331, nitrous, AOD: 28 splines enough?

[JC6715]

I'll be running a 331 built for a small shot of giggle gas, built AOD trans through a 9" rear. I guessing somewhere around 400fwhp without the nitrous... The rear currently has 28 spline axles. I'll be buying a TrueTrac this week and am trying to decide if I should go 28 spline and run the axles I have, or if I should pop for new axles and run a 31 spline setup.

For the combo I have, will 28 splines be sufficient? Thanks guys!

 

[SadbutTrue]

I'll be running a 331 built for a small shot of giggle gas, built AOD trans through a 9" rear. I guessing somewhere around 400fwhp without the nitrous... The rear currently has 28 spline axles. I'll be buying a TrueTrac this week and am trying to decide if I should go 28 spline and run the axles I have, or if I should pop for new axles and run a 31 spline setup.

For the combo I have, will 28 splines be sufficient? Thanks guys!

I've been told that the 28 splines are capable of holding 400 hps at the crank. I think you'll be in excess of that, especially with the nitrous (though you're vague on your engine combination, drivetrain, and goals).

Without the nitrous, it'll depend on your traction, where you're making your torque, gearing, etc. If you have slicks, 4.11's, and make 400 lb. ft of torque then you're probably going to break em sooner or later. If you are on street tires, have more of a winding 331 (one that uses rpms to hit that 400 fwhp target intead of torque), more streetable gears and what have you... then you may be okay.

I think you're pushing it with the nitrous either way.

I'd look at some higher end axles at a minimum if you stay with the 28s. I've heard Moser makes some hardened axles that are a good bit stronger tahn stock 28 splines. Switching to a 31 spline would be the best bet though.

 

[JC6715]

The car will be mostly for street, wanting the hp to come from low end torque, if that makes any sense... Looking for low end grunt instead of high rpm power I guess I'm trying to say...

The gearing will most likely be 3.89's.

But from your description, sounds like upping it to 31 splines is going to be a "better safe than stupid" kind of upgrade...

Am I correct in assuming to switch from 28's to 31's, all I'll have to do is specify a 31 spline TrueTrac and purchase 31 spline axles?

Thanks.

 

[10secgoal]

If your already setup for the 28's in the 3rd member you can keep them. The 28's will hold if they are good axles. Google calvert racing and the 428 68.5 mustang almost dragging the bumper on the home page is John Calvert. He runs 28's and runs in the 9's.

 

[SadbutTrue]

The car will be mostly for street, wanting the hp to come from low end torque, if that makes any sense... Looking for low end grunt instead of high rpm power I guess I'm trying to say...

The gearing will most likely be 3.89's.

But from your description, sounds like upping it to 31 splines is going to be a "better safe than stupid" kind of upgrade...

Am I correct in assuming to switch from 28's to 31's, all I'll have to do is specify a 31 spline TrueTrac and purchase 31 spline axles?

Thanks.

I wouldn't run stock 28 spliners with that combo. I did a 9" swap on a budget and reused my 28 spliners, but my combo is muuuch more mild. I've always planned on getting 31's when I do build engine.

You could call moser or some other axle companies and ask if they think their aftermarket 28's will do the job. They'll probably say 'maybe but you'd be safer with 31's' but you might find a guy who gaurantee's his product will work. Shrug.

 

[ForceFed70]

28's will be fine if you arn't running slicks.

 

[brianj5600]

Do the axles taper in the middle. I have seen them break, but they were from a 65.

 

[DK832]

Do the axles taper in the middle. I have seen them break, but they were from a 65.

I have about 400hp and a 28-spline, 3.70 geared, 9" rear with TrueTrac. Nothing broken yet, even with M/T Drag Radials. Will add nitrous in the fall and then that might soon change...

 

[Travis77]

A buddy of mine has been running his stock 28 splines and C4 in his 69 coupe. The motor is a 393 with trans brake and had no problems so far.

 

[JC6715]

Thanks for all the advice guys...

Just seems like the about $325 bucks it some insurance that could save me down the road from parts getting broken...

Still undecided though...

 

[SadbutTrue]

Thanks for all the advice guys...

Just seems like the about $325 bucks it some insurance that could save me down the road from parts getting broken...

Still undecided though...

Without slicks you will probably be okay for aw hile. But a tow home from a dragstrip can make up most the difference between upgraded axles or not. If you're set on nitrous and slicks, I'd upgrade accordingly.

 

[mikethebike]

NO.