Rear End Suggestions
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 1,154
Likes: 1
From: St Augustine FL
Rear End Suggestions
My car is an 82 mostly stock with the CFI. I am going to be doing some minor mods when I do rebuild that should put me with around 300+ hp. What is a good streetable rear end ratio that would work well with the 700r4 tranny and a 300 hp motor to give the car a little more get up and go off the line? The stock 2.72 is just not going to do it and I am afraid that the 3.73 that I was offered will be too much for the highway. Suggestions will be appreciated.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
I've always liked 3.55:1, SB (auto or stick) or BB (stick), but I'm thinking the 3.36:1 should probably work nicely for you, unless you plan on drag racing a lot. IMHO deeper gears are overrated for street machines, as they'll have you spending substantial time shifting and make for considerable revs on the highway.
Those are the two ratios I'd be looking seriously at.
Ooops, automatic here. Nevermind the shifting part.
Those are the two ratios I'd be looking seriously at.
Ooops, automatic here. Nevermind the shifting part.
Last edited by TheSkunkWorks; Aug 14, 2007 at 02:25 PM.
Heel & Toe
Joined: Nov 2006
Posts: 16
Likes: 0
From: Atlanta Georgia
The best way I find to decide on gear ratios is to use the below formula. Will tell you exactly what you want to know given the wide range of gears available and the specific tire size you are using.
Gear ratio = rpm x tire diameter/Mph x 336
If you want off the line, then use a lower MPH for a numerically higher gear (this is based on a final drive ratio of 1:1 out the tranny)
Gear ratio = rpm x tire diameter/Mph x 336
If you want off the line, then use a lower MPH for a numerically higher gear (this is based on a final drive ratio of 1:1 out the tranny)
Melting Slicks
Joined: Jun 2005
Posts: 2,938
Likes: 2
From: Arkansas
I’m in the same boat, I installed TPI and want to change my rear end gears to wake up the engine a bit and still make good use of the 700r4 tranny.
Where can you buy a decent set of 3:55 gears? Was gm rear ends all the same ie; you can swap gears around from any gm rwd vehicle? Or is it limited by models?
Where can you buy a decent set of 3:55 gears? Was gm rear ends all the same ie; you can swap gears around from any gm rwd vehicle? Or is it limited by models?
Race Director
Joined: Jan 2003
Posts: 15,177
Likes: 90
From: State of Confusion
When my '82 was stock with 2.87s, the ratio between the speedo & tach was roughly 4:1 (80 MPH = 20 [hundred] RPM ):
with 3.73s, it is now roughly 3:1 (60 MPH = 20 [hundred] RPM )
The above formula fails to account for the .7:1 OD ratio of a 700R4, so you'd have to divide that answer by .7
with 3.73s, it is now roughly 3:1 (60 MPH = 20 [hundred] RPM )
The above formula fails to account for the .7:1 OD ratio of a 700R4, so you'd have to divide that answer by .7
Drifting
Joined: Jul 2007
Posts: 1,712
Likes: 0
From: Tampa FL
I'm running 3.70's with a 700 R4 on my 1980 L82 and it's great on the interstate, no reason not to go that high. I got my gears from www.ikerds.com
Last edited by Ron R; Aug 14, 2007 at 09:15 PM.
Veteran
Joined: Oct 2005
Posts: 1,284
Likes: 81
From: Nashville, TN
I'm running 3.70's with a 700 R4 on my 1980 L82 and it's great on the interstate, no reason not to go that high. I got my gears from www.ikerds.com
I have 3.36 on my th400 3-speed 383 and am thinking about going to 3.70's. Right now at 3000 rpm I am right around 70 mph. Of course it also depends on cam selection and how much driving you actually do. Mine is a weekend toy so gas mileage is not a real concern. With a 700r4 you could go to 3.70's with no problem in my opinion.
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Pro
Joined: Apr 2001
Posts: 605
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From: las vegas
If you were going to be somewhat higher (370-400) in the HP and torque department I would says 3:55's, but with the HP in the low three hundreds you will be happier with a set of 3:70 gears IMHO. Three seventy gears will make that engine seems to be putting out a lot more power. You are making a very smart move here with the idea of changing to a more performance minded gear ratio! People who bought Corvettes back then and ordered 3:07 and lower gears should have bought a Volkeswagon instead.
Al
Al
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 1,154
Likes: 1
From: St Augustine FL
Thanks for the imput. So I just need to decide between 3.55 and 3.70. I have been offered a 3.73 ring and pinon for $100. They are basically new Have about 100 miles on them. The guy decided it was too much for his car on the highway ( he was sruning a Th350 tranny). What to do what to do????
Drifting
Joined: Jul 2007
Posts: 1,712
Likes: 0
From: Tampa FL
Thanks for the imput. So I just need to decide between 3.55 and 3.70. I have been offered a 3.73 ring and pinon for $100. They are basically new Have about 100 miles on them. The guy decided it was too much for his car on the highway ( he was sruning a Th350 tranny). What to do what to do????
