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I need help evaluating rear upgrade options (need lbp+ratio)
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Author:  radarsonwheels [ Wed May 02, 2007 1:47 am ]
Post subject:  I need help evaluating rear upgrade options (need lbp+ratio)

hello

my new motor is finally running like a top, except the stock trans and highway geared rear are missing my new slightly higher powerband. The car cruises great above 70 (around 80mph at 3000rpm). I just bought an OD883, so I figure that I can get a more performance feel if I step up the rear ratio, while still not screaming on the highway because of the overdrive.

I have a strong 225, with a 904 and a 2.76 (I think?) rear, on a '73 swinger. My math (suspect) tells me that I need around a 3.5 ratio rear to have the same cruising rpm on the highway with the OD. I would be willing to go a little higher- there is no need for me to cruise at eighty everywhere I go! Also, a little more pep off the line is always welcome, and I wouldn't mind messing with the local honda civic 'tuners' :D

What I need is a large bolt pattern rear with a ratio between 3.5 and 4.
I need it to be pretty close to stock width (narrow on the 73) so I can run the matching wheels I bought to go with the lbp disc brake upgrade up front. I don't want adapters. I don't want to spend too much, but if I can get a complete package for a fair price that's ok. I can weld and wrench, but this is my first four wheel project car. I am not afraid to go modern ford or I read a little about pinto/old mustangs maybe working? Mazda? Mopar? I won't be drag racing, but I do like to beat on my rides a little now and then!

Anyone have any options? Advise?

Thanks
Kevin in Philly

Author:  Ron Parker [ Thu May 03, 2007 7:27 pm ]
Post subject: 

Yep a 8 inch ford out of a Mustang or fairlane or a falcon about 64 to 68. There common . Still cheep at junk yards. Then put your gear in. Thanks Ron Parker :D

Author:  radarsonwheels [ Sat May 05, 2007 10:16 am ]
Post subject:  thanks

I wasn't sure if most of the info on here would apply to my '73 because of the narrow track of the rear. I couldn't find those older ford rears, so I measured twice and went out and got a 1995 ford 7.5"

thanks for the help.

rdr

Author:  SlantSixDan [ Sat May 05, 2007 11:10 am ]
Post subject:  Re: I need help evaluating rear upgrade options (need lbp+ra

Quote:
My math (suspect) tells me that I need around a 3.5 ratio rear to have the same cruising rpm on the highway with the OD.
Your math is in the right ballpark. The A833OD has about a 30% overdrive, so you multiply your rear axle ratio by 0.7 to figure out the effective final-drive ratio in top gear.

2.76 --> 1.93
2.94 --> 2.06
3.23 --> 2.26
3.55 --> 2.49
3.73 --> 2.61
3.91 --> 2.73
4.11 --> 2.87

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