How much power can an 8 inch handle?

SadbutTrue · Apr 28, 2004

Yeah, I've asked it before, but with decent tires (not slicks or DRs though), how much power/torque can an 8 inch take? I'm trying to decide between a posi 8 and a posi 9.

10secgoal · Apr 28, 2004

I have a sb pulling consistant 1.7 60 ft times with mickey thompson et streets. I would guess on the motor it has 400 hp, maybe a little more. Although it will depend on tranny. I've seen weaker cars with 4 spds break axles and 8 in before. An auto will be easier on the the thing with the same hp. I don't use nitrous out of the hole because of the axles, but I wait till the 60 ft mark to squeeze. But my 8 in has seen over 500 hp many a times.

85GTlover · Apr 28, 2004

I have read that the 8.8 is all you need the 9" is more old school and is used mostly because it is easier to narrow for big slicks. Just use 8.8 everything already matches up.

brianj5600 · Apr 28, 2004

Looking at your sig, I don't see any problem with an 8". Axles are the same for both so that is a non issue. If you have the axles that taper in the middle, they will be the weak spot on your 8". I have seen them break with a little more than you have on slicks. Street tires though, you should be ok for now.

taylor4g63 · Apr 28, 2004

85GTlover said:
I have read that the 8.8 is all you need the 9" is more old school and is used mostly because it is easier to narrow for big slicks. Just use 8.8 everything already matches up.

No, not true at all. Quite a bit of work has to be done. you have to weld on some leaf spring brackets, the pinion is off center so that causes some problems in itself, and im sure there are quite a few more that im not sure about.

9 inchers are generally used because they are THE best rear end for serious performance. Why else would even the chebby guys want ford 9 inchers to put in some of their cars? The 9 inch has alsp been around forever, and parts can be had incredibly cheap.

As for the 8 incher, i've heard stories of people breaking them with rather mild 302's, then some like 10 sec goal where there holding up to 400hp. I guess it just depends on how much you abuse it, and if its built correctly.

85GTlover · Apr 28, 2004

I was not sure that is why I said I read it,but if the 8.8 is in already or has one it needs no mods to fit I would think that would be better. They cal likely handle whatever he wants to do. To save the trouble I would stick with 8.8. Chevy guys use them cause thy are common and cheap and strong but so are 8.8's.

taylor4g63 · Apr 28, 2004

im willing to bet less than 5 people on stangnet (i don't know of any, but i remember hearing about 1 or 2 thinking about trying to put one in) that have 8.8's in their stang, i bet 50+ people here have 9 inchers...theres a reason for that.

HistoricMustang · Apr 28, 2004

Plenty if it is a good unit. I am seeing more and more 8" rears at road races. That says something.

HistoricMustang
www.historicmustang.com

xj220 · Apr 28, 2004

The 9s weigh more though too. I might up to a 9 as long as it was aluminum or thereabouts.

SadbutTrue · Apr 29, 2004

not 8.8... 8 inch. And the rear will have to deal with substantially more than whats in my sig.

Ronstang · Apr 29, 2004

To build up an 8 inch to suit your needs you will have to spend some serious money and they aren't any cheaper to build up than the 9 inch so if it were me I would invest the money in the 9 inch because it is also insurance for future engine upgrades.

BAD67FUN · Apr 29, 2004

Don't fix what ain't broke...

There are so many variables involved it's ridiculous.

Go with your gutt.

I kept the 8" because I'm more of a twisty lover.

My grandma can drive in a straight line....

Swede958 · Apr 29, 2004

Here's my take on it:

If you want to throw some serious power at it, find yourself a 9". It's rock solid, tough to crack (especially if it's built right) and parts o' plenty.
Drawbacks- the weight issue has already been addressed. I believe it weighs like 10-20lbs more... anyone know for sure. Also, just like a roots supercharger it's gonna cost you power for the benefits. The 9" has more mass and will there for sap some power away from the engine to just rotate the damn thing.

8": Also very common, though normally not up to the pressures a 9" is. You can build it up to handle the right power, but it will cost you, and for the money you might be able to get a decent 9". THough if you are not going to be throwing gobs of power at it or launching on slicks at like 5400 or something, a well built 8" should do you fine.

8.8": Supposedly the best of both worlds, nearly as strong as the 9", but just slightly heavier than the 8". Can be built plenty strong (hence one reason why Cobra owners who drag a lot swap them in for the IRS). Problems though are it is not a direct fit. You will have to modify the tubes (I've heard of a lot of guys just cutting them off completely and getting new tubes and axle flanges welding on) along with getting the spring perches on. ONe big benefit of this is that you may be able to get one with disk brakes...

That's the end folks, thanks for your time reading, the waitress will be around to bring you your tab.

The Swede

Edbert · Apr 29, 2004

According to Currie (THE voice of experience in the industry) the cutoff for an 8" car is the 400fwhp mark. If you make more than that you need to plan on a 9". The only reason I can think that the 8.8 is worth the hassle and expense is the ability to use inexpensive yet capable disc brakes from an Explorer or SN95.

PS...I think the 9" is more than 20 pounds heavier than the 8". That may be true just for the housing, or just for the ring and pinion, or just for the carrier housing or something. The 9" axle fully assembled is one heavy b1atch. Of course every car on the Winston cup tour has one under it for a reason, and they aint exacly drag cars.

85GTlover · Apr 29, 2004

When I answered this I did not look to see what car he was talking about. DUH. I would say go for the 9" over the 8" it is bigger, stronger, more popular, better. Next time I will read it all before I rush to get in my .02. In this case 9" absolutely

Edbert · Apr 29, 2004

85GTlover said:
When I answered this I did not look to see what car he was talking about. DUH. I would say go for the 9" over the 8" it is bigger, stronger, more popular, better. Next time I will read it all before I rush to get in my .02. In this case 9" absolutely

hehehe...you "late model" guys (haven't heard your '85 called late model lately have you?) crack me up!

JK

67 GTA · Apr 29, 2004

I have the stock 8" in my fastback with a little over 300hp. I swapped the 2.79 ratio out with 3.55's. I dog it pretty hard sometimes and have never had any trouble with it.

85GTlover · Apr 29, 2004

Edbert said:
hehehe...you "late model" guys (haven't heard your '85 called late model lately have you?) crack me up!

JK

I hope this is not intended as an insult, I don't take it as that, and I hope that is the case. Yeah 85 is an older car but I like it and it is in a lot better shape than many cars half its age. Sure it will be 20 soon and if it were a woman It would be in its prime. You don't call a 20 year old girl a late model. In my opinion there are things about my car I like better than newer ones.

brianj5600 · Apr 29, 2004

SadbutTrue said:
not 8.8... 8 inch. And the rear will have to deal with substantially more than whats in my sig.

What else?

rebel65 · Apr 29, 2004

late model means new...

How much power can an 8 inch handle?

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