Speedo's inaccurate after turbo engine swap

[Kalos]

Hello all,

I just finished swapping a 1989 7mgte and r154 tranny into my 1988 Supra N/A chassis. Right now I still have the N/A gauge cluster and my N/A differential (LSD). My speedometer reads 10 mph faster than my true speed at about 50 mph.
I researched and found some posts about replacing driven gears from the speedo cable,

"4.30:1 gearing needs 35:10 speedo gearing on the A70.

Speedometer Drive Gear: 33481-14080 (10 tooth - Same as 87-88 Turbo)
Speedometer Driven Gear: 33403-19235 (35 tooth - Same as All N/A)

Jeff"

but I don't really understand what it means. Also, do I need to change out my cluster for a turbo cluster? I know the markings are slightly different between the two...

Thanks!

 

[supraguy@aol]

I thin you'd need to replace the drive gear on the tranny.
OR, you could replace the differential, and not worry about it, and get better highway mileage/ lower rpm cruising.
aka- 3.91 diff.

 

[Kalos]

I'd rather just change the drive gear, but I don't know which to get. And do I need to change gauge clusters to turbo for the different speedometer markings?

 

[supraguy@aol]

Question- to anyone reading;
Will the W58 speedo drive gear fit the R154? If so, this should be an easy fix.
And no- you dont have to swap clusters. Did you get your tach modified to work yet?

 

[hvyman]

Might have to get the right speedo gauge for the trans.

 

[Kalos]

Actually, the tach seems to work just fine.

After doing some reading, it seems that many people enjoy the 4.30 for low end power, but I also read that a turbo would do best with taller gears in order to build more boost. Any thoughts on this?

 

[hvyman]

What are you doign with the car?

A 4.30 lsd would be good for drags and 3.73 would be good for high speed and/or freeway cruising.

 

[Kalos]

Its not my daily driver anymore, it's just for pleasure driving. I don't expect to do too much long distance trips. I do want it to have lots of power at low speeds, so it sounds like the 4.30 is the way to go. I was just surprised when we finished the swap, first and second gear felt so slow... third and fourth felt really good, but I wondered if the differential from the N/A isn't ideal for the turbo...?