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thinking about trying the 4.10 ratio

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  • #1

    thinking about trying the 4.10 ratio

    Contrary to some advice from others, I am going to try building my own 12 bolt rear. (Im stubborn like that). If it works, I can do it about 1000 - 1200 less than a moser. I bought bare housings - one 12 bolt, one 10 bolt f-body. I am going to do the measurements, cut and paste the bracketry, modify the length of the axles tubes, add an eaton posi, moser axles and c-clip eliminators, etc.... I'll let you guys know how it turns out.

    My question is..... Does anyone know how to figure out the rpm you would be turning through the traps with a certain gear ratio? I am going through at about 6500 on nitrous and I have about 300 - 400 more rpm to "play with". I was thinking of going with a 4.10 gear in the 12 bolt. Does anyone know how to figure out if it will work without having to shift into 5th gear before the traps?
    96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
    11.6 @ 123mph (1.6 60' - getting there )
    Tags: None
  • #2
    Well.... Fred may walk all over this, but ...

    The 4.10 is 9.92% difference from the 3.73 you now have.

    Sooo.... 6500 rpm x 1.0992 = 7145 rpm

    That's if all else is the same.

    Gordon

    Gordon Arnold - '00 WS6 T/A - Sold

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    • #3
      Thats kind of along the lines that I was thinking, but I didnt know if that would be right.
      96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
      11.6 @ 123mph (1.6 60' - getting there )

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      • #4
        How about trying a gear ratio calculator like this:

        http://www.f-body.org/gears/

        This one works pretty well I think.

        Brian

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        • #5
          According to that chart I can do 127 mph in 4th gear with 4.10's. Doesnt seem right.
          96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
          11.6 @ 123mph (1.6 60' - getting there )

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          • #6
            im going to try 4.10's and an eaton too (700r4)
            86 Camaro (350)
            79 Blazer (FI 350)
            98 Buick Riviera (S/C)
            96 Grand Prix (Sp. Ed.)

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            • #7
              Hey N20LT4Bird, how did you calculate 127 mph in 4th with 4.10s? I tried it with a 25.66 tire diameter, 4.10 rear end, and standard M6 gears and got it topping out at 106 in 4th (@ 5700 RPM). Unless, of course, your f-body can rev up to 7000 RPM??
              94 Black T/A GT, Advanced Induction 355, 3200 stall, built 4L60E, Moser 9", Baer Brakes, Shooting for 11s...

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              • #8
                I put in a 275 40 17 tire size and a 6800 RPM redline.
                96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
                11.6 @ 123mph (1.6 60' - getting there )

                Comment

                • #9
                  Considering you can hit that high of RPM, then why doesn't 127 in 4th seem right? A stock 3.42 geared f-body could hit the same mph in 4th, but of course, your redline is 1000+ higher than stock. Just my thoughts.
                  94 Black T/A GT, Advanced Induction 355, 3200 stall, built 4L60E, Moser 9", Baer Brakes, Shooting for 11s...

                  Comment

                  • #10
                    When I go through the traps in 4th gear, I am cranking around 6400 - 6500 rpm and I am doing just under 120 mph, thats with a 3.73 gear.
                    96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
                    11.6 @ 123mph (1.6 60' - getting there )

                    Comment

                    • #11
                      hmmm....well IMHO, it could be a slight speedo/tach error at high speeds (maybe off ever so slightly?).
                      I've double and triple checked the gear calculator...it is mathematically correct. I've even checked it agaist my car's readings and it's correct.
                      I'm stumped then...anybody have any ideas?

                      I forgot to add....don't forget that the trap is calculated from the average time of the last xx.xx feet, so when you cross the actual finish line, I'm sure you're past 120.
                      94 Black T/A GT, Advanced Induction 355, 3200 stall, built 4L60E, Moser 9", Baer Brakes, Shooting for 11s...

                      Comment

                      • #12
                        That chart says at 119 mph (my trap speed according to the slip of paper I get @ the track) my car is revving at 5800 rpm. I dont think my tach could be off by that much. Its a mystery!
                        96 WS6 Formula: Ram Air, 383 Stroker, Ported LT4 Heads and Manifold, 1.6 Crane Rollers, 58MM T.B., AS&M Headers, Borla Exhaust, Meziere Elec. H2O Pump, Canton Deep Sump Oil Pan, 100 HP OF TNT N2O!! , T56 Conversion w/ Pro 5.0 shifter, SPEC Stage 3 Clutch, Hotchkiss Subframe Conn., Lakewood Adj. Panhard Bar, Spohn Adj. LCA's, BMR Adj. T.A., Custom 12 bolt w/ 3:73's, Moser Axles, Eaton Posi, Moser Girdle
                        11.6 @ 123mph (1.6 60' - getting there )

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                        • #13
                          That is really strange. Maybe the N20 puts you in a time warp where the electronics stop functioning accurately lol. Kinda like the Bermuda Triangle. lol j/p... I don't know why else it would be doing that.
                          94 Black T/A GT, Advanced Induction 355, 3200 stall, built 4L60E, Moser 9", Baer Brakes, Shooting for 11s...

                          Comment

                          • #14
                            I'm not sure I agree with the entire principle..... If you are going with a power adder, You'll find that the torque will pull the car faster with a taller gear. Now if you are going to spin the motor to a higher rpm, then the 4:10s would be your best choice, unless you plan on running a much taller tire to compensate.

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                            • #15
                              I forgot to add....don't forget that the trap is calculated from the average time of the last xx.xx feet
                              Sorry Craig but that is incorrect!

                              When you break the first trap speed beam a timer starts, then when you break the second beam the timer calculates your exact speed when you cross the finish line. It calculates your speed based on this physics formula:

                              Speed = Distance / Time

                              There are either 66 ft or 132 ft trap distances to determine speed. So since the distance is already known, the only number the trap speed calculator needs is the time that has elapsed between the vehicle breaking the first beam then the last beam. This is not an average but a precise speed. An average of two speeds would be the sum of two measured trap speeds divided by 2. This would require 4 trap beams.

                              Hope this makes since.

                              And by the way N20LT4Bird, your 127 mph @ 6800 w/ 4.10's is correct. I am also fixing to put together my own 9" rearend. I already have the strange spool and aluminum center section. We might be able to help each other out on the do's and dont's

                              Here are some other valuable calculators:

                              http://murray.faithweb.com/formulas.htm

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