What are the best performance bolt-on accessories for the Civic Si?

This^ Also wanted to add that if youre on a budget, you should check out the 27WORM Performance Street Rear Motor Mount or the Whiteline Rear Motor Mount Bushing Insert. Honestly, the Whiteline insert is the cheapest way to fix that sloppy engine movement without the vibration of a full mount. For the intake, PRL Motorsports Stage 1 Intake System is basically the best value per dollar i've seen in years lol. It keeps the stock airbox but adds the sound you want!!

yo congrats on the 10th gen! honestly ive been tinkering with this platform since 2017 and ive learned a few things the hard way... unfortunately some 'budget' mods are just plain loud without much gain. For your situation, I would suggest focusing on the intake first if you want that turbo whistle.

Basically you have two paths: the 27WON Performance Hybrid Cold Air Intake System vs the PRL Motorsports Stage 1 Intake System. The 27WON is literally amazing for sound and throttle response cuz of the airbox design, but it's a bit pricier. The PRL Stage 1 is the best 'bang for buck' if you just want a better drop-in filter and silicone hose, but honestly the turbo noise isnt as good as expected compared to a full CAI.

For the RMM, I had issues with too much vibration on cheap ones, so seriously just get the Hasport Performance Rear Motor Mount 62A Street Bushing. It cleans up the shifting sooo much without rattling your teeth out. anyway good luck with the build!!

Totally agree that the motor mount is the best starting point—if you're doing the install yourself, just make sure you've got a 17mm socket and a torque wrench so you don't over-tighten the subframe bolts lol. For a really easy DIY that helps with that mechanical feel, definitely check out the Acuity Instruments Shifter Cable Bushings since they're cheap and take 20 minutes to swap in your driveway. Also, look at the Injen SP Series Cold Air Intake if you want that loud induction sound; it's a super straightforward bolt-on that doesn't require any professional help, just be gentle with the MAF sensor during the swap so you don't run into any sensor scaling issues!

Ok so, I totally agree with the above! Especially that mention of the rear motor mount insert—it's lowkey the best first mod for the 10th gen. But honestly, since you're new to modding this platform, I'd suggest being a bit cautious with the intake. I'm still kinda learning the ropes myself, but I've heard from a few guys that some open-box intakes can actually heat soak pretty bad if you're sitting in traffic, which isn't great for the engine's long-term health.

Before you pull the trigger, are you planning on staying in a really hot climate? And is this your daily driver or just a weekend toy? I'd just make sure to look for something with a decent heat shield so you don't lose power just for the sake of some cool turbo noises!! It's a slippery slope but SO fun once you start haha. gl with the build!

yo, congrats on picking up the 10th gen! Honestly, if you're looking for that turbo "whoosh" sound without spending a fortune, a basic short ram intake is basically the way to go. In my experience, you don't really need those super expensive carbon fiber setups if you just want noise and a bit better throttle response. Over the years, I've tried many different setups, and even a simple high-flow drop-in filter with a silicone hose from brands like PRL or Mishimoto makes a huge difference for way less cash.

For the motor mount, just a heads-up—it's the best bang-for-your-buck mod for feel, but it can be annoying if you go too stiff. Before you pull the trigger tho, what's your actual budget for these? And are you okay with feeling some extra vibration in the cabin when the AC is on? It's a trade-off for sure!! Good luck dude.

tbh I am in the exact same boat. I've been obsessing over data logs trying to find which bolt-ons actually help with throttle lag without messing with the factory fuel trims. Its such a headache when youre doing all the research yourself. Quick tip: check your fuel trims after installing any intake like the Mishimoto Performance Cold Air Intake to ensure you arent running lean. Also, use a breaker bar for the subframe bolts when swapping to something like the SiriMoto Phase 2 Rear Motor Mount or youll never get them loose.