I have recently purchased a stock 86 Z28 with a stock 305 with a 4 barrel carb and Automatic Transmission.
How many gears does this transmission have 4 or 5?
I don't think it is shifting into overdrive? Normal accelertion cruising at 75mph my tach reads about 3250rpm, Is this normal?

 

the 700r4 is a 4 spd

Depending on your rear end gears and tire size, it definately doesnt look like its going into OD.

A typical setup should be cruising around 75mph @ 1500 +/- if i recall


But even if it was in 3rd you should only be pulling around 2000rpm+/-... this sounds more like 2nd gear!


What size tires are on that thing? rear end gears?

 

It should be arond 1800 to 2000 between 75 and 80 if you have the stock 245/60/15

 

i would like to know what rear gear allows 70-75 mph at 2000rpm in 3rd!

i have 245/50-16 with a 3.42 rear. at 70 mph i'm turning about 2600-2700rpm. in od at 70mph, i'm doing about 2000rpm.

also, if you are using the factory tach, they are known to be wrong in the worst possible way.

 

I have all the original 2 owners receipts, I found one that listed 3.73 gear purchase from summit.
The current tires are 215/65R15 until thursday I am switching to 265/50R15.
I am using the factory tach.
I believe it also has a HypeTech Performance chip also previously installed.

 

The stock 2.73s will get you pretty close, especially when people tend to go a little bigger on the rear tires...




With those 215/65r15 tires, 3.73 gears and the OD gear of .7 you should be bouncing around 2500RPM @ 75mph


With the same setup but in 3rd gear it came out to 3600RPM. So it looks like its definately not going into 4th, have you checked the TV cable adjustment?


Just for kicks, buy a cheap tach and wire it up and go for a drive and see what it reads...

 

I am not familiar with the TV cable adjustment?