Just wandering what the size differences with the rotors and calipers are between early model SW20 GT and the later model SW20 GT?

early front 258x25 rear 263x16
 
late front 275x30 rear 280x22

Thanks.

Hello
Was just wondering for the above sw20 gt will the later model rotors and calipers bolt straight onto the earlier model?
 

Yes

Yes they will bolt on, but there are other things that will be affected apart from adding more unsprung weight - pedal travel and pedal pressure needed to stop.
The '90 model SW20 M/C is 7/8" bore.
So if fitting later model rotors and calipers, maybe also look at also fitting the later model 15/16" bore M/C to go with them, otherwise your pedal travel may be too great.
 
But further complications are that along with the larger calipers/rotors, there were booster changes in '92 and '94, and later model ABS systems are also different.
 
 
 
 
 

What are the differences to the boosters and how much difference would they make If the master cylinder was upgraded to either the 15/16 or even 1" On the early booster?

The fronts had twin 36.5mm pistons regardless of year, but the Gen3s were spaced out farther (114.5mm vs 107.9mm) so they had more leverage on the disk. That means greater braking force for the same pedal pressure, which is why they went up with the master cylinder size.
Rears went up slightly in both piston size and spacing, which kinda counteracts each other. Static front to rear ratio went from 60% Front (Gen2) to 58% Front (Gen3). I'm 99% sure they both use the same proportioning valve, which is pretty close to ideal for street tyres.

I've got a whole spreadsheet calculating all the ratios and weight transfer, etc, but in the end it pretty much came out that Toyota we're spot on with what they came up with (who'd have guessed :D)
As for master cylinders, most reports say that with Gen3 brakes, a 7/8" is decent but with longer travel, 15/16" is a good middle ground, and that a 1" gives great feel but with a fair amount of effort.

Was more curious about the booster and if the difference was worth the upgrade.

It definitely is Kris. Try and get as late a booster as you can too, as there were 1-3 revisions of the slimline boosters.