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Thread: Gearing for a stock predator on a short track

  1. #1
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    Gearing for a stock predator on a short track

    Ok so here is the question and why I ask. What gear would you run on a really short track with narrow turns with a stock predator 212 gov unhooked with a header only. I usually run a 12 tooth clutch with a 70 rear sprocket. Others run 11t clutch with 63-65 rear sprocket. Last race I went all the way down to a 64 rear sprocket with a 12T clutch and it was faster than usual! The rear gear being smaller was easier for the motor to turn taking a load off of the motor. I had tried a 68 in the past and it was weak. But making this jump down to a smaller sized sprocket worked. So it got me to thinking. What drive sprocket/rear sprocket combo are others running on a similar track. I have seen some running 19 tooth clutch with 66-70 rear sprocket online on short tracks. Would a bigger drive sprocket be better or too much for this predator motor? Just thinking outside the box. Any input is appreciated

  2. #2
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    Any thoughts on this? Anybody??

  3. #3
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    A spread of 11 tooth drivers to 19 tooth driver SOMEONES out to lunch and not even in the same zip code, If it's a really short track your in the ball park with the 12 driver the reason you noticed a difference is with the 12-70 you were gear bound and by pulling teeth you actually gained RPM's happens all the time, keep the 12 and keep pulling rear until it slows down on lap times or shows to much RPM drop.

  4. #4
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    Our Predator spec class no gov but stock muffler ran a 15 x65 this week on 1/5 pavement oval and turned 5600 rpm across the board. fun racing

  5. #5
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    19T driver?? That's got to be an error? Either that, or your idea of a short track is completely different from their idea of a short track. lol
    12/70 is pretty close to the same ratio as 11/64. 5.83 versus 5.82. 12/64 = 5.33. That's a huge difference in ratio! I can't help thinking that there must be something else going on. Maybe a huge improvement in the track or a huge improvement in the air density could account for it, but those improvements would have to be really huge..
    A lot of people are of the opinion that the larger driver is an improvement. But I've never heard anybody claim that a larger driver could be worth a 1/2 second in lap times.

    I'm in a quandary trying to figure this one out.

  6. #6
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    When I said 19T drive sprocket I was only referring to what I have seen others post for running on a 1/10 mile track. The track I run on is 1/12 mile. I was just curious if the larger drive sprocket would help of be too much for the motor to turn over. But as far as me dropping from a 70 to a 64. U can tell the motor is not in as much of a bind as it was with the 70. The motor sounds different. I never would have believed I could run a 64 on this track because I would lug the motor coming out of the turns with a 68 in the past. But the owner of the track runs a class below me and he is running a 12-62 and his kart is really fast. He has been telling me for a year now to drop the sprocket size and I could never see how it would work. Being a little heavier I had to go up to a 64 and needed a tad bit more stall in my clutch. But I was even pulling karts a kart length off the start before hitting the first turn. I will agree with the fact that it does not make sense and it feels completely different from what I am used to but I can promise it worked. May want to try it sometime. I have only ran one race with this gearing and the track was really tacky. I suspect as the track dries out it will work even better. But I will update on this after Friday night. And FYI I am running on a dirt track. Not pavement.

  7. #7
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    Quote Originally Posted by Champ2014 View Post
    When I said 19T drive sprocket I was only referring to what I have seen others post for running on a 1/10 mile track. The track I run on is 1/12 mile. I was just curious if the larger drive sprocket would help of be too much for the motor to turn over. But as far as me dropping from a 70 to a 64. U can tell the motor is not in as much of a bind as it was with the 70. The motor sounds different. I never would have believed I could run a 64 on this track because I would lug the motor coming out of the turns with a 68 in the past. But the owner of the track runs a class below me and he is running a 12-62 and his kart is really fast. He has been telling me for a year now to drop the sprocket size and I could never see how it would work. Being a little heavier I had to go up to a 64 and needed a tad bit more stall in my clutch. But I was even pulling karts a kart length off the start before hitting the first turn. I will agree with the fact that it does not make sense and it feels completely different from what I am used to but I can promise it worked. May want to try it sometime. I have only ran one race with this gearing and the track was really tacky. I suspect as the track dries out it will work even better. But I will update on this after Friday night. And FYI I am running on a dirt track. Not pavement.
    On a Track that small a 13 would be biggest you got a shot at pulling but I would say your gonna find best staying on that 12 and finding the sweet spot for the rear.

