Zfarm wrote:
>1) have you checked that the speedo is accurate ? That is, about as
>accurate as it can be expected to be ( 10% variation or less ).
>2) Have you got the standard size wheel/tyre combination fitted, or
>at least, something close, like a 195/70X14 on the rear.
>
>If the answer is Yes to both the above, then suspect that the diff is >from either a UK 260Z ( 3.7) or even from a US 4-speed model (
>3.36).
Hi Zfarm (everyone):
Hummm... let's think about this one. ;-)
The speedometer is driven off 4th gear in all the stock transmissions and they are all 1:1 in forth gear.
So if you change rear gears - to no matter what ratios... the speedo will still give the same "indicated speed" at any given RPM. Only your "actual speed" will change. Likewise changing tire diameter will effect your actual speed, not your indicated speed.
On the other hand - if you swap transmissions, without changing the speedometer gear to match the rear end ratio that you have - you will get a different set of "indicated speeds" holding your RPM the same.
For example, if someone pulled the original 240-Z five speed out and installed a 260-Z five speed, without swapping the speedo gears (to account for the change from 3.9 to 3.7)...you would get a different set of indicated speeds at the same RPM levels.
So first thing to do is figure out which rear gear you have, then the second thing to do is look to see if the transmission has the correct speedo gear for that rear end.
FYI:
3.364 : Yellow 16 teeth - #32703-78100 Assy-Pinion Speedometer(5spd.)
3.545 : Black - 17 teeth - #32703-78101 Assembly Pinion Speedometer(5spd)
3.7 : Blue - 18 teeth #32703-78102 ( 5spd.)
3.9 : White - 19 teeth #32703-78103 ( 5spd.)
4.11 Red 20 teeth (don't know the part number off hand)
Stuart:
The Euro Spec. 240-Z's were "pretty low" geared, came with the 3.9 rear gear and an overdrive 5th gear to offset that at cruise as I recall. Off the top of my head, 4000 RPM at 74mph doesn't seem too far out of line to me. The L24 is very happy turning that speed and the 3.9 certainly gets if off the line in a hurry.
If you are driving at an indicated speed of 74mph - is everyone passing you, or are you passing everyone else? What do you guess your "actual" speed is? If tire diameter is other than stock, you can adjust your indicated speed to more closely match your actual speed by changing the speedometer gears in the transmission. Actual speed can be calculated using your odometer over a measured mile. Well we use measured miles here in the US.
As I recall - adding or subtracting a tooth from the speedo gear tooth count - changes your speedo reading by plus or minus 6 percent at any certain RPM point.
kind regards,
Carl
Carl Beck
Clearwater,FL USA