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Topic: 3:07, 3.55 or 3.70 rear end ratios

in Forum: C3 Driveline Components

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3:07, 3.55 or 3.70 rear end ratios (1/25)
2/15/09 10:34am

gurtz
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baton rouge, LA - USA

Vette(s):
1981 dark metallic blue, dark doeskin leather interior, mirrored glass T Tops, 330hp/350ci GMPP crate engine, billeted aluminum serpentine system, Dewitts with dual spalls

Joined: 8/12/2006
Posts: 391

Anyone out there change out their existing 2.72 diff with any of the above diff and how do you like the change?

I have a 81

Thanks,

gurtz

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3:07, 3.55 or 3.70 rear end ratios (2/25)
2/15/09 6:31pm

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Flanders, NJ - USA

Vette(s):
1982 Black, ZZ4, Hooker Side Pipes, 3.55 Rear, Rebuilt & upgraded 700R4, All new suspension, brakes, & new Charcoal interior.

Joined: 1/27/2004
Posts: 2553

I had the 2.72:1 and went to 3.55:1 gears. big difference in acceleration.

I have the overdrive trans so my gas mileage is still good. If that's not an issue, the 3.55:1 is a good choice. You'll like it.

Dave

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Dave's '82

3:07, 3.55 or 3.70 rear end ratios (3/25)
2/15/09 7:03pm

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I went to 3.70 for perfomance.

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corvette440hp

3:07, 3.55 or 3.70 rear end ratios (4/25)
2/15/09 9:11pm

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Red Lion, PA - USA

Vette(s):
1974 White 350 Corvette, TH400 Automatic 1972 Tangerine /Go Mango Convertible 383 Stroker, 2004r Automatic

Joined: 10/27/2006
Posts: 1182

What r the costs of changing the gear ratio in a vette. Can you just change an already loaded rear or do you have to have someone change the ring and pinion.

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3:07, 3.55 or 3.70 rear end ratios (5/25)
2/15/09 10:07pm

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Flanders, NJ - USA

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If you're going to rebuild it anyway there is no difference in cost. And if you want to change ratios you might as well rebuild it, it needs to be torn down one way or the other.

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3:07, 3.55 or 3.70 rear end ratios (6/25)
2/16/09 1:49am

gurtz
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baton rouge, LA - USA

Vette(s):
1981 dark metallic blue, dark doeskin leather interior, mirrored glass T Tops, 330hp/350ci GMPP crate engine, billeted aluminum serpentine system, Dewitts with dual spalls

Joined: 8/12/2006
Posts: 391

I have an OD tranny with the 3.55 in another car and do well gas mileage wise.

I am in the middle of removing the existing TH350 and am installing a t10 4 speed. I want more acceleration, but I am not sure how bad the car will tach out with the 3.55 on the Interstates, as I take her for pretty decent runs when we go out.

That was probably the question I should have asked.

3:07, 3.55 or 3.70 rear end ratios (7/25)
2/16/09 6:44am

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Flanders, NJ - USA

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1982 Black, ZZ4, Hooker Side Pipes, 3.55 Rear, Rebuilt & upgraded 700R4, All new suspension, brakes, & new Charcoal interior.

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Posts: 2553

It should be alright. You could go with 3.30:1 gears also. I asume the 4th gear is 1:1 on the new trans. 3.70:1 rear would not be good for highway driving.

If it was me I'd go with the 3.55:1 rear.

Dave

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3:07, 3.55 or 3.70 rear end ratios (8/25)
2/16/09 7:22am

MikeMc71
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Tucson, AZ - USA

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1970 White L-46 Air Roadster, 1971 White LT1 Coupe, 1971 Red Auto Air Coupe, 383 stroker, 430 HP, 2002 Millennium Yellow Auto Coupe

Joined: 10/7/2007
Posts: 341

I really think it depends on what you plan on doing with the car. A lot of highway I would go 3.08, as long as you have the horspower to back it up. Our '71 stroker, auto has a 3.08, and its fine..GREAT on the highway. I have 3.36 gears in the Vert, not much freeway, around town is nice. 3.70 in the LT-1, its a MONSTER off the line, but runs about 3000rpm at about 60MPH. The freeways here are 75 MPH, so not much freeway for that car.

The 3.08 runs about 2100rpm at 70, and with 430 HP, its got plenty of get up and go!

