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Discussion Starter · #1 ·
After driving my '71 around for the past three years with it's TH700R4 and 3.08 gears I decided to treat myself to a set of 3.70's. I ordered them from Summit Racing and they should get here by Friday or Saturday. And I also ordered the speedometer gears needed to correct my speedometer.

With the 3.70's I'll be able to make full use of my lower three gears for 1/4 mile passes and still run only 2040 rpm at 60 mph in 4th. Can't wait to try them out.................
 

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Discussion Starter · #3 ·
you will love the 3.70 gears with the 700r4 ..its perfect match.. I got a little different gift for Christmas... A Bushmaster M4 ... I was a good boy this year

From my calculations it appears a set of 3.70's is a perfect match to a TH700R4 as the lower 3.70's will allow the first three gears to be fully used for 1/4 mile passes and then still allow cruising at 120 in 4th at only 4100 rpm. The best of both worlds.
 

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one of these days, I m gonna have to see just what mine will top out at.. I ve had it to 150+ and it wasn t near done.. its peak horsepower is at 6200rpm,with 6800 redline.. in 4th gear, with 27 inch tall tires, top end should be pretty high..problem is ,my Pro-Comp speedo stops at 160 !
 

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one of these days, I m gonna have to see just what mine will top out at.. I ve had it to 150+ and it wasn t near done.. its peak horsepower is at 6200rpm,with 6800 redline.. in 4th gear, with 27 inch tall tires, top end should be pretty high..problem is ,my Pro-Comp speedo stops at 160 !
Most GPS units will show your speed
 

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Discussion Starter · #7 · (Edited)
what type of ring & pinions do corvettes have, 2 series or 3
or are Corvette in a class of there own? I have 3.73's right now and i wanna try 4.10/4.11 (as long as I stay below 3,000 RPM's on the highway)
Nice Gift !

After talking to the Summit sales representative I found the 1963 thru 1979 Corvette gears are only used by the Corvettes as they aren't used in any of the other G.M. lines. So they are a bit harder to find and also a bit more expensive.

As far as the "series" goes a "2" series means the carrier will only accept ratios in the "2's" like 2.72's or 2.87's. The "3" series means the carrier will accept any ratios in the "3's" like 3.08's, 3.31's, 3.55's, 3.73's, and 3.90's. Then the "4" series carriers will accept ratios like 4.11's, 4.56's, and 4.88's. There are spacers available so you can put the thinner ring gears used for the 4.11's, 4.56's, and 4.88's onto the "3" series carriers but it requires longer bolts and isn't recommended for drag racing usage. Some gear manufacturers offer thicker 4.11, 4.56, and 4.88 ratio ring gears that will bolt up to the "3" series carriers without having to use a spacer and longer bolts.

As I'm running a TH700R4 the 3.70's will be ideal as I can buzz thru the end of a 1/4 mile in 3rd gear at 5100 rpm but buzz only 2040 rpm at 60 mph in 4th; thanks to it's 30% overdrive. And with it's 3.06 1st gear my launch will be ultra fantastic. And with it's 30% overdrive I'll be able to cruise at 120 mph at only 4000 rpm.
As I have 3.08's right now the 3.70's will bolt to my carrier with no problems.
 

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After talking to the Summit sales representative I found the 1963 thru 1979 Corvette gears are only used by the Corvettes as they aren't used in any of the other G.M. lines. So they are a bit harder to find and also a bit more expensive.

As far as the "series" goes a "2" series means the carrier will only accept ratios in the "2's" like 2.72's or 2.87's. The "3" series means the carrier will accept any ratios in the "3's" like 3.08's, 3.31's, 3.55's, 3.73's, and 3.90's. Then the "4" series carriers will accept ratios like 4.11's, 4.56's, and 4.88's. There are spacers available so you can put the thinner ring gears used for the 4.11's, 4.56's, and 4.88's onto the "3" series carriers but it requires longer bolts and isn't recommended for drag racing usage. Some gear manufacturers offer thicker 4.11, 4.56, and 4.88 ratio ring gears that will bolt up to the "3" series carriers without having to use a spacer and longer bolts.
Thanks for the info
found a set on jegs.com richmond gear was $300-400
but dont know if they have a thicker ring gear for 3 series
 

