Giving up on the M/T drag radials after years of trying, when the tracks were well prepped good traction, when not no traction. Just bought 28x10.5x 15 stiff sidewall bias ply. Car weights 3650 lbs, 650 hp, caltracs, trans brake.

Where should I start with air pressure? I was thinking around 9 lbs.

My street car runs 10.5Wx28 M/T, 3875lbs, 15 psi. Race car when I ran 10.5x29 M/T 13psi, 10.5Wx31 13.5psi, 3350lbs
Doug

12

I started at 12 but killed the tire so 13 next time for me............went 1.33 like that.........

Like stated, 12-15 psi should work for you. 9 psi, way too low for your weight.

Not all tire gauges read the exact same pressures, start high and look at the tire wear pattern and the time slip while going down 1/4 to 1/2 lbs at a time on the pressures to get the best results in your 60 ft times Are you running tubes and what width rims are those tires on? What RPM do you leave at?
On your deal I would start at 14 or 15 lbs and go from there If it dead hooks at that pressure go up 1 lb. at a time until it spins and then come back down to the best 60 ft. times
The last pair of 9x30x15 bias ply slicks I ran on my old M.W. stocker over 20 yrs ago had 18 lbs in them, they where mounted on 10 inch wide wheels and we where eleaving from 2700 to 3500 RPM foot braking, 1.42 60 ft times That was long before the drag radial tires where introduced

I tried my new M/T 315/60 Radial Pros last weekend and on the 2nd pass I broke a axle with 18 lbs of air with home made Caltracs and stock leaf springs. I will never run a slick again. This was on a Test & Tune night and track prep is not a priority. Had a 1.35 60 ft. on first pass.

No tubes. I have 8" rims, I know M/T says min 9' but it is what it is. I was leaving at 2700 rpm, will try to leave higher if they hold. My best 60' with radials was 1.41. I will start at 15 lbs see what happens. Thanks for your replys.

All cars and combos are different. Use what works bets in YOUR car. FWIW my Valiant ran 10.25 generally and went 9.0 at 150. The heads up car uses a 29.5x10.5SS tire and we are anywhere from 9.25-9.75 depending on the track conditions.

I have a 493 in a Super Street car that dyno tested about the same as yours. You are making a lot of torque for that little tire. How much converter? Try leaving about 2-400 rpm below max converter flash. The sidewall angling in from the tread to the rim width is kind of a small problem. M/T's provide a lot better starting line stability if the rim is wider than the tread. More so on a stiff sidewall. I agree on the 12-15 lbs. of pressure. I run a 3169W-33X10.5W. It's 11-3/4 tread on a 16 inch wheel at 2,800lbs. 10 lbs. pressure.

PTC 4400 stall converter.

Does it actually go that high? Or higher? Sometimes leaving at a lower rpm winds the converter up like a rubber band and it's too much for the tire initially. Not giving the converter enough room to do that sometimes will help. I went 1.22 60' leaving at 4,000. 6,100 stall converter. My car will react quicker at a higher rpm but usually those 60's are 1.24- 1.28. To be honest, I haven't tested the wide open program in the last couple of years. I'm always on the t/stop. With your kind of hp and tq, it seems like you should need wheelie bars.
90-10 shocks on the front?

that car is too heavy for anything less than 12lbs..
by the way .2 lb changes are a big change in a slick . so when you get close i would only go in 1/2 a pound increment changes.. then 2/10ths after that...
something else you can do is a hole shot on concrete and then look at the patch pattern left on the concrete.
if you see dark lines on the outside edges of the skid mark .. then you need more air..fwiw.
Too low air pressure in a car as fast as your will be all over the place at high speed/down track. and a hand full

my experience is to be down around the 10psi range the cars are 3000lbs or less.
imho

fwiw. my car weighs 3310lbs if i go below 11.2 lbs ..i know it cause the car wanders down track . Duster 28x10.5 x 15 M/T slick

Not sure what RPM I left at when it had a 1.41 60 ft. Peak tq at 4400 rpm, peak HP at 5600 rpm. I shift at 5600 rpm. I tried shifting at 6200 rpm, car slowed down. PTC convertor. Weighed car 49% on front, 51% back. Front end not very loose when trying to lift it. Only have about 4" travel front end Alterkation front end. Lifts front wheels about 2".