Topic: 3:07, 3.55 or 3.70 rear end ratios
in Forum: C3 Driveline Components
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I think ya'll have answered my questions. With the existing th350, motor and 2.72 rear, she is peppy but won't smoke da tires and she tach's out at 2600 rpm at 70 mph, which I don't care for.
Not saying I plan on smokin da tires all the time, it would be nice to on occasion. I am hoping to tach out in the 2400 to 2500 rpm range at 70 mph yet smoke da tires on occasion with the 4 speed.
Dats my goal!
I know I should have dropped the clams on the 5 speed, but concerened about the economy and could not pass the deal on the 4 speed plus I wanted to keep her as stock looking as possible.
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If you have not installed it as of yet, you may want to trade in the 4 for a 5 speed, and go with the 3.55. It's a very nice combination.
kstyer 2009-02-16 20:18:58
a 3.55 gear with a .8 overdrive will give you a final ratio in high gear of 2.84
3.55 with a .67 overdrive gives you a 2.38 final ratio
3.70 with a .8 is 2.96
3.70 with a .67 is 2.48
4.11 w/ .8 3.39
4.11 w/ .67 2.75
You can see where the overdrive makes a BIG difference. It really improves the highway mileage/engine rpm while providing a lot more launch.
It is way off in the future, but I, someday, will plan on the .67 overdrive with 3:55 gear for the 2.83 total final ratio.
You can also calulate the launch ratio. This ignores the overdrive, but allows for the first gear and the final drive ratio.
I presently have a 2.50 first gear and a 3.08 diff. That is a launch ratio of 7.70 While that is okay, it's not performance.
With a 2.5 and a 3.55 it would be . 8.88 a bit better.
The trans Iwould like to have uses a 2.75 first, and if I use the 3.55 I would then have a launch ratio of 9.76 a very big improvement.
The 2.75 with a 4.11 would be an awsome 11.3 The car would launch like a slingshot! That is a HUGE increase over my start point, but overall I would lose high end and mileage, so I choose the earlier combo. Someday maybe the budget gods will smile on me, and I can do this.
Remember to consider both ends of the range when selecting ratios.
Lifetime MemberHot Springs, AR - USA
Joined: 4/24/2004
Posts: 3236
Vette(s): 69 Conv #'s match 427, TKO-600/.64, 3.36HD-Posi, HT, T/T, PS, PB, PW, SP, Leather, Comp XE264HR & Roller Rockers & Lifters, Air-Gap RPM intake, Holley St Av 770 VS, MSD 6AL+Dist+Blaster SS, K&N, Jet-Hot Hooker Side-Pipes, Steeroids, Al Rad, Spal Fans
[QUOTE=kstyer]If you have not installed it as of yet, you may want to trade in the 4 for a 5 speed, and go with the 3.55. It's a very nice combination.
[/QUOTE]
cthulhu 2009-02-17 01:44:21
a 3.55 gear with a .8 overdrive will give you a final ratio in high gear of 2.84
3.55 with a .67 overdrive gives you a 2.38 final ratio
3.70 with a .8 is 2.96
3.70 with a .67 is 2.48
4.11 w/ .8 3.39
4.11 w/ .67 2.75
You can see where the overdrive makes a BIG difference. It really improves the highway mileage/engine rpm while providing a lot more launch.
It is way off in the future, but I, someday, will plan on the .67 overdrive with 3:55 gear for the 2.83 total final ratio.
You can also calulate the launch ratio. This ignores the overdrive, but allows for the first gear and the final drive ratio.
I presently have a 2.50 first gear and a 3.08 diff. That is a launch ratio of 7.70 While that is okay, it's not performance.
With a 2.5 and a 3.55 it would be . 8.88 a bit better.
The trans Iwould like to have uses a 2.75 first, and if I use the 3.55 I would then have a launch ratio of 9.76 a very big improvement.
The 2.75 with a 4.11 would be an awsome 11.3 The car would launch like a slingshot! That is a HUGE increase over my start point, but overall I would lose high end and mileage, so I choose the earlier combo. Someday maybe the budget gods will smile on me, and I can do this.
Remember to consider both ends of the range when selecting ratios.
ken you stole my talking points 
..
