How much power can an 8" really take ?

[Rusty67]

I always like to build for the future because I hate having to spend money twice and do work twice. Should I bother beefing my 8" or just switch to a 9" and forget my 8" ? I'm planing to put out between 300-350hp to the wheels. I'm going to be puting a 351w into my 67 eventually and I'm considering turning it into a 393 stroker. I'm sure the 8" will be fine for the 302 I'm building at the moment but when I put the 351 in there I'm wondering if a built 8" will handle the abuse if I drive it every day or maybe 3 days a week.

I want to put a 3.55 in there with a posi and a nodular case. Maybe some 31 spline axles. Should I just step it up to a 9" ?

 

[RUSTYNUT]

How are you planning using the car? If you aren't launching at the drags with slicks your 8" should hold up well. Check out Curries sight, they have new pinion support for 8" that helps with one of the weak spots for $99.00. I had talked to currie a few years back and said 31 in a 8" was a waste because the carrier will break befor even quality 28 axles. If you do get 31's they will fit in a 9" of the same width. If you are going to buy all new parts I would do the 9". Not much of any differance in price and the you might get lucky and find some 31's in it already. Soon you will hear about how heavy a 9" is, but it's not as much as you would think. I have been looking at same problem and after alot research I'm looking for a 31 spline 9" as we speak. If you go with 9" you may want up grade drive shaft [ bigger u-joints] to make the swap worth it . Run what you got and shop for the new goodies as bucks allow.

 

[HistoricMustang]

The Currie 8" will hold up just fine. Am seeing these do OK at track events.

If you are going to stay strictly street without too much playing around the standard 8" will be OK.

Most of the Ford rear ends are superior to others.

HistoricMustang
www.historicmustang.com

 

[ultrastang]

There's only one reason for installing a stroker, and that's because you want to romp on it whenever possible. --You've got to, because the temptation is too great not to do it.

The weakest link in the 8-inch rear end is the area around the driving pinion.

The weakest link of a 9-inch (with 28-spline axles) is the axles (generally the left, [short], axle).


An 8-inch will live longer behind an automatic than it will a standard, but a nine inch rear end's life expectancy is much greater no matter what the transmission is. A nine inch with an N-case and 31-spline axles would be virtually bulletproof.

You'll hear all sorts of things about the 9-inch being 75-100 lbs. heavier than the 8-inch and...bla bla bla. That is not true: . In reality, for example, a '65/'66 Mustang 8-inch drum brake rear end weighs 170 lbs. A '57-'59 Ford big car 9-inch drum brake rear end (same width as '65/'66 Mustang 8-inch), weighs 194 lbs. --That's only a weight difference of 24 lbs. (or spread out, that's only 12 lbs. per side heavier).

1. http://ultrastang.com/Rearinfo.asp?Page_ID=1

2. http://ultrastang.com/Rearinfo.asp?Page_ID=2

3. http://ultrastang.com/Rearinfo.asp?Page_ID=5

4. http://ultrastang.com/Rearinfo.asp?Page_ID=9

5. http://ultrastang.com/Rearinfo.asp?Page_ID=16

 

[Rusty67]

I've got a stick in the car. I'll provably break my T5 well before the rear end if I get some stciky tires on the car.

I'm going to drag the car occasionally but that isn't my main goal with it. When this car is something you could call "finished" (which provably wont be for another 10 years or so) I'm going to want an all around car that I can take to an auto cross track or a drag stip and have fun with on occasion but still be able to drive between 3 and 7 days a week.

The cheapest I've seen a 3rd member for brand new is like 800 with everything I want except I can't seem to find anyone with a nodular case. A lot of builders are using aluminum. I'm just scared of that.

Ultrastang, I know what you mean about tempation... I love to get on my car but typically I drive somewhat conservatively.... somewhat.... ok who am I kidding I'm provably going to drive it like I stole it for the first year or more I get it on the road for every day use.

 

[Jimmys66]

I had this same situation. For me this is what it came down to......

This car is going to get faster and faster with every build. period.

Eventualy, I'm probably going to break the 8" even if I put money into it.

And lastly, I will now have a broken rearend with hundreds of dollars into it.

IMO, keep the 8" until you break it, if you want to save money. Most of us here are just like you and on a tight budget.

If you are going to invest money into something, make it something you'll keep for a very looong time and will take the abuse of your future 351 turned stroker.

 

[Rusty67]

That is kind of what I'm starting to think myself. The only issue for me really is geting a 9" assembly. I wonder if I can trade some of my home made beer for a 9" ?

 

[ratio411]

You can do what ol' Shelby did when there were no 9" rears for his Stangs...
Take a 9" housing center and weld your 8" tubes onto it and stick the 8" axles into a 28 spline chunk. That is how Shelby and HiPo 9" rears were made in 65-66.
That way all you need to do is find a non-disirable rear from a big car or truck and keep your axles, brakes, mounting points, etc... Some of the common rears can be found cheap or free. The only 9" rears that command high prices are those that are hard to find. This method doesn't require a specific rear.

Also, I have broken several 8" rears with 306 cubes.
I don't trust them.

