sip

I swapped the engine/tranny form my old FD into my new RZ. I know the RZ has a 4.3 rear end, and I think this is the reason for the speedo being incorrect, but what can I do to solve it?

sip

anyone have any insight for me?

GoodfellaFD3S

iTrader: (213)

How do you know it's incorrect? You have your original 4.10 final drive so that's not an issue. The JDM trans does have a different 5th gear ratio in the trans.

sip

I swapped the engine and trans from a JDM 92 FD with a 4.10 rear end into a 92 JDM FD RZ with a 4.30 rear end.

I know because I hit my governor (115 mph) half way through the back straight at my track whereas before I would not even hit it at the end of the straight.

Also, I drive 90 mph (according to my speedo) on the highway and get passed by granny in a Buick.

DaveW

The rear end difference is only 4.9%. At 90 that is 4.4 mph. At 115 that is 5.6 mph. That's not that much.

GoodfellaFD3S

iTrader: (213)

Gotcha, I misunderstood what you were saying.

Not saying this is the 'best' answer, but if you run 275/40-17 on your drive (rear) wheels, that'll get you back to a stock type ratio, mathematically speaking. You'll have a 25.7 inch rolling diameter rather than the stock 24.9 inch.

sip

I did that same calculation but thought I must be erroneous in my math. There must be another cause then.

any ideas how a speedo can be wrong?

fd3rew

iTrader: (1)

The quickest way to get an estimate (without being clocked by a cop) is to use a gps unit that display current velocity/speed and do a comparison with your dash and see how much you are off. It should be only a couple of mph +/- off from your actual.

Mahjik

iTrader: (1)

Have a buddy pace along side you and see what speed his/her car is reporting verses yours. Then you can figure out if the variance is something tire/gearing related or if the speed sensor is jacked.