Re: Which rear gear ratio?
[Re: Dr Dave]
#2245915
02/02/17 02:37 PM
02/02/17 02:37 PM
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Joined: Jan 2003
Posts: 28,067 Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,067
Irving, TX
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4.10 is too deep for that car. The 2.87 first gear would be incredibly short with that rear.
You'll be fine with 3.73 gears.
We put a Tremec in a car with 3.54s and it liked 70 mph more than 60 mph in 5th gear.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: Which rear gear ratio?
[Re: Dr Dave]
#2245993
02/02/17 05:06 PM
02/02/17 05:06 PM
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Joined: Aug 2003
Posts: 43,163 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,163
Bend,OR USA
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On your deal I would opt for the 3.91 I ran from 3.73 to 4.30 in my old pump gas Duster, it ran almost the same ET(10.30s) and MPH(127.) in the 1/4 mile at Woodburn. It seemed like it spent more time in high gear with the 3.73 but it ran almost the same The stick tranny with the O.D. should still hook and book with the proper starting line RPM at the drags It won't be easy to get it correct on the first pass but it is doable with some testing You can spin or bog on the starting line, your right foot will control that BTW, Yukon makes a 3.73 gear set for the 741 center section Those are the ones I used in my car
Last edited by Cab_Burge; 02/02/17 05:07 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Which rear gear ratio?
[Re: Dr Dave]
#2246103
02/02/17 08:42 PM
02/02/17 08:42 PM
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Joined: Jul 2011
Posts: 956 Chicago
PurpleBeeper
super stock
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super stock
Joined: Jul 2011
Posts: 956
Chicago
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Dr Dave, as you can see the recommended gear ratios are all over the place. Why don't you decide for yourself? You can make the RPM calculator work for you like this:
1. Pick a rear end gear ratio to calculate on, say 4.10 for example.
2. Multiply that number by your overdrive ratio to get an "effective rear end gear ratio". In this case, 4.10 x 0.64 = 2.624
3. Use the standard RPM calculator to see what your rpm's would be with your tire diameter.
FYI - You can do the same sort of thing to get a feel for what your "shift point" would be in each gear at a reasonable rpm too. For example, with the same 4.10 gears and a 2.87 1st trans. gear you'd calculate like this:
a) 4.10 x 2.87 = 11.767 "effective gear ratio in 1st gear with 4.10's"
b) using your tire size, you can calculate a mph at a given rpm, say a 3000 rpm target shift point for daily driving, and see how many mph's you'd be going before you had to shift.
c) repeat the above with your other trans. gear ratios with a "target shift rpm" (like I just used 3000rpm) for the other gears to see how fast you'd be going in the other gears too.
Hope This Helps!
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
"Officer, that button is for short on-ramps"
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Re: Which rear gear ratio?
[Re: Dr Dave]
#2246214
02/02/17 11:45 PM
02/02/17 11:45 PM
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Joined: Nov 2007
Posts: 21,822 Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
Joined: Nov 2007
Posts: 21,822
Kirkland, Washington
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I don't know if going to a 3.55 from a 3.23 is worth the time and effort. Thoughts? I've done it twice, it's noticeable, but yea, you could argue not worth the trouble.
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Re: Which rear gear ratio?
[Re: dogdays]
#2246812
02/03/17 09:20 PM
02/03/17 09:20 PM
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Joined: Jan 2003
Posts: 5,789 Hamilton, Ontario Canada
Magnum
master
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master
Joined: Jan 2003
Posts: 5,789
Hamilton, Ontario Canada
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So you have a 2.87 First gear. For years I have used an overall ratio of 10:1 for the First gear, as a calculation goal. 10 / 2.87 = 3.48. This is good advice. Multiply the trans ratio and the rear ratio. Take the tire height into consideratio and make a choice. Too low of a 1st gear is like having a truck with bull low.
69 Super Bee, 93 Mustang LX, 04 Allure Super
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Re: Which rear gear ratio?
[Re: Dr Dave]
#2247019
02/04/17 02:41 AM
02/04/17 02:41 AM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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For a street car that's not after every last tenth of ET, I like higher gear sets. I also don't mind a short smoke show 1st gear. Right foot input will control that on the street anyway. Stop and go traffic? That short gear will be happier on the clutch.
I had a TKO with .64 OD. I hated having RPM so low that 5th gear was useless below 65 mph. I went 4.56 and loved it. Tire frying through 3rd if I wanted to, yet cruise the highway at 70 mph at 2400 RPM.
**Photobucket sucks**
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