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3:07, 3.55 or 3.70 rear end ratios (9/25)
2/16/09 8:24am

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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My '74 has 3:36 rear gears, and a 4 speed. It tachs out around 3000rpm @ 70mph.
Going from a 2:72 to a 3:07 isn't gonna be a big difference, but it will be a little more "peppy". The 3:55 will be a lot more "peppy", but it's gonna wind the engine up a lot tighter(at hiway speeds) than what you have now, for sure.
Any change in rear gear ratios will also require a change in speedo gearing, if you want the speedo to read correctly.
I would stay with the 3:08, or maybe the 3:55...but no more, unless you rarely go on the road with it. High rpms get to be annoying after a while...

[QUOTE=rod7515]
What r the costs of changing the gear ratio in a vette. Can you just change an already loaded rear or do you have to have someone change the ring and pinion. [/QUOTE]

If you have a diff assy that is already built/loaded, it's a simple(somewhat) swap...take the old one out, put the new one in. If you want to change the ratio of the diff you have, then it needs to be dis-assembled, and rebuilt with whatever gear ratio you want, that will fit in the carrier. The stock carrier will only allow you to go to a certain ratio before having to change the carrier. For instance, you couldn't install a 4:11 gear set in a diff that has a 2:72 in it now. The carriers are different. The carrier is the part that the ring gear actually bolts to. The lower(higher numerically) the ratio, the thicker the gears are, which requires the carrier to be different.

The cost to replace the diff assy with another one would be about the same as having your's built with a different ratio. Prices are different all over the country, so it's hard to put a price on it. Check with a local Corvette shop, or differential shop, for an idea of the costs.
A normal "rebuild" of the diff shouldn't be more than $250(labor) or so, if you take it out yourself. If a shop does the entire job, you could be looking at $1500 or more...

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3:07, 3.55 or 3.70 rear end ratios (10/25)
2/16/09 8:42am

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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

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I went to 3.70s. It will yank you out of bed. is also a screamer of 60 MPH on longer drives - not too many of those...

3:07, 3.55 or 3.70 rear end ratios (11/25)
2/16/09 4:13pm

gurtz
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baton rouge, LA - USA

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1981 dark metallic blue, dark doeskin leather interior, mirrored glass T Tops, 330hp/350ci GMPP crate engine, billeted aluminum serpentine system, Dewitts with dual spalls

Joined: 8/12/2006
Posts: 391

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.

3:07, 3.55 or 3.70 rear end ratios (12/25)
2/16/09 6:55pm

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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
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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.

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.

kstyer2009-02-16 20:18:58

3:07, 3.55 or 3.70 rear end ratios (13/25)
2/17/09 12:31am

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Hot Springs, AR - USA

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

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[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.

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.

[/QUOTE]

ken you stole my talking points LOL

LOL

..

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.

cthulhu2009-02-17 01:44:21

3:07, 3.55 or 3.70 rear end ratios (14/25)
2/17/09 1:51am

gurtz
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baton rouge, LA - USA

Vette(s):
1981 dark metallic blue, dark doeskin leather interior, mirrored glass T Tops, 330hp/350ci GMPP crate engine, billeted aluminum serpentine system, Dewitts with dual spalls

Joined: 8/12/2006
Posts: 391

great info gentlemen, just what I was looking for

3:07, 3.55 or 3.70 rear end ratios (15/25)
2/17/09 5:37am

KeBo
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Kendall Park, NJ - USA

Vette(s):
1981 - 59 Beige over Cinnebar leather. Edlebrock top end, 2200 stall w/shift kit, 3:55s, Mufflex maniback exhaust, nice stereo, 16 in AREs w/BFGs

Joined: 3/9/2005
Posts: 789

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..

3:07, 3.55 or 3.70 rear end ratios (16/25)
2/17/09 1:45pm

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DUNEDIN, FL - USA

Vette(s):
1969 COUPE CORTEZ SILVER, BRIGHT BLUE INTERIOR 383 cu. in. 512 HP. Hooker headers w/ side pipes PS PS AC AM FM STEREO. 68,000.MILES C5 5oth Anniversary Coupe , auto.350hp

Joined: 10/22/2004
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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.

3:07, 3.55 or 3.70 rear end ratios (17/25)
2/17/09 2:28pm

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Dorr, MI - USA

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71 Colonnade Hardtop Coupe Torch Red with black interior originally L48 built to push around 360hp

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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.

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3:07, 3.55 or 3.70 rear end ratios (18/25)
2/17/09 2:40pm

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Greensburg, IN - USA

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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...

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[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.

�

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.

