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Let’s talk about 10r80 Starting Line Ratios (SLR):

Discussion in 'Dragstrip and Launching' started by TX-Ripper, Jun 16, 2020.

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  1. TX-Ripper

    TX-Ripper Well-Known Member

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    Let’s talk about 10r80 Starting Line Ratios (SLR):

    The coyote engine has a 92.7mm stroke or roughly 3.65”

    cartechbooks.com says we should be around 10.5 to 11 starting line ratio (3500lb-4500lbs)
    457811-9a4a822f7b4b6c5eb75463507365bef2.jpg

    Per Wikipedia the Ford 10r80 has roughly a 4.70 1st gear ratio and 2.99 2nd gear ratio

    Using 2nd gear leave (2.99 gear ratio) gets you a much better SLR

    Quick math

    3.55 rear axle gear

    3.55 x 4.70 = SLR 16.685

    3.55 x 2.99 = SLR 10.614

    3.31 rear axle gear

    1st gear leave with 3.31 x 4.70 = SLR 15.557

    2nd gear lave with 3.31 x 2.99 = SLR 9.896

    3.15 rear axle gear

    1st gear leave with 3.15 x 4.70 = SLR 14.805

    2nd gear lave with 3.15 x 2.99 = SLR 9.418

    10r80 7th gear clutches die fast on Power adder cars and 3.55 have most shifting into 7th gear right at the 1320.

    But using a 2nd gear leave with 3.55 looks to have the most ideal SLR.

    What are your thoughts on SLR with 10r80? SLR.JPG
     
  2. barkingspud

    barkingspud Well-Known Member

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    So, in order to do a 2nd gear launch, you'd be in S mode, paddle to 2 then as soon as you launch, move to D? I'll give this a try next time I'm at the track.
     
  3. OP
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    TX-Ripper

    TX-Ripper Well-Known Member

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    Let me know if that works, I was under the impression that you needed custom tuning for it.
     
  4. barkingspud

    barkingspud Well-Known Member

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    If it does, I can take care of that.
     
  5. Ed M

    Ed M Well-Known Member

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    Yes, that is correct. But you must be at a complete stop before shifting up to 2nd, otherwise it will automatically shift back down to 1st. It is easy to practice this on the street (you don’t need to wait until you’re at the track).
     
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  6. IrishStallion

    IrishStallion Well-Known Member

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    On a street tire this might help, but if you on a slick/drag radial I’d leave it in first.
     
  7. gregsdart

    gregsdart Well-Known Member

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    #7 gregsdart, Jul 26, 2020
    Last edited: Jul 26, 2020
    With a stock torque converter and normally aspirated/bolt ons/e85 etc i would stay in first. These 5.0s are low torque at stock stall speed and can use all the help they can get.
    For a dedicated race car it is all about how much torque you can put to the pavement . i run a 11.17 SLR in my 880 hp 3050 lb dart racecar.
    Torque at stall speed of 6,000 is about 700 ft lbs times 2 coming out of the converter at launch (1400) x 11.17 = 15,000 ft lbs at the axles. I have huge bias slicks and can hold it on a well prepped track.
    A 14.69 SLR in a mustang with say 375 ft lbs torque at stall will have 750 x 14.69, or about 11,000 max torque at the axles . my guess is there is much less torque at the axles with a stock converter than my math shows since my "butt" dyno and being able to stick the tires says so.
     
  8. 80FoxCoupe

    80FoxCoupe Well-Known Member

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    This SLR chart is stone age, old school mentality.
     
  9. OP
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    TX-Ripper

    TX-Ripper Well-Known Member

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    Well that’s what we’re here to talk about.

    I would be glad to look at any newer reference material you have.
     
  10. 80FoxCoupe

    80FoxCoupe Well-Known Member

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    The proof is in the pudding. Look at what a bone stock 18up 10spd car with a tire will do with a high SLR versus what that chart says is ideal. I suppose that chart "could" be used as a guideline by someone, but need to be expanded to include weight, power etc.
     
  11. 80FoxCoupe

    80FoxCoupe Well-Known Member

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    Give the car what it wants. Do your own testing to understand what works and what doesn't. Setting up a car based on old school charts will put you at the back of the pack.
     
  12. OP
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    TX-Ripper

    TX-Ripper Well-Known Member

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    It seems like the guys that are going the fastest have the launch is set up properly. For whatever reason this chart seems to line up perfectly with the way Lund has people set up cars.

    3.15 gears and 2nd gear leave going pretty fast.
     
  13. 80FoxCoupe

    80FoxCoupe Well-Known Member

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    On a stock engine NA or 1200hp TT car?
     
  14. OP
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    TX-Ripper

    TX-Ripper Well-Known Member

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    For forced induction guys
     
  15. 80FoxCoupe

    80FoxCoupe Well-Known Member

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    Ok you didn't make any mention of combo in the original post. Ok so FI. Centri/pump 93/650hp?? Built engine/TT/e85/1200hp?? What tire?? Prepped surface?? 1/8 or 1/4?? What are we talking about here?

    The highest slr you can get away with will typically yield the best 60ft. But the factors above have to be taken into consideration. One maybe in a situation where SLR will be a compromise based on other factors. Racers dont use charts like this. Give a car what it wants.
     
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