i was wondering if the max hp rating of a ford 8 in in my 67 stang had a higher hp rating tehn about 300 hp? what is safe hp it can handle for driving? also what yrs did ford come out with that had the ford 9 inch that will fit my 67 stang? and the reason imasking about the ford 8 inch power is because after my motor is finished here in the next week im expecting around 300-340 hp out of my new motor
ford 8 inch? is the power ratting max at 300hp?
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302 coupe
Founding Member
well, Ford never put it behind a engine making more than 220 hp. Due to my experiences, I can't blame them. Most will agree that 300 is the max for any reasonable amount of durability.
If you are talking stock components the 8 inch isnt the strongest but if you use the right parts it can be made to handle some decent horsepower levels. with a good set of aftermarket gears and a good after market diff, and some good axles there is no reason it wont handle 400 horses and one advantage the 8 inch has over the nine is it takes less horsepower to spin it, less rotating mass and wieght. more useable horsepower to the wheels
ratio411
Founding Member
The other side to this arguement is:fastcoupe68 said:
9" stuff is so cheap compared to 8" stuff due to popularity.
Spend a bunch of dough to make an 8" handle 400 fwhp or spend the same or less and have a 9" that will handle whatever you put on it years from now.
Personal opinion:
I highly doubt you can build an 8" to handle 400 hp cheaper than you could do a 9".
I have shredded 3 with a 302 myself... no slicks and one with an auto tranny.
Good luck
Dave
mdjay
Premium Sponsor
I realize I shouldn't have put this much power in front of it approx 500 rwhp. But when we first put the SS together, I used a brand new 8" 3.55 limited slip thinking I could get by for a while. I smoked the clutches in 5 miles. The only reason I didn't leave it on the ground is it wasn't hooking up very good at the time.
ratio411
Founding Member
Don't feel bad...mdjay said:
I grenaded an 8" once behind a 460.
Shoulda known better, but the engine was there, the car was there, and I had nothing better to do.
The 8" was toast the day after the swap.
Dave
ratio411
Founding Member
Weaker than what?fastcoupe68 said:
Stock 9" = heckva lot stronger than modded 8"
BTW: It is a 'wive's tale' that 28 splines are weak.
It is nice that we can disagree on things like this , it gives everyone a chance to make up there own minds. IMO I would not use a stock 28 spline axle in anything I am planning on using at the track. As far as a wives tale 28 spline axles are weak. I have personally seen the splines dissappear after being used in a drag application in a 2700 pound car with less than 400 rear wheel horse power using slicks and a locker. For the street and radial tires they will last a long time, but you really never put any torque to them any way.
302 coupe
Founding Member
I've broken 3 8" diffs with a mild 302 and street tires, but haven't hurt a 28 spline axle yet. I don't understand how you can say 28 spline axles are weak and 8" diffs are ok.
It seems everybody forms opinions on two or three case studies that they have personally seen. Hardly empirical evidence.
I have run 8 inchers behind some power levels listed above and had no problems, but I didn't do anything to "shock" the system, like race with slicks or drop the clutch for burnouts very often.
Yes the 9 inch will be stronger and yes, the 31 splines will be stonger. It depends on the abuse you have planned to determine what you will need. Horsepower alone is only one factor.
I have run 8 inchers behind some power levels listed above and had no problems, but I didn't do anything to "shock" the system, like race with slicks or drop the clutch for burnouts very often.
Yes the 9 inch will be stronger and yes, the 31 splines will be stonger. It depends on the abuse you have planned to determine what you will need. Horsepower alone is only one factor.
I agree with MaxPower. I´ve heard people running 8" behind 400 hp engines. I broke mine with relatively mild 351... Yes, I was abusing it. I really can´t tell which broke first,the driveshaft, u-joints or differential housing... But I´m putting it back together, as soon as I get home from Brazil...A long three months..
mdjay
Premium Sponsor
This came from a thread that I would like to have forgotten. However it had a great link!
http://www.mustangsandmore.com/ubb/FordRearDimensions.html
http://www.mustangsandmore.com/ubb/FordRearDimensions.html
Here is how I can say it and I will probably upset alot of people with what I am about to say. Stock 9 inch 28 spline axles in anything other then a car that will be used for the street are weak at best. Put them in a drag application with anything making decent torque (400 ft pounds) slicks and a good hook and they will not last very long. And some of you guys are forgetting that I said aftermarket parts for the 8 are quite strong. Just spelling it out from personal experience.302 coupe said:
Route666
Active Member
Ok my interested in this subject has gained an all time high.
Looking at the aluminium carriers and housings that Currie stocks for 8" diffs, what sort of power could they handle reliably?
Looking at the aluminium carriers and housings that Currie stocks for 8" diffs, what sort of power could they handle reliably?
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