[Alan Roehrich]

That's a bit too much drop between gears. It needs to stay up above 5000.

I'd expect to use a 5.14 with your combination, I think you'll find the 4.88 won't run well. Consider that most run a 5.00 or 5.14 with a 396 or 427, both of which have 0.250" more stroke.

The secret to going fast is average HP between around 5200 and 7400, and having it recover really well from the shift. You cannot give up average HP to get peak HP, or it will not recover from the shift.

Call Tim, see if he has the lobes to grind you a cam with between 254 and 258 in the intake, and 266 to 268 on the exhaust, between 108 and 110 LSA, 109 LSA, in at 107 is probably a nice compromise. If you can't tighten up your RPM drop, you really need to look at a 107 LSA, in at 105. It may not make great peak numbers, it might not look great on the dyno. But on the dyno, it does not have to recover from the shift, in the car, it does, and if it drops below 5000, it's probably way below peak torque, and won't recover well.

The modern big block lobes will be stable to 8000 RPM, provided you have 250 on the seat, and 525 open, you need a spring rate around 525-550 per inch. You cannot control that big intake valve with anything less. If you're not running at least a 7/16" x 0.125" wall pushrod, it will never work. The pushrod will be a secondary spring, and make everything surge and bounce, even with a gentle lobe.

For a single step header, I'd expect to see something similar to an 1-7/8" to 2", with 16"-17" long steps, for a total of a 32"-34" primary, and a collector about 16"-18" long, merge style, tapering from 3" to 4". If you went for 2 steps, split the 2" section into a 2" and a 2-1/8" section, each about 8" long. That's a real simple merge, you could do more if you wanted.