Advise on Rear Diff Ratio
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,231
Likes: 7
From: Fort Pierce Florida
Advise on Rear Diff Ratio
I've made a similar thread before, but now Van Steel has my rear end and I need to make up my mind! 
I'm pretty sure anything shorter then 4.11 is too short and anything taller then 3.55 is too tall. My '82 starts to lug and jerk at a 40 mph cruise when it shifts into fourth despite. I've been told it's because my 3.55:1 gears are too tall for the .7 overdrive gear of the 4L60. Not sure, but it's really annoying and don't want the same thing with my '72. Anyway, here's the stats. Any help would be appreciated.
335/30R18 Tires (25.91 in. high)
T-56 Manual Tranny
1st 2.66:1
2nd 1.78:1
3rd 1.3:1
4th 1.0:1
5th 0.74:1
6th 0.5:1
Options for gears are 3.55, 3.7, and 4.11 I think.
550 HP @ 6,000 RPM's, 500 ft. lb. of torque (400 ft. lb. @ 2,300 RPM's) have been achevied with similar engine setups to mine.
Here's a calculator Gear-Speed Calculator
I'm leaning towards the 3.7:1 ratio.
I'm pretty sure anything shorter then 4.11 is too short and anything taller then 3.55 is too tall. My '82 starts to lug and jerk at a 40 mph cruise when it shifts into fourth despite. I've been told it's because my 3.55:1 gears are too tall for the .7 overdrive gear of the 4L60. Not sure, but it's really annoying and don't want the same thing with my '72. Anyway, here's the stats. Any help would be appreciated.335/30R18 Tires (25.91 in. high)
T-56 Manual Tranny
1st 2.66:1
2nd 1.78:1
3rd 1.3:1
4th 1.0:1
5th 0.74:1
6th 0.5:1
Options for gears are 3.55, 3.7, and 4.11 I think.
550 HP @ 6,000 RPM's, 500 ft. lb. of torque (400 ft. lb. @ 2,300 RPM's) have been achevied with similar engine setups to mine.
Here's a calculator Gear-Speed Calculator
I'm leaning towards the 3.7:1 ratio.
Last edited by SuprJames; Jan 30, 2006 at 03:22 PM.
Drifting
Joined: May 2004
Posts: 1,442
Likes: 2
From: Flanders NJ
Originally Posted by SuprJames
I've made a similar thread before, but now Van Steel has my rear end and I need to make up my mind! I'm pretty sure anything shorter then 4.11 is too short and anything taller then 3.55 is too tall. My '82 starts to lug and jerk at a 40 mph cruise when it shifts into fourth despite. I've been told it's because my 3.55:1 gears are too tall for the .7 overdrive gear. Not sure, but it's really annoying and don't want the same thing with my '72. Anyway, here's the stats. Any help would be appreciated.
I'm pretty sure anything shorter then 4.11 is too short and anything taller then 3.55 is too tall. My '82 starts to lug and jerk at a 40 mph cruise when it shifts into fourth despite. I've been told it's because my 3.55:1 gears are too tall for the .7 overdrive gear. Not sure, but it's really annoying and don't want the same thing with my '72. Anyway, here's the stats. Any help would be appreciated.Works great, around town I leave it in 3rd and no more chugging. When I go on the highway I put it in drive (od) and it locks up fine. I think I got it from Eklers, can't remember, it was $99.
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,231
Likes: 7
From: Fort Pierce Florida
Originally Posted by mooneyd
My '82 did the same thing, I got a chip that plugs in line at the trans and it prevents the converter from locking up unless your in 4th gear.
Works great, around town I leave it in 3rd and no more chugging. When I go on the highway I put it in drive (od) and it locks up fine. I think I got it from Eklers, can't remember, it was $99.
Works great, around town I leave it in 3rd and no more chugging. When I go on the highway I put it in drive (od) and it locks up fine. I think I got it from Eklers, can't remember, it was $99.
I usually just shift it into 3rd also and no problems after that. The .7 OD in my '82 really isn't any good even with 3.55's until 60 mph or so. With an even taller .5 OD ratio I'm not really sure what to run. They only run 3.42's in the C5's.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The years keep clicking by. So in 1988 or so I installed my 700R4 with .70 OD. I had 3.55 gearing and found that 4th was about worthless unless i was moving fast. So I installed 4.11. The bad gear ratio jumps of our tranny are closed up
From what I saw in Florida - high speed is not easy to do for very long.
If not 4.11 is 3.90 a choice? What is your max RPM
From what I saw in Florida - high speed is not easy to do for very long.
