How much power can an 8" really take ?

ultrastang · May 8, 2007

The first generation Broncos, 1966-1977 all came with 28-spline axles. Some of them didn't even have Limited-Slip/Traction-Lok differentials in them.

Most '65-'72 model Ford half ton pickups came with 28-spline axles/differentials. Most didn't have Limited-Slip/Traction-Lok differentials, but some did. The '73-'85 Ford pickups primarily had 31-spline axles, and again, most had open differentials, but there were some Traction-Loks installed.

Limited-Slip differentials were available up until 1968 (in both cars and trucks). After this, Ford revised the differential to an improved version and it was called "Traction-Lok". --However, 1969 is the worst Traction-Lok differential to have because of 4 large holes cast into the left (driver's side) half of the differential. These differentials are notorious for breaking in this area. The best Traction-Loks were produced from 1970-1985.

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

1320stang · May 8, 2007

An 8" rear won't survive behind a stock A-code 289 and a top loader 4-speed.......................................................................................................................................................................................
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with welded spider gears, no slicks, slapper bars and several 4000 rpm launches on a sticky track.
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don't ask me how I know.....
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it CAN, however, drive tot eh end of the track, then down the return road, picking up the 17 second time slip, and onto the trailer for the trip home.

GT1966 · May 8, 2007

8"

I had McCane Automotive Engineering (MAE) build an 8" 4-gear posi (with a waffle casting) for my 'stang and it can hold a 350hp drag launch. Beyond 350 hp, a 9" would be appropriate.

Jimmys66 · May 8, 2007

Rusty67 said:
So... uh.... anyone want to sell me a 9" that will fit my 67 ?

Sorry, I bought mine at a swap meet 13 years ago. I'm kinda' attached to it. Some really nice guy let me borrow his tape measure and then let me lay under his pritine mustang at a car show for 15 minutes making sure the sizes were right before I bought it.

Sure you wouldn't do an 8.8"? It's pretty much a GM 12 bolt.... plenty durable and probably cheap if you're on a budget.

CraigMBA · May 8, 2007

Rules to get an 8" to live.

- No slicks and no drag radials.

- No 4,000 RPM race launches on slicks or drag radials.

- No other rules.

You keep your car off of drag race rubber, you can put as much power as you like through an 8". You won't be able to get enough traction to break it. Those guys with LS1 powered F bodies have the same problem with the factory 10 bolts - you put enough grip in it to get it to run hard, and you will grenade the rear end.

TOM B · May 8, 2007

Hmmm, you guys are rattling my chain, I am still running my 8" with a power trax and 28 splines, Updated my blower to a Novi 2000 at 15 PSI Cog drive belt and 200 to 400 Nos,,,, only have 100 hp jets in it now.
I have three 9" rears in the garage , one is a 31 spline out of my 72 F100 TRUCK
the othe is out of a 59 car and the other is just a housing. Picked up a 9"
aluminum carrier at Carlisle.
Maybe just maybe it time to start building one.

ratio411 · May 8, 2007

DukeGnarley said:
Also consider an 8.8"... ...They also have the advantage of being a little lighter than the 9" (i believe)...

This is a myth that just can't be beat down.
The 9" is only a little heavier than an 8" unless it is built to the hilt.
Many 9" rears came with much larger brakes as well, which bolsters the weight myth if the swapping party so chooses to leave the heavy brakes in place.
The 8.8" is slightly heavier than the 9", by about the same amount the 9" is heavier than the 8".

Fwiw:
Those considering the Versillies disc rear, it uses VERY heavy accessory componets. The Lincolin style HD housing and ancient technology rear discs make the thing a real pig, without providing benefit.
A standard 9" housing and late model Explorer discs keep things light, cheap, and modern.

ratio411 · May 8, 2007

CraigMBA said:
Rules to get an 8" to live.

- No slicks and no drag radials.

- No 4,000 RPM race launches on slicks or drag radials.

- No other rules.

