1.6 to 1.8 rear diff swap speedometer accuracy
 

ok so the question is
when i get around to turboing my 1.6
and throwing in the rear from the 1.8
how do i make the speedometer accurate again?

btw i did tear down a complete 95 due to a wreck
so the body was bad
but everything mechanical is just find
so im sure i have what i need

but my question is what do i need to do to ensure speedometer accuracy?

thanks
jared

If you are going from a 4.30 to a 4.10 and leaving everything else the same...

A 4.1/4.3 ratio should see approximately a 5% change in reading. I.e., you'll be traveling approximately 5% faster than indicated with the 4.3 gear set (Every 20mph will read 1mph slower. What was read as 63mph then will be 60mph now.)

IIRC, it simply takes a speedo gear change to fix it if 5% is a make or break deal. Swapping the trannies too should take care of it without any ------- necessary though.

my speedo is more accurate now with the 4.10 gears over the 4.30...

The speedo is *not* accurate in a 1.6 with stock 4.3 diff. It reads very optimistically high... I'm right now having my 4.3 diff replaced with a 4.1 Torsen LSD my hope is that it will work well and last (the diff that just came out had metal chunks in it) and the speedometer will be accurate.

In other words, don't worry about it. You'll be a lot more accurate with a 4.1 than with the stock 4.3.