If not 4.11 is 3.90 a choice? What is your max RPM
Last edited by gkull; Jan 30, 2006 at 05:12 PM.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Beyond RPM in each gear, you also have to consider how much motor ya' got. An engine that peaks at 4,500 rpm will not be very happy with a stiff rear gear. You tend to go through rpm pretty fast with a low rear gear. Essentially, you shoot through your torque curve too fast when you're pouring the coals to it. A 3.55 with an engine that makes most of its torque off idle to 3k rpm and that 2.66 1st gear would probably be fine. Same gear with an engine that doesn't even turn on until 3k rpm would be a very poor choice.
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,231
Likes: 7
From: Fort Pierce Florida
Originally Posted by gkull
If not 4.11 is 3.90 a choice? What is your max RPM
dyno chart
Not sure if 3.9 is an option. I guess I could've asked...
Instructor
Joined: Jul 2000
Posts: 221
Likes: 30
From: columbia mo.
Corect Me If Rong But I Thought All 82 Had 3.08 Or 2.7 Something For Rear Gears.i Had A 72 With 3.08 And 700-r With The Vacume Controled Lock Up And At Around 40 Mph Or So It Would Go Into 4th And Would Lug The Engine To Much And Had To Down Shift To 3rd.
Now I Have A 72 With 700r And 3.70 Gearsthe Lock Up Is Controled By Pressure Insted Of Vacume None Of The Problems As The 3.08 Gears.
Also If You Go With 3.90 Or 4.11 You Wount Be Able To Get The Spedo To Read Corect Unles Use Some Aftermarket Gear Reduction Set Up
Now I Have A 72 With 700r And 3.70 Gearsthe Lock Up Is Controled By Pressure Insted Of Vacume None Of The Problems As The 3.08 Gears.
Also If You Go With 3.90 Or 4.11 You Wount Be Able To Get The Spedo To Read Corect Unles Use Some Aftermarket Gear Reduction Set Up
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Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I also do lots of long range driving. With my tire diameter I'm doing @3000 rpm in lockup OD at 85 mph. It's really doing more rpm than required. Something like 3.90 would drop me a few hundred rpm at 85, but still give me enough power to pass somebody without a down shift.
Another way to look at it is: how often are you going to ever get going 190 mph to red line your 6500 rpm. My motors turn 7500 and 7000 rpm. So I was never worried about hitting my rev limiter with 28 inch tall tires and 4.11 rear gears
Another way to look at it is: how often are you going to ever get going 190 mph to red line your 6500 rpm. My motors turn 7500 and 7000 rpm. So I was never worried about hitting my rev limiter with 28 inch tall tires and 4.11 rear gears
Premium Supporting Vendor
Joined: May 2000
Posts: 4,312
Likes: 70
From: Clearwater FL
Originally Posted by SuprJames
I do quite a bit of distance driving, so I'm on interstates quite a bit. A LS6 can rev to 6,500 RPM's. Here's a dynochart simlar to the setup I'm working on.
dyno chart
Not sure if 3.9 is an option. I guess I could've asked...
dyno chart
Not sure if 3.9 is an option. I guess I could've asked...
3:90's are available.
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,231
Likes: 7
From: Fort Pierce Florida
Originally Posted by gkull
Another way to look at it is: how often are you going to ever get going 190 mph to red line your 6500 rpm. My motors turn 7500 and 7000 rpm. So I was never worried about hitting my rev limiter with 28 inch tall tires and 4.11 rear gears
Wow, your tires are pretty tall. I don't like that mine are an inch shorter then stock, but I don't really have a choice as my choices in tires are limited when you get that wide.
Ugh, I'm between the 3.73's and 3.9's.
Thread Starter
Melting Slicks
Joined: Nov 2002
Posts: 2,231
Likes: 7
From: Fort Pierce Florida
Originally Posted by GTENIT
Corect Me If Rong But I Thought All 82 Had 3.08 Or 2.7 Something For Rear Gears.i Had A 72 With 3.08 And 700-r With The Vacume Controled Lock Up And At Around 40 Mph Or So It Would Go Into 4th And Would Lug The Engine To Much And Had To Down Shift To 3rd.
Now I Have A 72 With 700r And 3.70 Gearsthe Lock Up Is Controled By Pressure Insted Of Vacume None Of The Problems As The 3.08 Gears.
Also If You Go With 3.90 Or 4.11 You Wount Be Able To Get The Spedo To Read Corect Unles Use Some Aftermarket Gear Reduction Set Up
Now I Have A 72 With 700r And 3.70 Gearsthe Lock Up Is Controled By Pressure Insted Of Vacume None Of The Problems As The 3.08 Gears.
Also If You Go With 3.90 Or 4.11 You Wount Be Able To Get The Spedo To Read Corect Unles Use Some Aftermarket Gear Reduction Set Up
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by SuprJames
Wow, your tires are pretty tall. I don't like that mine are an inch shorter then stock, but I don't really have a choice as my choices in tires are limited when you get that wide.
Ugh, I'm between the 3.73's and 3.9's.
Ugh, I'm between the 3.73's and 3.9's.
