D/S Target

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Joe Percoco, Mar 5, 2018.

  1. Joe Percoco

    Joe Percoco Member

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    Can someone explain to me what the Drive Shaft Target is on the Racepak, what it means and what you should be looking for in relation to the drive shaft rpm/engine rpm? thanks,
     
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  2. rb0804

    rb0804 Member

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    Are you talking about one of the attached sheets on the bottom of the Racepak where is gives you your egts per hole , the max/average and your ideal driveshaft points or are you speaking of magical target numbers that tuners shoot for?

    In general the more driveshaft RPM the better things work out. There is a limit though as too much driveshaft is tire slippage and not accelerating the car. This is where the G meter comes in. The driveshaft numbers will also be different for different ring and pinions. A 4.72 and a 3.90 will have a very different driveshaft curve.
     
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  3. Joe Percoco

    Joe Percoco Member

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    I am talking about the channel buttons that show engine rpm, drive shaft rpm, temps, blower pressure, etc and DS target. The DS target will not be close to the actual DS rpm.
     
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  4. rb0804

    rb0804 Member

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    If I remember correctly if you hit the button on the tool bar that pulls up the run into, 60’, 330’, etc, weather, density alt.; there are some tabs at the bottom for clutch, engine, chassis setup, one of the last ones is the one that I am talking about with the egts and all. Here is where you can input your ideal driveshaft numbers and you can hit the D/S and the target D/S and see if you are above or below your ideal driveshaft scenario. Me personally I don’t use that channel as our data recorder on the Alcohol car came from an A/fuel guy so it has some weird looking driveshaft rpm curve in it. I will just over lay a known good run onto my current run and go from there. Just be careful when overlaying Runs that you are looking at the correct tab and the correct line, it’s easy to get confused and make tuning decisions off of a run that was two sessions ago instead of the most current run. The point I’m trying to make is the target driveshaft is something that you (or whoever had it before you) inputed as an ideal scenario for their rear gear ratio. If your combo is different, primarily the ring and pinion it’s going to be way off.
     
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  5. Joe Percoco

    Joe Percoco Member

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    Thank you. That is starting to make sense now.
     
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  6. jay70cuda

    jay70cuda Member

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    3600 rpms at 1.0 is a good target number to shoot for. The rest will sort itself out. Keep the check marks out of the graph early at the hit. You’ll be fine from there.
     
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  7. Joe Percoco

    Joe Percoco Member

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    From .07 to .66 of a second the drive shaft bounces up and down then continues up as it should. I can overlay my 5 best runs and it is the same on every launch. I don't know if it is spinning the tire (though the engine RPM isn't affected) or if the wheelie bar is unloading the tires or if the clutch may be grabbing too much at the hit and needs to slip a bit more. I don't hit 3600 driveshaft RPM until 1.4 seconds into the run. Understand, this is not a Top Alcohol car but a blown altered with early Brad stuff to run a Fast 16 deal at Bandimere. Best ET up here is 6.39. Typically in the 40's-50's.
     
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  8. greenracing

    greenracing Member

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    Jay - when you say 3600 @ 1.0, what rear ratio are you figuring? Wouldn't that change the desired DS speed? As would tire diameter, but I would assume that's with the typical 34.5's.

    Just thinking that if Joe is running a higher ratio rear, then his DS speed isn't going to hit 3600 until later, like he's seeing. Am I thinking correctly?
     
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  9. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    When comparing driveshaft numbers, rear end ratio has to be factored in. The number we look at on our data loggers is just that - driveshaft or pinion rpm. Generally speaking different types of cars will fall into a range at 1.0 seconds but if you are comparing two different cars with different rear end ratios, you need to calculate your axle speed then correct it to whoever's gear ratio you are comparing to.

    For instance if I wanted to compare an 1/8 mile Pro Mod to a 1/4 mile Top Alcohol Funny Car's early wheel speed numbers, this is how I would do it.

    FC has 3100 at 1.0 seconds with a 4.29 rear gear. 3100/4.29=722 axle speed

    The Pro Mod has a 5.0 rear gear in it. 722 axle speed X 5.0 = 3610.

    So to achieve similar incrementals with the Pro Mod, I would need to have roughly 3600 driveshaft at 1.0.

    That's why the A/Fuel graph looks 'lazy' when in reality it's flying.
     
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  10. Joe Percoco

    Joe Percoco Member

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    Interesting. Thanks Wil. Anthony at Racpak was able to give me some insight as to how to set up the DS target and once you see how to do it is very easy and should be able to help alot. There are a lot of guys that don't know what it means or how to set it up.

    PS did you get my email with the runs?
     
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  11. turbo69camaro

    turbo69camaro Member

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    low gear ratio,clutch or converter slippage are factors as well no ''magic'' number.The g meter is your friend .
     
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  12. Joe Percoco

    Joe Percoco Member

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    Just ordered one. Now if I can learn how to decipher it....
     
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