I would like to know if I left any on the table. I recently purchased a spool and 4.86 gears for my 72 Duster: 3060lbs(w/me), 340 .030 over,ported J heads,Racer Brown STH-42cam,1 3/4 headers, 2.74 low geared 904,29.75 tall tires, 4800 converter....crossed line @6200 w/4.56 gears. I was thinking if I went w/5.13 I would spin too far out of the torque curve.

Can you list the specs on the cam? I'm not familiar with RB.

This is LA engine. Specs: 254@50, 300 total, .520 lift 108 lobe CL, installed 105 ATDC.

What do you currently run with the 4.56? 11.50 @ 114?

12.03@111.2, Racer Brown cam took me from 12.38 to this point and it still pulls past finish.

Since you have the 4.86, I'd try them. 5.13 looks like it will be too much.
It's been my experience, 340s like tight lobe centers and alot of converter.

Thanks, I have a habit of second guessing myself.

"Question everything-assume nothing"

what carb/intake are you running? how much compression? what rpm are you shifting at? what valve size?

what size is the converter? I bet your leaving something on the table with 4800

Shift @63501st,67002nd,750 Holley w Proform main body-Quickfuel metering blocks, Holley Strip Dom. Converter stalls @ approx 4800.11.6:1 comp, 2.02 Valve

What rpm does the engine pull strong to?

Tough Question, only 4 runs on cam last year. Three w/tire slip, and one solid run after mods on the next outing. Seems to pull pretty good at 6700.

what size converter? 8"-9" ?

Turbo Action 19508XXSM42. Listed as an 8" actually is 9.5 Dia.

i assume that its an 8inch converter? i ran a very similar combo to yours years ago that ran around 11.20. the heads were all done around 6600rpm.i shifted both gears at 6600 trapped about the same.you definately don't need more than 4.86s have you tried advancing the cam some more say around 102? a 2inch carb spacer always helped on mine also.how long is the header collector? it needs to be about 18inches running the rpms your at.thats a few things you might try once you get back on the track...good luck