Race Director
Joined: Jan 2003
Posts: 15,177
Likes: 90
From: State of Confusion
Go for the 3.73, you won't be disappointed. I'm actually getting better gas mileage now than I did with the 2.8whatever's /TH-350 in there previously due to the 700 R4's overdrive. You won't be disappointed with the 3.73's, and I think if you go with 3.55's you'll wish you had gone higher in a couple months. I'm already kind of wishing I had gone to 3.90's.
when I wanted to switch, I'd heard that ZIP Products offered 3.90 & 4.10 gear-sets for the Dana-44 series-3 carrier, but they never returned my calls & e-mail, so I got Precision Gear 3.73s, and they've worked fine.
As-long-as you keep the 700-R4 in the car, the 3.73s will 'feel'-like 2.61s, because 4th/OD is .7:1 ratio:
4.11s with the 700-R4 would be the same-as the 2.87s with a 4-speed of that era in 4th Gear (numerically )
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 1,154
Likes: 1
From: St Augustine FL
Ok how do I know what manufacturer of gears to buy? I have no Idea what the stock rear end is on my car. Its an 82 non-collector and if Im not mistaked the stock gears are 2.72 or something like that. Do I just need the ring and pinion for the swap out? Also is ther any adjustment that I need to make to the speedometer so that it will read correctly?
Last edited by bluesilver82; Aug 15, 2007 at 12:00 PM.
Drifting
Joined: Jul 2007
Posts: 1,712
Likes: 0
From: Tampa FL
Ok how do I know what manufacturer of gears to buy? I have no Idea what the stock rear end is on my car. Its an 82 non-collector and if Im not mistaked the stock gears are 2.72 or something like that. Do I just need the ring and pinion for the swap out? Also is ther any adjustment that I need to make to the speedometer so that it will read correctly?
This is what you need right here:
http://www.ikerds.com/merchant2/merc...t_Code=300-078
Edit: The speedometer will need to be recalibrated, I forgot to mention that earlier, because your rear wheel will be turning faster. I didn't do this myself, so I'm not sure what to do, but maybe someone else can chime in.
Last edited by Ron R; Aug 15, 2007 at 03:28 PM.
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 1,154
Likes: 1
From: St Augustine FL
ok $100 for the parts and $650 to install??????I was quoted $650 for labor which sounds steep to me. (probably because I am supplying the parts) The guy at the shop told me it would take 8.5 hours so $76.47 per hour for labor and does it really take that long to do?
Drifting
Joined: Jul 2007
Posts: 1,712
Likes: 0
From: Tampa FL
ok $100 for the parts and $650 to install??????I was quoted $650 for labor which sounds steep to me. (probably because I am supplying the parts) The guy at the shop told me it would take 8.5 hours so $76.47 per hour for labor and does it really take that long to do?
Race Director
Joined: Jan 2003
Posts: 15,177
Likes: 90
From: State of Confusion
ok $100 for the parts and $650 to install??????I was quoted $650 for labor which sounds steep to me. (probably because I am supplying the parts) The guy at the shop told me it would take 8.5 hours so $76.47 per hour for labor and does it really take that long to do?
ring-n-pinion - $135
service & swap gears - $350
swap-out drive & driven gear in 700R4 for speedo-recalibration / parts & labor - $100
Total bill - less than $600 (in '03 )
My buddy who did the swap has owned and done Corvette IRS' for 30+ years, and knows his way around these cars:
he did the gears in my Z28 when I drag-raced it, and has built 12-bolts to survive in 8-second, tube-chassised cars.
We dropped-off the car @ 8:00 AM, and at 2:30 PM, we were burning-gas:
he even vacuumed-out the interior and cleaned the windows when he was finished, and was washing the car when I arrived ta his shop.
Pro
Joined: Apr 2001
Posts: 605
Likes: 0
From: las vegas
You need only change out the transmission speedo gear. Call Dr. Rebuild and tell him the color of the speedo gear thats in there at this time and the ratio that you are changing to. He will probably send you a couple of gears to try. I believe you need a green gear. Last cost I have in my catalog was $9.75. You sure as heel do not need to pay someone a hundred dollars to recalibrate your speedo when the part is ten dollars! Al
Al
Melting Slicks
Joined: Jun 2005
Posts: 2,938
Likes: 2
From: Arkansas
I went here to calculate the gears I needed for mine
http://www.700r4.com/speedoCalc/speedocalc.shtml
Then I bought my gears here:
http://www.transmissioncenter.net/sp...n_______va.htm
Very easy to do
http://www.700r4.com/speedoCalc/speedocalc.shtml
Then I bought my gears here:
http://www.transmissioncenter.net/sp...n_______va.htm
Very easy to do