The knowledgebase section contains up-to-date information about the Genesis Coupe 3.8 as of 2021. Much of the information that can be found on search engines is critically outdated, if not dangerous to aspiring modders. A lot has change since most people moved on for the forums, and the community has learned a ton over the last four years. Yet the newest information is often buried in Facebook groups that cannot be searched from Google. For example: what’s needed to tune a Gen for e85? This is the only site on the whole internet with a recent parts list.
In general: how does AlphaSpeed tuning work for the Genesis Coupe?
I want to buy new wheels/tires: What specs should I look for for flush fitment?
What is the thread pitch for the Genesis Coupe 3.8 PCV valve?
What exhaust design is appropriate for the Genesis Coupe 3.8?
Do CSF and Koyo radiators fit Genesis Coupe BK2? Or the 3.8?
Do test pipes or catback exhausts cause check engine lights (CELs)?
How does a turbo work?
- Cold air is drawn into the turbo via the filtered compressor wheel inlet at the front of the turbo.
- That cold air is sent through the front-mounted intercooler (FMIC) to reduce the air temperature, improving performance. The cold air reaches the intake of the engine, where it is sent to the cylinders to mix with fuel for ignition--just like any other motor.
- Exhaust gasses that would usually exit the vehicle are instead harvested to spin the turbine wheel on the back of the turbo.
- The compressor wheel (intake) and turbine wheel are connected. As the turbine wheel spins faster, so does the compressor wheel, forcing more air into the engine. This is boost!
- Unharvested or unused exhaust are spent from the rear of the turbo into your catback exhaust and/or vented to atmosphere via the wastegate.
- Unused/unneeded air trapped in the piping in Step 1 and 2 are released via the blowoff valve.
- Unused/unneeded air trapped in the piping in Step 4 is released via the wastegate at 6 pounds of boost in the Remnant Performance kit.
Auto: What transmission fluid do I use?
BK1 Model Years: Lifeguard 6 ZF Fluid
BK2 Model Years: Valvoline MaxLife ATF (SP-IV-RR)
Naturally Aspirated: How do I install an oil catch can?
Run a -6AN hose from the PCV valve to the catch can inlet.
Run a -8AN hose from the catch can to the intake manifold.
Position the can anywhere you want in the engine bay, but slightly downhill of the intake manifold is helpful.
See this video of the general overview of the setup and principles. Please note this is for a BK2, but BK1 has similar routing.
Where can I find service manuals for the Genesis Coupe?
How do I tune a Genesis Coupe for e85?
If you would like to tune for e85, here are the right steps:
Ensure you have installed ethanol-rated fuel lines (example lines for BK2)
Ensure you have installed an ethanol content sensor (example sensor for BK2)
Ensure you have installed an ethanol content gauge (Innovate MTX-D Ethanol%)
Ensure you have installed a wideband O2 sensor (Bosch LSU 4.9 sensor)
Get your current tank of gas as low as possible.
Refill the tank to full with e85.
Gently drive it to your tuner. Your car will run fine, but gas mileage will be poor.
Get the tune and go! Enjoy your 🌽.
NOTE: If you drive a 3.8T, there are some important limitations you need to be aware of. Please ask an expert.
In general: How does AlphaSpeed tuning work?
First: AlphaSpeed is the only viable tuner for the Genesis Coupe. Not BTR. Not SFR. AlphaSpeed only. They have the most sophisticated, safe, and powerful tunes for the Genesis Coupe and you should not waste your time with other vendors and/or canned tunes. The world of tuning has evolved a lot over the last two years, and this FAQ exists to give you candid knowledge about the current state of affairs in 2021. Cool? Let's continue!
Today's cars are heavily computerized. Electronic aspects of your car like traction control and stability control are often managed by the Body Control Module (BCM), while engine operation is managed by the Engine Control Unit (ECU).
When your car is assembled, the car's computer (ECU) is pre-programmed with engine management setting shared by all cars of that make and model. This programming is often very conservative. It's conservative so the engine has plenty of margin to absorb abuse from the worst drivers, worst maintenance, and worst climates--sometimes all three. But this also means there is additional performance in the motor lying dormant for users who are more responsible.
"Tuning" refers to the process of replacing the factory ECU programming with a new set of parameters (called a "map") that is more aggressive, so drivers can access that improved performance. Adjustments can include:
- Higher boost pressure at a given RPM (if turbo)
- Changing when the sparkplugs ignite the fuel mixture in the cylinder ("timing")
- Adding or removing fuel quantity for a given amount of air in the cylinders ("AFR")
With that out of the way, let's look at how tuning of the Genesis Coupe works with AlphaSpeed.
