To read that high you'll probably need to go pickup/digital, I'm not aware of any off the shelf cable driven speedo that will do the job.
Stack and SPA Technique both make digital speedos. Stack will be integrated into another cluster or gauge ($$$) but SPA sells a separate magnetic pickup style speedo for $200 or so, unfortunately they do not list the maximum speed on their website. You could call them though.
An automotive portable GPS should have no issues either, I know a Garmin 496 (aviation model) works at that speed with no issues but I haven't tried an automotive GPS unit in an aircraft to see if they have any sort of maximum speed capability.
A budget way with a cable speedo would be to change the gears or easier still to get a reducer gearbox and have it cut the speedo readings to an easy fraction, say 50%.
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1969 Chevelle
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Like you said this is the one the that SPA has they say it will go to 999.9 mph. This one uses a magnet that you can place on whatever you want, wheel , drive shaft, pulley.... http://www.spatechnique.com/product_...eedometers.asp
Just want to see all my options before getting one.
I have also heard about using a km/h and just slowing down the cable to that is is mph.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
I need a 250mph speedo gps or not
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