Mopar 8 3/4 "

[George]

Just how much power can the Mopar 8 3/4 take? In a 1500-1600# FED combo.

[dreracecar]

They could take that years ago because traction  was not as good as it is todays with todays tires and the cars were much lighter. The problem is that there is Pro-Gear material  gearset available (softer to take the hit and still hold up) and you only have a hard street gear thats designed to last 200,000 miles- so now you must get them annealed a little to flex and take the impact, but then they dont last. 1500hp will get you about 20 passes (no more and maybe less).  A customer running about what you have described (PG with brake)checks it every 10 passes gets about 40 passes and carries a spare with him.

[George]

The engine in the car now is a 640hp injected motor. It doesn't look like the car will sell this winter. I was planning on moving to a blown alky SBC in an altered car . The blown 377 may end up in the FED. I do have a 4.88 pro gear set in it now. I expect a 3.90-4.30 gear change if it gets the blower motor. The 8 3/4 has worked well and it's good stuff , aluminum center section, MW aluminum spool, MW drilled axles. NO doubt the Ford is stronger, I was curious as to what other FED racers have done with the 8 3/4. Thanks. George

[slingshot383]

I had a 8 3/4 full floater in my '68 Woody Gilmore car, with a 408 Chrysler wedge, it went 7.90's @170 with no problems, launching off a tranny brake at 6200 - 6500, shifting at 8000.

[George]

  Based on the replies , not many racers using the Mopar 8 3/4".

Thanks , dreracecar and slingshot383. George

[ricardo1967]

I agree with you George, not many cars are built with the Mopar 8 3/4" rear axle nowadays, unless it's a nostalgia themed car. Mine has it, but it's a 40-year old rail.

[dreracecar]

If one is building a new car, then the choice would be a 9", If on has a car already with a working 8 3/4, then there is no real bennifit in changing it out. Now if one is building a med hp car on a buget,  the mopar is a good unit

[George]

They could take that years ago because traction  was not as good as it is todays with todays tires and the cars were much lighter. The problem is that there is Pro-Gear material  gearset available (softer to take the hit and still hold up) and you only have a hard street gear thats designed to last 200,000 miles- so now you must get them annealed a little to flex and take the impact, but then they dont last. 1500hp will get you about 20 passes (no more and maybe less).  A customer running about what you have described (PG with brake)checks it every 10 passes gets about 40 passes and carries a spare with him.

Where is your customer getting the gear sets?

[Paul New]

We ran hundreds of passes in our 1600 lb fed with a blown SBC running 7.40's this was with Richmond street gears

[Paul New]

Oh yes but once we built a new chassis we did install a 9"

[George]

We ran hundreds of passes in our 1600 lb fed with a blown SBC running 7.40's this was with Richmond street gears

What ratio and tire were you running with the 8.75 ? 60' times? Thanks. George

[Paul New]

I looked though my log book and found my best pass in this car 3.55 gears 31" tires
60ft 1.119
330ft 2.978
660ft 4.545
660mph 156.92
1000ft 5.914
1320ft 7.109
1320mph 186.02
This car typically tripped the 60' with the rear tires. I also found 1.08 60's

[dreracecar]

Rough estimate is 200 rpm difference between each gear set

[slingshot383]

Problem is nowdays if you are using a factory housing, you've got to back brace it and that takes up room that an old style car doesn't have.  Neil and Parks has a real strong 9" rearend set-up that you can get in either Chrome moly or Titanium.  Super strong, light weight, and no need for a back brace.

[George]

Thanks guys. I am weighing several options. I would like to go with the N & P housing , aluminum center section with new axles and brakes but Santa didn't leave me a pile of cash. My greatest fear is the 8 3/4" coming apart and hurting someone.