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Thread: 4.10 vs 4.88

  1. #1
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    Default 4.10 vs 4.88

    In the rear, anyone sporting a 4.88 set on a second gen? Just wondering how the difference was/felt before looking at one

  2. #2
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    Jun 2006
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    Default

    A big gear is a necessity on these cars. Most guys run a 4.88 or a 5.12...there might be a few 4.30s too. I guess it really depends on the tracks you plan to race on, but the lack of torque these motors produce means we gotta rev the snot out of 'em and put in a big gear.

  3. #3
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    Buffalo, New York
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    Default

    or a smaller tire?

  4. #4
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    Used gears are very hard to find. 5.12 is the best all around gear but 4.88 is next in line. They never made any gears except a 3.9, 4.1, and 3.39 that bolt into these cars. All the other ratios must be custom made for them. I have the 4.88 and 5.12 in stock ready to bolt in or can do the modification to the various gear sets that fit. Just giving you some options, not pushing my products.
    Steve Eckerich
    ITS 18 Speedsource RX7
    ITR RX8 (under construction)

  5. #5
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    Sep 2008
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    Weare, NH
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    Default

    .

    I don't know anyone that is running other than 488's or 512's

    We did the calculations and found that one could be better
    than another at one track, and visa versa at another, based
    only on how many shifts you need to make...

    for example, at NJMP Lightning we are on the shift light in 4th
    (8300rpm) near start/finish on 488's with 45 tires, we then
    keep accelerating on the light to the braking zone. If we
    were on 512's with 45's we would need to go to 5th gear.

    On the other hand, we could go to 512's with 50 series tires
    and end up with almost the same ratio.....and since it is easier
    to change tires than diffs, 512's seem like a better choice...

    circumference / diff ratio = inches of travel per revolution of the driveshaft

    ((225*0.45*2/25.4) + 15)*3.14 = 72.1 / 4.88 = 14.78

    ((225*0.50*2/25.4) + 15)*3.14 = 74.9 / 5.12 = 14.63

    But at Pocono, we all need 5th gear, so in that case you
    might be able to tweak the performance with 488's to be better
    with different tire choices.....

    and then again....but in the case of....and conversely...

    Bottom line: the 488s were cheaper so we have them in both cars

    .

    Glenn Lawton
    GSMmotorsports
    #14 ITS RX7
    NARRC ITS Champion 2012
    NERRC ITS Champion 2013 12 11 10 09 08
    NERRC STU Champion 2010

    __________________

  6. #6
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    .

    of course, my calculations make the following simplifying assumptions:

    1. That the increase circumference due to increase in tire
    pressure during a race is exactly offset by the decrease in
    circumference due to tire wear

    2. That we discount the both the effect of decreased circumference
    at higher altitudes due to the reduced effect of the pressure
    differential of inside/outside tires, and the effect of increased
    circumference due to the change in gravitational force on the
    tire casing based on the distance to the center of mass of the earth...

    3. That we ignore any relatavistic foreshortening of the tire
    as the speed of the RX7 approaches the speed of light....

    oh wait...I think I hear my adopted cousin...

    Quote Originally Posted by JLawton View Post
    Shut up and drive!
    .

    Glenn Lawton
    GSMmotorsports
    #14 ITS RX7
    NARRC ITS Champion 2012
    NERRC ITS Champion 2013 12 11 10 09 08
    NERRC STU Champion 2010

    __________________

  7. #7
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    West Milford, NJ, USA
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    Default

    Quote Originally Posted by seckerich View Post
    Used gears are very hard to find. 5.12 is the best all around gear but 4.88 is next in line. They never made any gears except a 3.9, 4.1, and 3.39 that bolt into these cars. All the other ratios must be custom made for them. I have the 4.88 and 5.12 in stock ready to bolt in or can do the modification to the various gear sets that fit. Just giving you some options, not pushing my products.
    Steve,
    PM sent (a while back) - Do you still have a spare/used 5.12 w| Torsen available?
    Dave Youngren
    NER ITA RX7 #71

