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Thread: What gears

  1. #1
    FEP Power Member tonysilver82's Avatar
    Join Date
    Dec 2011

    Default What gears

    Curious to what u guy think on rear gears between 3.73 or 4.10 car is a 5 spd dss 331 185cc trickflow heads cam is 533-544 nitrous cam will run between 100 to a 200 shot of nitrous on every once in a while mostly just motor passes in a eight of a mile

  2. #2


    What ratio low gear?

    Automatic or stick?

    most guys shoot for 12:1 FD in low gear with a 26x10 slick. One ratio Lower with 28's as the tire is taller.

    what is your rev range? The last thing you want to have to do is shift with the hoops in the air or run out of revs and nose dive the frontend or miss a gear and tear the car up.

    If you can rev to 7000 you can run one ratio lower than you can if you can only run 6500.

    I would use an RPM calculator to figure out RPM at the target final trap speed in the final target gear.

    Often 3rd in a 5 speed car in the 1/8th mile or 4th in 1/4.

    You need to be able to consistently launch very hard without putting the tires up in smoke. How fast your engine revs up and how much grunt is there at launch RPM make a huge difference. This can be fine tuned by removing or adding rotating mass at the flywheel, adjusting advance, using less or no spray out of the hole, etc.
    Last edited by erratic50; 02-28-2017 at 09:00 PM.

  3. #3


    Also the rate in which you engage the clutch makes a HUGE difference. In theory you can launch a car with almost any ratio that can spin break traction at the tire as long as you have the correct clutch application controlling wheel speed. If the clutch will take the heat that is.

    It's when you rev that 2.73:1 up and simply pop the clutch that it sits there and melts the tires.

    3.35:1 T5 usually likes a 3.55 or 3.73:1 or a 3.90:1 depending upon target trap speed, slick, etc.

    2.95:1 T5Z usually likes a 4.10. 28" tires often justify a 4.56 if you have the R's on the big end to carry it.
    Last edited by erratic50; 02-28-2017 at 09:08 PM.

  4. #4
    FEP Senior Member
    Join Date
    Jan 2011
    Vancouver BC Canada


    Is this a race car or street car? If its just a drag car, you want to gear it so you are at or a bit above your shift point or redline at the finish line.
    For example, both my 85 Mustang and 78 Fairmont use Jerico 4 speeds with 3.19 low gear. The Mustang has 29" tall slicks, and at 128 MPH in the 1/4 mile, with 4.88 gears is taching almost 7200 RPM in high gear. I shift it at 6800 RPM, and normally launch at 6000-6200 RPM.
    The engine is a flat top piston 331 with AFR 185 heads, and a solid flat tappet cam, a Victor intake and 650 Holley, it makes 485 HP at the flywheel.
    Last year I pulled the 9 second 427 FE out of my Fairmont, and installed the same 331 from the Mustang. The Fairmont has ladder bars and bigger slicks (12.2x 31.25" tall) Because of that, I dump the clutch a bit higher, normally 6600 RPM, still shift at 6800, and with 5.13 gears, it revs just over 7000 at the finish line.
    With the big block, I ran 4.56 gears, with 31" tall slicks, with the big block, I would dump the clutch at 6200 RPM, shift at 6200 as well, and go across at 6400 RPM, at 132 MPH. Earlier on, I ran 4.88 gears, the car was quicker everywhere, but with a mostly stock bottom end using 50+ year old cast crank and stock rods, I went to the 4.56s, as I just didn`t feel comfortable spinning all that heavy old stuff at 6800 RPM, the 4.56s dropped it down to 6300-6400 RPM. Since both engines are naturally aspirated, I don`t concern myself with power added gains, but if I did, I would gear it for using the boost or Nitrous, but obviously running "all motor" would not be ideal gearing wise.
    If its a street car, compromise dictates what your gearing tolerance will be. Minimal freeway driving would allow for steeper gearing than lots of high speed driving would allow.
    1978 Fairmont 2 door sedan, 428CJ 4speed. 9.972ET@132.54mph. 1.29 60 foot
    1985 Mustang LX hatchback NHRA Stock Eliminator 302 4 speed best in legal trim 12.31@107 mph, but has gone 11.42@115 with aftermarket intake, carb, and iron Windsor Jr. heads.New for 2012! 331 cube SB Ford, AFR 185 heads, solid flat tappet cam, pump gas; 10.296ET@128.71 mph, 1.37 60 foot.
    1979 Zephyr Z7, all original 302 auto, 2nd owner.

  5. #5


    You have to running some pretty impressive 60 foot times to get into the 9's in N/A form with that steep of a rear gear. Sounds like a blast.

  6. #6
    FEP Supporter cb84capri's Avatar
    Join Date
    Jan 2003
    lansing, mi


    4.10s all day long over 3.73s. Don't fear the gear!


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