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3:07, 3.55 or 3.70 rear end ratios (19/25)
2/17/09 5:00pm

gurtz
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baton rouge, LA - USA

Vette(s):
1981 dark metallic blue, dark doeskin leather interior, mirrored glass T Tops, 330hp/350ci GMPP crate engine, billeted aluminum serpentine system, Dewitts with dual spalls

Joined: 8/12/2006
Posts: 391

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

3:07, 3.55 or 3.70 rear end ratios (20/25)
2/18/09 4:32am

gurtz
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baton rouge, LA - USA

Vette(s):
1981 dark metallic blue, dark doeskin leather interior, mirrored glass T Tops, 330hp/350ci GMPP crate engine, billeted aluminum serpentine system, Dewitts with dual spalls

Joined: 8/12/2006
Posts: 391

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!!!!!

3:07, 3.55 or 3.70 rear end ratios (21/25)
3/8/09 5:11pm

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Gloucester, VA - USA

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1979 T-Top, Metallic Green ZZ4 350/355 hp 405 ft/lbs torque Dual Spal Fans 700R4 4 Spd O/D Transmission 2004 Z06 Commemorative Edition

Joined: 1/29/2005
Posts: 1453

Okay Just reread this post...

Ya'll know I put the 700R4 in a while back and I'm unhappy with the performance as far shifting. Reading this thread makes me think the problem might be that the gearing in the 700R4 and the stock rear rations might be too close?

Am I just babbling? I'm guessing it's still the 3.55:1.

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3:07, 3.55 or 3.70 rear end ratios (22/25)
3/8/09 6:06pm

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Hot Springs, AR - USA

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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

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[QUOTE=JimG]Okay Just reread this post...

Ya'll know I put the 700R4 in a while back and I'm unhappy with the performance as far shifting. Reading this thread makes me think the problem might be that the gearing in the 700R4 and the stock rear rations might be too close?

Am I just babbling? I'm guessing it's still the 3.55:1. [/QUOTE]

your 700r4 has 3.06, 1.63, 1.00 and .70

so your launch ratio is 10.863

should be pretty good.

OD final ratio is 2.485

what about your shifting dont you like?

3:07, 3.55 or 3.70 rear end ratios (23/25)
3/8/09 9:23pm

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Kingston, PA - USA

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1977 L-82 originally white/buckskin interior. Currently undergoing a frame-off resto. and modifications.YEEHAW!!!

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I had the Super T-10 with a 3.70 final drive. The 1:1 ratio in 4th gear gave me 4000rpm at 80 mph. That's too much screaming for highway speeds.

I'm currently in the process of installing a Tremec TKO600 in my never-ending rebuild. I'm counting on this to take that "problem" away.

3:07, 3.55 or 3.70 rear end ratios (24/25)
3/9/09 2:43am

gurtz
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baton rouge, LA - USA

Vette(s):
1981 dark metallic blue, dark doeskin leather interior, mirrored glass T Tops, 330hp/350ci GMPP crate engine, billeted aluminum serpentine system, Dewitts with dual spalls

Joined: 8/12/2006
Posts: 391

Gribble, If I could do it over, I would do exactly what you are doing. Your rpm's are supposed to drop off about 33-36% off the 4k at 80 or 2680 - 2560 plus your first gear is much better also!

What are your plans with your t-10? Are you keeping her or selling off whole or in parts. I ask because a buddy of mine is putting a t-10 in his 59 vert and needs a BW shifter.

Let me know what you do!

Thanks, Rick

3:07, 3.55 or 3.70 rear end ratios (25/25)
3/9/09 5:30pm

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Gloucester, VA - USA

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1979 T-Top, Metallic Green ZZ4 350/355 hp 405 ft/lbs torque Dual Spal Fans 700R4 4 Spd O/D Transmission 2004 Z06 Commemorative Edition

Joined: 1/29/2005
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[QUOTE=cthulhu][QUOTE=JimG]Okay Just reread this post...

Ya'll know I put the 700R4 in a while back and I'm unhappy with the performance as far shifting. Reading this thread makes me think the problem might be that the gearing in the 700R4 and the stock rear rations might be too close?

Am I just babbling? I'm guessing it's still the 3.55:1. [/QUOTE]

your 700r4 has 3.06, 1.63, 1.00 and .70

so your launch ratio is 10.863

should be pretty good.

OD final ratio is 2.485

what about your shifting dont you like?

[/QUOTE]

Hard to explain...Just doesn't feel "right".

I am on the other hand running about 1800 RPM at 70 MpH.

I'm also getting a sound like something is slipping. I dunno, I just need someone else to drive it and see if I'm losing my mind.

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