another 8" vs. 9" debate...

jst6 · Nov 17, 2004

ok, i've been planning to get a 9" with 3.50's or 3.55's and a detroit locker with 31 splines for the extra strength and worry free opperation. however, some guys at the local speed shop (these guys are hardcore drag racers and run plenty fast) told me that the 8" if properly built should get me to the 11's with with 3.55's and a locker. That seems kinda far fetched as i've never read anyones post saying that 8's will handle that kind of power.

i know this will be a question so... the motor that's coming is a 331 with AFR 205s and a custom cam turning 430lb/ft of torque. i'm still debating myself as to the five speed conv or beef up the c-4.

so do you guys think that little 8" can hold that kind of juice?

mustangbrad · Nov 17, 2004

I'm a big fan of the 8" rear, but with that kind of power I would go with the 9". I agree that a 8 could make into the 11's, but for how long. For miles and miles of durability with that kind of power go 9".

stangman67 · Nov 17, 2004

I guess it depends on your tranny choice. With a racing C4, Id say 9" but if you you use a T5, it would break before you rear does. On the other hand, you are most likely considering a tremec 3550 or TKO 400 or 500, in which case mr. eight would be the weak link. I myself am running a 289 with maybe 350 ft/lbs, and I plan to get a T5Z with 4.11s, powertrax lockrite, upgraded 28 spline axles, all with the 8". I feel that it should handle some strip abuse and typical street driving.

WORTH · Nov 17, 2004

I don't understand any of this debating over 8" or 9", 9" is stronger for fact, why would anyone what to spend money on an 8".

Max Power · Nov 17, 2004

Cuz it's lighter and uses less horsepower. Most people already own one as well.

That being said, I would still go 9 inch in your application.

302 coupe · Nov 17, 2004

I agree with you Worth. Play it safe and swap in a 9". Ford never put an 8" behind an engine making more than 225 gross hp, why would you? The people that designed the 8" knew it couldn't handle more power.

66P51GT · Nov 17, 2004

WORTH said:
I don't understand any of this debating over 8" or 9", 9" is stronger for fact, why would anyone what to spend money on an 8".

I agree the 9" will handle more and I contemplated it for a long time. In the end it came down to total price and the fact that my build is on the upper limits of the 8". I'll have ~380 FWHP running through a four spider 3.80 8" traction-loc with street tires. I'm also running a T5Z, centerforce clutch, and billet flywheel.

I'm doing my build on the cheap. I spent $500 for a built 8" center section. Comparing this to $1,000+ for a 9" center plus housing was the kicker for me. If I do eventually break the RR, at least I can justify to the wife why I need the extra cash for the 9er.

My total drivetrain budget was $2,000.
Total net drivetrain cost to date: $2,010

T5Z Tranny - $700 (used)
Billet Steel Flywheel - $50 (used)
Centerforce Clutch - $90 (used)
Lakewood Scattershield - $100 (used)
Aluminum Driveshaft - $80 (used)
8" 3.80 Traction Loc Pumpkin - $500 (new gears, rebuilt diff.)
Mustang Steve Cable Clutch - $200 (new)
T5 Mounting Bracket - $75 (new)
Tranny Mount - $15 (new)
Refurbished Pedals - $125 (used)
RR Bearings - $75 (new)

WORTH · Nov 17, 2004

Max Power said:
Cuz it's lighter and uses less horsepower. Most people already own one as well.

That being said, I would still go 9 inch in your application.

SHow me the Mustang that doesn't need more weight in the rear.

65fastback2+2 · Nov 17, 2004

WORTH said:
SHow me the Mustang that doesn't need more weight in the rear.

exactly, that would be the reason the front of mine is smashed up

12sec67 · Nov 17, 2004

66P51GT said:
My total drivetrain budget was $2,000.
Total net drivetrain cost to date: $2,010

T5Z Tranny - $700 (used)
Billet Steel Flywheel - $50 (used)
Centerforce Clutch - $90 (used)
Lakewood Scattershield - $100 (used)
Aluminum Driveshaft - $80 (used)
8" 3.80 Traction Loc Pumpkin - $500 (new gears, rebuilt diff.)
Mustang Steve Cable Clutch - $200 (new)
T5 Mounting Bracket - $75 (new)
Tranny Mount - $15 (new)
Refurbished Pedals - $125 (used)
RR Bearings - $75 (new)

i spent that much on my rear end with gaskets and fluid
then again on my tranny and conversion, then again on my rims

its worth every penny

jbsteven · Nov 17, 2004

WORTH said:
SHow me the Mustang that doesn't need more weight in the rear.

we were just joking about this today. As some of you know I am in the middle of a build up right now which includes amoung other things a 9 inch rear end (which was installed today).

spend the money now and not worry about it again even if you add another 100hp. Add 100hp on the 8 inch and you will then HAVE to get the 9inch.

jbsteven · Nov 17, 2004

12sec67 said:
i spent that much on my rear end with gaskets and fluid
then again on my tranny and conversion, then again on my rims

its worth every penny

yep, mine was $2350 for the rear end. Add $2650 for the transmission, $8000 for the engine, $2400 for the coil over front and at least $3000 for all the other goodies and counting.

I hope my wife does not see this because I would have to buy her a new set of boobs or something.

thehueypilot · Nov 17, 2004

I am in the process of replacing my 8" with a 9". I have not hurt it badly yet, but it is starting to get louder and started leaking around the pinion housing. I am looking at the "Currie" stage 3 rear axle assemble.

another 8" vs. 9" debate...

jst6

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