Required Equipment
First and foremost, you should have a Wideband O2 sensor and AFR gauge for proper tuning. The Innovative MTX-L PLUS kit comes with everything you need in this regard. This gauge allows your tuner to see how much air and fuel is being mixed for combustion. It will let them see if there's opportunity to safely be more aggressive with your tune, and how your car is reacting to the "base map" that's installed before tuning starts. Don't know what a base map is? No problem! Read on!
The Tuning Process
A combination data logger and ECU writing device will be plugged into your OBD2 port. The data logger will allow a PC to capture the performance of your vehicle during operation, and the ECU writing capability will allow AlphaSpeed to write the tune to your car's computer.
A “base map” will be flashed to your car’s ECU via a laptop connected to the OBD2 device. The base map contains more aggressive performance parameters for your make and model of car, but will not be highly optimized for your particular engine. This base map will not yet account for any mods that you have done. It’s a conservative/safe “one size fits all” solution for the purposes of driving the vehicle and analyzing its performance to create a better tune.
You or your tuner will conduct a few high-speed pulls in 3rd gear or 4th gear (depending on the performance of your car). Pulls are five seconds in duration at wide-open throttle (WOT) from a 20MPH rolling start. During this time, video will be taken of your gauges, and a computer will be logging data from the engine.
This video and computer-logged engine data will be sent to AlphaSpeed HQ where another tune file is generated for your car. It will be customized for your engine, in your car, with your fuel and your mods.
This new tune is flashed to your ECU via a laptop and the OBD2 device, overwriting your base map.
You will once again conduct the pulls described in Step 3, which may or may not result in another round of tune customization to dial in the performance and safety. If no further customization is required, you’re tuned! The final custom tune is more aggressive than the base map or stock ECU programming, but not so aggressive that engine health is compromised. Engine safety margin and sensors are preserved.
It is also possible (in rare cases) that the base map is sufficient for your vehicle, as the base map has become increasingly sophisticated and dialed-in over the last 24 months. Don’t be alarmed if this happens.
Once you are tuned, you should only fill your gas tank with the type of fuel you were tuned on. For example, if you tuned with 93 octane pump gas, you are now obligated to continue filling with 93 octane pump gas. Your engine health and performance depends on a specific type of fuel.
Contacting an AlphaSpeed Tuner
AlphaSpeed uses a network of local tune dealers located all over the U.S. and Canada. You can contact AlphaSpeed on Facebook to find the closest tune dealer to your location. If no tune dealer is sufficiently close to your location, a remote tuning kit can be sent to your door.
The remote tuning kit allows you to perform steps 1-8 on your own. You will receive detailed instructions on what to record, when to record it, and how. You should ideally have a passenger with you that can record the AFR gauge and operate the laptop for ECU data logging.
The tune process takes approximately 30-60 minutes, and prices vary based on the nature of your tune. Contact AlphaSpeed for details.
What are the OEM wheel and tire specs?
The Genesis Coupe BK1 and BK2 generations have slightly different wheel specs, but these specifications work just fine if you're looking to compare new wheels to OEM size and fitment.
18” non-Track:
FRONT: 18x7.5+33 wheel with 225/45R18 tire
REAR: 18x8.0+33 wheel with 245/45R18 tire
19” Track:
FRONT: 19x8.0+35 wheel with 225/40R19 tire
REAR: 19x8.5+35 wheel with 245/40R19 tire
What are the OEM alignment specs?
These are the factory alignment specs for all model years of the Genesis Coupe 3.8 and Genesis Coupe 2.0T.
| Alignment Spec | Factory Range |
|---|---|
| Front Caster | +7.0 to +8.0 |
| Front Camber | 0.0 to -1.0 |
| Front Toe | +0.06 to +0.22 |
| Front Total Toe | +0.12 to +0.44 |
| Rear Camber | -1.0 to -2.0 |
| Rear Toe | -0.02 to +0.18 |
| Rear Total Toe | -0.04 to +0.36 |
| Thrust Angle | 0 |
| Steer Ahead | -0.05 to +0.05 |
| King-pin Angle | 13.7 |
Flush fitment on the Genesis Coupe: What to look for?
