Topic: Re: change differential ratio
in Forum: C3 Driveline Components
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tonytheroofer said: The gears of a std 4spd are 1.00 in 4th ,, same with all the automatics 1.00 in 3rd ..
I have the 1980 with a 3.55 rear and at 70 or so i was at 3200 plus or minus a little and that also was not in my opinion a good place to run the engine day in and day out , so I would drive 55 and be the corvette every one passed ha ha ha ha ha ..................
The solution for me was the 700R4 including a new cross member and most importantly a new shifter detent that not only gave correct access to all 4 forward gears but also gave me the correct lens readings so when you look down at it you see R N D 3 2 1. It looks so stock only us corvette nuts will notice and I bet ya people who see it will ask is this an 82 ?
Is it factory original ? NO , but the sad fact is unless it is a 0 mile or 50 mile original its value today and for the foreseeable future is low . ( c-3 low 5k high maybe 15k ) Low mileage heated storage never touched museum piece 25k to 35k and that is not going to apply to a 77 or 80 ..
With the 700R4 My first gear is now 3.06 when multiplied by rear ratio I am getting a 10.8 t/q multiplier that a good street car would want if it seeks decent performance, and I am now 30% less rpm to go 70 add the lock up converter and I drop 100 or so more rpm when on the highway. Making the car a dream to drive and I have to be careful because I am so use to the revving noise I tend to keep my foot in it and realize I am at 90 lol...
So it is all a compromise , even original numbers matching can be maintained by storing the th350 in a crate wrapped in plastic .. I long ago loving the body style decided power and good street manners trumped all else yet also felt the car should look correct to observers and even under my hood it should be less flash and more oem in how it looks.
430hp
430tq
3.55 rear
And to look at it and here it one would be hard pressed to suggest any serious changes have ever been made and I am proud of that .
More and more I am beginning to think this is the best option fo me. My L48 has the original THM400; I have looked at a Keisler RS500 kit as I wish my car had a manual. It can be converted with their kit very well but it gets expensive. I've been looking at a Bowtie Overdrive conversion with the 700R4, the crossmember, TV cable and shifter and the price is more reasonable with nearly similar performance/mileage gains. I have the 3.08 rear; my THM400 has a 2.48 first vs the 700R4 with the 3.06 first. This will give me the equivalent hole shot of a 3.80 rear gear with the .70 overdrive netting a 2.16 highway ratio. Best of both worlds I think. I agree that my '75 will only increase in value about equal to inflation, maybe a bit better. I bought the car for me to enjoy and getting lousy gas mileage is keeping some of the enjoyment out of it.
|UPDATED|11/17/2012 11:37:41 AM (AZT)|/UPDATED|
2012101154624r.jpg)
Build Date: May 7, 1975. 383 w/267 RWHP/310 RWTQ
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Case75 said:
More and more I am beginning to think this is the best option fo me. My L48 has the original THM400; I have looked at a Keisler RS500 kit as I wish my car had a manual. It can be converted with their kit very well but it gets expensive. I've been looking at a Bowtie Overdrive conversion with the 700R4, the crossmember, TV cable and shifter and the price is more reasonable with nearly similar performance/mileage gains. I have the 3.08 rear; my THM400 has a 2.48 first vs the 700R4 with the 3.06 first. This will give me the equivalent hole shot of a 3.80 rear gear with the .70 overdrive netting a 2.16 highway ratio. Best of both worlds I think. I agree that my '75 will only increase in value about equal to inflation, maybe a bit better. I bought the car for me to enjoy and getting lousy gas mileage is keeping some of the enjoyment out of it.
tonytheroofer said: The gears of a std 4spd are 1.00 in 4th ,, same with all the automatics 1.00 in 3rd ..
I have the 1980 with a 3.55 rear and at 70 or so i was at 3200 plus or minus a little and that also was not in my opinion a good place to run the engine day in and day out , so I would drive 55 and be the corvette every one passed ha ha ha ha ha ..................
The solution for me was the 700R4 including a new cross member and most importantly a new shifter detent that not only gave correct access to all 4 forward gears but also gave me the correct lens readings so when you look down at it you see R N D 3 2 1. It looks so stock only us corvette nuts will notice and I bet ya people who see it will ask is this an 82 ?
Is it factory original ? NO , but the sad fact is unless it is a 0 mile or 50 mile original its value today and for the foreseeable future is low . ( c-3 low 5k high maybe 15k ) Low mileage heated storage never touched museum piece 25k to 35k and that is not going to apply to a 77 or 80 ..
