[Unknown User]

> i have a 78 280Z 2+2 4-speed and i was
> reading something on an earlyier post that
> said 4000 rpms= 65 in top gear
> this is not the case with my Z i run 90 at
> 4000 and about 2500 at 65

Hey! I have a '72 with the 4spd, and I'm pretty sure the rear-end is stock. I haven't paid attention to the RPM when going on the freeway, but it's by no means revving when going 65. I'll check it out next time I drive it and post the RPM. I think it's pretty low though. I suspect that the 4000 RPM @ 65 mph thing could have been a little exaggeration.

type to you later,
-rr
.

 

[Unknown User]

> Matt,
> According to the manuals your 2+2 has the
> same 4-spd and rear differential as the
> coupe.
> That means that originally you had a 3.545
> differential which would give you about 80
> mph at 4,000. Even installing the earlier
> 3.364 ratio would only get you to about 85
> mph at 4,000.
> something isn't right here.
> Phantom

If you are running larger (taller) tires than what came stock, it could account for higher speeds at lower rpm. I did this once on my Honda because I wanted to cut the rpm/speed ratio to improve milage and reduce engine wear, but for the next set of tires I went back to stock because the power suffered with the little engine and the milage did not improve. The rpm/speed ratio is linearly related to the tire height, so you can calculate where you are relative to stock tires. Cops love this one when they pull you over.