4spds and 3.90s (archive)

For the day and a half I had a 3.90 in my '76 (diff was dying/noisy and had a spare 3.64 in my basement) after I bought it, I made careful note in my head of the rpms/indicated speed. Also went out and checked the accuracy of the speedo w/GPS out of curiosity after switching to the 3.64. The problem now is that I have a hard time remembering any of it.

Thank you, Dwight Chew, we can use his spreadsheet (also has 4spd ratios/speeds for 3.64 and 3.9) to check the accuracy of what floats through my head. The 'sheet seems to be along the lines of what I remembered - roughly a 5mph drop in speed at any given rpm in 4th. My baseline - and the one I remember - was 4000 rpm. W/the 3.9, was an indicated ~70. Based on traffic flow, seemed like it was almost accurate. w/the 3.64, is still an indicated ~70, but actually works out to be ~75, based on what the GPS says.

Who knows what this means. But I think the 3800 and 75 mph might be off, Nick. :)

I mean, really, how many of us ACTUALLY have an accurate speedo anyway? I don't think I'd know what to do with one. Give it funny looks, maybe. Then calibrate it to be five slow.

Sam
'76 inka, 38/38, 3.64, speedo that was actually close to accurate (I guess) w/the 3.9 but is now 5 slow, tii manifold, 13 inch wheels, 165s.

FYI - My buddy's '69 (actually a REALLY early '68, not that it matters - is titled as a '69) is at an indicated 80 MPH at 4000. First time I got in the car and saw that we both just started laughing our @sses off. :) Riiiiiiiiight. And the speedo sits there and quivers against its spring action...

...or at least mine does...I'm turning lower rpms than my friend's MGB with a 1:1 4th gear and a 3.90...not that my speedo is accurate, but its about 3800rpm @ 75 mph...any 3.90 4-speeders out there to compare?

nick ('80)
2002 ('76)
toyota truck ('78)

Are you sure about the California '76 having a 3.64 rear differential gearing? My '76 back in the the '70s had a 3.90 or at least I thought it did.

BTW, I test drove a converted tii with a 5 speed and 4.11 rear end. It was a blast. Good acceleration with reasonable rpms at highway speeds.

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