You keep your car off of drag race rubber, you can put as much power as you like through an 8". You won't be able to get enough traction to break it. Those guys with LS1 powered F bodies have the same problem with the factory 10 bolts - you put enough grip in it to get it to run hard, and you will grenade the rear end.

I didn't break any of your rules and I have broken 3 with 306 cubes.
I also broke one with a stock 460, but I never mention that one in these "8 inch strength" threads that pop up all the time...
I mention it now though, because I didn't break any of your rules with that one either! I took out a 302 and dropped in a stock 460. The rear was toast less than a week later.
I have broken 3 with auto tranny and 1 with toploader. None with sticky tires and all 3 broken with a 306 were in very light cars (Mavericks).

CraigMBA · May 9, 2007

ratio411 said:
I didn't break any of your rules and I have broken 3 with 306 cubes.
I also broke one with a stock 460, but I never mention that one in these "8 inch strength" threads that pop up all the time...
I mention it now though, because I didn't break any of your rules with that one either! I took out a 302 and dropped in a stock 460. The rear was toast less than a week later.
I have broken 3 with auto tranny and 1 with toploader. None with sticky tires and all 3 broken with a 306 were in very light cars (Mavericks).

Okay. What part did you break?

Rusty67 · May 9, 2007

I'm not going with an 8.8 because I hate that rear end for one and also, the work involved to make it fit into my car is not going to be that much cheaper then geting a 9" into my car.

Vinyl66 · May 9, 2007

One thing to remember is that wheel hop can break any rearend. Even on street tires.
I still have an 8" in my Stang and am using drag radials and have many runs in the high 11's without a problem. I also have an automatic and traction bars so easier launches and no wheel hop.

CraigMBA · May 9, 2007

That's true

I didn't consider 'user abuse' to be the sole shortcoming of the 8" - some people are animals and can break anything.

I broke an 8" too. I wheel hopped the car real bad when it was peg leged to get the car out of the intersection when it stalled to avoid certain death from a random 18 wheeler.

What I broke was the axle tube on the DS around the spring perch. Crushed tube too. It was so surreal to drive. You'd gas it and it'd turn. You lift and it'd turn the other way. It took weeks to figure that one out.

Does axle tube failure due to owner abuse count?

ultrastang · May 9, 2007

ratio411 said:
This is a myth that just can't be beat down.
The 9" is only a little heavier than an 8" unless it is built to the hilt.
Many 9" rears came with much larger brakes as well, which bolsters the weight myth if the swapping party so chooses to leave the heavy brakes in place.
The 8.8" is slightly heavier than the 9", by about the same amount the 9" is heavier than the 8".

Fwiw:
Those considering the Versillies disc rear, it uses VERY heavy accessory componets. The Lincolin style HD housing and ancient technology rear discs make the thing a real pig, without providing benefit.
A standard 9" housing and late model Explorer discs keep things light, cheap, and modern.

That's another example that people think is in the 100 lbs. range heavier than an 8-inch rear end. In reality, a Versailles disc brake nine rear end weighs 45 lbs. more than a narrow housing ('65/'66) Mustang 8" rear end, or 21 lbs. heavier than a '57-'59 Ford (narrow housing) 9-inch drum brake rear.

Divided across the rear end, the Versailles would be 22.5 lbs. heavier, per side, than a '65/'66 Mustang 8-inch.

I'll agree that there are better rear disc choices these days over the Versailles, but it's not as heavy as a lot of claims you see on the forums.

Up until last year, I've had a '79 Versailles disc brake rear under my '68 since 1997. I bought an '80-model Mercury Monarch 9-inch drum brake rear end to replace the Versailles with. I made some adapter brackets for the Monarch 9-inch housing to adapt some '94-'04 Cobra rear discs to it. This 9-inch Monarch rear end will replace the Versailles that was under my '68;

1. http://www.ultrastang.com/images/2006/cobrabrakehosemount0243cf_2.jpg

2. http://www.ultrastang.com/images/2006/cobrabrakehosemount0255tn_1.jpg

SadbutTrue · May 9, 2007

ratio411 said:
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.

