Tunning help PLEASE

Discussion in 'PSI Superchargers Tech Questions' started by suddendebt, Jun 30, 2010.

  1. suddendebt

    suddendebt Blown Altered

    Joined:
    Aug 16, 2009
    Messages:
    133
    Likes Received:
    0
    Hey everyone,

    Just a question or two,

    Ran into a bad (slick) track tonight and was trying to de tune the motor so that we could get out of the hole and keep the tires glued on the big end at the same time.

    I started out with the tires at 5.25 did good out of the hole but did spin some 1.12 60'
    shook from the 330 on to the 660 ran a 4.89.
    2nd Pass 5.50 shook 1.5 to 2.0 full turns out of the hole still pulled out a 1.07 60' then you guessed it shook from the 330 to the 660 ran a 4.83 I also took the shift point from 7000 to 6500 just to see what the car would do if I lugged the motor alittle ( just seeing if the blower would be forced to work some more or not.)
    3rd and final pass, 5.00 shook hard off the hit ( like a fueler almost) 1.14 60' then more tire shake and then smoked em from about 200 out to the 660 ran a 4.93.

    So all that said what are your thoughts on the tire pressure. Go up for traction or down. Keep in mind I have 15 in wheels not 16 in I hear that makes a diff on what you do.

    Thoughts on pulling some timing out to calm it down a little? dont know what do you think?

    Any real benifit to lugging the motor more or should I go back to 7000. Plugs look good and happy each run still a little fat on 2 or 3 but still some good heat in them. Timing is good as well on the strap. Oh its a chevy on alky with a 671 125 in altered. our best so far is a 4.53 just something to compare to.

    Thanks for any and all advice
    Bob and the sudden debt team.
     
    #1
  2. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    I am hoping you get some responses on this topic as well, since I have some of the same questions.

    There have been several threads on this forum discussing tire pressures and shake. It seems that the prevailing wisdom says more pressure for stick, less pressure for slip. As for shake, it has been posted that immediate violent shake can mean too much power, while any other shake is too little. Since I am very new to this, I can only give you the benefit of what I've read here.

    In my case, I am pulling timing and increasing tire pressure in small increments. I am in a dragster, so it may not apply to your car, but so far mine has gotten better each time I add air (spins less at launch). My last run, which hazed through the 60 foot, but didn't break into full uncontrolled spin, was 5.5lbs, my next will be 6.0lbs.

    -Brian
     
    #2
  3. JustinatAce

    JustinatAce Member

    Joined:
    Oct 20, 2008
    Messages:
    599
    Likes Received:
    9
    Couple questions in return..

    Bob,
    Are you running beadlocks or liners? Did you try taking some gear away to slow it down or is that an option for you?

    Tire shake usually comes from two directions, driveshaft lugging the motor or not carrying your wheel speed from the hit 100 feet down track. 9 times out of ten when you knock the tires loose 100 feet out its because it shook and broke loose due to lack of power to keep the tires accelerating. If you spin hard off the line and can't keep the tires accelerating because the motor is getting pulled down to the drive shaft, watch your 60ft. If your wheel speed is killer off the line but your 60ft is slow, you need more bite(more air, little higher wheelie bar, weight out of the front). If more bite doesn't work, then you have too much gear for the motor and clutch, try a couple points taller and leave the static alone and pull a little counterweight so you don't dip the motor. These tips really only apply in good air/bad track conditions.

    Bad Air/Bad Track, you may not have enough gear to keep it driving with a lot of bite, or you have too much counterweight for the motor/track to handle with that gear.

    If all else fails, THEN take power out. Very rare occasion where you should take power out of the motor when you're shaking.
     
