It seems to me, there should be an "all around" gear ratio to use. One that is good for city and highway use. Now the strip is a totally different situation. I am thinking the 3.75 is that "all around" choice, with a 5 speed overdrive tranny of course.
you might wanna consider some decisions on the 5 speed before the rear end. sorry if you're already a step ahead of this
2 things
1) you want the box that can handle your [unspecified] torque (which may or may not be a standard T5)
2) you want to know the ratios, particularly for 1st and 5th.
examples
too low ratio 1st with a 4.11 means early change (eg '84 SVO T5, engine at 5000rpm = 21mph). too high ratio 5th with 4.11 means still revving fairly high at highway speeds (4.11 with 0.87 5th = 3.57 final drive). too low in 5th with 3.75 means less pull in 5th (3.75 with 0.69 5th = 2.58 final drive)
Aussie66, your calculations are a little off on the last example. with a 3.75 gear the final drive would be 3.26. (3.75x.87).
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Tuners are like Tampons... Every Pussy has one! 72 Mustang Coupe. 347 stroker with Edelbrock Performer RPM Heads. Coast High cam. RPM air gap intake with a 650 Demon. Ceramic coated headers. MSD billet distributor, 6AL box, Blaster 3 coil, MSD wires.
Posts: 2035
Joined: 9/5/2006 From: Barossa Valley, South Australia Status: offline
different 5th gear - 0.69 in this example, 0.87 5th in the other one
3.75 x 0.69 = 2.58 on my calc
but thats the point...unless you know which gearbox (and therefore what the overdrive 5th ratio is) you may end up in a part of the rev range you dont wanna be.
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quote:
A 2007 study found on average Australians walk 900 miles a year. We drink 26 gallons of beer. That means, on average, Australians get about 34 miles per gallon. Not bad hey!
If I might add, their is not a lot of difference between the .82 5th and the 1.0 4th gear. Also, if its a low hp and low torque engine, then the .82 may be better. My 428CJ runs about 3000 rpm at 60 mph. A .67 final would be very nice in this situation. Use the calculator and factor the tire size before you spend money.
Just in case you or anyone else is interested. I have a 9" third member ready to drop in sitting in my garage. It has 4.11 gears with either a locker or spool, not sure. All you will need is your pinion and a gasket and your ready to bolt up. Email me if interested.
You can't mismatch pinions and ring gears. They both have to be machined together, and you have to set the pinion depth properly, which is hardly what i'd call 'bolt on.'
Opps, did not mean pinion, meant the pinion yoke. I just had to swap my original out with the one that came on the diff that I ordered. yes this is true bolt on and go. Pinion depth is already set. Oh, it is 28 spline. Forgot to add that in.
Posts: 2035
Joined: 9/5/2006 From: Barossa Valley, South Australia Status: offline
quote:
ORIGINAL: 67 evil eleanor
If I might add, their is not a lot of difference between the .82 5th and the 1.0 4th gear. Also, if its a low hp and low torque engine, then the .82 may be better. My 428CJ runs about 3000 rpm at 60 mph. A .67 final would be very nice in this situation. Use the calculator and factor the tire size before you spend money.
hehe...low hp and tq for Richard means less than 500 of each
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quote:
A 2007 study found on average Australians walk 900 miles a year. We drink 26 gallons of beer. That means, on average, Australians get about 34 miles per gallon. Not bad hey!
Ok, so I got bored again and plugged some info into that Richmond calculator and here's what I got:
With the Ford Racing Cobra R T5 (with a 2.87:1 1st and 0.82:1 5th) and a 26" tall tire and 3.73's, I'd be turning just shy of 3k rpm at 75mph. Seeing as I'm running at about 3300rpm @ 70mph right now with my crappy 3sp manual, 24" tires, and 3.25's out back, I'd call this a pretty good deal. Two more gears to play with and slightly better cruising ability. I think I found my tranny/rear combo :D
Posts: 2035
Joined: 9/5/2006 From: Barossa Valley, South Australia Status: offline
ok, what would you need to do (5th and or diff ratio) to be doing say 2400 at 75.
my eventual dream is to make sure my car is not running at between 2050 and 2200 in 5th as exhaust tends to drone in that range.
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quote:
A 2007 study found on average Australians walk 900 miles a year. We drink 26 gallons of beer. That means, on average, Australians get about 34 miles per gallon. Not bad hey!
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RE: 3.50??? or another??? - 
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