@evilhighway is going to ask you to introduce yourself first in the “ALL NEW PEOPLE” category, so please introduce yourself here :
A strutbar isn’t necessary in terms of performance (in my opinion) since they came with some sort of strut braces from the factory. If you want one for looks, you can look up Ultra Racing, they might have one. Showoff Imports is a dealer for Ultra Racing in the Netherlands, so they’d be able to source one. I think it would cost around €150, maybe a bit more, but you won’t find a new one for anything less I’m afraid.
I terms of ride, I’d recommend VMAXX (Someren, Noord-Brabant) or Cobra (Utrecht) springs. VMAXX is a bit more bang for buck (still very decent), Cobra is a bit more expensive but I really like the ride of those springs. Springs will alter the ‘frequency’ of your ride and reduce body roll, but if you want to really stiffen the ride (= bumpy) you should look at shocks. Based on your wishlist, I’m guessing that’s not what you’re looking for, and having tested quite a few setups on Daihatsu’s in the Netherlands myself, I’m pretty sure you’d be very pleased with Cobra springs!
In terms of seats, you’ll most definitely end up having to make something yourself. For us Cuore-peeps, Sirion seats are already an upgrade, so there’s no real plug 'n play upgrade from there on. I got Copen seats myself and had someone weld a new frame, which lowers the seating position about 10cm compared to Sirion seats. I would recommend those seats, but since a Sirion is a bit wider you could throw in any seat you’d like since you will have to make a custom frame anyway.
Wouldn’t recommend an open air filter. Air filter box placement sucks on Daihatsu’s from that era since they’re placed directly behind the radiator which causes the engine to suck in hot air.
I used a 2.5 inch version of hose like this on my K3VE2 Sirion. I’m not concerned by the convoluted design of the hose as the air will become uniform after passing the standard air filter. The standard air filter has larger surface area compared to a K&N panel cotton filter.
As for better handling you can switch out the rear springs only for some hardened standard height springs. It will reduce understeer. It’s an odd feeling at first but the handling becomes very predictable. Unlike a thicker rear anti roll bar it’s doesn’t add more unsprung weight to the rear axle.
Hey there and welcome! You could have a look at my thread here to see what I did to make my Cuore nice and stiff without coils! It might help you in your search. You can always message me for details and questions.
Funnily enough, I looked at some bushes from Siberian Bushings just a few weeks ago. Paying for them is the issue. You can’t use a credit card or debit card because of EU sanctions, and I couldn’t make a bank transfer either for the same reason. They used to have an ebay account, but US sanctions has closed that. Grrr.
Thank you all for the reply’s. Actually forgot to reply becouse lots of other things happened. But i read all your solutions, Im still saving money for the DAF 66 first for the Engine revision since its very expensive and sadly it costs a bit more than i thought so springs have to wait for my Daihatsu. But all the tips wont be forgotten becouse the sirion will stay as a daily and i really want other springs (current springs are really annoying)