(Apologies, this post should have photos but they turned out all wonky. I'll add them when I get good photos)
What and why
I bought a set of Silvia 3-projector headlights to upgrade the 626 light output. Common for the designs of the late eighties, the GD never received praise for it's headlights, and now HID projectors setting the bar their shortcomings are more obvious than ever. Given that in winter time we get light for far less than a third of the 24h day, good headlights are very important for visibility and fighting driver fatigue.
Silvia projectors are of course old and halogen based; they won't turn into modern headlights by tossing in HID conversion bulbs. Optics quality and light distrubution differences in the bulbs would make sure the light output would stay far below modern standards. However, the enclosure offers a good platform for HID projector retrofit. A modern enclosure would look out of place in an eighties car; Silvia headlights instead have common design language with Mazda.
One great problem with the mod is the legislation. Since fixed headlight Silvias were never made for Europe (or anywhere else for that matter), there are no E-marked headlights, and also the light pattern is wrong. Earlier it would've meant automatic disqualification at vehicle inspection, but since then the rules have slightly laxed, with projectors it's usually enough if the projectors are ECE-approved and the glass is approved wherever.
The shape of a Silvia headlight is familiar; slim and long trapezoid with rearward slope and lower corners pointing inwards. At a passing glance the lights appear almost identical, but the looks are deceiving; upon closer inspection, differences become obvious. Even though the plastic housing is about the same size in both, the glass in Silvia headlight tapers considerably. On side-by-side comparison, the silvia headligh is slimmer and narrower (and much more so with the wide euro headlight). Also the glass is much steeper, almost vertical. Mazda glass on the other hand is flatter, Silvia is more convex. The steeper headlight angle adds an interesting feature on the fascia; it gives a similar stepped grille appearance as certain Hondas and early Lancer Evos. Carefully planned chamfers and fillets to fill the gaps between the bumper and headlights could actually subtly modernize the look, without deviating from the original style too much.
Mazda headlight is attached to the car by four axial fasteners and two extra braces. The silvia unit has two axial bolt holes in the inner and two radial on the outer edge. This means unlike the euro headlight, the Silvia one is probably impossible to line up with hood edges, and given how much narrower the S13 light is, it's not even desirable. Fabricating mounting adapters is, all things considered, a pretty trivial task.
With the Silvia headlight geometry and mounting envelope differences known, it's obvious there is no way the Mazda corners are going to fit the Silvia headlights. There is a slim chance the US style corner light wraps far enough front to cover the side mounting studs without too much of a gap, but it's impossible with the euro corners which mount flush on the headlight chamber wall. However, deciding to go Silvia corners is jumping to conclusions. There is a third option, more of it next.
The original light setup is, from center outwards, an H3C fog light, a single H3 high beam and a single H1 low beam. Regular driving lights will be replaced by ECE approved HID units for performance and legal issues with bi-xenon projector providing low beam and dual high beam, but fogs will be gone for good. For best performance, fogs should be placed low and wide apart. It also makes certain feature much more useful; connecting fogs independently to the direction indicator switch they become nice cornering lights. Some cars, like most new Peugeots, offer such functionality as a factory feature. I originally planned to use LED DRL's in their place, but I found out there weren't small enough DRL's to fit. Upon realization the corners were going to cause a lot of grief and remembering Mazda6 headlight layout I had a smalltime epiphany; I'm going to use the vacant spot for a Hella 55mm front turn indicator. Corner lights are thus no longer required, and they can be made purely decorative without approval requirements. It allows nicer finish without the legal and technical hassles involved in modifying live units.
Putting it all together
I bought the headlights to better know how I should proceed once I get to building the front end. Right now my #1 priority is to get the body rolling; I've set myself the goal of having the car on it's wheels by the end of the year. I'm not hurrying with the updates on this part of the project, until it's actually time to start building the front end.
I did a sketch of how the front end might look like after the modification; the style is based on KüWe bodykit which I like very much.
It's a very rough sketch, but at least for me it's a guideline on how to plan ahead with the modifications. I'm not absolutely convinced I'm doing a favor to the looks of the car, but as long as it doesn't look like a hack job and gives 3000 lumens at 4300K, I'm happy.