^ winner

I did this. Found a shop to fab me a 9" housing for about 200 bucks, got a posi 3.25 center section on ebay for 300-350ish, and reused my 28 spline axles. Posi rear that should be able to take 400 hp (at least 300+ at the wheels) with normal tires for under 600 bucks complete.

Well, woulda been if the bastard on ebay hadn't screwed me on the posi. But thats another issue.

SadbutTrue · May 9, 2007

ratio411 said:
This is a myth that just can't be beat down.
The 9" is only a little heavier than an 8" unless it is built to the hilt.
Many 9" rears came with much larger brakes as well, which bolsters the weight myth if the swapping party so chooses to leave the heavy brakes in place.
The 8.8" is slightly heavier than the 9", by about the same amount the 9" is heavier than the 8".

Fwiw:
Those considering the Versillies disc rear, it uses VERY heavy accessory componets. The Lincolin style HD housing and ancient technology rear discs make the thing a real pig, without providing benefit.
A standard 9" housing and late model Explorer discs keep things light, cheap, and modern.

Eh, lifting the 8 out of my car and putting the 9 in, I definitely felt a difference in the amount of beef on the two. Whether the car would also feel that difference, dunno. But I did.

Rusty67 · May 9, 2007

Where am I going to find a 9" housing for cheap ? I guess I don't exactly know where to look.

1320stang · May 10, 2007

Hmm, I got my '57-'59 9" rear end for free......it was also chromed..... and rusted.

My buddy busted the axle tube where it goes into the center section on his 8" in his '67 coupe. Drove it to the shop like that.....

57fairlane · May 11, 2007

wow these 8 inch threads are worse than debating the t5's strength.

Some people can break a bowling ball in a sandbox with a plastic hammer or however that saying goes. Other people can "mysteriously" make their junk work.

whatever.

Rusty67 · May 12, 2007

I was going to go to a 9" eventually but I think this will make me decide sooner. I just don't know if I want a large or small bearing 9" at this point.

ultrastang · May 12, 2007

57fairlane said:
wow these 8 inch threads are worse than debating the t5's strength.

Some people can break a bowling ball in a sandbox with a plastic hammer or however that saying goes. Other people can "mysteriously" make their junk work.

whatever.

The saying I always heard was; someone (insert name) could tear up un anvil with a Q-tip.

In it's stock form, the 8-inch rear end might take 350-400 hp, but it wasn't designed to do so. You may get away with it for some time, but sooner or later at those levels, it's time will be up.

If the factory 8-inch rears were capable of handling 400 hp, then why didn't Ford use them in the K-code 289 Mustangs or the Shelbys? The K-code was only putting out 271 hp (129 hp less than 400) and the Shelbys were only generating 306 hp (94 hp less than 400). The reason is because the Ford engineers knew the 8-inch wasn't up to the task of reliably handling the power from even a 271 or 306 hp engine.

The installation of some aftermarket 8-inch rear end parts may beef things up, but it will most likely only put the 8-inch to the level of a stock, run-of-the-mill 9-inch.

Many people want to increase the power of their engines, and usually the first line of attack is to start putting performance parts on/in their engine. Maybe I'm backwards, but I think the first place to start hopping a vehicle up should be with the brakes, suspsension, and drivetrain --then the engine.

Most early Mustang stock brakes and suspension are marginal at best with the factory-installed engines they came with. Add more power to the engine, and you are making a bad situation potentially worse. Going fast is fun. But, all the go-fast-in-the-world it isn't worth anything if you can't control the vehicle, or more importantly --STOP IT!

In the end, the arguments on the subject of 8" vs. 9" will never end. I've seen it going on for years now on the forums. Personally, since I never plan to run a factory-stock small-block, I'll continue to use 9-inch rears, because I know that it will handle any power level that I would ever attain with the engine, and not only will it handle it, it was engineered to do so.

How much power can an 8" really take ?

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