down by about 750 or so at 70 mph. Good luck with yours.

  9. 71GS455

    71GS455 Best Package Wins!


    It sounds like you're having some fun with those new gears!

    You should look into the taller tires to tame the rear a bit.

    Of course the biggest detriment to gas mileage with the jump from 2.56's to 3.9's is directly connected to the relationship between your smile and your right foot. The more you push down, the bigger the smile gets. This, of course, is in reverse proportion to your gas mileage which will get smaller.
  10. Beamer

    Beamer Suncoupes Rule !!!

    Steve, YOU SAID IT RIGHT !!!

    It is definately awesome. The one thing I have going for me is that I do not buy that much gas anyways. Just for my Toyota truck to pull my boat and for the boat which is a 90HP Yamaha. My family vehicle is a Dodge Caravan that work supplies me and pays for gas, even for personal use. So I am not even bothered by the gas deal yet at all. But it sure is fun.

    I may look into getting a set of tires widened, and going with some monster 70 series tires to get the ratio down some to do just that. My question is how they will do for traction, with the sidewall being taller? If I air them down some when necessary, will they hook up good?

    Thanks, Mike

  11. 70 gsconvt

    70 gsconvt Silver Level contributor

    If you have a th400 and a 26" tire, you'd be going through the traps at almost 5100 rpm's. With a 28" tire, rpm's will be around 4700, and finally with a 30" tire, you'll go through at just under 4400 rpm's. I ran this through on my DeskTop Dyno.

    BFG did make a 295/65R15 drag radial. It was a TALL tire at just over 30", and it is wide also, about 11.5". But I have never known anyone to put it in our stock fenderwell.
  12. Beamer

    Beamer Suncoupes Rule !!!


    I take it you are quoting RPMs for an 1/8th mile track, correct?

    I was thinking I would do pretty good in an 1/8th, but I am a firm believer that the 1/4 is the true run. It sucks that 1/4 mile tracks are dying away due to liabilities and such. I guess it takes a lot more track these days for stopping and people do not want to use the real estate for it.


  13. 70 gsconvt

    70 gsconvt Silver Level contributor

    Yes, those numbers were for 1/8 mile. 1/4 mile numbers are:

    26" 5121 6300
    28" 4745 5862
    30" 4439 5444

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