Considering gear swap, Updated Quest: 3:73's or 3:91's?
#435267
08/11/09 09:34 PM
08/11/09 09:34 PM
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Joined: Jan 2005
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S.E. Conn
Hoof Hearted
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Running a 496, auto, 166k conv., 3:23's, 275/60 MT drags(28" tall) in 3800lb 69 Bee; Considering jumping to either 3:73's or 3:91's.
Anyone made a similar swap and how much rpm increase at cruise speed(70mph) should I expect compared to my current 3:23 setup.
Any first hand experience or recommendations regarding the 3:73 or 3:91?
Ran a best of 11.98 @ 113, any overall ET improvements to expect or just better 60ft times?
The cruise rpms at say 70mph is my main concern.
Last edited by Hoof Hearted; 08/16/09 10:29 PM.
2005 300C Hemi
2014 Ram ProMaster 2500
I Rekey, Repin old Chrysler locks and cut keys by code
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: Hoof Hearted]
#435268
08/11/09 09:47 PM
08/11/09 09:47 PM
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Joined: Feb 2006
Posts: 1,949
land of 10,000______'s
BDS871Cuda
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Quote:
Running a 496, auto, 166k conv., 3:23's, 275/60 MT drags(28" tall) in 3800lb 69 Bee; Considering jumping to either 3:73's or 3:91's.
Anyone made a similar swap and how much rpm increase at cruise speed(70mph) should I expect compared to my current 3:23 setup.
Any first hand experience or recommendations regarding the 3:73 or 3:91?
Ran a best of 11.98 @ 113, any overall ET improvements to expect or just better 60ft times?
The cruise rpms at say 70mph is my main concern.
At 70 it will rev about 3500-3800 rpm with 3.91
gear. somebody had the perfect gear-rpm-tire calc.
site on here once.
I know 3.91's will rev over 3500 rpm cause my
buddy's 68 runner has a 4 speed with a 28" tire
and 3.91's and they are running some good rpm's just at 60.
Snap your neck, mega G-force launch, is all I want!
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: BDS871Cuda]
#435269
08/11/09 10:12 PM
08/11/09 10:12 PM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
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With 3.91 gears and a 28 inch tire you will cruise about 3350 at 70 mph with 3.71 gears 3200 will give you 70 cruise. The mechanical advantage of a 3.91 over a 3.23 will get you .35 to .4 tenths maybe a smig more. the 3.71s will gain .25 to .3 in my experience. better 60 foot's always give better quarters and the mechanical gear advantage is there the whole quarter. 
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: BDS871Cuda]
#435271
08/11/09 10:48 PM
08/11/09 10:48 PM
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Anonymous
Unregistered
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Anonymous
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Quote:
Quote:
Running a 496, auto, 166k conv., 3:23's, 275/60 MT drags(28" tall) in 3800lb 69 Bee; Considering jumping to either 3:73's or 3:91's.
Anyone made a similar swap and how much rpm increase at cruise speed(70mph) should I expect compared to my current 3:23 setup.
Any first hand experience or recommendations regarding the 3:73 or 3:91?
Ran a best of 11.98 @ 113, any overall ET improvements to expect or just better 60ft times?
The cruise rpms at say 70mph is my main concern.
At 70 it will rev about 3500-3800 rpm with 3.91
gear. somebody had the perfect gear-rpm-tire calc.
site on here once.
I know 3.91's will rev over 3500 rpm cause my
buddy's 68 runner has a 4 speed with a 28" tire and 3.91's and they are running some good rpm's just at 60.
My Charger with 383, 4-speed, and 3.91s runs 3200 rpm @ 60 mph.
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Re: Considering gear swap, how much rpm increase at cruise?
#435272
08/12/09 01:16 AM
08/12/09 01:16 AM
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Joined: Feb 2006
Posts: 1,949
land of 10,000______'s
BDS871Cuda
top fuel
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top fuel
Joined: Feb 2006
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land of 10,000______'s
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Quote:
Quote:
Quote:
Running a 496, auto, 166k conv., 3:23's, 275/60 MT drags(28" tall) in 3800lb 69 Bee; Considering jumping to either 3:73's or 3:91's.