With the 700R4 My first gear is now 3.06 when multiplied by rear ratio I am getting a 10.8 t/q multiplier that a good street car would want if it seeks decent performance, and I am now 30% less rpm to go 70 add the lock up converter and I drop 100 or so more rpm when on the highway. Making the car a dream to drive and I have to be careful because I am so use to the revving noise I tend to keep my foot in it and realize I am at 90 lol...
So it is all a compromise , even original numbers matching can be maintained by storing the th350 in a crate wrapped in plastic .. I long ago loving the body style decided power and good street manners trumped all else yet also felt the car should look correct to observers and even under my hood it should be less flash and more oem in how it looks.
430hp
430tq
3.55 rear
And to look at it and here it one would be hard pressed to suggest any serious changes have ever been made and I am proud of that .
More and more I am beginning to think this is the best option fo me. My L48 has the original THM400; I have looked at a Keisler RS500 kit as I wish my car had a manual. It can be converted with their kit very well but it gets expensive. I've been looking at a Bowtie Overdrive conversion with the 700R4, the crossmember, TV cable and shifter and the price is more reasonable with nearly similar performance/mileage gains. I have the 3.08 rear; my THM400 has a 2.48 first vs the 700R4 with the 3.06 first. This will give me the equivalent hole shot of a 3.80 rear gear with the .70 overdrive netting a 2.16 highway ratio. Best of both worlds I think. I agree that my '75 will only increase in value about equal to inflation, maybe a bit better. I bought the car for me to enjoy and getting lousy gas mileage is keeping some of the enjoyment out of it.
I still need to see what my rear ratio is as well, I'm thinking the 700R4 conversion as well
has anyone done this yet...on a budget :) the trannys are pretty cheap on ebay. someone
has one out here for 300.00 but I dont know what im looking for in a tranny.
I guess this might be subject for a diff topic.
1975 Corvette Coupe
My first Vette.....trying to fix stuff
My Project:
https://docs.google.com/folder/d/0B6uOAIjGf3cWejQ5TjNkcVRybGs/edit
ROCKRDR said:
I still need to see what my rear ratio is as well, I'm thinking the 700R4 conversion as well
Case75 said:
More and more I am beginning to think this is the best option fo me. My L48 has the original THM400; I have looked at a Keisler RS500 kit as I wish my car had a manual. It can be converted with their kit very well but it gets expensive. I've been looking at a Bowtie Overdrive conversion with the 700R4, the crossmember, TV cable and shifter and the price is more reasonable with nearly similar performance/mileage gains. I have the 3.08 rear; my THM400 has a 2.48 first vs the 700R4 with the 3.06 first. This will give me the equivalent hole shot of a 3.80 rear gear with the .70 overdrive netting a 2.16 highway ratio. Best of both worlds I think. I agree that my '75 will only increase in value about equal to inflation, maybe a bit better. I bought the car for me to enjoy and getting lousy gas mileage is keeping some of the enjoyment out of it.
tonytheroofer said: The gears of a std 4spd are 1.00 in 4th ,, same with all the automatics 1.00 in 3rd ..
I have the 1980 with a 3.55 rear and at 70 or so i was at 3200 plus or minus a little and that also was not in my opinion a good place to run the engine day in and day out , so I would drive 55 and be the corvette every one passed ha ha ha ha ha ..................
The solution for me was the 700R4 including a new cross member and most importantly a new shifter detent that not only gave correct access to all 4 forward gears but also gave me the correct lens readings so when you look down at it you see R N D 3 2 1. It looks so stock only us corvette nuts will notice and I bet ya people who see it will ask is this an 82 ?
Is it factory original ? NO , but the sad fact is unless it is a 0 mile or 50 mile original its value today and for the foreseeable future is low . ( c-3 low 5k high maybe 15k ) Low mileage heated storage never touched museum piece 25k to 35k and that is not going to apply to a 77 or 80 ..
With the 700R4 My first gear is now 3.06 when multiplied by rear ratio I am getting a 10.8 t/q multiplier that a good street car would want if it seeks decent performance, and I am now 30% less rpm to go 70 add the lock up converter and I drop 100 or so more rpm when on the highway. Making the car a dream to drive and I have to be careful because I am so use to the revving noise I tend to keep my foot in it and realize I am at 90 lol...
