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C7 3:90 & 4:10 Gears

 
Old 01-16-2019, 06:53 PM
  #201  
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Any chance that the company making these kits will also be making some aftermarket spider gears? There is a large need for those as people keep breaking them and many of us do not want to go with a wavetrac.
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Old 01-16-2019, 10:09 PM
  #202  
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Originally Posted by FYREANT View Post
Any chance that the company making these kits will also be making some aftermarket spider gears? There is a large need for those as people keep breaking them and many of us do not want to go with a wavetrac.
We've been swapping in spider gears for awhile now. I have a diff core or two here too
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Old 01-16-2019, 10:12 PM
  #203  
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Originally Posted by [email protected] View Post
We've been swapping in spider gears for awhile now. I have a diff core or two here too
I may need to call you. I need a carrier bearing, race, and one or two spiders. Maybe you have some of that laying around?
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Old 01-17-2019, 10:20 AM
  #204  
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Originally Posted by [email protected] View Post
We've been swapping in spider gears for awhile now. I have a diff core or two here too
I did break my spider gears too
Llease explain me the difference in those spider gear and carrier.
prices and delivery?
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Old 01-17-2019, 12:18 PM
  #205  
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Originally Posted by robz View Post
Without knowing all the details of your car, for best et, I would shoot for crossing the line around 7000 rpms based some of the info you posted. I'd also shift over 7K as well and as always make sure the entire setup is capable of that rpm.
An accurate dyno graph in several gears and some PUC calculations will get you even closer to the best shift points for et as well. I like to try and be very accurate and account for all parameters less obvious like tire growth, etc. But for most cases a good general educated estimate is fine.
My car is an M7 and basically what I'm asking is, my trap speed is ~4mph under what the top of the gear would be if I went to a 4.10 (141mph with a top speed of 145mph at 7,000rpm). Assuming I went with 4.10 gears, would my trap speed increase and by how much approximately? I wouldn't want to switch to 4.10 gears and end up hitting redline right before the finish line. I've never really played with gear ratio's so I have just been trying to learn about them after going through this post to see if its a modification I want to consider.
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Old 01-17-2019, 01:52 PM
  #206  
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Originally Posted by blue_bomber697 View Post
My car is an M7 and basically what I'm asking is, my trap speed is ~4mph under what the top of the gear would be if I went to a 4.10 (141mph with a top speed of 145mph at 7,000rpm). Assuming I went with 4.10 gears, would my trap speed increase and by how much approximately? I wouldn't want to switch to 4.10 gears and end up hitting redline right before the finish line. I've never really played with gear ratio's so I have just been trying to learn about them after going through this post to see if its a modification I want to consider.
I struggle with this as well.. I think maybe something in between 3:42 and 4:10 may be the way to go.
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Old 01-18-2019, 11:26 PM
  #207  
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Originally Posted by FYREANT View Post


I struggle with this as well.. I think maybe something in between 3:42 and 4:10 may be the way to go.
I can only speak to my experience going from 3.42 gear set in my C6 with manual shift, that 4.10s were freakin' awesome. So much fun, night and day difference, big big smile in every gear, and every shift.


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Old 02-09-2019, 06:21 AM
  #208  
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Default Finally, after three years !

Ladies and Gentlemen,

After three years of development I am pleased to announce that C7 3.90 and 4.10 differential gear sets are in country and ready for sale and installation. Please contact Jeremy at RPM Transmission - (800) 406-1109, x 201.

Suggested ratios:

- Stingray = 4.10

- Grand Sport = 3.90

- Z06 and ZR1 = 3.90

Enjoy ! ! !

Last edited by Pumba; 02-13-2019 at 08:48 AM.
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Old 02-09-2019, 09:07 AM
  #209  
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Old 02-09-2019, 11:03 PM
  #210  
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Originally Posted by Pumba View Post
Ladies and Gentlemen,

After three years of development I am pleased to announce that C7 3.90 and 4.10 differential gear sets are in country and ready for sale and installation. Please contact Jeremy at RPM Transmission - (800) 406-1109, x 201.

