Bin fighting this all year. Only difference from last year is the flywheel. Last year and years before I had been running an aluminum wheel. Found it was warped over the past winter. Installed a steel wheel which is about 20# heavier. Now the car blows the tires off at launch. I've dropped my 2 step all the way down to 3K from 5K. I've dropped tire pressure down from 15 to 12 psi. I've loosened the rear shocks from 9 to 7. I can't get the car to plant or even control the amount of off line spin. I'm pretty confused at this time..

car weight with me in 3926#
slicks 29 12.50x15
gears 4.56
Rancho 9 ways out back
90/10 up front
Mopar SS springs

Any suggestion?

I'm no expert but I can see 20lbs of additional rotating mass at the flywheel driving the tires much harder at the initial hit exposing shortcomings in the suspension.

There is a lot of knowledge on this site so I'm sure you'll get lots of good info but the common thread is always get some video showing what's happening. I'm in the same boat and making progress thanks to this forum.

Take care.

How old are the tires and how many runs on them?

Yes. 20 pound increase is significant in a flywheel. Lots of extra inertia. You've already changed your shock settings and air pressure. It might be time for new tires, maybe a little wider, if you have the room. What clutch and trans are you running? Might need a little lighter clutch plate to allow some slip.

Kind of figured that adding 20#'s to the flywheel would mess up my set up, but also thought that I could adjust for it with 2 step, shocks and tire pressure. Tires.... They are old, BUT, still have good depth and I treat them with VHT before every race. I can put my finger nail into the tread area and it leaves and indentation. Like I said, last year I had no issues 'til toward the end of the season when the flywheel started going bad.
I have ALWAYS run an 11" CFDF clutch. I drive my car on the street. I don't want to get into adjustments and such. Too old to be crawling under the car before a street cruise or race event. I also realize that what I do with my car is different in a lot of ways than most. There are certain things that I can do and won't do. It's one of those "nitch" things that only a few of us fall into. A good friend of mine just suggested lowering the tire pressure down to 10 psi.

On the tires..........how old is OLD. If they are more than a season old, they are likely junk, no matter what you treat them with or the depth of the holes. The sidewalls are SHOT on a 3900lb stick car....BANK on it

Oh! they are way older than one year. Probably closer to 5 years, but I don't race every weekend. Maybe 4-6 times a year is all.

The slicks are removed after every race and stored. Last year they were working good for me except for the flywheel issue I had.

I remember one season when I was having troubles going any faster than 9.6s. Kept doing things to make more power. MPH would go up, but never a better E.T.
I ended up getting new tires. When I took the old ones off, they were so structurally wasted, that the tire wouldn't stand up and keep it's shape when off of the rim. These were 31w tires(stiff sidewall) The new tires with no other changes went 9.20 on the first hit.

Remember, I said that I started with the shocks on the highest setting (9). Went lighter thinking that it would hit the tires harder. Usually I run the shocks on the highest setting (9).
From what I've read so far, it seems that a new set of slicks maybe the ticket. I'm going to hate pitching these slicks, even though they look good to me.
What about,...I also run tubes in the slicks. Maybe dropping the tire pressure way down (for me), to about 9 or 10 psi? Do you all think maybe this might work?

Sell the old slicks on craigslist for 100 bux

9 or 10 pounds is kind of light for the weight of your car. Be aware of the way the car handles down the track when trying. Maybe try adding 100 pounds ballast to the trunk first. New tires does seem like the ticket, though.

I'd try a set of stiff walls, with tubes.

'thought soft sidewalls were the way to go with a stick car????

You might try letting the clutch out under 3000 RPM to se if the car will bog or go My old 1970 NHRA A/S Hemi Cuda( a 383 car originally converted to the hemi drivetraiin and motor) would bog with 4.10 and the 1968/69 OEM 173 tooth heavy flywheel on a good track on 9x28 inch slicks. I had Bob Lambeck put a set of 4.89 ratio gears in the rear and it never bogged again umtil I put a 18 lbs 130 tooth aluminum flywheel in it I would have the old aluminum wheel surfaced to see if it would be useable agian or not

Sounds like it's time to step up to a shock with stiffer rebound valving. You were full tight and now you're hitting the tire even harder. A good slow motion close-up at launch will lead you to what is needed.
Doug

Cab,
My aluminum wheel cannot be resurfaced. It's a Mcleod wheel, and they want way too much to either replace the insert or for me to buy it outright and replace it myself. (I do have that capability). Anyway, from what I've learned, aluminum wheels don't last long in a street/strip application. mine lasted only 2 or 3 years. (can't remember exactly}.
If I have to drop the 2 step below 3K, what's the use in having a slick?
Last season, my 2 step was set between 48 and 5200. Tire pressure at 15 psi. No bog. Launched hard, but due to the aluminum flywheel issues, the clutch would slip in high gear. Hell, I'm using the same clutch assembly from last year with the steel wheel and it grabs hard.
Nothing has changed from last year 'til now except the steel flywheel. This is what's so confusing....

I think replacing your 5-year-old slicks would be my first step..

Negative, there ghost rider........LOL!!!

3900lb stick car, I would want stiff sidewall tire, tubes, beadlocks and anything else I could do to stiffen em up.......LOL!!!

As to your 5 year old slicks. The sidewalls were probably toast about 4 years ago depending on how many licks they had

If they are Hoosiers, the sidewalls were too soft when first aired up.