.. I fully agree with ken.. getting more gears solves your problem. allows you to have your cake and eat it to. anything less usually results in a one trick pony.
i try to shoot for a 10.0 launch ratio... anything higher and you cant get traction i prefer no less than 9. if you go less.. you have to drop the clutch at 3500 to lose traction.
i bought the tko-600 with offset shifter
3.36 * 2.97 in first = 9.98
3.36 * .64 in fifth = 2.15
great for spinning and great for cruising.
remember also. with a manual trans.. you take take engine torque x launch ratio - 10% and that is your effective torque.
example 500 lb-ft * 10.0 launch = 5000 lb ft - 10% = 4500 lb ft
consider the encumbered weight of your car? you should always try to keep this above your weight if driving for fun.
400 * 7.0 = 2800 - 280 = 2520 lb ft. when trying to move a 3000 lb car this will feel sluggish in first gear.
though I guess it depends on what you drive normally.
great info gentlemen, just what I was looking for
I have an 81 also and went from the stock rear to a 3:55. Of the line is a BIG diff. At 75mph its a little to buzzy. I was planning to run a 700r but we all know how that goes..
i went from 3.08`s t0 3.55`s. running headers and sidepipes . roars like a lion , and will break loose the shoes without any trouble. drove it from fl to bowling green with a smile on my face. it`s a personal preference so decide what`s comfortable for you.
I like Joel am running 3:36 with M/T in my 71. 3000RPM @70mph. I'm getting 18 mpg as long as I keep my foot out of it,which is really hard for me. With the HP to back it up I can break em loose and burn em for pretty good stretch. 3:36 works for me.
Lifetime MemberGreensburg, IN - USA
Joined: 9/24/2003
Posts: 5188
Vette(s): Previous: 1984 Silver / Charcoal Coupe, 1988 Maroon Coupe / 1989 Artic White Coupe / 2001 Speedway White Roadster / Present:1976 Stingray Black / Black, Auto, 350 slightly modified (355 hp) Luxor Wires Redline Tires. / 1989 Roadster Bright Red...
[QUOTE=gurtz] I think ya'll have answered my questions. With the existing th350, motor and 2.72 rear, she is peppy but won't smoke da tires and she tach's out at 2600 rpm at 70 mph, which I don't care for.
Welcome Back Gurtz after a small hiatus away from us. I like the part where you are wanting to keep her stock looking as possible.
Brother if your gonna do that you better get her to the body shop and have um glass the hood down. Cuz that motor will burn their eyes when the go to lookin for the stock stuff......
I side with the 355 gears myself. They should give you what you want for performance and comfort.
Not saying I plan on smokin da tires all the time, it would be nice to on occasion. I am hoping to tach out in the 2400 to 2500 rpm range at 70 mph yet smoke da tires on occasion with the 4 speed.
Dats my goal!
I know I should have dropped the clams on the 5 speed, but concerened about the economy and could not pass the deal on the 4 speed plus I wanted to keep her as stock looking as possible.
[/QUOTE]
Welcome Back Gurtz after a small hiatus away from us. I like the part where you are wanting to keep her stock looking as possible.
Brother if your gonna do that you better get her to the body shop and have um glass the hood down. Cuz that motor will burn their eyes when the go to lookin for the stock stuff......
I side with the 355 gears myself. They should give you what you want for performance and comfort.
Well you know TUX, Lil T, my girls name in BLUE, doesn't show her motor to just anyone.
I was talkin' bout the stick! IF I knew how to post pics, I would post updated photos of da motor, looks mucho better than what you see now, but I am a DUNCE on da computa!
I gotta tell everyone, since I read KStyer and Chultu's response, it sure has me thinking about the 5 speed again, I really want to bring the tach down on the Interstates. I take Lil T on long drives alot. Don't care for the traffic in south LA roads in town.
I am very close to dropping the existing 350, but I think I'm a gonna drop the diff this weekend instead and study the quotes from Keisler and Classic Chevy 5 speed before I put the manual in.
I have been doing more reading here in the past few months than posting, but I have been looking in nightly!
Hope all is well with everyone and thanks for the responses!
g
I also failed to mention TUX that I manage a commercial roofing company here in BR and we had a little bit of a set back in time with Hurricane Gustav! Been a little busy keeping clients dry and happy!
BUT everyone is happy and dry now and I'm back to the more important things ini life - FAMILY LIFE & OLD CARS!!!!!
in Forum: C3 Driveline Components
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