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Discussion Starter #1 (Edited)
I decided to try one of the OBD2 HUD units available online as a solution to the annoying 7% speedometer error in my 05 Elise. I know that a corrected cluster panel exists ($150), but I didn't want to mess with disassembling a perfectly functioning cluster if another option existed, and this solution adds a decent HUD as a bonus!

I got this unit on Ebay for $60. It plugs into the OBD2 port under the dash. I have a tinted windshield, so I did not have to install a square of tint to ensure a clear reflection. The unit allows you to adjust the speed correction factor and mine now reads exactly 7% less than the cluster speedo. I have not checked it against a GPS but it is adjustable regardless, so I can change it if my error is more or less than the usual 7%. The sampling rate appears to keep pace with the cluster speedo, so no issues there for me, YMMV.

My install is velcroed for now as I’m not certain where I want the display to be. The unit comes wired with an inline on/off switch, but we don’t need this for the Elise because the OBD port shuts off with the car. It may appear blurry in the pics, but that is just the iPad struggling to focus. It is crystal clear in real life.

Points to consider:
1) You will get a double image reflection if you do not use a square of tint for reflection (this would annoy me, but some don’t mind). A piece of tint was included in the box.
2) It sits on the dash, exposed to heat and sunlight, and is surely made in China, so it may not last for long.
3) It causes a weird quirk with the fuel gauge where sometimes when you start the car it reads empty and the fuel light comes on, then it gradually rises to its true fuel level over the next 5 minutes as you begin driving. So far this happens occasionally, and usually on warm restarts, but not always. I use mileage as much as the gauge to judge the fuel level, so this is a minor annoyance to me.
4) Direct sunlight (evening setting sun) will wash it out, but I think this is true of most HUDs.
5) I noticed the price has gone up to $65.
6) The ad says the tach goes to 8500 rpm but it goes to 7500. Not a big deal, I just want the correct speed displayed. The ad makes other claims I have not verified (auto dimming, headlights on warning, etc).
7) The extreme rake of the windshield may obscure the display a little depending on where you place it, but several good options exist.

Apologies for the excessively long post. I tried to anticipate most questions. :eek:

Here is the one I purchased:

Add W1 Car Hud OBD MPH Head Up Display OBD2 Interface Plug Play Speed Gauge | eBay
 

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Wow, thanks for that review and pics. Very interesting.

What did you think of the actual display. were you happy with the layout, is it too bright or distracting?

This looks like it may be a great project for someone to take on who is willing to modify their dash. Possibly make a recessed position within the dash to both:
1) compensate for the rake of the windsheild
2) hide the wiring
 

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Discussion Starter #3
Wow, thanks for that review and pics. Very interesting.

What did you think of the actual display. were you happy with the layout, is it too bright or distracting?

This looks like it may be a great project for someone to take on who is willing to modify their dash. Possibly make a recessed position within the dash to both:
1) compensate for the rake of the windsheild
2) hide the wiring
I like the display. It's not too bright unless I place it right in front of me. Then it is distracting at night, which is why I have it in the center of the windshield.

This is a temporary setup while I evaluate it, but I will probably eliminate the enormous power switch, after which the remaining wire won't bother me. I wouldn't recommend chopping into the dash only because this unit may not hold up for the long term.
 
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