I have a 69 Dart 496, 650 hp car weights 3600 lbs, caltracs with mono leaf springs, double adjustable Afco shocks all around.
I have been running drag radials for the past 10 years. I had my best 60' on a well prepped track at 1.40. Most tracks are not well prepped so I gave up on the radials and went to bias ply M/T 28' 10.5. Last week I have a best 60' at 1.46, most were 1.50s. It feels like the car hooks than releases. I feel the car is hitting the tires to hard. The caltracs are adjusted in the bottom hole. Slicks have no tubes in them. How much air pressure are you running in your slicks with a 3600 lb car? I am running 15 pounds now.

Start letting air out and watch the 60' numbers. Also try tightening the shocks and watch the time slip. Car is quick enough to benefit from a good DA shock.

I have DA Afco shocks on it on all four corners. When leaving the line, the car lifts a small bit than drops when I lose traction. I am limited with shock travel because of the Alterkation from end.

Work in 1/2 pound increments. You should be pretty close.

Air pressure is dependent on vehicle weight, IC, shock settings, clutch/converter, launch RPM, track temp, burnout and I'm probably missing a couple of things.

That said, you want to hit the tire as hard as you can, without beating the tire to death and being able to control the tire once you smack it.

IMO, you are probably 3-5 pounds too high on air pressure. Maybe. Depends on your shock settings. And all the above.

I try to use as much pressure as I can and still hook it. With a DA shock you can control the suspension not only easier, but with much more accuracy.

3450lbs b body here:
12.75 to 13 lbs air in slick.
rear shocks full tight on rebound
lower front end travel is a blessing for you.
we leave at 1800 to 2000 rpm depending on track- foot braking.
5100 stall

wheels up and carrying a bit.
Suggest putting car on 4 corner scales to dial up best weight distribution you can.

My guess is car should be somewhere between 11.5 and 13.5 lbs air pressure.
just guessing as we dont know much about car, if your on a trans brake , converter/clutch.

secondly- see if you can get someone to shoot video of car leaving- tire video and then one showing chassis working.

Just my thoughts.

I ran 29.5x11.5 MT slick for years, but was only at 3200 lbs going mid to low 11'0s. The car had super stock springs on it and later backhalved the car to ladder bars and went with the 29.5x13.5 MT slick. I ran 11 lbs in both slicks without an issue. Car currently has been a best of 10.49 with a 1.46 60ft. Have Hoosiers on there now (31x14 running 13 lbs), but will be switching back to MT on the next time I buy slicks.

You need to know that not all low air pressure gauges read exactly the same so use your gauge only(do NOT LOAN it out either ) and experiment with the air pressure in 1/4 to 1/2 lbs. increments to find what works best on your car at your track
I have three good low pressure gauges and none of them read exactly the same on the same tire I had to learn the hard way about not lending out my low pressure tires gauges out at the race, twice
Dang Murphy anyways

after putting cal-tracs on my 63 belvedere 3400lbs,29.5x9x15 M/T bias 14psi,the car went left first pass right 2nd pass.I just figured it was the track as I had never been there before,anyway lost 1st rd and just loaded car up a few weeks later the track posted picks and there was a good pic of my car just squashing the [censored] out of the slicks.the moral of this is you need someone or or video to see what is going on.I haven't been able to get back to the track and start adjusting shocks,WORK sucks.

493 Dodge wagon,4.30,caltracs, QA-1 single adjustable about 70 per cent of full stiffness,8inch converter.Phoenix F-9 30 X 9 bias slicks with tubes. I find that any. Pressure less than 18 lbs tears up the tire. Tried less air with variety of shock settings without success. Also tried Hoosiers DO-7 compound which were too hard and spun similarly to what you described. This was all with tubes. My car leaves pretty good with the 18 lbs Phoenix setup running from 1.39 thru low 1.40's depending on conditions. Just my experiences.Others have said I'm off with that much air but I don't have double adjustable shocks to play with at this time so this seems to work for me.

I will get someone to video my car leaving the line this weekend. It feels like the car hooks and than spins. It feels like the tire is running over it self. I have tried lower same thing but worst. very loose on top end. I will try some off your suggestion.Thank you.

Are you running a trans break or foot breaking..
the car is talking to you.. you think its running
over the tire.. it most likely is.. up the pressure
and stiffen the rear shocks.. get vid from the rear
quartering angle so you can see the rear and the
front of the car.. my wife use to video every pass
so I could see whats happening.. BIG HELP

10.5Wx31, 13.5lbs. Car weights 3340-3440 depending on ballast. 1.25-1.30 60 ft. 10.5Wx28, 15lbs. Car weighs 3890. 1.53-1.55 60ft. Sounds like your rebound settings are too loose. We've had good luck with M/T radials/ Afcos. However they have been revalved stiffer by Menser Shocks. The heavier the car, the smaller the slick, the more air you need.
Doug

I know you don't want to hear this, but put tubes in these tires. With this much weight you need to stiffen up the side walls as much as possible. With out tubes, you will use up the sidewalls very quickly.
My car weighs 3250 lbs (w/ driver), has reworked super stock springs, MT 11.5x29.5, 13.5 lbs, footbrake with 60' time 1.42.

Brian

I was told by M/T to put tubes in the slicks, I will next year. Trans brake, on a 2 step leaving at 2200 rpm, I have tried higher no difference. I have tried lowering the pressure not good results. I will up the pressure this weekend and try that.I believe the problem is what you say, big tire less air pressure, small tire more pressure. I have had the shock setting all over the place no difference. Thanks for all your advice. Will leave you know how it works out.

I put tubes in my 10.5wx31 this year. Also had the shocks serviced. Night and day difference. The car now repeats over an entire weekend within .00X 60ft best to worst.
Doug

I bet your front end is too stiff for a proper drag car. It should lift those tires off the track and set them down gently.