Genesis Coupe owners have been putting wheels and tires on their cars for 11 years, now. This is a well-tread path. Most drivers stick to what I'll call "The Easy Combo" as it's known to fit well, maximize traction, and sit flush with the body lines. You can't go wrong by buying the easy combo, because it will definitely fit and look good.
The Easy Combo
- Front: 19x9.5+22 wheel and 245/35R19 tire
- Rear: 19x10.5+22 wheel and 275/30R19 tire
More Choices
The below table offers additional options for people who may want different wheel sizes. The goal of this table is to maximize flush fitment with the car's body lines. Note that the blue entries are generally accepted as the best/easiest solution, but the other rows will be pretty flush for their size.
Will X Combo Fit my Car?
Drivers ask this all the time. They link a random wheel/tire combo and ask if it'll fit. There's an easy way to test for this yourself. Visit Will They Fit? and enter the specs for a front or rear wheel/tire from The Easy Combo in the "Existing Setup" boxes. Then enter the specs for your desired/new wheel/tire in the "New Setup" boxes. There will be a diagram generated that shows you how the new wheel/tire compares to the known-good fitment of an Easy Combo wheel. If it's a few millimeters in either direction, you're likely good to go! The diagram shows how the tire shape changes in the new configuration, too.
As an example, here's the Easy Combo rear wheel against a larger tire and a lower offset. This new rear wheel and tire isn't much different from the known-good fitment of the Easy Combo. It will fit. But because the tire sidewall is a little taller, people slamming their cars may have to increase camber or back off on lowering the ride height.
As another example, if you're not going for slammed: 19x10.5+22 will fit with a thiccccc 305/30R19 tire (fitment image). This is about the best traction you can get on a Gen, but you can't get ultra-low with it. But you can still get low!
Can you teach me more about differentials?
The “differential” is the component of your vehicle, between the rear wheels on your Genesis, that converts the motion of the drive shaft to the motion of the wheels. It’s how your motor ultimately applies power to the wheels via the axles.
Before we really dig in, however, we need to talk about drive ratios. The "drive ratio" of the car changes with every gear used by the transmission. Drive ratio is expressed as X:Y. Higher numbers for X are called "shorter gears," and lower numbers for X are called "taller gears." Yes, this is confusing.
The Y stands for one complete revolution of the drive wheels (rear wheels for the GC, of course). The X stands for the number of drive shaft revolutions. So why is it a ratio of X to Y? As you may begin to see, the “drive ratio” refers to the number of revolutions the drive shaft must complete to result in one full revolution of the wheels. As an example: a gear ratio of 3.53:1 means the drive shaft is spinning 3.53 times for one turn of the wheels.
In terms of building a transmission with multiple gears, all the gears are sized relative to the final drive. At last we come to the differential! You may have seen the term “final drive” several times in the Gen community, because the Gen reached the market with many different rear differential configurations that are often interchangeable to customize the performance of the car.
The final drive specifically refers to the drive ratio for the last set of gears in the drivetrain. That last set of gears in a drivetrain is in the differential! In practice, that means a Genesis Coupe with a 4.18 final drive differential will have “shorter gears” as it shifts, compared to a 3.53 final drive with taller gears throughout. Why does this matter? Short gearing (higher ratios) are faster to accelerate, while tall gears (lower ratios) have higher top speed.
Again using our 4.18:1 vs. 3.53:1 example: the 4.18:1 Genesis Coupe will be able to get to top speed faster than a 3.53:1 Coupe, but the 3.53:1 Gen will have a higher top speed.
If this is still confusing, don’t worry. Gears are confusing, and there’s an example from your childhood that may help: the bicycle.
Remember how the low gears were great for acceleration and easy to pedal? That's because you were moving your legs a lot for one revolution of the back wheel. It was easy to apply the torque of your legs to get the bike moving. Acceleration was great! That’s similar to first gear on a car! Those big, easy-to-pedal gears are short gearing. But you’ll also remember those early shorter gears weren’t great for going fast. So as you moved into cruising, you would move into one of the taller (physically smaller) rear gears that required you to pedal much less for each revolution of the wheel.
So, what diff do you want? That’s hard to say. It depends on your ambitions for the car. ;) Ask your friends in the Remnant Performance Turbo chat.
What is the thread pitch for the Genesis Coupe 3.8 PCV valve?
This is the only website on the internet with the right answer: it is 1/8″ – 28 British Standard Pipe Taper (BSPT). It is not M10x1.0 as other sources indicate. You should use Loctite Blue 243 on this thread and follow the NPT thread guidance above for torque.
