Quote:
Originally Posted by 74proii
The old Tbird irs are basically junk for what you wan. The 2006 and up Explorer are way stronger and way easier to get. No matter what you will end up making your own adjustable control arms and shortening the axles to the desired track width. i looked very long and hard for quite awhile before making the decision not to.
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With the exception of pinion length and chassis attachment points the strength of the two different generations of Ford 8.8" rear ends are essentially the same.
Ring and pinion torque transmission capacity is a function of ring gear diameter and pinion shaft diameter. The pinion shaft needs to be of a large enough diameter to transmit the torque delivered without shearing off. The reason for the old Pro Series 9" Ford gear sets was the larger diameter pinion shaft, improved 9310 metallurgy not withstanding.
Once the pinion shaft was upgraded the subsequent changes were to the ring gear diameter, gradually increasing it from 9 to 9.5 and then a 10 inch ring gear. The larger diameter ring gears both had a higher ultimate torque handling capacity while also allowing for the use of larger hypoid teeth on both the ring and the pinion. The last incarnatioin for that design after the 10 inch ring gear was the final 10.5 inch ring and pinion. To accommodate the rapidly increasing torque in the fuel motors, Strange took a big step upwards in terms of strength and torque capacity by going to a 12⅓ ring and pinion that is the current strong man.
Adequacy is a beautiful concept. A properly set up 8.8" ring and pinion is way stronger than you will ever require in a replica. These cars are so light and the ability to hook up any significant power without spinning the tires negates the need for larger gear sets.
The original Cobra's and even modern day Vipers very successfully use the 8.5" Dana ring and pinion. A road race car does not require the kind of brute torque handling capacity a drag race car needs. In the FWIW bucket even the drag race 8.8 rear ends
properly set up go for many racing seasons in 3600 lb. low 8 second cars without any significant maintenance other than the periodic
oil change.
The new 8.8 rear ends from Ford in current showroom vehicles are no stronger than the previous 8.8 rearends. They just use different packaging because they are adapted for a new chassis and new subframe along with using a CV joint instead of a traditional u-joint connection between the driveshaft and the pinion.
In terms of fitment, the earlier design is much easier to work with if you are fabricating. With the availability of the new style in aluminum there is essentially no longer a weight penalty for choosing the new rear end design however there is also no upside strength-wise. The internals are virtually identical strength-wise.
The seductive draw the new style has is the widespread availability in Mustang chassis for a half dozen or so years making salvage yard sourcing easy. After you get done sourcing the complete IRS cradle you still have to narrow it to match the Cobra rear track and then buy custom length axles.
If you have ever tried this you will quickly recognize it is easier to build a new IRS subframe than modify the OEM unit and of course you still have to deal with the extended pinion length that aggravates the already severe drive shaft angle offset in the horizontal plane.
In the end this is one of those beauty is in the eyes of the beholder deals however, strength is unchanged. What is not unchanged is the difficulty in correctly adapting it to the chassis of the target vehicle.
Ed