    #3
  4. jim phillips

    jim phillips ta/fc

    Joined:
    Apr 29, 2007
    Messages:
    1,242
    Likes Received:
    0
    tire shake happens when down on power and not enough wheel speed if it spins then goes into tire shake it might be to low of pressure i for shit tracks it very tuff to get down but it can be done and still be fast you can knock some time out that will work how much will depend on the application i have also fattened the motor up like if your running a high speed flip it over and dont take the fuel away i wouldnt lower the air pressure leave it where you normally run it and tune to the track with fuel are timing good luck
     
    #4
  5. suddendebt

    suddendebt Blown Altered

    Joined:
    Aug 16, 2009
    Messages:
    133
    Likes Received:
    0
    No beadlocks, changing the gear not an option for us.

    So I need a little more tire speed out of the hole. and a little more power down track.
    If I cant make that happen its time to look into detuning until I can make it happen.

    thanks
    bob
     
    #5
  6. jim phillips

    jim phillips ta/fc

    Joined:
    Apr 29, 2007
    Messages:
    1,242
    Likes Received:
    0
    can you leave at a higher rpm maybe just a few hundred rpms i know if i leave to low of rpm it will leave good but go right into tire shake about a 100 ft out 5200 im good 4800 it will go right into tire shake with the front end up then i have to whak the pedal are tire and drive through it and thats hard on everything (but i run a clutch )
     
    #6
  7. suddendebt

    suddendebt Blown Altered

    Joined:
    Aug 16, 2009
    Messages:
    133
    Likes Received:
    0
    Ill have to look into that. We are going to Pacific Junction Ia next week Ill have to see what happens.
     
    #7
  8. mark6052

    mark6052 Member

    Joined:
    Jul 24, 2005
    Messages:
    397
    Likes Received:
    0
    bad tracks

    I was told, taught, by some of the best around here to set the tires at 6lbs,+/-1/4 with a VERY good gauge and learn to tune the car else where. 5 1/2 tire pressure is not the cure for anything. timing, fuel go along way. for me they also said to work with the clutch. this advice was given to me by div6 hitters and afew others that took pity on me to help me learn. do people adjust tire pressure? sure , after they understand what the car and track is really doing. some tracks I have ran in the past are the old spokane all pavement track and acouple air strips. even had to stop the race when a plane wanted to land. :eek: as always everybody knows something different. good luck.
     
    #8
    Last edited: Jul 2, 2010
  9. Dale Finch

    Dale Finch Member

    Joined:
    Dec 29, 2004
    Messages:
    271
    Likes Received:
    2
    Running an altered makes it easy to see the tire from the start line. First, is the car up on the tire or is the tire wobbling....what is the pattern on the track? What kind of tire and size? Can you up the blower to give it more power? Do you have a data recorder that can measure wheel speed? We have run as low as 4.5 lbs on a hoosier to get wheel speed and as high as 6 1/4 on a goodyear to slow it down. What was the track like? Pull your shoes off or very poor after 200 ft. See, I personally have a lot of questions. If you have a data recorder....what is the wheel speed at .25, .50 and 1 second. That may help us give you some ideas to solve the problem.
     
    #9
  10. outlaw02camaro

    outlaw02camaro New Member

    Joined:
    Oct 1, 2009
    Messages:
    53
    Likes Received:
    0
    so dale, increasing tire pressure slows wheel speed and decreasing tire pressure increases wheel speed? can you explain how that actually works in simple turns? thank you, new to the blower/high hp engines and trying to take it all in!
     
    #10
  11. Dale Finch

    Dale Finch Member

    Joined:
    Dec 29, 2004
    Messages:
    271
    Likes Received:
    2
    Changing the tire pressure shrinks or expands the contact patch and the ability of the tire to grow. Sort or speeds up or delays the growth. There is lots of ways to skin a cat so to speak. Personally I don't like to mess with the clutch or you screw up the pull down at the shift and end up going through valve springs and a few other things. You still need the car to get up on the tire and weak the car will just shake. You need to have enough clutch to keep the car accelerating.

