I try to stick to universal items available from junkyards, eBay, RockAuto, etc... aside from specific things like cams, exhaust items, or other 3800-specific items vendors have.
You can base your build around the things you NEED to rely on the 3800 vendors to get, and get creative with the things you want to make yourself or find via alternate means (junkyards for 75mm TB's, bigger MAF's, wiring connectors... Solder the harness yourself, and buy or build your own adapter plate). Just as an example, but there's a bunch of options to stay moving forward...
ZZP is the only active company still producing new items, since 3800's are a big % of their business, despite trying to move into the GM 4cyl markets (with some success, but much less dedicated owner base).
Intense seems to basically be keeping the lights on by shipping out from remaining inventory John (current owner) got from Scott (original owner). It's a shame they don't push to get more going, because people liked having competition and ZZP's sales show there's people still messing with 3800's (even Zoom discussed missing the competition on their podcast).
At one time we had a good handful of vendors. ZZP is the only one that seems to still working & developing things for our cars albeit slower than they once were. Otherwise Intense, PFYC & Milzymotorsports are still around, however just seem to be selling off old inventory
PFYC is a dead company walking, too (sad, because I bought my 1st couple mods there in ~2003), and Milzy seems to be in over his head trying to be a viable operation.
We're in a declining volume market of an out-of-production vehicle/engine, so without being something more prized, like LS's, 5.0's, etc., don't expect much to remain out there when there's not much money to be made for their businesses. Yes, there's millions of cars, but most are rotting away and have tons of miles. Plus, this is no longer a popular, modern platform people are going for in big enough numbers to support a variety of parts manufacturers anymore.
It was fun while it lasted, but the people coming in now are late to the game.
It sucks to admit it, but your right dezldave961. I'm happy to see people still coming into the scene that still want to unleash the potential of these cars, but alot of us old timers have since moved on. Who knows, maybe now that these cars are starting to inch into classic territory maybe there will be a resurgence. I'm sure as hell excited to own an almost classic car even though it may never be held in the same regards as others from the era such as the LS1 cars.
I wouldn't quite label them as "classic" material, but more of a "niche" market going forward. Take care of your chassis especially, if it's in good shape, because that's the only component you can't do much do upgrade or replace.
For parts, I'm about to dig into a fresh engine and this popped into my head again. For example, the following parts had/have me doing this:
SFI/8-rib harmonic balancer: RockAuto has them for $30+ less than 3800 vendors
Crank bolt: 3800 vendors happen to be the easiest place to get the GM bolt
Valesprings: Summit/Jegs typically carry the LS1-style Comp, etc. ones that 3800 vendors list, and many more... Shop around and chart the spring comparisons
Cams/heads: these are limited to the 3800 vendor offerings, so if you're not DIY'ing things, that's all you can get
Throttle body: see my post above, but nice adapter parts from vendors can make it a cleaner job
Transmission: vendors are dwindling, and TEP was the go-to unless you have your own resources... 3800 vendors have the only hardened parts still on the market, and differentials/chains are only the legacy ones we had. This is a big hang-up for modding too far past bolt-ons, so have a plan.
Fuel pump: drop in replacements are offered by vendors and sold thru Summit, eBay, Amzn, and elsewhere for our baskets (usually needs swap to pre-00 lower basket to fit better, but haven't messed with it since converting my '04)... Relay/re-wire harness kits for GM cars are available from many places like Racetronix, or you can DIY, but it's also nice to have 3800-specific vendor's for simpler install, too.
Suspension: junkyards will have the GM upgraded parts (sways, trailing arms, etc.) on things like GXP's and Police Impala's. Some better used struts may be had that way, too, and strut tower braces are found on many W-body's in the yards. Poly bushings/endlinks are available anywhere from AutoZone/etc. to RockAuto or a 3800 vendor.
Brakes: Any junkyard 00+ Impala/Monte has the 12" front brake bracket for our calipers, or a 93-02 F-body for their version that just requires a bolt adapting. There's also the GXP's for the 13" front and 12" rear upgrade with nice calipers. Grand Am rear aluminum calipers are also out there.
I can kinda explain the thought process for a variety of parts, and how the acquisition has evolved from the vendor peak ~2003-2006, through now. Oddly enough, today people can build a 3800 to be much quicker with less growing pains than we had at the start, but lessons learned tend to not occur about the details unless an issue arises. The main headache is availability for specific upgrades that ensure more strength and longevity at critical points, since manufacturing ended a decade ago for many things.
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