I just got an AE86 and I remember them being more fun 15+ years ago. In any case I want to swap out the 4ag for something peppier and more fun. I will be using a stand alone system so that'll make my life easier. I prefer to use another Toyota motor but an sr20det isn't out of the question either. Any info would be great. Also want to consider parts availability.

1uz at least that's what I'm doing, have 2 motors and two mk2 supra w58s for the swap lol.

Why not just make the current motor peppier?
The 4A has a ton of potential.
What kind of power are you looking for?

4AGZE

If that don't do it then twin charge

Max

get the 2gr

I've decide to go with a 2RZ turbo. looking to get 400-450 hp at the wheels.

You need it to be legal in CA? If not the sky is the limit. If it does need to be legal in california, you are limited to just about nothing. You could do an f20 which would be awesome, but you need to take care of the evap system which it seems few have done.
4agte, 1uz, sr20, 13b, 1uz, vh45, f20c etc. if smog is of no concern.

Personally I started to move away from the 4ag after realizing how limited it is. The t50 really does suck and the motor is becoming pretty obsolete for parts. For a comparison, you can get a running 1uz all day for ~$300. You spend 1k on thebellhousing adapter, 5-700 on a w58 and the rest is just wiring, mounts, and driveshaft. In any case I would consider changing/upgrading the rearend.

I'm in Mass so smog is no issue I got the motor already looking for a r154 trans. Already started cutting a ford 8.8 rear end, haltech ems, once I have everything in running and driving again, I'll focus on the turbo system for more power. I hope to be done by spring.