Suggested ratios:

- Stingray = 4.10

- Grand Sport = 3.90

- Z06 and ZR1 = 3.90

Enjoy ! ! !
Holy smoke, awesome!
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Old 02-10-2019, 12:21 AM
  #211  
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Can’t wait to read some reviews!
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Old 02-11-2019, 01:43 AM
  #212  
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Anything for the A8 guys? 3.90 is way too steep for the Auto trans cars. 3.27-3.42 would be nice
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Old 02-11-2019, 09:06 AM
  #213  
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Originally Posted by Poppacapp View Post
Anything for the A8 guys? 3.90 is way too steep for the Auto trans cars. 3.27-3.42 would be nice
pretty sure you can use an M7 rear gear or diff in your car.....
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Old 02-11-2019, 04:42 PM
  #214  
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Originally Posted by Poppacapp View Post
Anything for the A8 guys? 3.90 is way too steep for the Auto trans cars. 3.27-3.42 would be nice
get with C7&7. He has a spare Z51 3.42 diff laying around out of his M7.
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Old 02-11-2019, 05:50 PM
  #215  
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Originally Posted by A320Flyer View Post

Canít wait to read some reviews!

.


I definitely want to hear some end user reviews. Hear from owners who have them installed.

I am always concerned with the 1st batch of anything, especially given the high cost of the labor to install them along with the high cost of the gears and parts associated with the installation.

Even with as much desire to get these installed, all the problems with 1st year C7, and all the problems with 1st year C6 give me concern about installing these before several people post their experience with these gear sets.

I am concerned of the possibility of the 1st batch, or two, making noise, or being too soft and shedding metal, which no one is going to cover under warranty unless they are installed by RPM which is easily a thousand miles away which makes it too far to take back when problems come up.

Looking forward to great reviews. Hope they are flawless.


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Old 02-11-2019, 07:16 PM
  #216  
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Spoke with a friend of mine who is also a GM performance tech and his concern was that with blower cars you donít want a lot of gear, it winds out to quick and wonít stay in the power band long. Our A8 has a 2.41 and winds up pretty quick.
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Old 02-12-2019, 02:47 AM
  #217  
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Originally Posted by Higgs Boson View Post
pretty sure you can use an M7 rear gear or diff in your car.....
Yeah I know that is an option. But with a new GM diff it's an approx. $3300.00 swap. Figured a simple gear swap would be a better option if the ratios are available.

Originally Posted by FYREANT View Post
get with C7&7. He has a spare Z51 3.42 diff laying around out of his M7.
Thanks for the lead Fyreant. I may end up going this route if I decide to keep the Grand Sport. Z06s are looking more enticing with their advantages too. May end up trading also.
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Old 02-12-2019, 08:35 AM
  #218  
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Default 3.42 dif

I did install a complete 3.42 z06 M7 diff and install it on my 2015 z06 A8. Very costly! This was easy installation because bolt pattern and input shaft are the same. No problem. The 42% higher ratio made a big change of torque in all gears and I can spin the tire much easily in 1 and 2 gear. The total drive ration in first gear is 4.56x3.42=15.6 this is very high compare to a manual M7 2.97x3.42=10.15 or 2.97x4.10=11.8 If you do it you must have very good drag radials and traction because in first gear I canít go to 100% throttle. The side effect is the first gear is much Shorter and you will have to shift in 2 sooner. Depending on your ľ miles speed the transmission will shift in 5th gear instead of staying in 4th.


Originally Posted by Poppacapp View Post
Yeah I know that is an option. But with a new GM diff it's an approx. $3300.00 swap. Figured a simple gear swap would be a better option if the ratios are available.



Thanks for the lead Fyreant. I may end up going this route if I decide to keep the Grand Sport. Z06s are looking more enticing with their advantages too. May end up trading also.
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Old 02-12-2019, 11:39 AM
  #219  
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Originally Posted by c7z06a8orange View Post
I did install a complete 3.42 z06 M7 diff and install it on my 2015 z06 A8. Very costly! This was easy installation because bolt pattern and input shaft are the same. No problem. The 42% higher ratio made a big change of torque in all gears and I can spin the tire much easily in 1 and 2 gear. The total drive ration in first gear is 4.56x3.42=15.6 this is very high compare to a manual M7 2.97x3.42=10.15 or 2.97x4.10=11.8 If you do it you must have very good drag radials and traction because in first gear I canít go to 100% throttle. The side effect is the first gear is much Shorter and you will have to shift in 2 sooner. Depending on your ľ miles speed the transmission will shift in 5th gear instead of staying in 4th.
Thanks for the observation. I have been wanting to get some info from someone who has actually done the swap. My current setup is already trapping near 128mph and hitting traps in 5th gear. From the gear calcs I am seeing a 3.42 gear will put me in 6th gear at the end, which is the 1:1 gear. May not be a bad thing with that being the power gear.

Still debating rear diff and keep GS or get a Z06 tho. Its too easy to run 9s with boltons in a Z06.
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Old 02-12-2019, 07:26 PM
  #220  
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What's the approximate cost of this? I'm not racing just hoping to add some thrust. And I seldom use 6 or 7th gear.
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