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Discussion in 'PSI Superchargers Tech Questions' started by rb0804, Oct 25, 2017.
Figured I’d bring this thread back to life in hopes for some education on slip joints.
BLUF: tighten them or run them loose? Spitzer 272”, blown alcohol hemi deal, average .950 60’, 2.4x 330’, low .70’s in the 1/8th in heads up trim.
The chassis has two sets of slip tubes. One on each upper frame rail in front of the cockpit and one on each upper rail behind the cockpit. We leave the ones behind the cockpit tight but loosen limiters on the fronts to about 3/8”.
I’m trying to calm the chassis down at the hit, specifically from wheel stands. It’s not uncommon for us to click the 60’ timer with the rear wheels. We have over 50 lbs in the nose and it helps but I’d like to find another solution. I have always thought tightening the front limiters would cause it to wheel stand even more, but haven’t tried it (yet). Thoughts??
I had a conversation with Brad Hadman one time about slip tubes/joints. His opinion was those slip joints and tubes are very dependent on track conditions to make the car work the same way every time. I don't recall his cars having any slip tubes or joints.
Uyehara cars worked damn good with no slips either. I've worked with Uyehara cars at 41.5" out to 46" out. 43 was the best. Later model Uyeharas would have a slip tube on the front upright on bottom. I think this was more to keep the tube from cracking/breaking during tire shake.
Crampton has Hadman's jig and they front halved Joey Severance's car there.
Hadman, Uyehara and Uncle Bob are retired. Chase Copeland, Jonnie Lindberg and Crampton are doing a fine job as the next generation....
Thanks Will. Definitely agree on track condition dependent. I’m just trying to understand what the variable is so Q1 isn’t a guessing game. I’ve noticed the slip tubes really start working against me when I hit the bar too hard, the chassis unloads too much and turns into a slinky if you will. It goes into a weird oscillation of springing/flexing at the front joints and it’s difficult to tune through the first 100-120’ because of it. If I can keep the car from squatting so much at the hit so it doesn’t go into that cycle, the run is much smoother. I just feel like I’m always chasing my tail on wheelie bar height and early wheel speed numbers without a clear understanding of how the slip joint adjustment plays a factor.
Spitzer built this car in 08 with the angled motor mounts as well so I have that working against me too. I feel we are close on the setup, but I need to figure out how to get the car moving horizontally instead of vertical then horizontal/flexing all over the place in the first 60’.
Whether it be wheel speed, bar height, or slip joint setup I’m just missing the mark on something.
We had a car with slip tube upper rail behind the driver. It was pretty consistent and would go down a dirt road but the engine was pretty far out and it didn’t tag the bar or if it did, it was really light.
In my experience it’s hard to slow the tire down after a good tag on the bar unless your cars set up to do so. It seems it either wants to keep going and zip it off or it wants to grab the track really hard and either shake or be slow. There seems to be some trickery or Magic or something that makes this work. It needs to be the correct amount out from the rear, with the correct crank centerline and the correct stiffness wheelie bar.
Out of curiosity have you tried hitting it harder so the tire spins initially instead of instantly transferring and tagging the bar?
Agreed. In all reality, I am pushing the limits on this chassis. It was built to run 6.0’s with a nitrous motor, definitely not what we’re doing with it so overall I am happy with how it handles the power. It’s just tough tuning down low. If I can get it past the first 100-150’, the car does great. A back half, moving the motor out and adding some length to the car is really what it needs but that’s not in the cards right now.
To answer your question, yes. Absolutely. On a good track, I’ll usually leave on full timing (or very close to it) and let it get up on the tire for a couple tenths then start the retard sequence. It still tends to grab the tire and dip wheel speed around .4 but pulls through and climbs again around .6. The trick to getting the curve to smooth out is what I’m after. It’ll still go into a pretty good wheel stand even when I do this, and carry the front end 12”+ over 100’ out. It’s close, just need to figure out what to pick at.
How consistent do you monitor tire pressure? Definitely a factor down low.
Chris Saulnier - Team Tigges
Mechanic Falls, Maine
Yes. We monitor and adjust for track conditions. I have thought about adding some to keep the tire from squatting so much, but don’t want to slow the tire down too much and have it change the whole tuning curve early.
Out of curiosity where are you at on tire pressure?
Your answer to the problems you are having is in the sequence you describe; with full timing it leaves and gets up on the tire in .2; then you pull timing (power) and it falls down and (sticks the tire); then you put timing back in (power) and it wheel stands (with power and a stuck tire). The fix is pretty clear and the car will speed up as well. If you do not want to go quicker pull timing in high gear but don't mess up the early run. My .02. Jeff Johnsen
the more flex the chassis has, you are creating more pinion angle and bite. same thing the more the car squats, the rear drops and creates more pinion angle.
my experience with converter cars is the launch rpm helps the initial hit of the tire get right. at that point, the car only knows how hard you hit the tire and how much static weight is there.
obviously once the car starts moving the chassis and wheelie bar comes into play. how hard is the 'lever' driving the tire into the ground? i would be inclined to lock the slips most of the time and just unlock them on really hot tracks and/or shithole tracks. as Hadman said, I feel like you may have a different amount of bite every time depending on how the car hooks initially.
i don't have any experience messing with them to tell you if full stiff will make your car wheelstand more or less. may be more since it's full stiff, may be less because it will take some bite out.
since you pack the front end, you may consider a 'rub bar' set up under the bottom frame rail to control squat like a top fuel car does and let the wheelie bar be just that - a wheelie bar.
with a converter car I think you should be able to hit the tire hard enough to keep it from squatting and really needing an anti-squat stop/bar. if you do need something to control squat, the lower you can get away with, the less it will upset the car IMO. you can hit the nail harder the further the hammer is away.....