Making The Weak 7-1/4 Rear Axle Live... Kinda
I'm building a 318 for my 73 Dart, it should make somewhere in the ballpark of 300HP. It will be bolted to the A904 auto transmission with a stock-ish stall converter. The car's weight is somewhere around 3450 pounds with driver.
at 300hp and the cylinder pressure at same as before the build, your 318 at stockish stall will have about the same power as the stocker did, up to about 3000rpm; so I wouldn't worry too much about it. But I would highly recommend a Suregrip to split the torque between both spiders.
Typically tho, guys don't bring the cylinder pressure up on their 318 "performance" builds and if the pressure is less than stock, at stock-ish stall, then then the power down there will be LESS than stock, so then your conversion will be easier yet, on the rear gear.
Next, install enough rear tire so it can't spin at all at any rpm in first gear, and then the 7.25 will last forever, so long as you don't do silly stuff like neutral-drops and chit-hooks.
If your cone-type SG loses it's sure grippiness, it can be reconditioned. If you wait a lil too long, well, you wanted an 8.75 anyway .........
Two things kill the 7.25;
1) shock loads shatter the pinions, and
2) peglegging it welds the crosspin to the spiders. Make sure you install good oil and plenty of it for cooling.
