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Anyone change gear ratio on C7Z A8 car? Need input
So I知 in the process of upgrading my rear differential, and cv axles. I知 doing this because this car is mainly used for drag racing, and I want the rearend to be able to withstand repeated 1.3X 60 foot times for a long time.
My last round of mods has me at 690/720 on 93 unleaded, and 753/763 on E70.
Originally i had no interest in changing my rear ratio, but after doing some calculations there may be some gain there.
Currently my car is trapping 142-143 mph on 93 unleaded. I have not run it yet on E70, but it has 65 more RWHP on E70.
Its a 2016 C7Z A8 with 2.41 rear end ratio, it's crossing the 1/4 mile in 5th gear, which is a 1.27 trans ratio. In 5th gear the effective gear ratio is 3.06.(2.41x1.27=3.06)
With it's current 26" tire, it's crossing the finish line at about 5650 rpm.
I plan on doing a 15" conversion at the same time as the diff&axles upgraded, and i expect the car will probably run a 27" tire in the future. At the above trap speed, that brings the rpm down to 5450 at the finish line.
The shift points are currently set for 6500, so it seems I would realize a gain if i could install a steeper gear to have the rpms up around the 6300-6450 rpm area at the finish line.
Let's say it traps at 145 mph on E70, and we run a 27" tire, with the 2.41 ratio that puts me at 5500 rpm at the finish line. If we change the rear axle ratio to 2.56, then it traps at 5860. If we change the rear axle ratio to 2.73, then it traps at 6260rpm. 3.42 rear ratio results at 7800rpm (will force a shift to 6th at 6500).
Also, the new 3.9 ratio, and finishing in 6th gear, would put me north of 7K rpm.
If I did the math correctly, it looks like 2.73 would be the best ratio.
im not an expert here, i would just like to ask one more additional question, you or someone else may know the answer to...
why not entertain the idea of finishing in higher rpm in 6th gear also?
lets say RPM is not an issue, since lets face it, these cars are a square of power on the dyno, so even at the lowest RPM after a WOT shift, the car is still making great power at the entry of the next gear, is it not?
So I would think going through the gears faster may give you more power yet... but im not sure since the power is such a square, it might not be of any advantage.
And if shifts rob you of that much time, then there is always the other direction of finishing high in RPM in 4th gear and avoiding 5th gear.
Mike, i think you have some valid points about the super flat power band, and that MAY be why there isn稚 much to be gained with this type of change.
As far as looking into finishing at the top of 6th gear, I actually did touch on that briefly, by doing the calculations on the 3.9 ratio. The 3.9 would force a 6-7 shift just before the finish, not ideal. The only currently available ratios are 2.41, 2.56, 2.73, 3.42, 3.9, & 4.1.
As as far as finishing at the top of 4th, at these trap speeds we would need a gear ratio much higher (or lower numerically) than a 2.41, which isn稚 available.
One thing to note, all of these calculations are assuming that the online gear/mph calculator is accurate, and the torque converter is 100% locked, which I would assume it is. I have not data logged to verify my ACTUAL rpm at the finish line, as of yet.
i know JHebert likes the spiders. RPM up in indiana likes the wavetrack. RPM claims to me that the wavetrack is a superior setup... i countered and said "for the drag strip, not the road course, correct?" and they went on to say that it is superior on the road course as well and many of the top road race guys use them. I guess we should start a poll thread to see what the truth actually is. RPM said the ELS diff is a gimmick for marketing with chevy.
I dont know enough about it to know either way. What i do know is that the c7z stock, handles very well around high speed curves, and the nannies are helpful. I would hate to go to the wavetrack and find out that I have lost something, and go spinning off the road when the car does something i did not expect.
i know JHebert likes the spiders. RPM up in indiana likes the wavetrack. RPM claims to me that the wavetrack is a superior setup... i countered and said "for the drag strip, not the road course, correct?" and they went on to say that it is superior on the road course as well and many of the top road race guys use them. I guess we should start a poll thread to see what the truth actually is. RPM said the ELS diff is a gimmick for marketing with chevy.
I dont know enough about it to know either way. What i do know is that the c7z stock, handles very well around high speed curves, and the nannies are helpful. I would hate to go to the wavetrack and find out that I have lost something, and go spinning off the road when the car does something i did not expect.
There are some threads about road course behavior between the NON-Z51 cars with LSD (non-electronic) and the Z51 cars with eLSD, and there were some clear advantages to the eLSD on track times and traction & yaw control out of the corners, etc. Road racing isn't my main concern, but if the eLSD is used in conjunction with the stabilitrac to keep your car straight under poor traction conditions, you would think the eLSD would be safer on the street where traction is always going to be marginal at higher power levels.