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I started with a 3.07 paired with a 4 speed which was not too good bottom end. Then I switched out to a 3.70 and is a lot better bottom end, but sucked on the highway. I swapped out the 4 speed to a T56 6 speed. Now it is so much better all around! :woowoo: You will really enjoy the 3.70 with the OD trans. :thumbsup3:
 

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Discussion Starter · #12 · (Edited)
I started with a 3.07 paired with a 4 speed which was not too good bottom end. Then I switched out to a 3.70 and is a lot better bottom end, but sucked on the highway. I swapped out the 4 speed to a T56 6 speed. Now it is so much better all around! :woowoo: You will really enjoy the 3.70 with the OD trans. :thumbsup3:

I started in at 5:00 A.M. this morning and had it sitting on the floor at 7:30 A.M. Then I started in on the gear installation and got it wrapped up around 4:30 P.M.

Tomorrow morning I'll dive into the re-installation around 5:00 A.M. and expect to have it sitting back on the ground before noon.

TCI e-mailed me yesterday and told me my speedometer gears are back ordered but are expected to ship on January 4th. The 44-tooth driven gear is readily available but the oddball 15-tooth drive gear is somewhat hard to come by because very few people ever need them. So for the next couple of weeks my speedometer will be reading about 17% fast. No big deal and once they arrive it'll only take me about an hour to change them.

With the 3.70's my big-block '71 will REALLY wake up and will be able to pull it's hardest from about 65 mph to 100 mph. So the lower 3.70's will be a perfect match for my TH700R4 and free-breathing Edelbrock Air Gap intake manifold.

And then there's the possibility my fuel mileage will improve as I usually drive in 4th gear at the same rpm my marine cam is still loping at; 1300 rpm. By changing over to the 3.70's my engine will be spinning 2040 rpm at 60 mph or about 300 rpm faster than the 1707 rpm that it spins now; putting it a bit higher in it's power band and where my engine runs smoother.
 

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Discussion Starter · #13 · (Edited)
Thanks for the info
found a set on jegs.com richmond gear was $300-400
but dont know if they have a thicker ring gear for 3 series

What ratio are you wanting to install? Some manufacturers make the lower gears like 4.11's and 4.56's with real thick ring gears so they can be installed on 3-series carriers and ring gear spacers are also available to accomplish the same thing but it's not advised to use a spacer with a ring gear for drag racing.

I bought my 3.70 Motive gears from Summit Racing for $219 but the Ratech installation kit was $129. I didn't need everything that came in the kit as it was a complete "total overhaul" kit with all new bearings, shims, and seals.
 

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Discussion Starter · #14 ·
Regarding the "3" and "4" series carriers here's why the offset of the carrier flange has to be different when going to the 4.11's and 4.56's.

As the diameter of the pinion gear gets smaller the ring gear has to get thicker. Then there is a point in which the carrier has to be changed OR the ring gear has to be made REAL thick.

Here's a picture of my new 3.70 ring gear next to my old 3.08 ring gear. As the 10-tooth pinion gear of my 3.70 ratio is smaller in diameter than the 11-tooth pinion for my 3.08 ratio the new 3.70 ring gear is about 3/8" thicker.


I have about 100 miles on my new 3.70 gears so far and the difference in performance is fantastic. I can pull the 6% 10-mile long grade coming home in 4th with the greatest of ease and it accelerates a lot quicker in each gear. It was well worth the $350 expense.
 

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I debate on 3.50 verse 3.70, it winds up super fast in first gear with the 3.08's and the 3.06 1st in the 700r4. traction is already at a minimum, 3.50 will make it even quicker to wind up and will make traction in first and second iffy at best. 3.70's would eliminate most traction and make shifting out of first gear happen super quick. For what its worth, I've been told for a street strip that you want to keep the combined ratio of 1st gear in the transmission and the rear differential in the 10.00 to 10.99 range. 3.50 puts it at 10.71 & 3.70 puts it at 11.322. The 3.70s would definately suit my needs for 2nd gear through overdrive and I agree completely about overdrive and 3.08s.
 

