Magna86

Alright the 66 is running and driving finally :-) but the speedometer is way off. It's running 25mph faster than I'm going based on GPS speedo app. So when I'm going 65 it says I'm going 90. The car is running a 700R4 with a green driven gear and and orange/red drive gear. 3.90 gears out back and 27" tires. Based on what I've found there are no gear combo that will work. So it looks like I need an adapter but which one do I need to slow it down and read accurately or pretty close.

olds_freak

You'd need to change your drive gear to the gray one which has 15 teeth compared to your red one which has 17. Then you'll need either a 43 or 44 tooth driven gear. Either of those will get you close as it's calling for a 43.65 tooth driven gear.