C3 Diff gearing for TH700
Thread Starter
Cruising
Joined: Nov 2015
Posts: 11
Likes: 0
C3 Diff gearing for TH700
Hi guys
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
Hi guys
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Just put a little thought into it. How did it drive in third gear with a 3.08? What RPM do you want to have with your tire diameter and normal freeway speeds. What is the max rpm of this new 383?. They have all kinds of rpm and mph online calculators.
i went through this same dilemma when I installed my 700R4. But I had an agenda of a top speed and the power to get there.
Just some math with a .70 OD 4th gear make these effective rear end gears
4.11X.70 = 2.877
3.90X.70 = 2.730
i opted for the 4.11 and drove it for 20 years. I always thought in retrospect that the 3.90 rear would have been a good choice on lower rpm motors. I had high rpm 383 and later i went to a somewhat lower rpm 427 small block.
I wanted to enter the Nevada silver state open road race, 93 miles of two lane highway. My class max allowed speed was 175 mph. My peak hp was right at 6300 rpm and I was using 27 inch tall goodyear racing tires. 4.11 put right at 175 mph and the ability to get up there as fast as possible. My 700R4 was modded for no kick down to run wide open throttle in 4th gear.
http://www.angelfire.com/fl/procrastination/rear.html
i went through this same dilemma when I installed my 700R4. But I had an agenda of a top speed and the power to get there.
Just some math with a .70 OD 4th gear make these effective rear end gears
4.11X.70 = 2.877
3.90X.70 = 2.730
i opted for the 4.11 and drove it for 20 years. I always thought in retrospect that the 3.90 rear would have been a good choice on lower rpm motors. I had high rpm 383 and later i went to a somewhat lower rpm 427 small block.
I wanted to enter the Nevada silver state open road race, 93 miles of two lane highway. My class max allowed speed was 175 mph. My peak hp was right at 6300 rpm and I was using 27 inch tall goodyear racing tires. 4.11 put right at 175 mph and the ability to get up there as fast as possible. My 700R4 was modded for no kick down to run wide open throttle in 4th gear.
http://www.angelfire.com/fl/procrastination/rear.html
Last edited by gkull; Nov 9, 2015 at 04:12 PM.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Hi guys
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
A set of 3.73's will give you a 2100 rpm @ 60 mph cruising speed.
Thread Starter
Cruising
Joined: Nov 2015
Posts: 11
Likes: 0
It sounds like a seriously fun toy,
The previous setup was 261 hprw, TH700, 3.08 diff, 27 inch tyres.
In third gear it drove fine on the highway,in 4th gear it bogged down to 1900 RPM @ 60 MPH. Sluggish around town.
The new motor is 450 HP @ 5700 with tall 27 inch tyres.
The other issue is with a performance roller cam motor i've heard that you should keep the highway RPM around 2500 for lubrication.
I also read somewhere that the perfect all round diff ratio for a TH700 is 3.36 which sounds similar to a 3.08.
The previous setup was 261 hprw, TH700, 3.08 diff, 27 inch tyres.
In third gear it drove fine on the highway,in 4th gear it bogged down to 1900 RPM @ 60 MPH. Sluggish around town.
The new motor is 450 HP @ 5700 with tall 27 inch tyres.
The other issue is with a performance roller cam motor i've heard that you should keep the highway RPM around 2500 for lubrication.
I also read somewhere that the perfect all round diff ratio for a TH700 is 3.36 which sounds similar to a 3.08.
Thread Starter
Cruising
Joined: Nov 2015
Posts: 11
Likes: 0
Burning Brakes
Joined: May 2014
Posts: 884
Likes: 128
From: Rhine Georgia
I have a factory 3.55 in mine and I'm happy with it. I would probably be just as happy if I had the 3.73. You can't go wrong with either. First gear is over fairly quick. Even more so with a 3.73
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Burning Brakes
Joined: Feb 2008
Posts: 1,168
Likes: 17
From: Iowa
I have 3:55's and am happy with them. (383 roller cam motor.). I had a 2400 stall converter and got sick of it for normal driving. It was a pain in the *** trying to regulate speed in town in 3rd gear. I put a 1600 stall in and like it much better. Don't need much stall with the low first gear of a 700R4 combined with the torque of a roller cammed 383.
More stall would do nothing for me as I can liquefy the tires taking off from a stand still with out touching the brakes.
I don't understand the reason for keeping rpm's above 2500 on the highway. I've never heard this before.
More stall would do nothing for me as I can liquefy the tires taking off from a stand still with out touching the brakes.
I don't understand the reason for keeping rpm's above 2500 on the highway. I've never heard this before.
