Just so you know, G35 Tachs aren't super precise, if you can get the data from the ECM you're much better off. I'll check mine tomorow for you. Also, basic math will help:
If you're running 3000 at a given speed with a 3.3 then:
3000/3.3*3.5=3182

 

I am doing this for multiple reasons. I think that some people don't realize what differential they have. I want to know the average rpm at 80. Trying to see if all 6MT got 3.5 and all X got 3.5. Most 5AT are 3.3 but it seems some are 3.5.

 

Gotcha. You should also ask tire size as well.
I know mine is the 3.3 open diff, but I may be getting a 3.5 vlsd from a z.

 

I realize tire size can change things, but it seems that most people are using something very close to stock size.

 

Will do. I don't do much highway driving so it might be this weekend before I get a more accurate number.

 

When I drive home this from school this afternoon I'll observe the EXACT RPM @ 80mph and report back here.

 

great, thanks.

 

I got 3050 rpm @80mph, not exactly sure which FD I have other then its has a VLSD.

stock tires 235/45R18

 

Exactly 2,900RPM @ 80MPH.

Stock tire size of 215/55-17, VLSD, with the 6MT "Sport Package".

 

Hopefully I'm grouping these into the right FD since some people don't know.

I'm assuming 6MT came with 3.5 and 5AT are 3.3. I think 2005+ X are 3.5 as well.

 

Would it be plausible that the FD changed between years? I only say this because my 2004 is at 2900, while CandlestickPark's 2005 is at 3200, even though you grouped ours together.

 

I am also wondering how you know RPM differences (of even a couple hundred) can determine the FD. What would be the benefits of a lower FD, higher?

 

^Could tire size explain the difference. I am running 245/35 255/35. Mine does seem a little high, almost the same as Mike's 3.7 gears at 3250. I'm sure mine is at 3200 though (at least based on visually seeing the tach sit right on the 3200 line).

 

More RPMs needed to hit the 80MPH mark, but I don't think ~400RPM would = ~2MPH. If you get what I'm saying?

 

Candlestick is 5AT, you are 6MT. That will make a difference, as well as tire size. If you have larger than stock tires, you will reduce your rpm, and vice versa.


6MT in 6th gear with 3.3 should be around 2850
5AT in 5th gear with 3.3 should be around 2900

6MT in 6th gear with 3.5 should be around 3050 ish
5AT in 5th gear with 3.5 should be around 3150 ish

6th gear in manual is taller than the 5th gear of the auto.