How do I tighten dash AN fittings?
Assemble to finger tight, then use a wrench to rotate the fitting one quarter turn tighter. Make a mark at the 12:00 position on the fitting, and tighten until the mark reaches 3:00.
How do I tighten NPT fittings?
NPT fittings use the turns past finger tight (TPFT) method. All NPT fittings are generally alright with 2.5 full revolutions with a wrench after you've tightened the fitting with your fingers. Mark the fitting at 12:00 with a Sharpie, then rotate 2.5 times until the marker lines up with the 6:00 position. When in doubt, consult an NPT TPFT guide.
What kind of exhaust design is appropriate for the 3.8?
A good exhaust consists of two parts: ideal performance, and acoustics you find pleasant.
Let's start with performance first. What exhaust is best for performance on the 3.8? That depends entirely on your engine and how much horsepower it makes! This is because horsepower correlates strongly with air output from the motor, which can be measured in cubic feet per minute (CFM).
The right exhaust from a performance perspective utilizes piping that can flow slightly higher CFM than the engine's output. Below you'll find a common selection of exhaust diameters, and how much horsepower they can support as a result of the CFM the pipe can flow.
2.25" Pipe: 185 engine HP per pipe
2.5" Pipe: 232 engine HP per pipe
3.0" Pipe: 339 engine HP per pipe
3.5" Pipe: 401 engine HP per pipe
4.0" Pipe: 656 engine HP per pipe
Using the factory BK2 Genesis Coupe as an example, this vehicle is rated with 348 engine horsepower. The factory exhaust is 2x2.25" downpipes (370 HP flow) narrowing to 1x2.5" (232 HP flow) catback. Notice the stock exhaust has the appropriate airflow on the downpipes, but the stock catback is too narrow to support all of the engine's power. This is why going to an aftermarket catback can improvement performance.
Notice also that most Genesis Coupe BK2 exhausts use 2x2.5" pipes for 464HP of combined airflow. This piping is slightly higher than the engine's factory airflow, and you can see that it follows the "rule" that an ideal performance exhaust offers slightly more airflow than the engine itself. Even the ISR Single Exit exhaust at 1x3.0" is perfect for the Genesis Coupe at 339 HP of flow--it essentially matches the BK2 3.8 in overall power.
At this point, it's important to know that an exhaust that's theoretically too small isn't necessarily a hard wall in terms of performance. Raising engine HP on the same exhaust diameter will still show higher performance on the dyno, but the gains just won't be as large as they could be with a more appropriately-sized setup. And conversely, running an exhaust setup that's too big won't rob you of power, but it will push the power gains higher in the RPM band where you are less likely to be driving. These general rules are why the ideal performance exhaust offers a flow rate around the engine's performance level: it unleashes all available performance, and makes sure that performance is available across a wide range of RPMs.
Special Rules for 3.8 Turbo
More flow is always better (to a point) on a turbo car, and big turbo vehicles work best when they are evicting engine airflow as quickly as possible. For example of how exhaust can help or hurt a big turbo: this large turbo MkIV Supra gained ~50HP moving from a 3.0" to 3.5" exhaust at about the same engine horsepower as a 3.8T (~525HP).
Overall, dual 2.5" exhausts are the bare minimum for a 3.8 Turbo, but dual 3.0" or single 4.0" are likely even better dyno performance at the same engine horsepower. You will need to have this type of exhaust custom-made by an exhaust shop.
3.8T setups eliminate the OEM downpipes. Instead, your 3.8T exhaust should ideally connect to a "Y-Pipe" that splits the turbo's exhaust outlet into a pair of flanged connections that serve as your new catback connection point. You can collect this Y-Pipe down to a single exit, or run two pipes to the muffler area, using the above diameter rules. See this diagram for additional insight on the layout of the Remnant Performance turbo kit, but it's a good example of the layout for any big turbo V6 setup.
As a final thought on the topic of acoustics: turbos add a lot of extra piping. This acts as a natural resonator, which quiets the exhaust down a great deal. You won't need much muffling on a 3.8T if you want an aggressive exhaust note; large cannister resonators may be enough.
X-Pipe, H-Pipe, etc.
H-Pipes and X-Pipes are only for naturally aspirated Gens. They function by equalizing exhaust pulses between the two banks of the engine, which can improve performance and acoustics.
X-Pipes, in particular, allow for a smooth and continuous flow of exhaust gas. This improves power, but can increase rasp. H-Pipes are better at fighting exhaust rasp to V6 engines by lowering the pitch of the exhaust note, but produce (very slightly) less power than an X-Pipe in testing.
