To show the up hill battle with gears your against, this will be with 27" tire hitting peak hp at finish line no converter slip calculated. Obviously you don't have to gear for max 1/4 mile time but will shows how compromised of gear choices we choose.
400 hp 318 make 400 hp around 6000 rpm and 360 at 5300 rpm for comparison sake.
Say we cover the range of 100 to 110 mph in the quarter mile. Gears are rounded.
318 @ 100 needs 4.88 gears to hit 6000rpm
318 @ 110 needs 4.30 gears to hit 6000rpm
360 @ 100 needs 4.30 gears to hit 5300rpm
360 @ 110 needs 3.91 gear to hit 5300rpm
For those that talk/see in torque say the 318 and 360 are making 1.2 lbs-ft per cid.
318 = 382 lbs-ft, 360 = 432 lbs-ft , 382 x 4.88 = 1552 lbs-ft to the tires, and 432 x 4.30 = 1548 lbs-ft to the tires, practically the same.
3.21 @ 100 = 3995 rpm
3.21 @ 110 = 4394 rpm
Need some kind of stroker big block to hit 400 hp at these rpm.
Bottom line 3.21 gears would be optimal for like a 400 hp 470-500 cid engine and even though both a 400 hp 318 vs 360 need deeper gears the 360 would be a lot better off with 3.21 vs 3.91/4.30 gear than 318 with 3.21 vs 4.30/4.88 gear.
Not saying build a bigger engine, just showing how much of an up hill battle gearing wise a decent hp smaller displacement is up against, imagine how much gear a 400 hp 273 would need.
(400 hp 273 @ 7000 rpm = 110 mph = 5.13 and 100 mph = 5.62)