swapped my worn one wheel peel 9bolt 3.27 to a 3.55 ford 8.8. but i kept the stock speedo and gears in the trans when i rebuilt it. i figured it was close enough to not cause a huge incorrect speed gap.

but will the speedo read higher or lower than im actually going now?

 

you'll be going slower than what your speedo says. So when it says 60, you should be doing about 55.4, and when it says 30, you should be doing about 27.7 It really does work as percentage. 5 mph off at 60 does not mean 5 mph off at any or all speeds. If you're running an automatic I can help you calculate the correct speedo gears.

 

hmm well thats good iguess. at least i wont be getting that many 10mph above the speedlimit tickets

yes im running the 700r4, speedo gears are stock with the red one on the tail shaft and the light green one on the speedo. rear gears are 3.55 from the stock 3.27. what speedo gears would i need?

 

Assuming your driven is 42 tooth, and assuming you're running a 245/50R16 rear tire, or something the same outside diameter of 25.65" or so, you just need a gray 15 tooth drive gear, GM PN 8642620