Last edited by tixeon; Nov 9, 2015 at 09:22 PM.
Thread Starter
Cruising
Joined: Nov 2015
Posts: 11
Likes: 0
I have 3:55's and am happy with them. (383 roller cam motor.). I had a 2400 stall converter and got sick of it for normal driving. It was a pain in the *** trying to regulate speed in town in 3rd gear. I put a 1600 stall in and like it much better. Don't need much stall with the low first gear of a 700R4 combined with the torque of a roller cammed 383.
More stall would do nothing for me as I can liquefy the tires taking off from a stand still with out touching the brakes.
I don't understand the reason for keeping rpm's above 2500 on the highway. I've never heard this before.
More stall would do nothing for me as I can liquefy the tires taking off from a stand still with out touching the brakes.
I don't understand the reason for keeping rpm's above 2500 on the highway. I've never heard this before.
Thread Starter
Cruising
Joined: Nov 2015
Posts: 11
Likes: 0
I have 3:55's and am happy with them. (383 roller cam motor.). I had a 2400 stall converter and got sick of it for normal driving. It was a pain in the *** trying to regulate speed in town in 3rd gear. I put a 1600 stall in and like it much better. Don't need much stall with the low first gear of a 700R4 combined with the torque of a roller cammed 383.
More stall would do nothing for me as I can liquefy the tires taking off from a stand still with out touching the brakes.
I don't understand the reason for keeping rpm's above 2500 on the highway. I've never heard this before.
More stall would do nothing for me as I can liquefy the tires taking off from a stand still with out touching the brakes.
I don't understand the reason for keeping rpm's above 2500 on the highway. I've never heard this before.
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Burning Brakes
Joined: Feb 2008
Posts: 1,168
Likes: 17
From: Iowa
My car is a daily driver in the summer, so I chose gears, cam, and stall speed to match my driving style and the speeds I would be driving in real life 99% of the time. My torque converter is a 1600 stall lock up converter to be more specific. My cam may be considered mild. I am running the LT4 hot cam. I chose it so I would have good torque at the speeds I actually drive. It gives me great throttle response and drive ability in. We all dream of more HP and it takes some discipline to pick a cam to match our driving styles and not go overboard. For a daily driver too much cam is worse then not enough. My car is a 80 with the weaker rear end setup and so far with my mild cam I have managed to break a u-joint, yolk, and half shaft messing around on the street. Dave
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
Some good info here and some conflicting info.
The rear gear needs to be steep enough to keep motor RPM in a area where the power out put is not over taxed in normal driving conditions.
But not steep enough as to cancel out the 700R4 low first ratio . ( 3.06)
Gkull: I used 3.92 it was almost perfect .. But do agree a need to stay with 3.55 and above in most cases fills the sweet spot.
Stall converter , you need recommendations from cam manufacture .. Stall should be matched or closely to what the cam maker is saying it requires.
The rear gear needs to be steep enough to keep motor RPM in a area where the power out put is not over taxed in normal driving conditions.
But not steep enough as to cancel out the 700R4 low first ratio . ( 3.06)
Gkull: I used 3.92 it was almost perfect .. But do agree a need to stay with 3.55 and above in most cases fills the sweet spot.
Stall converter , you need recommendations from cam manufacture .. Stall should be matched or closely to what the cam maker is saying it requires.
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
from the way it sounds to me you would have more fun with a 373 around town and still be highway friendly if you wanted to take a long trip. I 355s in my car and its great on the interstate but if I ever have a problem with it I'll do the 3.70 12 bolt option 
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,559
Likes: 7,006
From: New Or-leens Loo-z-anna
Hi guys
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
I finally bit the bullet and sold my old engine ready for a 383 crate motor upgrade.
The 1st question is what diff ratio would you recommend for a th700 box, i need it snappy around town and good for weekend highway cruising. the diff in it now is a 3.08.
2nd question, is what torque converter would you recommend,brand,stall,lockup,and why.
im sure there is a early c3 out there with the same upgrades 383 450hp,th700 box with that perfect diff ratio and torque converter setup.
Thanks again i appreciate any advise.
Those weekend cruises are going to determine the diff. gearing. Engage the "lock-up" module on the open road.
I would keep the engine at 2500 rpm or less going 70mph.....look at it as "saving revolutions" on the engine (2900 rpm vs. 2500 rpm....400 rpm X 60 minutes X 4 hours/round trip = 96,000 "saved" rpm divided by 2500 rpm @ 70 mph.
You just saved approx. 1/2 hour of engine wear on a single 4 hour round trip.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Your 2200 - 2500 is fine it keeps your motor from lugging. The myth is that lower rpm = higher mpg. Well it takes a certain amount of HP to go say 70 on a level freeway. If you try to do it at 1800 rpm you would have to have a wider throttle opening to make the same amount of power as the gearing doing over 2000 rpm.
