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Thread: Need help with pro tree reaction time

  1. #1
    Senior Member DYNO OPERATOR
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    Need help with pro tree reaction time

    I've posted about this issue before, but still haven't found the answer. I have a 63 Vette SG roadster and can't go red on a pro tree. Every other Supergas car pulls the front out of the beams and mine just won't. What 4-link or other chassis adjustment will make a car wheelstand?

    Car specs:
    107"wheelbase
    522 bbc 840hp
    pg with 1.80 low
    4.30 gear
    33x16 D1 Goodyears
    4-link/swingarm
    strut front
    23" front tires

    Car runs strong & straight, 8.40's @ 160, 1.20 60's, but will barely lift the front off the ground. Great bracket car, but mid teen lights if I'm really on the tree, just aren't competitive in SG. Any suggestions?

  2. #2
    Senior Member DYNO OPERATOR
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    forgot this
    total weight with me & full of fuel 2175lbs
    1115 on the front and 1060 rear
    single adj struts and double adj rear shocks
    current IC is 51.5" long and 4.6 " high

  3. #3
    Senior Member RACING JUNKIE fla1976's Avatar
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    Lights

    Are you using a delay box? If your lights are consistent, just pull a little time out of it. As for pulling the front end up, if the car is running straight and has 1.20 60 foot times, I'd leave it alone. Sounds like you're getting good weight transfer and hooking good. Wheels up launches are showy, but they are a waste of momentum. JMO

  4. #4
    Senior Member DYNO OPERATOR
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    Here are a few things that will help wheel stand.
    Lighter rear springs
    Higher instant center
    Shorter instant center
    Lighter rear shock rebound setting (extension)
    Lighter rear shock bump setting
    Increase staging RPM
    Looser converter (higher rpm stall)
    These are just a few variables that you have control of without making drastic changes to the drive train, like using a three speed trans and changing the rear gear ratio. You have a light car and what seems like a good basic scale report and 4 link set up. I will bet your crank is lower than 11.5" at ride height up front. If so, it is set up to have big torque like a pro stock engine may. Your engine is likely to tame in the torque department for that low of a CG and can not drive under it, there for no wheel stand. If you are not on the bars in the first 4' of the run then the crank height issue is one worth looking at.
    If the car is dead hooked now, then tightening the rebound on the front struts, this will make the tires pick up out of the lights too. But only if you are dead hooked now. Otherwise you will cause spin.

  5. #5
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    Re: Lights

    [quote="fla1976"]Are you using a delay box? If your lights are consistent, just pull a little time out of it. As for pulling the front end up, if the car is running straight and has 1.20 60 foot times, I'd leave it alone. Sounds like you're getting good weight transfer and hooking good. Wheels up launches are showy, but they are a waste of momentum. JMO[/quote]

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  6. #6
    Senior Member RACING JUNKIE
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    Re: Lights

    [quote="DrivingMissDD"]
    Quote Originally Posted by fla1976
    Are you using a delay box? If your lights are consistent, just pull a little time out of it. As for pulling the front end up, if the car is running straight and has 1.20 60 foot times, I'd leave it alone. Sounds like you're getting good weight transfer and hooking good. Wheels up launches are showy, but they are a waste of momentum. JMO[/quote]

    2X bigtime. SHOW doesn't GO !!
    Its a waste of momentum if your trying to go faster. Most cars running on a pro tree will run alot faster than the class index they're in. Whats hard is cutting a red light on a 4 tenths tree from a shallow stage. For that reason its more important to cut a quick reaction time than to run a tenth quicker et.

  7. #7
    Senior Member RACING JUNKIE
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    Re: Need help with pro tree reaction time

    Quote Originally Posted by johnracer
    I've posted about this issue before, but still haven't found the answer. I have a 63 Vette SG roadster and can't go red on a pro tree. Every other Supergas car pulls the front out of the beams and mine just won't. What 4-link or other chassis adjustment will make a car wheelstand?

    Car specs:
    107"wheelbase
    522 bbc 840hp
    pg with 1.80 low
    4.30 gear
    33x16 D1 Goodyears
    4-link/swingarm
    strut front
    23" front tires

    Car runs strong & straight, 8.40's @ 160, 1.20 60's, but will barely lift the front off the ground. Great bracket car, but mid teen lights if I'm really on the tree, just aren't competitive in SG. Any suggestions?
    I agree with everything topspeed said. I myself would run a stiffer sidewall rear tire. Most of the D-1 are soft sidewall. You'll also need a 6000 to 6500 stall converter. Change one or both and you'll see dramatic changes.

