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373 gear ratio rear end $2500 installed.

12K views 23 replies 17 participants last post by  AAIIIC 
#1 ·
Hi Guys, for the auto guys, i have a drop in rear section to upgrade your 323 or 342.


It wakes up the car substantially on acceleration.

Great sotp mod as well. It makes the car feel alot more aggressive.
 
#12 ·
It's limited by absolute transmission output shaft RPM, so taking the simple ratio between 3.23 and 3.73 into account, I estimate it would knock off almost 25 MPH from the top end. Not that 150 MPH is, um, slow...
 
#5 ·
This might not be the best solution for 1/4 mile drag racing. By my calculations (inputing in a calculator), the 3.73 gearing is going to cause a 4-5 shift at around 115mph. That is in contrast to the 3.23 allowing you to go through the traps in 4th gear provided you trap under 130mph.


Transmission One: 3.23 Gear
Tire Size & Redline
or or " tire
RPM Redline
Gear
Ratio Max MPH
1st Gear :1 38.03 MPH
2nd Gear :1 64.79 MPH
3rd Gear :1 99.93 MPH
4th Gear :1 132.95 MPH
5th Gear :1 179.88 MPH
6th Gear :1 228.2 MPH
Final Drive :1


Transmission Two: 3.73 Gear
Tire Size & Redline
or " tire
RPM Redline
Gear
Ratio Max MPH
1st Gear :1 32.94 MPH
2nd Gear :1 56.1 MPH
3rd Gear :1 86.54 MPH
4th Gear :1 115.13 MPH
5th Gear :1 155.76 MPH
6th Gear :1 197.61 MPH

Tom
 
#6 ·
With a 6600 rpm shift, you would have until 122 mph before it would shift into 5th gear.

With my calc here, first gear would shift at 34mph, then second 58mph, third 89mph then hold 4th to the finish.
 
#8 ·
If I plug in a 6,600 RPM redline, I come up with the same figures. I assumed a 6,200 RPM redline as my auto shifts at around 6,200 RPM. So you would have to raise the TCM's shift point and possibly raise the engine's rev limiter to get to 6,600 RPM.

Although, I think the 4 to 5 shift even at 122mph is less than ideal for the modded cars trapping in the 122-124 range. The 1/4 mile trap speed is really a mathematical average of the time to cover the last 66' of the 1/4 mile run. So if a car is shifting right before the final trap lights, it is going to hurt both the trap speed and the ET because of the late shift.

Tom
 
#13 ·
Is this the rear center section from the manual transmission V?
 
#15 ·
My question was aimed at seeing if the center section was a bolt-in replacement. Obviously it is a lot of labor to dismantle everything and pull the axles so the center section can be removed. But if then all we have to do is swap the center sections and re-assemble, it is a whole lot easier than having to change out the entire rear end assembly. And the cost for major parts would only be the center section. This is the lowest cost change you could ever make to get lower ET's.
 
#16 ·
I am upgrading 2011 v-coupe.....cam, heads, headers, upper/lower pulley, plugs....the whole 9 yards. Auto with 323 rearend....Does anyone think a 373 rear would give me more torque feeling without compromising engine life and highway driving? The car has overdrive. Any ideas if torque converter would be helpful? thanks for the help.
 
#19 ·
If my memory serves correct, most who put 3.73s in their A4 LS1/LT1 Camaros and Firebirds weren't all that happy with their decision based on excess noise at cruising speeds and reduced gas mileage. Most of those A4s came with 3.23s (although some had 2.73s) and although 4th was an overdrive (0.70:1), most A4 people were happy going from 3.23s to the 3.42s, which was the stock gearing in the M6 (which had a more extreme 6th gear overdrive ratio of 0.50:1). Even with 4.10s, the manual cars would still cruise at 70 mph at around 2200 rpm and deliver around 27 mpg!
My gut feeling about installing 3.73s in your modified V is that it is too much gear and would present a real problem getting traction and putting the torque to the ground - especially with that numerically high 1st gear!

Best regards,

Elie
 
#23 ·
I realize this is an old post but was wondering if this would be an easy swap for my 03 cts? Is there any reason this would cause me issues of any kind and is it as easy as topping my diff and replacing it with this 373?

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meant to say "...DROPPING my diff and replacing..."
 
#24 ·
I realize this is an old post but was wondering if this would be an easy swap for my 03 cts? Is there any reason this would cause me issues of any kind and is it as easy as topping my diff and replacing it with this 373?
This diff isn't compatible with your car. Wrong generation of CTS.

meant to say "...DROPPING my diff and replacing..."
So click the "Edit Post" button and fix it rather than "Reply".
 
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