700r4 also has bad gear spacing. first is too low and second is too high. Going with 3.73 or 3.90 closes this spacing up. Even with 4.11 I could go about 90 in second gear
As to the stall: If you buy highly efficient 9.5 inch like from Precision Industries. Like the Vigilante TC Just get a 3500 with or without lockup. It doesn't really matter i only noticed a couple hundred rpm change in lockup. I drove mine for two years without lockup because my 5 lockup clutch unit went bad. Lockup clutches can't take much TQ before they start slipping. You can run the bigger pump and the pressure will help couple the plates. But that is why they came up with the multi clutch faces to more than triple the clutch faces holding Square inches.
Drifting
Joined: Sep 2003
Posts: 1,325
Likes: 6
From: FRANKLIN GA
See my Signature for my specs. I have a little more hp than you, but close.
For your first question: Definitely go with the 3:73. You will never regret it. It's been so long since I did mine, but I sent it to a company in Pennsylvania that specializes in vette rears. Excellent work, I'll try to find the name of the company if you are interested, just let me know.
For the second question: I went through/burnt up 3 cheap converters before I found one that wouldn't break.The best converter you can put in there and hold up is a Vigilanti. I went with their 9.5 multi disk lock up with 3400 stall. I know this sounds like too much for the street but this converter drives around town better than my cheap 2500 and 2700 stall converters did. Also the lock up function works great with the overdrive. It honestly feels like a stock converter when I'm driving around town but turns into a BEAST when I stomp on it. They are not cheap and they build everyone to the specs of your particular car. I love mine. I feel like it is the perfect setup for my car.
For your first question: Definitely go with the 3:73. You will never regret it. It's been so long since I did mine, but I sent it to a company in Pennsylvania that specializes in vette rears. Excellent work, I'll try to find the name of the company if you are interested, just let me know.
For the second question: I went through/burnt up 3 cheap converters before I found one that wouldn't break.The best converter you can put in there and hold up is a Vigilanti. I went with their 9.5 multi disk lock up with 3400 stall. I know this sounds like too much for the street but this converter drives around town better than my cheap 2500 and 2700 stall converters did. Also the lock up function works great with the overdrive. It honestly feels like a stock converter when I'm driving around town but turns into a BEAST when I stomp on it. They are not cheap and they build everyone to the specs of your particular car. I love mine. I feel like it is the perfect setup for my car.
Last edited by EDDIEJ82; Nov 10, 2015 at 04:19 PM.
Thread Starter
Cruising
Joined: Nov 2015
Posts: 11
Likes: 0
It's going to depend on your cam specs and driving style, but I don't think oiling is a issue. New Vettes operate at lower RPM's on the highway. On average road grades my motor happily turns 1400 RPM @ 45 MPH with no problems, 1900@60, 2200@70, 2500@80.
My car is a daily driver in the summer, so I chose gears, cam, and stall speed to match my driving style and the speeds I would be driving in real life 99% of the time. My torque converter is a 1600 stall lock up converter to be more specific. My cam may be considered mild. I am running the LT4 hot cam. I chose it so I would have good torque at the speeds I actually drive. It gives me great throttle response and drive ability in. We all dream of more HP and it takes some discipline to pick a cam to match our driving styles and not go overboard. For a daily driver too much cam is worse then not enough. My car is a 80 with the weaker rear end setup and so far with my mild cam I have managed to break a u-joint, yolk, and half shaft messing around on the street. Dave
My car is a daily driver in the summer, so I chose gears, cam, and stall speed to match my driving style and the speeds I would be driving in real life 99% of the time. My torque converter is a 1600 stall lock up converter to be more specific. My cam may be considered mild. I am running the LT4 hot cam. I chose it so I would have good torque at the speeds I actually drive. It gives me great throttle response and drive ability in. We all dream of more HP and it takes some discipline to pick a cam to match our driving styles and not go overboard. For a daily driver too much cam is worse then not enough. My car is a 80 with the weaker rear end setup and so far with my mild cam I have managed to break a u-joint, yolk, and half shaft messing around on the street. Dave
What you saying makes sense.
Below are my Cam specs.
Hydraulic Roller Camshafts for OE Roller Applications
180265-10 Duration @ .050 IN 233 OUT 241
2400-5800 rpm Rough idle, Hot Street & Bracket Racing. 10.0:1-up CR 2800 rpm + stall
This seems to be going pear shape?
I either work with this or get the next cam down that's milder with a 1600 to 5400 rpm range.