Spark plugs for JB4 tune - In my specific circumstance*

[zombiedude]

Hi, first post here! Just recently purchased a 2025 Genesis G70 3.3t after spending some time in a buddies Stinger 3.3T.

To cut to the chase, I've just purchased a used JB4 off of him and looking to install it shortly, but at a crossroads for which plugs to run. OEM plugs are notably not great when tuned and at a minimum need to be regapped. Alternatively many have purchased 1-step or 2-step colder plugs such as Denso 5346/5347 or HKS M45IL.

In my specific circumstance, I use this car as a daily driver, and my work is only about 3 miles away ~10 minute drive + 2-3 minute idle to warm up the car and let the RPMs drop. During the drive, besides 1 long stretch without stop lights where I hit 60mph, I'm usually stuck at lights doing 25-40mph so not generating much heat. I make this drive 4 times a day (I go home for lunch) 4 days a week, beyond that, I take spirited drives on the weekend around town frequently hitting redline shifts.

With these driving habits, would I be at too great of a risk of fouling plugs and not burning excess carbon due to the short trips? or will a couple hard drives a week make this a non-issue? Should I use 1 or 2 step colder plugs, or just regap OEM? Any suggestions?

Also, I plan to run Map 2 on pump 93 octane. I have catless midpipes, BMS Intakes w/ silicone turbo inlet tubes, and Tial BOV. Going to buy Borla cat-back once it's released for the G70. No plans to run Ethanol or WMI/CPI. Keeping it pretty tame.

 

[Brendan @ K8 Stinger Store]

Hey @zombiedude,

Welcome to the forum and congratulations on your G70!

It is not recommended to run stock plugs on a tuned car, even if re-gapped. However, we recommend swapping to the HKS M45iL Spark Plugs whether you are stock or tuned. We've seen these plugs help cars run smoother, last longer, and overall these are higher quality.

Feel free to reach out if you have any other questions!

HKS M45iL Spark Plugs

Specifically sold for use with the Kia Stinger 3.3TT, G90, & G80 vehicles. HKS M-Series Super Fire Racing spark plugs are high-performance Iridium plugs designed to handle advanced levels of tuning and provide Improved ignition performance, durability & anti-carbon build-up. FREE SHIPPING WITHIN...

www.k8stingerstore.com

 

[oddball]

Get HKS plugs. Go one step colder, not two steps. One step is not that big of a deal.
I ran Denso plugs initially and they completely wore away within 5k miles. Similarly, mine is just a daily driver.

The problem you run into with the stock plugs is the spark blows out at high boost, so you have a misfire right at the top end and then the ECU panics.

In general, that daily commute is not terrible. A 3 minute drive would be. Just change the oil regularly.

 

[zombiedude]

Get HKS plugs. Go one step colder, not two steps. One step is not that big of a deal.
I ran Denso plugs initially and they completely wore away within 5k miles. Similarly, mine is just a daily driver.

The problem you run into with the stock plugs is the spark blows out at high boost, so you have a misfire right at the top end and then the ECU panics.

In general, that daily commute is not terrible. A 3 minute drive would be. Just change the oil regularly.

Thank you very much. I will do just that! Appreciate the input!

 

[Thomby]

Get HKS plugs. Go one step colder, not two steps. One step is not that big of a deal.
I ran Denso plugs initially and they completely wore away within 5k miles. Similarly, mine is just a daily driver.

I will do just that!

That's interesting, I went with Denso 1-steps as part of the BMS kit, and am running strong (on Map 5/E30) over 15k miles later. Then again I'm pretty easy on my car day to day, and the ethanol has its own cooling effect.

Here's what BMS says -- no difference in performance, just a bit longer life from HKS:

We are frequently asked which plugs are better for the Kia/Hyandai platform, HKS, or Denso. We've used both brands on our development cars and have found both to be good quality. Generally speaking HKS plugs tend to offer a longer life of 20-35k miles before they need to be replaced, while Denso plugs tend to only last 15-25k miles before needing replacement. For that longer life you do pay a price premium. We've found timing corrections and overall engine performance between them to be otherwise equivalent.

 

[oddball]

That's interesting, I went with Denso 1-steps as part of the BMS kit, and am running strong (on Map 5/E30) over 15k miles later. Then again I'm pretty easy on my car day to day, and the ethanol has its own cooling effect.

Here's what BMS says -- no difference in performance, just a bit longer life from HKS:

Yup, that's why I bought them in the first place. Started getting a rough idle so I checked the plug that was easiest to get to - it was fine! A few months later started pulling others and every other plug had worn down..... So Densos are fine, just check them all.