60 Foot help needed
 

Hi guys,
Need some of your wisdom on setup for launching this thing.
70 GTO stock body 3950 race weight.
~550HP, TKO 600, 4.10 rear, RXT Mcleod dual disc clutch
Adjustable uppers/lowers, no hop bars DMR
BMR anti roll bar, -2.5 pinion angle
8" rims stock width 12 bolt, fenders, etc.
MT ET Street R 28x11.50-15 Bias with tubes.

although the below pic and a couple outings i have made it hook, it is 1 out of 10 launches. Mostly spinning the tires. Tried all over the place on air pressure, shock adjustments, etc. spoke to suspension guy, says to look at my tires. had to go almost all the way stiff on compression to get rid of hop.

speaking to Hoosier they recommended their Slick non DOT 29x9-15 with D07 compound for stick cars. The tread width on these is actually more than i have with the MTs. I dont need DOT rating.

Video 12psi 4500 launch tires smashed all the way down. still spin
https://youtu.be/nBpIAicgp54

next one 14 psi 4000 launch more spin
https://youtu.be/3NzubSEvb3o

more details on shocks in video description. Thanks in advance

what shocks? stiff side wall or tubes may help. can you tighten the rebound on the rear? I think you need to tighten the front maybe with limiters, if the shocks wont tighten rebound also. Also, i think you are just in the groove, with a small tire and good power, it may make the difference in hooking or not. looks like you are getting plenty transfer, by the picture. you just need to keep it the front extended and the ass down. The front is rising but then unloading the rear when it drops back down, now if th etires are spinning it will drop the front right, but if it slowly descends th erear will stay loaded.

mystic,
QA 1 double adj in back. had them at 17C and 12R. goes up to 18 full stiff.
front are Calvert 90/10.
whoops lined up to the right.
i am running tubes.
i can stiffen the Rebound on rear. i can try to slow front end or if i can get initial traction keep it elevated.

i am no expert but when i was tryin gto get my tbrake car to hook on radials it was difficult for me to find the sweet spot. i think you have the right equipment. if it was mine, i would try to limit the front arms dropping so much first and see where it goes. if the arms dont drop as much, more motion should be transfered to the rear tires, which may ''fix'' it.
the car is trying to go up with good power and transfer, but the front end is falling down before it has enough momentum to not unload the tires in my opinion

I wouldn’t be afraid of trying more air pressure in your slicks, try 16 or 17 psi

Have you tried putting an automatic in the car? :bolt:

Seriously, it looks like in the second video that the right tire jumps up at the hit and the left tire gets squished. Might need more control from the shocks and more tire pressure? Could also be something to be gained with a control arm adjustment.

Hi Greg, see you in a couple months at drag week.
lose 1000 lb and put in a th400. got it! wink.

so far, i heard
slow front end travel. i have some CE 3 way adj front shocks to try slow the front.
more air in rear tires.
line up correctly doofus
tighten rebound on rears.
look at C Arm and anti roll bar adjustment.

thanks you guys are great. hopefully save me $700 not buying new tires/tubes.

is the MT r2 compound close enough to the st rating for a manual transmission tire?

Have you checked the extension of the shocks? It does look like the rear is twisting hard and picking up the driver rear tire. We went through this recently on a leaf spring car but it is the same idea......the shocks didn’t have enough travel and would bottom out quickly literally picking the driver side rear up just like this. It’s a full spool car and white smoked the driver tire. I’m no expert but our little bit of misfortune and learning may help you lol.

I’ve found and heard that 14-15psi with a stick is about where you want to be; and hard walls or tubes in bias slicks. Stick car here and above 15psi it’s spin city; I have M/T ST tires and tubes fwiw. How much bite the track has has been a problem for me; also I don’t have a slipper clutch, same as you. THAT is the hot ticket tho! I’d try lowering the launch RPM until it just about dead hooks; you want a little tire spin.

The no hop bars may be killing you... You're killing the tires. With the standard transmission you should be able to plant the tires with launch rpm and power. Do some reading on anti squat and instant center. Then plot yours. Or, take the bottom bar up(rear attachment point)in increments if they are adjustable.

Scott65 has a good point and maybe more negative pinion angel.
I ran a lot of negative angel when I was running a stick and try to get more
travel in the front.

GT.

I will get it up on boxes and do all the plotting for IC and my neutral line.
it usually leaves level with the ARB pic attached from another outing with same spinning issue. Also attached is the rear stuff. I dont have lower CA adj up and down at mounts but i probably could fab something. upper i have one hole left to go up or get rid of the no hop bars to go down at the axle mount.
Thanks again all.

I would have to wonder, is it possible those diagonal links could cause binding? Maybe that has something to do with why the passenger side tire wants to come up despite the anti roll bar? Maybe I'm seeing it wrong, but I'd think those could be counterproductive, especially at the track. Is the car at ride height in the picture of the rear suspension?

Due to the ring gear trying to climb the pinion gear this in turn rotates the rearend and lifts the right tire, so from a physics standpoint that makes sense; but yes the ARB should negate that. I’m no expert on ARBs but can’t they be preloaded some?

Curious what DMR recommends? Have you spoken with Dick Miller about the situation?

Yes, they can be preloaded. When right they should negate that affect, at least the great majority of it.

Unfortunately, that's not going to happen....the "Drag Week cancelled" email went out this morning....:(

Scott, those pics are at ride height. The rear with everything seems to move very freely in the garage. Don't know if they bind on track. they are track locators from Dick supposed to keep rear centered. When i didnt have compression high i was wheel hopping like crazy so i know it moves.

DMR said tires. of course. stiffer side walls. and slipper clutch. he is the one that spec'd all this stuff including no hop bars. He is saying im hitting tires too hard which goes back to the feedback on IC and %Antisquat.

Found this guy's video on geometry. interesting.
https://www.youtube.com/watch?v=IRHn...aCN_r9QEI1Q00I

Something to thing about is the redneck racepak. Take some zip ties and put them around the shaft on the rear shocks at the top. Make a hit and look and see if it has pushed the tie all the way down into the bumper on the shock. If so, may be a good indication that you need to go stiffer on compression, and maybe looser on rebound to try to promote some separation ( anti squat ) Obviously its hammering the tires, and maybe a combination too little compression and too little air is make the car wheel hop. Im not saying this is the answer, it's just a thought.