Fighting tire shake

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Neil Morley, Aug 29, 2017.

  1. Neil Morley

    Neil Morley Member

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    I know I have a challenge on my hands but I have a 65 nova grudge car with a blown BBC making approximately 2200 hp, the car is a ladder bar car and is very heavy ( 3850lbs with me in it) , the car leaves initially pretty good with good wheel speed but gets out 30-50 ft and violently shakes the tires(33/15/15 MT). I've tried air pressure from 7-8-9 psi I've got Santhuff's double adjustable shocks on all four corners and had the extension set 2 from full tight on the rear it is smashing the tire pretty hard but on my data logger I'm seeing the convertor is only flashing to 5000 rpm and Im leaving on the two step @ 4000 rpm , I have three holes for the front of the ladder bar and currently it's in the middle hole with the lower bar pretty much level, now I know I'm asking a lot with such a heavy ladder bar car but I'm thinking my convertor is way too tight, let me know what you guys think? Thanks!
     
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  2. Neil Morley

    Neil Morley Member

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    I'm sorry I forgot to mention it's a powerglide with 1.80 first gear and 4.56 rear
     
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  3. Mike Canter

    Mike Canter Top Dragster

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    There are two main types of tire shake. One is low speed or when the you fall off the tire and then there is high speed where the tire slips a little, grabs a little, slips a little and continues until you blow off the tires. If the chassis is right and the shocks are correct then everything depends on wheel speed. My guess is you are either not getting up on the tire or you are falling off the tire and you need more wheel speed just before you start getting the shake. Santhuff baseline starting recommendation for your car with aluminum body shocks is from full tight (clockwise) Rebound on top is 4 sweeps out from full tight and compression is 8 clicks out from full tight. How does that compare with your setting from full tight? Your car is is very heavy.

    http://www.santhuffshocks.com/technicalinfo.html
     
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    Last edited: Aug 29, 2017
  4. Neil Morley

    Neil Morley Member

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    Rear extension 2 from full tight 10 on compression front is 7 from full tight 7 on compression and do you think my convertor is too tight mike?
     
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  5. Mike Canter

    Mike Canter Top Dragster

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    Who made the converter?
     
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  6. Neil Morley

    Neil Morley Member

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  7. Neil Morley

    Neil Morley Member

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    It's a 10.5" weld together, if I remember lane at PTC called it one of their pro mod convertor said but it wasn't terribly expensive
     
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  8. Neil Morley

    Neil Morley Member

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    Also I wanted to ask if anyone has ever used the tire shake box built by RPM and if so did it work??
     
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  9. Mike Canter

    Mike Canter Top Dragster

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    Call PTC and talk to them about the converter and what rpm you are seeing and see what they say. When you say a Promod converter that doesn't mean much because your car is way heavier than most Promod. Have you got a data recorder? If so what wheel speeds are you seeing at .25, .5 and 1 second?
     
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  10. Neil Morley

    Neil Morley Member

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    I do have a data logger and I can record drive shaft RPM and I will take a look at it and get back , thanks mike, also I have some video that shows the tires all wadded up and distorted
     
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  11. bob szabo

    bob szabo FC / altered

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    We found we could modulate the launch power with enrichment to avoid tire shake. We used the high speed, set to open just after the hit, to lean out to the best power level for the run.

    We had good success with different combination of main bypass and high speed jet sizes to increase the launch enrichment to soften the hit and still maintain a best power high end.

    For example, a 0.040 inch high speed bypass with a proper main bypass brought up the power on the hit on our blown alc racecar.

    A larger 0.050 inch high speed bypass with a proper (smaller) main bypass would kill a noticable amount of power in the launch, softening the hit, with the same high end power.

    FYI: Our ProCalc calculator determined that the 0.040 inch high speed jet in our blown alc engine made an AFR difference of about 0.15 points between the low end and the high end. That smaller amount set up a high launch power.

    The 0.050 inch high speed jet made a greater AFR difference of about 0.2 points which killed a noticable amount of horsepower at launch; then a kick in the back when the high speed opened. That is discussed in our fuel injection secrets book.

    Even larger high speed jet sizes with the appropriate (smaller) main bypass can be set up for just about any AFR difference. The launch power can be softened with more enrichment to work better with the converter. The proper combination will maintain the best high end power.

    It is really easy to modulate the launch power with enrichment (to soften the hit) by changing the launch AFR while maintaining the high end AFR for best power. That can be done simply by using the proper combination of main and high speed jet sizes with an opening poppet pressure just beyond the launch.

    Our calculator was developed to do all that for different air densities, fuel splits, fuel distributions, blower overdrives, and different percentages of nitro, as well as blown or NA.

    Bob Szabo
    http://racecarbook.com
    bob@racecarbook.com
    Ca, USA (916) 419 6694
     
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  12. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Can you run a bigger tire? You got a lot of weight so square area will help.

    Most likely it's going to take a very loose converter to make that gear ratio work in my opinion. For that heavy of a car, that's a pretty tall gear. Without knowing a lot of details, if the converter is that tight, the car is that heavy, something's gotta give, and it's the tire.

    I will add to the 'weak shake' discussion, in my opinion. There are two types of weak shake which shouldn't be confused.

    Drive over the tire shake. This usually has a tell-tale flat spot on the driveshaft right before the vertical tire shake spike signature. This can be from never getting on the tire and the tire cycling through a spin hook cycle due to the sidewall wadding up. It can also be influenced by taking too much power out, hence 'sticking' the tire.

    Not enough wheelspeed/ground speed shake. This is also 'weak' shake. Let's say you didn't just wad the tire up, but you have a conservative amount of wheel speed, then you put power to it, clutch/converter comes in, and the car tries to accellerate too fast in a small amount of time because of the lack of wheel speed. Technically the shake is 'aggressive' shake, but the root cause was not enough wheel speed.

    A lot of people love the weak shake theory, because the solution is something we usually WANT to do - more power. However if your driveshaft is nice looking arc without a bunch of spin hooks, well, it's probably too aggressive.
     
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  13. Neil Morley

    Neil Morley Member

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    I do have a data logger and I can record drive shaft RPM and I will take a look at it and get back , thanks mike, also I have some video that shows the tires all wadded up and disto
     
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  14. Neil Morley

    Neil Morley Member

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    Thanks will for your response as well, as far as a larger tire I can't go any taller without raising the back of the car and it already has a little rake to it and as far as wider I could probably squeeze an inch wider but as far as Mickey Thompson the next size is a 33/16/15 but the section width is actually like 2" wider and would rub on the frame and if I moved it out I would have to cut the quarter panel which I won't do but like mike said earlier I need to study my data logs carefully and try to figure what's going on, I was just thinking that what they claim typically causes tire shake on a clutch car is the clutch locking up to early which I think essentially the convertor is doing the same thing, just a fluid coupler instead of mechanical? I don't know and you guys probably do know but I've heard the convertor should stall ( flash)no less than 6000 ? Mine is only flashing to 5000 and the data logger shows it taking a full second to get to 6000 where is already shaking and I'll have too look again but I want to say it's barely making 20 lbs of boost but will make 38 lbs at 7900 rpm. But thanks again for all you and your knowledge, I appreciate all the help I can get!
     
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