    I would sure like some of you 5:50 funny car guys who are lurking our there to give us your thoughts on wheel speed and tire pressure and wheelie bars......come on, Randy is a 5:50 car and he shares.......great of him too !!!! Come on and join in....don't just watch. Take part......
    Love to hear from Randy and Clint too!!!
    thanks
    Dale
     
    #11
  12. TAFC 5 81

    TAFC 5 81 Member

    Joined:
    Apr 9, 2007
    Messages:
    108
    Likes Received:
    4
    I ran a similar Rodeck/ BBC engine combo in a BB/FC (1978) and AA/DA (1979-80) but had 16" wheels w/ liners and Goodyear 1490 tire. We had a tire spin problem with the BB/FC; too much clutch, old tires, and not enough experience (first race car). Dragster with new tires behaved better, but still had its moments. Increasing the liner pressure helped w/ shake most times. What stroke engine and what type of trans do you have?
     
    #12
  13. altered boy

    altered boy Outlaw Altered

    Joined:
    Aug 4, 2003
    Messages:
    418
    Likes Received:
    3
    well if it's a p/glide car and you're NOT running a throttle controller you are kinda wasting your time imo... it's just not repeatable without one

    from there it's just a matter of getting the car up on the tire. and i know that sounds like a bs 'simple' answer... but it boils down to actually KNOWING what is happening. are you videoing the car from the starting line so you can replay it and really see what it is doing?? or are you going by what the driver 'thinks' it's doing? they are often VERY VERY different things

    'it shook the tires' is soooo universal. and soooo often mis-diagnosed. and i can say that because i tune AND drive and i usually try to keep my mouth shut until after i watch a video and/or look at pics of the footprint before i make myself a liar

    good luck
     
    #13
  14. suddendebt

    suddendebt Blown Altered

    Joined:
    Aug 16, 2009
    Messages:
    133
    Likes Received:
    0
    Thanks all,

    Car was really fat all weekend and then hurt a lifter or two on the last pass, no shake, some spin from what the pattern looked like and the 60's, Other than that no much to say, still try different things and learning what works and does not. also from here as well.

    Keep em strait
     
    #14
  15. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
    Staff Member

    Joined:
    May 6, 2003
    Messages:
    6,706
    Likes Received:
    132
    balance

    From the discription of the car shaking from 330 to 660, sounds like you have a tire balance problem. Did you bubble or spin balance your tires? Do you mark your tire to see how much it has turned on the wheel? If you bubble balanced your tire and they have moved more than 8" your tires are probably out of balance. You could also have a tube bunched up causing a bad balance problem.

    Take your tires somewhere and have them spin balanced with weights on the inner and outer. For reference have them spin them just the way they are to see how far out of balance they are before you peel weights off.

    The car shouldn't shake that far down track. If it's not balance it's more than likely underpower shake or a bad set of tires. More than likely I'd bet on balance. Altereds/FC's are very sensitive to balance, more so than a dragster. Always spin balance when possible, makes a big difference.

    Like Dale said, when you increase the tire pressure, you increase the hook of the tire by increasing the contact patch. At some point I'm sure you can put enough pressure in the tire to stiffen the sidewall enough to where you loosen the tire a bit. By dropping the tire pressure you allow the tire to cup a bit and put less rubber on the ground, allowing for more spin.

    With a beadlock it's a fine line because you don't have the liner to work as a dampner. You can drop tire pressure to get some wheelspeed with the beadlock, but you can create a problem with the tire squatting too much. I've got pictures of Lee Callaway's dragster a few years back with the beadlock literally no more than 4" off the ground it squatted so hard. You don't have that problem with the liners as much.

    Weak shake occurs when the tire hooks too hard, causing it to coil up, then uncoil, then coil, then uncoil. If you have a data logger, it's easy to see this spin hook cycle. Eventually it spin hooks hard enough it will take the tire off. Technically it had too much wheelspeed, then got into shake, but the root of the problem was not enough wheel speed. This is a real problem with beadlocks.

    With the liners it's not as much a problem due to the dampning effect of the liner. However, it is possible to weak shake, just you have a wider window. On a driveshaft graph, weak shake will nearly always show a flat spot in front of the shake 'hump' on the graph.

    Hope this helps.
     
    #15

Share This Page