  8. #8
    Senior Member DYNO OPERATOR
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    Thanks for the responses. I definately not trying to put on a show though. Running in Supergas on a 4-tenths pro tree, I have no time in the delay box and can't get anywhere close to red. The car works great running flat out on a full tree where I can have delay in the box. If that's all I wanted to do, I'd leave it alone for sure.

    Dparker, I've considered trying a stiffer tire, like maybe a D6. However, I have to run around 4.5-5psi to get it to hook consistently now and figure a D6 would make it worse. That brings me to what Topspeed said.

    I run the struts at full soft when running flat out, and tightening them up makes it spin, so traction is obviously an issue.

    You're right about the crank height. It's at about 11 1/4" at the current ride height. Do you thing raising the front ride height would help? That would also reduce front travel and may cause spin with the current 4-link setting. You definately got me thinking here......perhaps moving the IC back & up a little would plant the tire hard enough to allow me to run more tire pressure and a stiifer front strut setting without spinning. Might even be able to run a stiffer sidewall........what do you think?

    I have 90lb rear springs and 250lb fronts. It had 200 fronts but I changed them to try to help reaction times. It may have made it worse.
    Thanks again,
    Johnny

  9. #9
    Senior Member RACING JUNKIE
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    If chassis tweaking isnt getting there, converter would be next on the list. A lot of people pull the chip and leave on the wood on pro-tree stuff
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  10. #10
    Senior Member DYNO OPERATOR
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    Getting closer to a good answer

    Quote Originally Posted by johnracer
    Thanks for the responses. I definately not trying to put on a show though. Running in Supergas on a 4-tenths pro tree, I have no time in the delay box and can't get anywhere close to red. The car works great running flat out on a full tree where I can have delay in the box. If that's all I wanted to do, I'd leave it alone for sure.

    Dparker, I've considered trying a stiffer tire, like maybe a D6. However, I have to run around 4.5-5psi to get it to hook consistently now and figure a D6 would make it worse. That brings me to what Topspeed said.

    I run the struts at full soft when running flat out, and tightening them up makes it spin, so traction is obviously an issue.

    You're right about the crank height. It's at about 11 1/4" at the current ride height. Do you thing raising the front ride height would help? That would also reduce front travel and may cause spin with the current 4-link setting. You definately got me thinking here......perhaps moving the IC back & up a little would plant the tire hard enough to allow me to run more tire pressure and a stiifer front strut setting without spinning. Might even be able to run a stiffer sidewall........what do you think?

    I have 90lb rear springs and 250lb fronts. It had 200 fronts but I changed them to try to help reaction times. It may have made it worse.
    Thanks again,
    Johnny
    The change to higher rate front springs will make it harder to pitch rotate just like stiffening the rebound on the front struts. D6 has nothing to do with sidewall. That is a compound rating by good year. D1 is the softest compound that is available to us sportsman racers and is available in stiff sidewall construction and non stiff or high growth. This is the only tire compound I would run on a light car like yours personally. The crank height should not be raised by the spring pre load. This will top the struts out earlier and not give good results as you speculated. One way one can do this is by using larger diameter tires without re engineering the front end geometry . This will leave the crank higher in the front as if you mounted the engine higher in the chassis and give better pitch rotation that you are after. I don't know who's brake you are using, (not a big fan of 2 speeds) but some are much faster than others. They are often called pro brakes and on 3 speed trans and requires the use of the trans brake sol. to back up with the shifter in the neutral position on my 3 speed hydro job's . One more item I left out due to the amount of work involved is if you like the IC choice you have, you can maintain it and put the bars on the differential and front chassis bracket closer together (Less Spread) this will give faster housing reaction but can hurt down track traction if you were close to the edge now, but with the power you have currently, it is not likely. You just calculate the IC to the same position as previous but with less spread on both ends. I would lower the top bar down on both ends the same distance from point of beginning. Do not make the rear spread less than 10" for your power level. You probably have over 11.5" spread currently for a big torque combination.
    One more thought, do you have and anti roll bar in the rear of this car. This will help directing the vehicle forward quicker as well. just a few more thoughts to ponder.

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