If your current 420 lb springs are being compressed 3.63" then you have ~1525 lb on the nose of your car. To get an 18" Moroso spring to compress to 9" without cutting coils you'd take 1525/9 = 170 lb spring.

If you can't run bottom 10's and into the 9's with your planned combo and a 4" stroke you're in serious trouble.

Todd Geisler, a good friend of mine runs 9.60's @ 138, 3450 lb with a basic N/A 13.3:1 460, BMF 310's TH-400, 4.10's and 275/60 drag radials.

How much SLR is appropriate for a 3500-3600 lb small tire, leaf spring, 3-speed, 700 HP BBC N/A powered combo, 7200 RPM shifts?

My current SLR is 11.83:1 with 30" tires.

P.S. With the tall tires the rear gear would simulate a 4.52:1 with a TH-400.

Fill us in on the combo details of your 512 incher please.

You'll never consistantly hook a 4.25" stroke on 9 or 10" tires. You hear that Bob West?? Might as well give it up! :lol: Welcome to the site 40 Coupe... Bob's worked his ass off to get that thing hooking. On marginal tracks it's still got traction issues. He was at Mokan last weekend and...

I think it depends on your chassis setup and planned/intended usage. To generalize "bigger is better" is a pretty broad generalization. If your car is 2900 lb and backhalved it will easily run mid 9's with a conservative 13.5: 468. Certainly, if this is a "small tire" bracket car...