Anyone made a similar swap and how much rpm increase at cruise speed(70mph) should I expect compared to my current 3:23 setup.
Any first hand experience or recommendations regarding the 3:73 or 3:91?
Ran a best of 11.98 @ 113, any overall ET improvements to expect or just better 60ft times?
The cruise rpms at say 70mph is my main concern.
At 70 it will rev about 3500-3800 rpm with 3.91
gear. somebody had the perfect gear-rpm-tire calc.
site on here once.
I know 3.91's will rev over 3500 rpm cause my
buddy's 68 runner has a 4 speed with a 28" tire and 3.91's and they are running some good rpm's just at 60.
My Charger with 383, 4-speed, and 3.91s runs 3200 rpm @ 60 mph.
Are you at or above 3500 rpm at 70 mph?
I think his tach might be off a couple hundred
rpm. When I ride in it, the factory tach seems
to read high.
Snap your neck, mega G-force launch, is all I want!
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: BDS871Cuda]
#435273
08/12/09 01:35 AM
08/12/09 01:35 AM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Lincoln Nebraska
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what ever your actual rpm is, going from 3.23 to 3.91 will up it 21% (3.73-15.4%) if the converter slippage is the same
live every 24 hour block of time like it's your last day on earth
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: RapidRobert]
#435275
08/12/09 09:18 PM
08/12/09 09:18 PM
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Joined: Jan 2003
Posts: 25,200
Upper Midwest
MoparforLife
Too Many Posts
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Upper Midwest
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Quote:
what ever your actual rpm is, going from 3.23 to 3.91 will up it 21% (3.73-15.4%) if the converter slippage is the same
With a 26 inch tire you can about double the first 2 numbers of the tach reading for the MPH.
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: MoparforLife]
#435276
08/13/09 06:59 AM
08/13/09 06:59 AM
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Joined: May 2005
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Florida
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Florida
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: Hoof Hearted]
#435277
08/13/09 01:56 PM
08/13/09 01:56 PM
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Joined: Aug 2007
Posts: 6,095
Valencia, España
NachoRT74
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Valencia, España
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well, that's easier that you think
if 3.91 is 21% increase on ratio, then the RPM increase will be about the same
3.73 is 15.5% increasing on ratio from 3.23
With a Charger born in Chrysler assembly plant in Valencia, Venezuela
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: Hoof Hearted]
#435279
08/13/09 07:34 PM
08/13/09 07:34 PM
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Joined: Feb 2005
Posts: 4,311
Prospect, PA
BSB67
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Prospect, PA
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Quote:
Running a 496, auto, 166k conv., 3:23's, 275/60 MT drags(28" tall) in 3800lb 69 Bee; Considering jumping to either 3:73's or 3:91's.
Anyone made a similar swap and how much rpm increase at cruise speed(70mph) should I expect compared to my current 3:23 setup.
Any first hand experience or recommendations regarding the 3:73 or 3:91?
Ran a best of 11.98 @ 113, any overall ET improvements to expect or just better 60ft times?
The cruise rpms at say 70mph is my main concern.
What is your 60 ft now?
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: BSB67]
#435280
08/16/09 10:21 PM
08/16/09 10:21 PM
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Joined: Jan 2005
Posts: 2,179
S.E. Conn
Hoof Hearted
OP
top fuel
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OP
top fuel
Joined: Jan 2005
Posts: 2,179
S.E. Conn
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Quote: "What is your 60 ft now?"
Reading the 2 year old faded time slip from LVD:
reaction time: 0.0186
60 ft: 1.792
1/8th mile: 7.668
Note the awkward stance of the rear tires when she launches, she lifts up, and goes, no slipping, no spinning; Mopar XHD rear springs, adustable pinion snubber, stock 440 t-bars, stock cheapo shocks all around...oh yeah, running a simple Eddy 800cfm mounted on a TM7.
11.98 @ 113.52 (w/3:23's, 275/60/15-28"T) M/T Drag Radials
Anyone got an educated recommendation for gears? Leaning towards 3:73's or 3:91's, no steeper than that as the car is driven on the street alot.
