Rear Shackle Geometry - how are you adjusting it?

[Duke5A]

Re: the other tech stuff...hmm, my thinking goes along the lines of 'if there is another way to a better result I am willing to look at it, even if that means changing some hardware'. What @Duke5A shared is pretty good stuff, I know this works for him very well. It is not the sort of stuff I could use b/c of my crazy ass insistence ontrying to max out that factory setup with barely any other changes (exception being replacing rubber with poly bushings).

You have 300# T-bars in the front end, right?

Now, I'm not a chassis expert by any stretch of imagination, but I would be concerned that using this approach is going to yield something that will perform both poorly on the street for handling and lousy at the track for traction. It's the entire reason why I have Cal-Tracks and the Viking shocks. Take it to the track it's all a matter of adjustment to get it to something that performs reasonably. When it's time go home just set it back and get the handling characteristics back. Getting that tunability in the suspension that allows you to have the cake and eat it too.

Something to ponder.

 

[Oldiron440]

Those times were recorded before tracks were spayed from one end to the other, maybe 50 to 75’ with a pump up spray bottle was all they got. I seriously don’t think the spring shackles are a problem at this point but the springs themselves and possibly the shocks being to stiff and to short.

 

[Oldiron440]

I was thinking about this tonight and something else that will effect how your rear suspension works and your sixty foot times is your torque converter. Not knowing anything about your combination do you have enough converter?

 

[M_Body_Coupe]

I was thinking about this tonight and something else that will effect how your rear suspension works and your sixty foot times is your torque converter. Not knowing anything about your combination do you have enough converter?

The converter is a 9.5" Dynamic 4K stall piece. Flashes to about 4200-4300 now with the 408 stroker, previously it was spot-on at 4K with the 360 motor.

If anything, especially given the street setup, I think this may be too much converter as I simply haven't been able to launch the car w/o any wheel spin, and this is even with a good burnout.

The tires are Nitto NT555Rs, 275-60R15s, and 4.10 gearing out back.

Challenge of course is that the cam (CompCams hydraulic roller, XR292 but on a 112LSA, 240/248 @0.050") needs a good amount of stall speed to get into the powerband, and given the resulting tire spin I am concluding that I need to plant the tires harder, and this of course led me down the path of: maybe the rear suspension is NOT doing what it's supposed to be doing to enabled that?

I suppose @Duke5A is spot on in his assessment: the car setup is really NOT meant to allow that kind of a chassis movement. Heck, I'm running KONI adjustable shocks (5 way valve - rotating the shock adjusts it's rate) so that is pretty much a static setup - once set you live with it until you decide to dig into things and re-adjust. I have them set at about 3/4 right now because I am focused on controlling the chassis movement, which is essentially counter to what I should be doing to allow the chassis weight xfer to occur.

 

[M_Body_Coupe]

You have 300# T-bars in the front end, right?

Yup!

...Now, I'm not a chassis expert by any stretch of imagination, but I would be concerned that using this approach is going to yield something that will perform both poorly on the street for handling and lousy at the track for traction...

I suspect you are quite correct on this Mark.

The more I think about this, the more I am starting to conclude that getting this 'brick shithouse' to handle simply means it's NOT going to perform at the 1/4 mile track!

Seems like a no-brainer, yup, I'll be the first one to admit it...LOL, but man, that shackle geometry just begged to be examined ya know???

 

[Oldiron440]

The need for the shackles to lean back towards the the spring end is for the simple reason that you don’t want it to over enter with the spring fully arched. You need to remember the shackle is a follower and other than length it doesn’t contribute anything to geometry at all. So the only concern is that of over center and the folding the leaf spring in an arch that would be dangerous possibly causing a wreck.