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what rear gear ratio?

Discussion in 'The Hokey Ass Message Board' started by paperdog, Mar 14, 2011.

  1. trying to figure gears?

    is there a web site for this or master formula?

    our goal...to run tens? at the strip (strictly strip use)

    some basic info?

    64 plymouth tudor(brick shape)
    wheel base -stock
    weight. 3400-3500
    cu.in 500= 440 stroked
    heads - perf.alumn.
    tire height -30.4 inches
    tire width ...10-12 (slicks)
    hp 500-600+
    trans - 727 auto

    what else do we need to factor in?
     
  2. MAX RPM. If your engine will only turn 3500 and you run a 4.56 gear you won't being go fast enough on the big end to be running tens. I'm using an extreme example for ya not talking directly about your engine setup.

    How fast do you want/need to be going on the big end?

    Its kind of a juggling act.
     
  3. Rebel 1
    Joined: Oct 25, 2010
    Posts: 568

    Rebel 1
    Member

    Have you had the motor on the dyno? That's a lot of weight to be moving around. You will need every bit of 600hp, if not more. Like PorknBeaner said - Need to know what RPM you are wanting to operate in.

    A 10 second pass is in the neighborhood of 135 mph. Moving a 3500 lb car in the 1/4 for a 10 second pass will take roughly 672hp. There are a lot of variables here and these are just rough estimates. Good luck.

    Here's a sight to help you out.
    http://www.hotrodpitstop.com/tools.html
     
    Last edited: Mar 14, 2011
  4. currently we are following a gudeline as of engines we have put together before ..
    avg 550-600hp
    max rpm ?
    peak hp /rpm?

    the last engine is in a 63 dodge with manual trans 4-11 gears ran 12:40 on street tire. thru the muffler and tailpipes..single 4 bbl 700cfm full interior

    the 64 plymouth will be dedicated minimal interor , mini tubs frame connectors wide slicks al set for drags =weight transfer



    we know a screaming rpm with to low a gear breaks parts pronto
    gosh anything over 6500-7500 and up seem high?
    but not out of the question

    we want this to live after use and not be scrambled after 3 runs
     
    Last edited: Mar 14, 2011

  5. here is the 63 dodge

    we will be setting up the 64 more nose up ad prolly not as good looking ..
     

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  6. 49ratfink
    Joined: Feb 8, 2004
    Posts: 18,828

    49ratfink
    Member
    from California

    somewhere on the interweb you will find a tire size/RPM/gear ratio calculator.

    that would get you somewhere in the ballpark.
     
  7. What has to be considered is what RPM can you pull through the lights with it. It is where you drop torque off that is important.

    Let me give you a real world example. The 350 in my old push truck was capable of spinning 7K and got winged to that RPM on a regular basis.

    I normally ran 13s in it but with the gear I had a quarter mile was not enough track to get it past 5K in high gear. My gear was too tall for a dedicated race car which it wasn't. The end of my torque curve was about 5,200 by about 5,800 the torque had dropped substantially. In the lower gears it didn't matter.

    If your torque curve drops off at say 5K then you have to gear accordingly, you may not want to run nose up if you are trying to get into the 10s. At speeds in excess of 100 MPH a car that is nose up is catching a lot of air and then aerodynamics take effect.

    The engine you are using should make enough torque to pull into the upper RPM range for the motor with a relatively tall gear it all depends on what has been done with the engine (no need to defend it, MOPARs are good dragster motors). But these are all things that need to be taken into account. Does any of that make sense?
     
  8. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    It is??? I must be a LOT better chassis man than I thought!
     
    Last edited: Mar 14, 2011
  9. AnimalAin
    Joined: Jul 20, 2002
    Posts: 3,416

    AnimalAin
    Member

    A thirty inch tire and 4.57 gear needs a little more than 6000 rpm to go 135 mph. I would think that pretty ambitious with the weight you are pulling, but it might be a starting point.
     