2005 300C Hemi
2014 Ram ProMaster 2500
I Rekey, Repin old Chrysler locks and cut keys by code
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: Hoof Hearted]
#435281
08/16/09 11:50 PM
08/16/09 11:50 PM
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Joined: Jan 2003
Posts: 2,402
Wichita,KS
Blakcharger440
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Quote:
Quote: "What is your 60 ft now?"
Reading the 2 year old faded time slip from LVD:
reaction time: 0.0186
60 ft: 1.792
1/8th mile: 7.668
Note the awkward stance of the rear tires when she launches, she lifts up, and goes, no slipping, no spinning; Mopar XHD rear springs, adustable pinion snubber, stock 440 t-bars, stock cheapo shocks all around...oh yeah, running a simple Eddy 800cfm mounted on a TM7.
11.98 @ 113.52 (w/3:23's, 275/60/15-28"T) M/T Drag Radials
Anyone got an educated recommendation for gears? Leaning towards 3:73's or 3:91's, no steeper than that as the car is driven on the street alot.
Hey what is your engine combo? Compression,headers,cam and what heads do you have? Just trying to get an idea of what numbers to expect with that stroker combo.
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: Blakcharger440]
#435282
08/17/09 12:52 AM
08/17/09 12:52 AM
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Joined: Jan 2005
Posts: 2,179
S.E. Conn
Hoof Hearted
OP
top fuel
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OP
top fuel
Joined: Jan 2005
Posts: 2,179
S.E. Conn
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496/, .30 over, Moly rings,(440source guts), Lunati .533int./.552exh.-284/292adv.-242/252 dur.@.050 Hydr. cam 105 ctr., Mopar alum. wedge heads(unported), TM7, Eddy 800(worked over), 1 7/8 Hooker super comps, 3" collector, 3" duals, w/"H" pipe and Flowmasters. 727,manual reverse V.body, $210 Mopar "Economy Hi-Stall" 166k converter... Enough info? Very simple cheapo setup. Has terrific street manners and runs high 11's with an overwieght italian with his right foot planted firmly to the floor.(I hear 100lbs wieght loss will net me 1/10 on 1320...) Long term goal is to be able to run consistant mid 11's w/ no juice. Now, gear ratio advice please. 
2005 300C Hemi
2014 Ram ProMaster 2500
I Rekey, Repin old Chrysler locks and cut keys by code
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Re: Considering gear swap, how much rpm increase at cruise?
[Re: Hoof Hearted]
#435284
08/17/09 09:05 PM
08/17/09 09:05 PM
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Joined: Feb 2005
Posts: 4,311
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,311
Prospect, PA
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Quote:
Quote: "What is your 60 ft now?"
Reading the 2 year old faded time slip from LVD:
reaction time: 0.0186
60 ft: 1.792
1/8th mile: 7.668
Note the awkward stance of the rear tires when she launches, she lifts up, and goes, no slipping, no spinning; Mopar XHD rear springs, adustable pinion snubber, stock 440 t-bars, stock cheapo shocks all around...oh yeah, running a simple Eddy 800cfm mounted on a TM7.
11.98 @ 113.52 (w/3:23's, 275/60/15-28"T) M/T Drag Radials
Anyone got an educated recommendation for gears? Leaning towards 3:73's or 3:91's, no steeper than that as the car is driven on the street alot.
If the only change you will consider is a gear change, and you want the most et improvement, go with the 3.91.
However, your 60' isnt bad for a street car. You might get it down to a 1.70 with the 3.91, and that will drop your et .15 to .2. Add a good 9.5" converter and drop to maybe a 1.60 sixty ft., and an additional .15 to .2 off the et.
The 113.5 mph seems a little low to me. The gear change won't effect this as the mph is a function of horsepower. If the tune is good, I would check that you have good fuel pressure through the traps, borrow and try a 850 DP Holley and maybe try some carb spacers too. I think it could run 116 or 117, and would drop the et by .25 to .35, and you can keep the 3.23s and $ in your pocket
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Play with this calculator and go with as much gear as you can tolerate on the highway. I've got 3.55's and I do a little over 3k rpm at 70. But I also have a 27" rear tire.
