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Discussion Starter · #1 ·
Ok heres the story. O dark 30 on the way to work I go to pass this Honda looking car (it was dark). Iwas doing about 85mph and I went to pass this car as I went faster he went faster we get up to what my speedo says is between 115 & 120mph and he backoff and looked to me like he pulled onto the shoulder, I was to far up the road to see for sure (again it was dark). Anyway hers my question How accurate are speedos up top. Here more info on my run. I was doing between 115 & 120mph the tach was just over 5500rpm. It's a unmodified 75. Tire size is 225-60-14. One more thing It's a 81zx 5spd but I lost 5th gear about 2 weeks ago so I was running in 4th gear. Stock diff in it. Speedo cog was changed out to match stock diff. I find it hard to belive I was doing that speed in 4th. But it was smooth.
 

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Sounds okay to me. If the diff is stock then you should have some top end. With 4th being 1:1 ratio at 5500 rpm unmodded you should have been about topped out for a 4spd car. I know my old Z with a 3.54 rear and 4spd with the same size tires as you would say the same 115-120 at 5500 rpm. Remeber Road & Track used to say the Z's top out at 125 and they didn't use 5th gear ever as it is not intended for hard acceleration. All 4th gears are the same 1:1 ratio in stock trannies.

I never know how fast I am going my speedo's off by at least 8mph.

Most factory speedo's are not very accurate up top though.

Later
Matt
 

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Discussion Starter · #3 ·
When I was running my 4speed (long since blew it up.) with a 3.54, I used to run (according to speedo) 130 at about 6200 RPMS.

So I guess that sounds about right Sizzler...

Brett
 
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