    Good Luck !!

  8. #8
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    Id have to think that anything bigger than a 14 on a track that small is just going to lug/bog down the engine, and would take a few laps at least to get up to speed, plus the slightest on track mistakes will kill your momentum and cost you precious time. I agree with racing promotor 100%. There is a predator stock class at one of the local tracks where the track seals hemi's and sells them to the racers, they are using 15 and 16 drivers on 1/5 mile, turning around 16 sec laps @ 5200-5500

  9. #9
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    There's only one place to set the stall on the clutch and that's at peak torque. Any other place and you're just getting less horsepower at the rear axle. If you get a dyno test, it's pretty easy to see where the engine is reaching peak torque. The idea that slipping the clutch above the point where the engine is producing peak torque is just wrong. Totally and completely wrong. Torque is work, horsepower is a "calculation" to determine how much work. Only when the clutch is not slipping is the torque at the engine the same as at the axle, multiplied by the gear ratio.

    One thing, you've got to trust your dyno, and if you don't have one, you have to trust the person who runs the dyno test on their dyno. It's so easy to get skewered (intentional or not) results, you've gotta be careful.

    One thing about the, "scale between the front of your kart and a strong wall" is, "it's you doing the tests". Unless the bathroom scale is total junk, it's the very best way to test for the very best stall RPM.

    There are people that claim that doing it this way is bad and that it will burn up your clutch, and you can, if you run your test for too long a time. If you do it right, it's no different than pulling onto the track at full throttle, or testing the stall on the stand by holding the brakes.

  10. #10
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    I guess if you went WOT and held it there while you boil the back tires and put a lot of strain on the engine, then the scale test would seem excessive. but! if done right, using it to set up your clutch according to the peak "push" against the scale the rpm your turning should give you a very good starting point.

    sort of like the multi-engine pulling tractors...at least that's the way I see it....they run the engines up and drop the clutch....the hardest that they pull is right at the end where the wheels are still pulling ....and the engines are all at peak rpm....I think at that point, they are making the most power and it's just before the wheels overcome the track and they start to spin with no forward movement.....you want to be right at that peak with your kart too...right where your making the most power, delivering the most to the rear wheels and not loosing touch with the track.....anything less and you can't overcome the track....anything more and you've over come the track and spinning your wheels.....

  11. #11
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    Quote Originally Posted by mikey56 View Post
    I guess if you went WOT and held it there while you boil the back tires and put a lot of strain on the engine, then the scale test would seem excessive. but! if done right, using it to set up your clutch according to the peak "push" against the scale the rpm your turning should give you a very good starting point.
    Boil the back tires? Lot of strain on the engine? It's pretty obvious you've never done the test.

  12. #12
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    is this an oval track?

  13. #13
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    I run a 15/60 on my predator 212. small dirt oval track me and kart weigh in at 340. going to try a 15/58 this week and see what happens. i have plenty of power on starts and on corners but im not fast enough on the straights

  14. #14
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    Quote Originally Posted by a542m View Post
    I run a 15/60 on my predator 212. small dirt oval track me and kart weigh in at 340. going to try a 15/58 this week and see what happens. i have plenty of power on starts and on corners but im not fast enough on the straights
    You might be surprised at what a big difference two teeth can make. I remember a time when I dropped two teeth on my Mac 101 and how amazed I was at the difference it made. I went from third place in the first heat, to a really wide margin win in the second and third heat. Quite a difference, but this was at a track with a very very long straightaway.

    15/60 to a 15/58, at six thousand RPM, makes a difference of 1.6 mph. That doesn't sound like much, but trust me, it's a ton. And consider this, if you lose two hundred RPM, you will be adding no speed. Consider this; if you change just one tooth, and you lose 105 RPM, you will be going the same speed on the top.

    I would suggest trying one tooth first.

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