Drive Shaft Speed Convertor Swing Arm Car Tire Shake Help

I have a 540 big chief Littlefield HH Retro 20% OD setback ~2 in. PG, 1.80 low, 10" Converter stall 6400, swing arm ohlins gas shock, MSD 10, 245" Top Dragster. 34.5 M/T (3186) on 15" wide beadlocks, 3.90 rear gear, leave rpm 4200, pull 10* timing for 1.5s to try to have 1.00 60's to save drivetrain stress.

Intermittent shake starts about 60'. Not every run, but usually once or twice during weekend and usually causes me to lose during eliminations.

Need help with suggested drive shaft speeds for converter driven suspended dragsters.

With this combo for last 2 seasons, my 0.25s averages in the 1800 range and the 0.5s is usually in the 2000 range. I have had slightly higher and slightly lower at interval. There does not seem to be a pattern to the shake. I have seen it shake with the same numbers that it does not shake on another run.

One thing that I do see it that if the 0.25 and 0.5 are close or the 0.5 is slightly lower then it shakes.

I set this up to hit the 1.00 60' range to be easier on drivetrain parts. However, I have not changed this over two seasons. I am willing to make wholesale changes to eliminate the shake that is costing me rounds/races.

I have shock setting in the middle, I do plan to significantly tighten both rebound and compression at next race/test session.

Should I be shooting for lower DS or higher DS?

How does higher DS speed (read: spin) effect consistency?

Is the timing curve contributing to not staying up on the tire?

Options:
-Leave harder/softer.
-Reduce/increase launch timing. (although I have crab cap so more than 10* could cause rotor phase issues)
-Reduce retard timing duration.
-Shock setting.

Thanks very much for your help.

 

No real experience with a suspended car of this nature; some PM stuff but not a digger. If I say that wheelspeed is wheelspeed and the shock only controls it before the fact....then I think you're too low. I think you're gearing is ok for your setup, nothing too aggressive. I think the timing that's coming out of it is way too much. I'd go half that much and see what happens. Don't forget that tire psi. will play into this as well; so will the setup of the torque converter. If the stator is way too tight then it could be a beast down low requiring all the timing out, but a total pig on the top end because the motor doesn't make the power to utilize it.

Brandon Booher
NHRA TAD #34

 

will's question

I am seeing an lazy "s" curve on the graph.

Most have a step ramp up and then a step short ramp down a couple of hunderd RPMs then it starts gradual climb up. If there is shake on the run most times there will be the lazy "s" curve.

I assume this would lend itself to your point that I may be loading and unloading the chassis.

 

tire PSI

yea forgot to post about that. we have historically run 6.5# in our M/T but this set the 6.5# had the tire rounded and the run pattern at end of track was a lot narrowed than in the past. So we lowered to 6.25 and the wear pattern spread back out.

Will verify gauge accuracy.

 

shake

here's maybe useless doorcar advice...it won't weak shake. Wherever it's shaking pull out timing. You're .5 wheelspeed is not crazy. You could try making more and see if the tire is happier. You can tighten rebound on the shocks or hit it with a faster ramp.
M/T is rarely seen with an auto. I've heard too aggressive. Hoosier owns the record book with converters.
As far as pulling timing it's all relative but don't base anything on hemis. The roots bigchief hits hard down low and will rattle easily.
I would soften the bad spots on the graph until it runs clean and then slowly tweak timing in until you find out what it will take.

 

Leave the compression alone on the shock. 2 clicks from full stiff on extension.
Drop the tire pressure and see what the wheelspeed numbers give u at .25 and .5

The combination of too much tire and and the shock moving too quickly on extension is killing the wheelspeed. If it still refuses to get on the tire do as Brandon suggested and change amount or time of timing retard.