  10. thanks i have found some ratio conversion charts on line

    and of coarse there is only so many options for gears

    we need to study the rpm range potential a little more

    i guess we are trying to get a reasonable consistant running car simular to early 60's mopar stock class with out a hemi ...
    we have dicussed some ways to save more weight

    and we are close to being on the ground roller stage so some things will change but the rear gearing needs to be ordered soon so getting in the ball park without being way off..the narrowed slightly rear end will be ordered as a complete unit ..
     
  11. A lot of 10 second cars are running in the upper 120 to mid 130s. If you can get one to hook and get going as fast as you are going to go by mid track you can still run 10s at a much lower speed. I think there is a thin line between being over powered and under powered.

    I still like to run one with a good broad power band but that I think is because I drive my cars dailey and just race on occaision. Dedicated race cars can have a narrower powerband and get by.
     
  12. thanks p-beaner

    itsa brick shape for sure ..

    by nose up i know we can adjust the torsion bars
    the 63 just looks so good low in front
    the 64 can be set more level aiding weight transfer ..

    there is talk of pulling the front wheels with the wider slicks .hahahaha
    the engine is not together but the components list is almost exactly per the engine builders "set e.t range"
    $$$ how fast do ya wanna go guidelines !
     
  13. I have managed to make some silly underpowered looking combinations go pretty fast over the years. But I'm just lucky with that stuff.

    You'll get it tweeked just fine before you are done no doubt. if you set a goal of a certain speed or ET you can attain it. It may take some adjustments or changes beflore all is said and done. But determination along with $$$ is what it takes to make one go fast.
     
  14. SinisterCustom
    Joined: Feb 18, 2004
    Posts: 8,277

    SinisterCustom
    Member

    4.10's
    A freind has a '63 330 with a 440 making @ 500 hp and he's in low 11's with the 4.10's.
     
  15. thanks to all
     
  16. chop32
    Joined: Oct 13, 2002
    Posts: 1,077

    chop32
    Member

    That neighborhood is a fairly large one...My good friend took his throttle stopped 10.90 Camaro out without the stop and ran a dead hook 9.93 at 131. If your car doesnt hook well, you will need more trap speed (more H.P) to make up for it on the big end.
    Id lean towards gearing it for max rpm at a bit higher mph so the gear wont be a limiting factor if /when you find that sweet tune-up that nets a bit more power.
     
  17. customcreationsllc
    Joined: Mar 3, 2011
    Posts: 25

    customcreationsllc
    Member

    I just did the calc out real fast for you.
    @135mph with 30 inch tires.
    3.83=4500rpm
    4.11=4900rpm
    4.56=5500rpm
    5.13=6100rpm
     
  18. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Yea, thats a little more realistic. 135 Mph is well into the nines. If I was running 10s at 135 mph, I would figure the chassis was a total pos. I have gone 10.20s @ 130 on 9" wide dots with the car loose past the tree. Other combos, 10.90s @ 119 and change, and 10.70s @ 121, all on small dots, the last one on "outdated" slapper bars. 135 mph is good for a SOLID nine second time slip, unless maybe you are running on pie-crusts or something...
     
  19. Peter Mc Mahon
    Joined: Jan 1, 2009
    Posts: 199

    Peter Mc Mahon
    Member
    from Ontario

    I was always told you do 10.0 @ 135mph calculations. 10.0x135=1350. If you run 10.5 you should trap at [1350/10.5=128mph] If you run a 6.0 et you should trap at [1350/6.0=225mph] .......15sec. et. 1350/15=90mph . If you run say 10.5 at 140 mph [10.5x140=1470] you are not running efficiently. You are PROBABLY spinning a lot. Tune with gearing, traction, launch technique etc. until you are at 1350 [the magic number] and then make your car faster if you wish. I think if you run 9.0 at 135 you have too much gear, the car should have more top end.[150mph] Anyone else heard this? Peter
     

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