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  1. #1
    Senior Member 355lux's Avatar
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    Default shift points for drag racing

    Havent posted in a while but what are peoples thoughts on shift points for best acceleration over the 1/4... mainly looking at 3 speed autos... but always learning so any real world examples of motor peak TQ and Peak HP and relation to shifts would be great to hear. Alot of the calculators online ( that use actual dyno numbers of the engine and the trans/final ratios and tyres ) come up with very high shifts - most between 500 to 1200 rpm past Peak HP ( yes HP not TQ).. The theory is sound but Im not sure if this holds true - eg say a 355 with peak hp at 6900 , the calcs are looking at over 8K on the 2-3 shift... any dedicated drag boys like to chime in?
    "life is about a bag of luck and a bag of experience..the trick is to fill the bag of experience before you empty the bag of luck!!"

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    Do you ever leave? EH179's Avatar
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    In my neck of the woods, we work off 10% over peak HP rpm.
    eg: 6900 + 10% = 7590rpm.

    Of course this is dependent on whether the engine is built to handle this rpm, and the gearing/rear tyres used.

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    Do you ever leave? EH179's Avatar
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    Forgot to add converter slip into the equation, which needs to be worked out and factored in.

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    Senior Member 355lux's Avatar
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    So if you have 8% converter slip ... which way do you go ?
    "life is about a bag of luck and a bag of experience..the trick is to fill the bag of experience before you empty the bag of luck!!"

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    Quote Originally Posted by EH179 View Post
    In my neck of the woods, we work off 10% over peak HP rpm.
    eg: 6900 + 10% = 7590rpm.
    Is this 10% over business to ensure that on the next gear you are not too far back down on the curve when you shift?

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    Senior Member 355lux's Avatar
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    Correct - there are some good forums and write ups on the matter, but I'm curious to see what some of the people in here actually turn their motors too when racing to accommodate the shift drop in RPM
    "life is about a bag of luck and a bag of experience..the trick is to fill the bag of experience before you empty the bag of luck!!"

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    Gearing, find peak torque and rpm drop on shifts, turn it hard enough to fall back onto peak torque on the shifts then gear it to hit shift point at 1000', run it out to the stripe and hope you have enough valve spring.

    Check the increments and experiment some more, spend a lot of money to go a little bit quicker then do it all again until it breaks something then spend a lot more.

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    The 10% rule gets it in the ball park.
    I used a program at one stage to look at shift points, it wanted the shift from 1st to 2nd in the low 5's and shift into top at 7600.
    It did hurt the time but not by as much as I would have thought.

    Has he got that FJ going up there yet ?

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    Do you ever leave? paulzig's Avatar
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    Try 1-2 change 10% UNDER PEAK HP (or less) and 2-3 change 10% OVER PEAK HP.

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    Senior Member 355lux's Avatar
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    Has he got that FJ going up there yet ?[/QUOTE]

    Yep .. finally put it all together last weekend... very happy bloke at the moment.. first time he has had a converter matched to a combo.... so next off street drags we'll both go down there for a play .. hence the shift point curiosity.
    "life is about a bag of luck and a bag of experience..the trick is to fill the bag of experience before you empty the bag of luck!!"

  11. #11
    Senior Member 355lux's Avatar
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    Has anyone got some actual data on playing with shift points in their car? Would be great to see what did and didnt work with some combos.
    "life is about a bag of luck and a bag of experience..the trick is to fill the bag of experience before you empty the bag of luck!!"

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    I'm actually trying some shift points myself now. Engine made peak power at 7400 and I used to shift at 7300 into second and top but ran a pb the other night shifting at only 7000 into both second and top. I've never tried shifting over peak power yet. I suppose every engine responds differently

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    Do you ever leave? cava454's Avatar
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    Quote Originally Posted by paulzig View Post
    Try 1-2 change 10% UNDER PEAK HP (or less) and 2-3 change 10% OVER PEAK HP.
    Care to explain Paul?

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    254RWHP boat anchor EVL253's Avatar
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    also have to factor in wether the power curve hangs on or falls off a cliff. i beleive its about being in the most average power curve
    11 second E85 bottle fed boat anchor

  15. #15
    Senior Member 355lux's Avatar
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    The Optimal Shift Point

    That site has some interesting data - in particular the graph of torque vs speed - its using a skyline as a reference so no throwing the hate around But shows even with the motor " falling over" it still is optimum in this case to change after the peaks drop right off. POMMA - looks like you spend some time at the track ... would be interesting to see what effect this has on your MPH/ET.
    "life is about a bag of luck and a bag of experience..the trick is to fill the bag of experience before you empty the bag of luck!!"

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