WHAT HP GEAR AND CONVERTER A NEED FOR RACE AXLES

Car weight 3050, HP 350,Detroit locker w/ 4.30 gear, converter 9" specific to this set up and a 8-9" slick(9" might not fit). Do I need an after market slick or can I get by with the factory axle?

What rear end and axle sizes are you wanting help on?

8 3/4 either a 742 or 489. Standard A body length,

At 3050 lbs, my sense is the stock axles will stand up pretty well, but OP must have typo’d the HP number. Certainly you’re not worried about axles with 250 HP (???).

OOPS! I made that much with my tweaked 273-2 bbl. Your right 350HP.

unless you throw trans brake into the combo... I'd say you'll be ok.

Remove the driver side axle and look closely at the splines to see if there is any twisting of them in the splines, if not your golden Go race the car and look at the axle every other year until it starts to twist the splines, once it twist more then one full spline replace them both with a good set of race axles.
If the splines are twisted now more than one spline now go buy a new set of race axles and look at them as needed every couple of years

fwiw we ran stock spline Dutchman axles with pretty good success, but they did end up twisting. Of course then we were stuck with a decision upgrade that left four different gear combos useless without new spools. It was at that point I sold all the gear sets and went D60 in my old car. The same scenario pretty much played out in the Duster too... even now I'm waiting for the axles to be shipped back with the larger 5/8ths studs we should have gotten in the first place. If I only had all the money back I'd spent twice

My '71 Demon was raced for years w/ a 340 running 7.40s in the 1/8 w/ stock axles in the 8.75. They still look great. Not sure on the weight, but nothing was removed from the car...all steel and full interior. I feel very confident this motor was making a good bit more than 350 hp.

When I took the rear apart, I did find the remnants of about 3 teeth off of the ring and pinion. They were leftovers from a previous breakage b/c the gear in it still had all its teeth. Whoever repaired it didn't do a very thorough cleaning.

The spline may not be the only place to catch failure.
Bill Jenkins painted a stripe along the axle 40 years ago.

This^^^^^needs to be watched too.

when you compare a stock 12 bolt axle to a stock 8 3/4 axle it will help you understand why some racers do something differently than others
The stock Dana 60 12, 17 and 23 spline axles needed the paint stripes

Unless someone can state without exception that all shafts maintain a consistent diameter from the diff spline to the bearing retainer end ( no reduced diameter in other words ) then one needs to consider the whole shaft in regards to twist, hence the suggestion to watch for shaft twist and not just spline twist.

I have seen shafts with a reduced diameter between the flange and diff - on THIS shaft - what is going to twist first?

Like the 71 Demon above my Duster with a 383 and 4.88 8-3/4 stock axles and 12" slicks ran 11.60s and had no problems, of course I only had the factory street Hemi vert. I think no matter what engine, once you start high rpm launches then the problems arise. 5000 converter and radials, look out axels +

All the broken or damaged 8 3/4 axles I've seen or heard of all twisted the driver side axle spline at the end of the splines nearest the brake backing plates I have broken two 8 3/4 axles at that point also
Mopar rolled those splines on those axles, they are not machined like race axles are

To the original poster...everyome has their opinion on this. I will give you mine.

My car made it around 200 passes on a 100% stock 8 3/4 3700lbs, drag radials, and a trans brake. Went a best of 10.08@136mph on boost.

Only when I accidentally let the transbrake go on 20psi of boost at 5000rpm did it finally break. And it didn't break an axle, it broke the pinion gear.

In my opinion...No way is a car 600+lbs lighter on slicks with half the power going to break an axle. Dont let anyone tell you different.

FWIW...my Demon had an 8" converter, low gear set 904 (footbraked), 4.86 gears, and 28x10.5 bias ply slicks.
If you plan to run radials, I'd probably lean towards getting some good axles.

I guess aftermarket axles is not a bad idea but possibly a waste of money at your hp level. I ran an all steel 3600lb 340 '71 Cuda with stock 8.75 (489 case) and leafs for 6yrs on bias slicks, first with 3.55's/3500 conv, then with 4.30's/4200 conv. at varying hp levels from 315/375>528 depending on the N20 hit all off the line, no probs whatsoever.