My main priority is to put something in my car that isn't going to break while consistently launching 1.3 60's, at my power level. IF I can accomplish this with less expense, AND my car is "safer" in poor traction conditions due the the stabilitrack/eLSD/yaw control still functioning properly, then that seems to be the better option for me. The "easier" option is just to write the check for the wavetrac, and I certainly have not ruled that option out. I am the type of person who likes to do research for my own needs, and I don't always take the path that the rest of the herd takes.
Now, back to the main question... Who has changed their gear ratio, and was it worth the change? OR, based on my calculations, who thinks it would be worthwhile to change the ratio?
ACS I am also very interested in this because my auto car is making 803 TQ on 50% E85, peaking just over 3,400 RPM's, and I plan on drag racing it this season. Big consideration for me is reliability at this power level. Have considered the wavetrac but don't want to go that way if it does not handle as safely on the street as the stock setup. Will be watching to see what you decide based on your research.
ACS I am also very interested in this because my auto car is making 803 TQ on 50% E85, peaking just over 3,400 RPM's, and I plan on drag racing it this season. Big consideration for me is reliability at this power level. Have considered the wavetrac but don't want to go that way if it does not handle as safely on the street as the stock setup. Will be watching to see what you decide based on your research.
Whatsup buddy. There is a shop down here in miami area that Byers has the name to, and their phone number, they do the rear end swap out for like 3500 i think he said, with the better gears and 4 of them instead of 2. Once you have that, you will be good to go. The wavetrack is about the same money. Its looking like you might need to come get your car clear filmed and rear end enhanced while vacationing to FL for a week
Would be interesting to see how much 60' you would pick up with a 2.73. Here's a chart I ran using 26" tire. Might make 8th gear a little more responsive on the highway. 2.73 maybe the best choice if you plan to avoid a shift to 6th. With a 27" tire you could go even faster without a shift to 6th.
Whatsup buddy. There is a shop down here in miami area that Byers has the name to, and their phone number, they do the rear end swap out for like 3500 i think he said, with the better gears and 4 of them instead of 2. Once you have that, you will be good to go. The wavetrack is about the same money. Its looking like you might need to come get your car clear filmed and rear end enhanced while vacationing to FL for a week
Yeagh Mike Kentucky sucks January through March. Snow on the ground here when I got up this morning and cold.
Has anyone checked into the new stronger/redesigned spider gears GM installed in all the 2019 Corvette models including the ZR1?
Myself and my friend are both getting our cars upgraded with 4 gears instead of the 2, and both of our cars are 2019's (i dont have mine yet, he has his)
THe shop in miami who does the work, told him they do not have a 2019 yet into their shop to look at the gears... but the understanding is the 2019 still have only 2 gears and not 4... at least that is the rumor I have heard.
Either way, the next problem with the 4 gears is that the "replacement" gears are supposedly not exact fitting for our c7 cars as they come from a c6zr1 perhaps.
To make matters worse, the 2019 will be tricky to upgrade to 4 gears as those gears are not for sale yet either.
I think Jhebert bought an extra c7 rear end just to pull the 2 gears out of, so that his gears all match exactly. Apparently the c6zr1 gears have a bit of play. So you have 4 gears, but there is play between the teeth, which is not ideal.
Hopefully something i just rambled out was of use to someone here.
I run the 2.73, I feel that a car trapping 145-150 will run best with it. Delay the shift to 6th until 7k rpm, I find it best to cross the line at or above shift rpm. If your a8 is capable of 150-plus mph and your shifts are not at 7-7200 rpm (most of us are not that high) then forget the 2.73 and stick to the 2.41.
I run the 2.73, I feel that a car trapping 145-150 will run best with it. Delay the shift to 6th until 7k rpm, I find it best to cross the line at or above shift rpm. If your a8 is capable of 150-plus mph and your shifts are not at 7-7200 rpm (most of us are not that high) then forget the 2.73 and stick to the 2.41.
J any advice on the wavetrac vs the 4 spider gear conversion.
J any advice on the wavetrac vs the 4 spider gear conversion.
i have zero experience with the wavetrac, but I feel the 4 pinion properly done, with c6 or c7 spiders, is way stronger than stock. The next thing to break in the diff would be the stub shafts. Call Jeremy at rpm and get those while your doing the diff.
Jstewart, john is like the inventor of this on these c7 cars, if he has something and says it is good, its good. If you can work out a deal with him, i think youll be happy
03-07-2019, 11:48 PM
Anyone change gear ratio on C7Z A8 car? Need input
