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Discussion Starter #1
Im contemplating putting a built rear end in the car in a couple months. I have the stock 3.42 in it right now. Is there much difference in acceleration? Are there any other differences? Im contemplating the kit from A&A or the stage II from dynotech engineering. Suggestions?

thanks,
Jim
 

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The main question is: Do you have enough traction now?

If the answer is NO, then the gears will just make your tires spin more.

If the answer is YES, then the gears will get you about .1 second less and .8 mph more in the 1/4 mile. And your fuel economy will drop a little, not that that matters to us Z06 owners ;) . IF you could do 0-60 in 4.0 seconds with the 3.42, you could do 0-60 in about 3.8 seconds with the 3.73. But this all depends on traction.

At least that's what my computer programs says. And if you're talking about a stock Z06.

Rod
 

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I had 3:73s in my H/C 02-ZO6...I thought they were a great compromise for daily driver and track use...with the ZO6 tranny ratio 4:10s were a bit steep for a daily driver. However 3:90s are very popular and may be the best choice for both street and strip. Just depends on what your primary goal is. regardless 3:73s made stop and go a little easier, 5th gear became usefull in traffic and at the strip 1st gear still had some legs.
 

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Oops, just saw your signiture. Anyways, the gear change will still be worth about .1 sec improvement in the 1/4 mile.

Rod
 

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Discussion Starter #5
I ran a 650 rwhp whipple charged cobra on a 35 shot sat. From a 40 roll, I was able to pull pretty well (2nd gear, 40 mph, around 4200rpms) but we did a few pulls from 60mph and we were dead even because I was out of my powerband (3rd gear, 60mph, 3700rpms).

I'm running Nitto 555RII's in back and have no traction issues from a 40 roll.

Im kind of wondering what rpms 40 is in 2nd and 60 is in third with the 3.73 rear end.

thanks,
Jim
 

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The rpms at different speeds with stock size tires should be about:

MPH....................RPM
..............3.42..............3.73
2nd gear
30...........2750.............3000
40...........3700.............4000
50...........4550.............5000
60...........5500.............6000
70...........6400.............7000

3rd gear
50...........3100.............3450
60...........3750.............4100
70...........4450.............4800
80...........5000.............5500
90...........5700.............6100
100.........6300.............6850

With tires that are a different size the rpms would be different.

All you need to do to find out what rpms your car will run with a different gear ratio is find out what rpms it runs now at a given speed and multiply that by the new gear ratio and divide that answer by the old gear ratio.

So, if at 50 mph you turn 4500 with 3.42's then with 3.73's you'd turn
4500 x 3.73 / 3.42 = 4900.

with 3.90's you'd turn
4500 x 3.90 / 3.42 = 5130

and with 4.10's you'd turn
4500 x 4.10 / 3.42 = 5395

Or 3.73 / 3.42 = 1.09. So all of your rpms will be 1.09 times higher than they were at a given speed. That's a 9% change for 3.73's over 3.42's.

Rod
 

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Discussion Starter #7
Rod,

This is exactly the information I was looking for!!!! It looks like a 3.73 will put me right at the beginning of my powerband and exactly what I want. You guys have helped me make my decision.

Thanks all!!
Jim
 

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HotRod said:
The rpms at different speeds with stock size tires should be about:

MPH....................RPM
..............3.42..............3.73
2nd gear
30...........2750.............3000
40...........3700.............4000
50...........4550.............5000
60...........5500.............6000
70...........6400.............7000
Rod
Am I reading this chart correctly?
Are you saying that at 70 mph in 2nd gear w/3.42 gears you're churning @ 6400 rpms? Something sounds off about that.
 

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I went with 4:10's yea u switch quicker but man there fun.. :sneaky:
 

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Last time I was out, I tried running 2nd gear slowly up to 40 mph to answer this question and my tach read 4300 RPM's. Still an excellent place in the powerband.
 

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Discussion Starter #11
Kickin said:
Last time I was out, I tried running 2nd gear slowly up to 40 mph to answer this question and my tach read 4300 RPM's. Still an excellent place in the powerband.
Agreed, 4300 is right where the procharger starts comin on......HARD!!!! :sneaky:
 

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I put the 3.73's in the Z06 and I'm very impressed with its civility and its ability to pull harder.

Good mod.
 

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To VettTheRipper,

You are reading the chart correctly. I took my Z06 out today and ran it up to 35 mph in 2nd gear, and held that speed, while I check out the tachometer. When I used the speedometer I got 3300 rpm's and when I used the HUD I got 3200 rpms. Obviously at least one of them is wrong (or possibly both) but the result is that if 35 mph = 3250 rpm's (split the differnce) then 70 mph is 6500 rpms. Close enough to the 6400 rpm's that the chart says. :)

Rod
 

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VettTheRipper said:
Am I reading this chart correctly?
Are you saying that at 70 mph in 2nd gear w/3.42 gears you're churning @ 6400 rpms? Something sounds off about that.
That's about right.

Stock Z06 max speed in 2nd is recorded at 69 mph.
 
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