Repiv

Just to follow up, it ended up being the tacho. Dropped in a 3wire from a 280z and my RPMs dropped 300 just at idle. You can imagine how much it was off at the higher RPMs.

Now that I have access to my car I can say for sure I have 205/60R14 tires/rims. I meant range in the sense that I couldn't see my mark where it stopped at.

I just counted the drive shaft turns and it is somewhere closer to the ~3.364-3.545 range than 4. It does have a new clutch so maybe that is it.

I'm at 60 at 4k

How do I tell if my tach is off and how do I adjust it? It idles at about 900 rpm which seems normal.

The 4speed doesn't sound like it'd be that bad with a normal 3.364 rear. I think I want a 5spd though with all the interstate driving I do. 81-83 5spd with a 3.7 or 3.9 rear seems like the sweet spot.

Is there even a 4.38 rear diff that works with the z?

Me and my buddy took his 260z out with the GPS and checked his 4th (he has a 5spd swap) since they are both 1:1 and 60 was 3k, 70 was 3.3k and by 4k we're nearing 90. Same tire size and stock rear end as far as he knows. Basically what that calculator says. I wish I could figure out what was causing this. Even 4.11 gears doesn't explain the HUGE difference.

What's with the conflicting results?

I'm not using the speedo. I'm using a GPS. My speedo is way wrong 'cause according to it at some points I'm going 100+

205/60R14 I believe

I got it out on the interstate again with it again. I got it up to 5k and I was only going 70-75 mph according to the GPS. Highly confusing. I'm picking the car up from getting wetsanded and buffed tomorrow so hopefully I can figure out what is wrong.

As far as I know it is a stock rearend. My speedo is all out of whack though which may lead me to believe it is not stock. I used a GPS to get the speed I was going. [edit] Actually, putting 4.11 into the calculator makes everything close to how it is. 4k around 70mph and 2.3k around 40mph. I don't know why someone would add such a high gearing without changing the transmission though

I just started driving my 240z and am wondering what my rpms should be at around 60-70mph. I have the stock 4 speed and at about 62mph it is at about 4k! http://www.geocities.com/z_design_studio/ according to this I should almost be to 90 at that point. Thanks.