  8. #8
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    Dec 2006
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    Dallas, TX
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    Quote Originally Posted by seckerich View Post
    They never made any gears except a 3.9, 4.1, and 3.39 that bolt into these cars.
    Is that 3.39 supposed to say 4.30? The GTU's had a 4.30 from my understanding.
    Mark B. - Dallas, TX
    #76 RX-7 2nd Gen
    SCCA EP
    Former ITS, ITE, NASA PT

  9. #9
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    Correct Mark, it is 4.37 I believe. Have to count teeth I guess. I sold the last used 5.12 I had at Barber so all I have are new. Mazda is now over $700 for the 5.12 before we do the modification. They are expensive but it should last forever if you just change the fluid after every other race.
    Steve Eckerich
    ITS 18 Speedsource RX7
    ITR RX8 (under construction)

  10. #10
    Join Date
    Jan 2008
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    Default

    steve & i have built gears for a given track , and thats works well at those tracks . but the best overall gears are the 4.88s or 5.12s. we like the 5.12s. racingralph its 86

  11. #11
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    anchorage alaska...aka hoth
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    We are running 225/45/15's, with a 4.10 rearend now, and i will look at the 4.88's. Our track is usually an old runway(flat), with a fairly long straight. The top of 4th was held for about 2-3 seconds there. I saw an old thread with 4.88 vendors. Any suggestions on who to use?

  12. #12
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    Jan 2008
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    with the stock 4.10 or 3.9 , you will use 2nd , 3th ,& 4th rarely or never 5th.with the 4.8 or 5.12 you will use 3th , 4th , & 5th and you will get off the corners quicker. these cars/engines don't have any torque , so you have to go with RPMs . i now have a spare 5.12 so i need to will my "old" spare 4.8(ltd) in a housing with axle stubs , ready to put in a 2nd gen rx-7 . racingralph

  13. #13
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    Jan 2008
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    messed up, will sell 4.8 . sorry, racingralph

  14. #14
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    Halifax, NS, Canada
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    I've been looking for a 4.88 or 5.12 for a while.

    What's the going rate for a good used one these days? (I doubt new is in my budget)

    Racingralph: What's your location?

  15. #15
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    This might be of some help. info on where to get gears from other cars for the mazdas http://www.turbomagazine.com/tech/08...ech/index.html
    Steve Elicati
    ITA 1994 Mazda Miata
    Central Florida Region

  16. #16
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    Right diameter, wrong length. All these gears have to be lengthened to fit the 86-91 RX7.
    Steve Eckerich
    ITS 18 Speedsource RX7
    ITR RX8 (under construction)

  17. #17
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    Jan 2005
    Location
    Alachua, Florida
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    Default

    Quote Originally Posted by seckerich View Post
    Right diameter, wrong length. All these gears have to be lengthened to fit the 86-91 RX7.
    Damn and i thought i found a cheap source for gears for the miata as well.
    Steve Elicati
    ITA 1994 Mazda Miata
    Central Florida Region

  18. #18
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    West Milford, NJ, USA
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    Steve, you need to clean out your inbox! It's FULL.
    Dave Youngren
    NER ITA RX7 #71

  19. #19
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    109

    Default worth it

    I went from 4:30 to the 4:88 and it's really a huge difference on the track.

    The factory gearing is so tall it's dumb. I also don't understand the huge gap between 4th and 5th in the regular tranny. (The GTUs 5th helps that.) I think it's an old-fashioned way to do gearing. They'd never make a Miata or RX-8 set up like that these days.
    -----------
    '89 RX-7 ITS

  20. #20
    Join Date
    Jan 2001
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    Chicagoland, IL
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    I have been recommended to put in 4:88's in my Miata for ITA. Sounds insane, but I used to run ITA, so I'd definitely try it out. :cool:
    Racer of old BMW's.
    MCSCC ITS Class E30 325is
    Racing where IT still exists: http://www.mcscc.org/

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