I still see so many questions like, "I just got a 3.8, what should I do first?!". There is a ton of info out there on the forums, but for the most part, it's found in disparate locations and scattered throughout random threads in a sea of troll posts. I thought I'd chime in and give a guide for...
This post has a lot of information and Titans posts are a gold mine in general.
But in regards to the typical things...
Intake: don't do an it, the stock one is better than any SRI. You will see gains with a short ram intake at first but once heat soak sets in, it'll likely perform worse than stock.. but if you want a CAI, which is proven to make gains then R2C & 3point8performance has cold air intakes, honestly that whole store has great things, particularly the engine leash and subframe shims.
Exhaust: Ark grip catback + test pipes or H pipe. They're having a tax season sale in their site. But their exhaust is a bit more expensive than others, but it's for a reason. It has honest to god 0 drone. It's tastefully subtle when cruising but can scream when you're applying the pressure, it has a deeper less raspy tone when combined with an H pipe. Plus it has proven HP & TQ gains, I think it's ~10HP & ~14TQ midrange.
suspension: coilovers, just skip the lowering springs cause you'd end up going coils down the road anyway. And the best bang for buck IMO is Silvers neomax or PartShopMax Competition coils (PBM/PSM, they changed names so you'll see them referred to as either of those in the forum) and if you wanna spend a couple hundred more dollars for the real deal like drift/track ready battle coils, PBM also has their Pro coilovers. But srsly, PBM is IMO the overall best we can get without spending multiple thousands on some crazy boutique type **** lol. They also have a air cup that you can add to your strut which is super tight if you're a slammed boi. They'll be fully restocked end of May 21', i know because I actually ordered a set 2 weeks ago lol
wheels + tire: I'm not even gunna attempt to suggest anything lol. Just good luck going through the official Fitment thread on here.. But I can say I have 19x9.5 +22 Aodhan ds07s' on 245/35/19 firehawk Indy 500s up front & 19x11 +22 on 275/35/19 out back. No rub or scrub at full turn but I'm also not low. It's flush up front and slight poke in the rear on -1 degree camber, so add a Lil more and it's flush. But I like poke.
Less common things....
-oil catch can, on out direct injection engines it should come from factory but the average customer would probably forget to service it, also Hyundai has profit margins to meet lol. But seriously. Do this first. It'll save your engine down the road from getting gunked up
- engine leash & rear shims. like I mentioned earlier, 3point8performance has the SAUCE, honestly they have a lot of the stuff im bout to rattle off... so just go on their site. And if they ask, tell them Nick Mullen sent you.
-4th differential mount, either add an extra OEM bushing after cutting out the appropriate hole or ATQ has a kit to replace all the current bushings and an extra for the 4th once you cut the hole out. Makes a BIG difference
-SHORT THROW SHIFTER + polyurethane shifter bushings . Garage line has the cheapest and it's also really good, nice and thick (pause) but the best is Coolworx, it's also the most expensive but WILL remove 2nd gear lock out entirely. I'm upgrading to that after I knock a few other things off my list
-Megan transmission mount, helps clean up shifter slop, it's essential. Also cheap cheap cheap
- Redline transmission & differential fluid and engine oil, just do it. Don't ask questions. It's just what we
-intake manifold riser, 3point8performance again... Ima abbreviate it's 3p8p now okay. But it'll toss another 15hp/tq mid range without a tune.
-intake manifold port & polish, clean that slop job Hyundai did and promote clean airflow. 3p8p offers this service but you can probably find someone local to do it... but.. 3p8p will split the upper manifold open and work on it, I swear I'm not sponsored or anything. They're seriously just the goat for out lil Korean 2003 mustangs lol
-throttle body bore, but you will need a tune afterwards, otherwise your ECU is likely gunna send you into limp mode/fuel burn mode.
-grounding kit to keep voltage stable at like 14.1 or whatever it is.... 3p8p has a kit lmao
- thermal tape wrapping your intake air box & intake manifold, control those temps and you'll harness the full power of tree breath
-uhhhhh I'm blanking. Forgive me, kinda drunk and just rambling
-headers? Ark made some great ones but now you can really only find CNT, J2, NGM, DNA & turbokits.com headers new, just DONT get cnt headers... or exhaust for that matter. Super sloppy welds and porting. Wouldn't be surprised if the headers had worse airflow than stock.
if you wanna ask any specific questions I can try to help. I know a decent amount but it's mostly recycled information from being on the forum for the better part of a decade and just looking into Gen coupe stuff because I've loved the car since it came to the states in 2010. I'm no expert. But I can try to help or at least point you in the right direction, cause I know it's a bitch to find that "my specific question" needle in the hay stack of forum posts. Also I have a saved note of every store that sells stuff for our car.Mostly domestic but some import sites / eastern market sites.
Oh oh oh also check out Ghozt lightings Instagram page, they repost a lot of custom Genesis headlights and taillights and they are THE ****. Also very expensive.. but the ****. Anyway. I'm going to bed. I've been typing away on my phone for far too long.