 

[Rusty67]

I'd rather just find a 9" that fits straight away with no foolin around. Looks like its time to research for hours on the ultrastang website as well as others....

 

[96 DOHC Cobra]

I have broken several 8" rears with 306 cubes.
I don't trust them.

I agree. I wouldn't leave an 8" behind most any V8. My brother used to have a 78 Granada with a 250ci straight six, C4 and an 8" rear. His wife drove it mostly, and the 8" didn't survive 30,000 miles.
I also agree if your long-term plans include a 393 stroker motor, don't waste money on the 8" rear. Save what $$ you can and build a sturdy 9" for your car.

 

[57fairlane]

ultra had it pretty much dead on. With an automatic, I have yet to see one break. With a stick, that would probably be another story.

There is a guy that comes to the shop I work at with a 66 falcon with a 8" with an auburn in it. Basic 306 with ported Gt40p heads, b-cam with 1.7s, RPM with a 650 holley. With the AOD it makes 250 or so to the tires and has gone some 8.20s-8.30s in the 1/8. On 150, it makes 370 and has been some 7.20s.

Mine only makes 270 on the motor to the tires with a c4 but it is coming out shortly for a t5. We shall see what happens . . .

 

[Rusty67]

So... uh.... anyone want to sell me a 9" that will fit my 67 ?

 

[DukeGnarley]

Currie or Strange will, but they don't fall into the cheap or free catagories.

Also consider an 8.8" out of a fox or newer mustang for a '67. they are about the same width i believe, you'd just need to grind off the suspension mounts and weld on some leaf spring perches. They aren't quite as strong as a 9", but they will handle plenty more power than an 8". They also have the advantage of being a little lighter than the 9" (i believe).

Personally, i went with a nine for my future engine, just tossing out the idea.

 

[calpolymustang]

While we're talking about breaking axles and rear ends...

How much of a beating can a 9" from a '77-'78 Versailles take? Lets assume an AOD is in front of it.
I know its only 28 spline and isnt as strong as a Currie, but its stronger than the 8".

I recently bought a complete one, emergency brakes and all. It has the 4-piston Trac-Loc and so I'm planning on re-gearing it and swapping to a u-joint yolk from a 69 Galaxy. I hope to eventually put the 9" in a '67 FE Fairlane/Comet.

 

[BornInAFord]

I agree. I wouldn't leave an 8" behind most any V8. My brother used to have a 78 Granada with a 250ci straight six, C4 and an 8" rear. His wife drove it mostly, and the 8" didn't survive 30,000 miles.
I also agree if your long-term plans include a 393 stroker motor, don't waste money on the 8" rear. Save what $$ you can and build a sturdy 9" for your car.

And my 8" had 400,000 miles on it behind a 289 A code and 4 speed. I agree that the 8" isn't the strongest rear end on the planet, but honestly! You make it sound like all of us should ditch our 8" for the 9" ASAP. I mean, even the 8" three ribbed pre-67 castings have survived quite well behind some Mustangs making pretty good horsepower. As long as the 393 stroker doesn't put traction to the ground, the 8" should last quite a while. As will the T5. True, you can make a case he should start looking for an upgrade like the 9" with 31 splines, but for most of us the 8" will work great.

In your brother's case, perhaps the late castings (like most of the later 70s stuff, including the 302 blocks) aren't as good as the earlier ones. There may have been some other factors, too. A teenage son, perhaps?

As far as advice for Rusty67, I think there has been some very good suggestions so far. Build the stroker. Get a 9" ready while you build. Meanwhile, upgrade to the 3.55 8" for your 302 and sell the whole rear, housing and all, when you upgrade to the 9.
Daniel

 

[jikelly]

I've got an 8" rear behind my 351w with a Tremec. I get on it a lot. 60,000 miles behind the 351 without any adverse effects.

 

[Rusty67]

I know a (properly) build 8" can take just about anything a 302 will throw at it. People complain a lot about the 8" but its actually a good rear end. I know my 393 stroker is going to eat the 8" for a midnight snack and then come looking for more... at least the way I'm going to be driving it one I get it up and running. As for an 8.8 I've already decided against it. I don't like the way that rear end goes together. The gears comming out the back and not comming out in a pumpkin ? No thanx.

I'm not sure I even want to sink any money into my 8" at all. It would cost me like 800 bux for a decent carrier with a posi all brand new and I don't want to spend 400 bux having a carrier I buy for 150 dollars rebuild because that puts me at 650 and thats just too much. I think I'll just step up to a small bearing 9". Is there any reason to move up to the big bearing 9" ?

 

[RUSTYNUT]

You get larger[ stronger ] tapered bearings and the options for larger cheap brakes and the houseing is stronger but heavier. You can save some bucks buy not getting the n case and getting one already equiped with 31 axles. If you are driving on the street you would be hard pressed breaking a standard carrier.

 

[67GTCOUPE]

I have a 67 with a 8" rear behind my toploader behind my 393 stroker which puts out north of 500hp at the flywheel.

I will eventually build a 9", but it is working for now.

 

[DukeGnarley]

If you're on a budget you can get a used center section off of ebay. look for ones out of mid 70s broncos and trucks. some of them had the factory 31 spline trac-lok limited slip differential.