Dual electric fans, self-bleeding cooling system with a more modern pressurized expansion tank system, and load-based digital VVT actuation come to mind. Engine has higher compression pistons, 4-into-2 exhaust manifolds, and slightly hotter cams, worth like 10HP on paper, I believe. Digital timing control with no manifold pressure sensor to fail on you.
If you like the S3 body style the '90 is the best of the bunch given the upgrades they did. It's kind of like the '82 where you got the S2.5 body with L-jetronic in that regard: they're both very interesting years.
Edit: also active idle control, now that I'm thinking about it
I have a 1990 and just got a 1986. The 1990 is white and the 1986 is gray/blue metallic. My wife likes the look of the 1986 better than the white 1990. Also have a 1985.
I do like the room in front of the engine on the 1990 versus earlier S3 cars and I like the S3 body style
Somethings gotta go.
Jim, I bet you will!
Now add in the cost of a new top, a hard top, a new clutch and hydraulics, a rebuilt transmission, new tires, new brake calipers, new pads, new battery, new fuel pumps, sender and hoses, refurbished gas tank, new belts and hoses and whatever else i can't remember and we "might" be talking.
I never should have told you what I paid for it but you already knew. Feelin' the love! LOL
My wife says I should paint the 1990 the same color as the 1986 and keep it. Changing colors is a lot bigger deal than just a repaint of the same color but she does not get that.
The paint is not that good but I still don't want to change the color. Been there before on other cars. I am content with a white car with a tan interior myself. Maybe keep both and sell my red 1985 spider.