So it is all a compromise , even original numbers matching can be maintained by storing the th350 in a crate wrapped in plastic .. I long ago loving the body style decided power and good street manners trumped all else yet also felt the car should look correct to observers and even under my hood it should be less flash and more oem in how it looks.
430hp
430tq
3.55 rear
And to look at it and here it one would be hard pressed to suggest any serious changes have ever been made and I am proud of that .
More and more I am beginning to think this is the best option fo me. My L48 has the original THM400; I have looked at a Keisler RS500 kit as I wish my car had a manual. It can be converted with their kit very well but it gets expensive. I've been looking at a Bowtie Overdrive conversion with the 700R4, the crossmember, TV cable and shifter and the price is more reasonable with nearly similar performance/mileage gains. I have the 3.08 rear; my THM400 has a 2.48 first vs the 700R4 with the 3.06 first. This will give me the equivalent hole shot of a 3.80 rear gear with the .70 overdrive netting a 2.16 highway ratio. Best of both worlds I think. I agree that my '75 will only increase in value about equal to inflation, maybe a bit better. I bought the car for me to enjoy and getting lousy gas mileage is keeping some of the enjoyment out of it.
I still need to see what my rear ratio is as well, I'm thinking the 700R4 conversion as well
has anyone done this yet...on a budget :) the trannys are pretty cheap on ebay. someone
has one out here for 300.00 but I dont know what im looking for in a tranny.
I guess this might be subject for a diff topic.
In 1975, L48 automatics came with the 3.08 rear and a 2.73 rear was optional (why anyone would order this I can't imagine!). If it was an L48 manual, it came with the 3.36 gears and the 3.08 was optional. L82 autos came with 3.36 gears with 3.55 being optional. L82 4 speed wide ratios came only with 3.55 gears while close ratios had 3.55 std and 3.70 optional. :)
Build Date: May 7, 1975. 383 w/267 RWHP/310 RWTQ
201281983954r.jpg)
Thank you for the data on the various combinations of the '75 Corvette differentials. Those just re-enforce my wanting to change my '77 L82 from a 3.70 to a 3.36.
I wonder how the L48 did with the 3.08 with a 4-speed??? I think that would have been a good combination for mpg, but not too good for performance. Anybody out there have/had that combination?
ok checked mine, numbers are AWW 318 E2 so I guess I have the 3.08 in mine
1975 Corvette Coupe
My first Vette.....trying to fix stuff
My Project:
https://docs.google.com/folder/d/0B6uOAIjGf3cWejQ5TjNkcVRybGs/edit
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
I'm loosing it...
somewhere in this thread(or the one on 700s), someone mentioned having the original gear set out of their car from the PO, and I mentioned how to determine the ratio of that gearset by counting the teeth, or looking at the markings. Anyway, I cannot find that post now, so I'll add the pic I was looking for at the time here instead, so ya'll will know what to look for.....
Not ALL gearsets will have the actual ratio stamped on them, as this one does....but they will all have the ring and pinion tooth counts stamped(or engraved).
somewhere in this thread(or the one on 700s), someone mentioned having the original gear set out of their car from the PO, and I mentioned how to determine the ratio of that gearset by counting the teeth, or looking at the markings. Anyway, I cannot find that post now, so I'll add the pic I was looking for at the time here instead, so ya'll will know what to look for.....
Not ALL gearsets will have the actual ratio stamped on them, as this one does....but they will all have the ring and pinion tooth counts stamped(or engraved).
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Man, better use that ratio for racing only!
|UPDATED|11/21/2012 7:15:32 AM (AZT)|/UPDATED|
Barry
|UPDATED|11/21/2012 7:15:32 AM (AZT)|/UPDATED|
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
Or pullin stumps....or rock climbin...or just 'cause it's there....and it was free...
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
3.36 would be perfect. I wish I had done that.
So can I put a 2.64 first gear in my tranny if it doesn't already have one? I assume the LT-1 came with a close ratio tranny.
As far as originality in your rear end.
I don't think the NCRS checks the actual rear end ratio. I assume they just check the numbers stamped on the rear end housing. Kinda like changing the internals of an original engine. What they can't see they can't check.
Go for it.
So can I put a 2.64 first gear in my tranny if it doesn't already have one? I assume the LT-1 came with a close ratio tranny.
As far as originality in your rear end.
I don't think the NCRS checks the actual rear end ratio. I assume they just check the numbers stamped on the rear end housing. Kinda like changing the internals of an original engine. What they can't see they can't check.Go for it.
in Forum: C3 Driveline Components
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