Just to reiterate: 3.8 Turbo cars do not need or benefit from H/X-Pipes. 3.8 Turbo should have the largest possible downpipe from the turbo's exhaust outlet, then a Y-Pipe into 2x2.5" diameter (or larger) flanges for the "catback."
Test Pipes
In the entire exhaust, test pipes are the biggest performance improvement for the Genesis Coupe 3.8. No, you will not get a check engine light; the Gen doesn't care if you have test pipes. They should be 2.5" diameter. An H-Pipe design helps with rasp. Test pipes are dumb metal tubes with flanges, and it doesn't matter what brand you buy.
Rasp
This is a V6 motor problem, not a Gen problem. You can fight it by integrating an H-Pipe into your exhaust setup, and by wet wrapping your downpipes with a fiberglass wrap like DEI Titanium. But increasing the exhaust flow with test pipes or headers will only make the exhaust more raspy. Good luck.
What brakes and rotors should I use?
Opinions are like assholes; everybody has one. But it's the author's position that EBC Redstuff pads and R1Concepts rotors are a great choice for any Gen owner.
Brembo Pads
- Front: EBC dp31210c
- Rear: EBC dp31140c
Non-Brembo Pads
- Front: EBC dp31856c
- Rear: EBC dp31806c
Rotors
Note: Drilled rotors are good for rain, but tend to wear unevenly and crack under high stress. Slotted rotors are beneficial for consistent braking under repeated heavy use, but tend to cause early pad wear. And blank rotors are a great all-rounder: quiet, long pad life, large bite surface, no cracking, good dry or wet, etc. You're not a tow truck or a real race car, so get blank, ok?
What are good mods for Genesis Coupe 3.8?
If you're not going to go big turbo, the 3.8 does not gain much additional performance from mods. That said, there is a clear-cut path to upgrade your motor and a clear-cut set of mods that are "worth it" vs. "not worth it." For example: short ram intake? Not worth it; it's a downgrade! But e85 fuel? Worth it!
Please review the famous 3.8 Upgrade Path post for detailed guidance.
What is a good oil for the Genesis Coupe 3.8?
Oil recommendations for the Genesis Coupe are 99% broscience. The "wisdom" that exists basically consists of a bunch of senior forum members shouting "idk it works for me bro" the loudest, and everyone else just follows the recommendation.
Shell Rotella T6? It's garbage. It causes black sludge to build up in your motor, and it's not even tested for gas engines anymore. Royal Purple? It's garbage. It will literally corrode the metal of your engine due to ZDDP content. Some random brand of 5W20? There are a handful of amazing options, but most are just prone to shearing on our hot motor.
In review, these are the three most common recommendations for the Genesis Coupe. So, this begs the question: if it'll create sludge in your motor, eat your metal, or turn to water under high load, why do people recommend these oils? Because of useless broscience.
Let's look at what real oil performance testing tells us about good oils! Some fantastic options for the Gen include:
5W30 Renewable Lubricants Bio-SynXtra Super High Performance Passenger Vehicle
5W30 Valvoline Full Synthetic High Mileage with MaxLife Technology
These are not necessarily top-5 best, but they're certainly top-20 in the whole industry and widely available for you to buy. These have been tested objectively to have great wear resistance and high-temp resistance for your motor.
But don't forget the GOLDEN RULES: Full oil on the dipstick, oil change every 3 months/3000 miles, use OEM Hyundai filters, and check your oil levels monthly! If you want to run longer OCIs, do an oil analysis with Blackstone Labs and let them make a factual recommendation. I can't guess how you drive your car, so all I can offer is a safe and conservative answer.
Do CSF and Koyo radiators fit the Genesis Coupe 3.8? How about BK1 vs. BK2?
- Koyo VH13059 fits BK1 and BK2 Genesis Coupe 3.8.
- CSF 7038 fits BK1 and BK2 Genesis Coupe 3.8.
- Mishimoto MMRAD-GEN6-10 fits BK1 and BK2 Genesis Coupe 3.8
- **WARNING to AUTO TRANS: These aftermarket radiators do not have the automatic transmission coolant loop. You MUST obtain or build a standalone auto transmission cooling loop to run one of these radiators.
Do test pipes or catback exhausts cause check engine lights (CELs)?
No.
What test pipes are best?
They're all the same: a dumb tube of metal with flanges. Get 2.5" at the best price.