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I debate on 3.50 verse 3.70, it winds up super fast in first gear with the 3.08's and the 3.06 1st in the 700r4. traction is already at a minimum, 3.50 will make it even quicker to wind up and will make traction in first and second iffy at best. 3.70's would eliminate most traction and make shifting out of first gear happen super quick. QUOTE]

I agree.... in the traction part... my motor makes 310 hp at best, but I can easily spin the tires at take off and and first gear is only seconds long
I wanted the 4.10's so that my car doesn't make that drastic change from 1 to 2 gear
 

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I debate on 3.50 verse 3.70, it winds up super fast in first gear with the 3.08's and the 3.06 1st in the 700r4. traction is already at a minimum, 3.50 will make it even quicker to wind up and will make traction in first and second iffy at best. 3.70's would eliminate most traction and make shifting out of first gear happen super quick. QUOTE]

I agree.... in the traction part... my motor makes 310 hp at best, but I can easily spin the tires at take off and and first gear is only seconds long
I wanted the 4.10's so that my car doesn't make that drastic change from 1 to 2 gear
First gear with 4.11's in a 700r4 would be like a tow truck, what size stall converter are you running? What kind of lock up device do you utilize? When i wind up to 5800 or more the drop dosent seem that bad, but im running a 2400 t0 2600 rpm stall and i stole tobrokes idea of locking up the coveter in 4th gear only. I cant remember for sure but i beleave that its patc that builds a first gear for the 700r4 that is a slightly reduce ratio somethin g like 2.86 to 1 which would be ideal in my thoughts, but for a complete transmission the want 4800$.
 

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the engine power range is key with the 3.06 1st gear... my redline is 6800 rpm, yes, it goes thru 1st in a blink of an eye, but when I hit 2nd, I m going faster and its not a noticeable drop in power because the engine is higher in the range than a 310 HP shifting at 5000.. besides, the tires are still spinning in 2nd ... I ve seen the tests on that PATC w/smaller ratio 1st.. it made the car faster by about 3/10 sec ...I would love to have one of their 6 speed Autos, but its about $6000 plus an ECM to run it.. .but the gear spacing is perfect
 

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the engine power range is key with t 3.06 1st gear... my redline is 6800 rpm, yes, it goes thru 1st in a blink of an eye, but when I hit 2nd, I m going faster and its not a noticeable drop in power because the engine is higher in the range than a 310 HP shifting at 5000.. besides, the tires are still spinning in 2nd ... I ve seen the tests on that PATC w/smaller ratio 1st.. it made the car faster by about 3/10 sec ...I would love to have one of their 6 speed Autos, but its about $6000 plus an ECM to run it.. .but the gear spacing is perfect
.30 is an awesome gain, but alittle steep at $4800. Tci also builds an electronic 6 speed and i wonder if its not a 6l80, i love the one in my truck, but the 3.46 first combined with 3.73 reaf gear and its next to impossible not to hit the rev limiter when shifting manual.
 

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Discussion Starter · #20 ·
TH700R4's And 3.70 Gears

.30 is an awesome gain, but alittle steep at $4800. Tci also builds an electronic 6 speed and i wonder if its not a 6l80, i love the one in my truck, but the 3.46 first combined with 3.73 reaf gear and its next to impossible not to hit the rev limiter when shifting manual.

When I selected the 3.70's I didn't have drag racing in mind. What I wanted was better pulling power in 3rd and 4th gears as that duplicates freeway passing conditions. With the 3.70's I can cruise at 65 mph then when it downshifts into 3rd I'm right at the beginning of my maximum torque band.

Since I installed them I have noticed a huge difference in it's 4th gear pulling power when I climb the 10 mile long 6% grade going to my house. And when cruising at 60-65 mph it feels the same as it did with the higher 3.08's; just 300 rpm higher.
 
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