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Total car modding rookie with some questions

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#1 · (Edited)
Hello from Austin!

I'm the owner of a 2013 AT GC 3.8, and I've been lurking for a really long time. I recently got the modding bug when I found this Flowmaster Series 80 video and realized that I could make my sports car sound like a sports car for about $200. Yeah, I got that done, and it sounds terrific--super deep rumbly at low RPMs, and exotic as hell in 3K-4K. But now I want more.

I've been reading @Vacmurse's adventures, and used some of his guides and I'm totally hooked! But I've never been much of a gearhead until recently. I managed to install the R2C SRI on my own, and my quest to learn more about the insides of my car continues. Even so, I'm definitely a rookie that isn't totally familiar with all the jargon and slang that goes with working on a car. I just bought my first toolset with all the wrenches and sockets I'll need to work on the GC, in fact.

To the point: I've done a ton of searching and reading, but some things still aren't 100% crystal clear to me and I was hoping people could clear things up or confirm my knowledge.

1. A test pipe is a secondary cat delete, right? This can improve HP and tone because the 2nd cat restricts flow and isn't acoustically optimized?

2. If I used a test pipe, I wouldn't throw a CEL and would still pass Texas emissions inspection?

3. Test pipes can be "straight" or "H", with straight test pipes sounding more raspy? Is there a good video that illustrates the difference?

4. 3" tubing will sound deeper than 2.5" tubing? (e.g. ARK DTS vs. ARK GRiP). I know lots has been written about the "ideal" exhaust system for the Genesis Coupe, but what's the latest thinking on ARK or other competitors as a good solution with great acoustics? I hate drone, and I hate sounding "ricey." But dammit I paid for a sports car, and I want it to sound like one. Is it people's opinion that the deeper bass notes are often lost on YouTube recordings?

5. Downpipe connects to O2 housing/primary cat, test pipe connects to that and replaces secondary cat. Then you have the catback exhaust pieces like mid pipe, muffler, etc.?

6. If I eventually wanted to turbo, I should go with 3" tubing off the bat? It's my understanding that switching to FI on the 3.8 is best with 3" exhaust piping.

7. BTRcc tune? SFR tune? I understand this is a controversial topic.

8. Do I need to retune when I change exhaust? Or are the ECUs intelligent enough to adapt to this sort of change? Are there any mods I can undertake that would definitely need a re-tune? I'm assuming turbo is one of them... :laugh:

9. How much boost is too much boost? How do people know? I see 3.8 Gens in the 8-9 PSI range. How do you figure out a beneficial but safe boost value that won't blow everything to bits?

I'm sorry for all the questions. Thank you in advance.
 
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#2 ·
It sounds like you're starting your modding adventure off on the right track, and welcome to the forums by the way!
I was basically in your position a few years back when I bought my coupe, in fact I took an auto repair course in college with very little experience turning wrenches beforehand, just a love for cars and an eagerness to learn. I started out with small things on my car like an intake and worked my way up from there, don't be afraid to tackle a project as long as you've got a good idea of what you're doing beforehand.
I'll try to answer your questions as best as I can, so here I go:

1. Correct, but your HP gains will be limited by the remaining restrictions in your exhaust. I recently installed a downpipe/testpipe and can verify a nice change in the tone, particularly in the mid-rpm ranges
2. You won't get a CEL from deleting your 2nd cat, only the primary cat is monitored by 02 sensors. I can't say for sure if you'd pass emissions, it depends on how strict texas regulations are
3. Not sure, I own a 2.0 so I've never really paid a lot of attention to parts for the 3.8. Lol
4. Yes, wider tubing should give you a deeper/louder tone. With regards to brands I can't really recommend one over the other, and it is sometimes hard to hear the true sound of a system over the internet. Your best bet might be checking product reviews and maybe some threads on here from people who've installed some of the different brands and types.
5. Yes, that's all correct
6. For a turbo- charged engine, the least amount of back pressure in your exhaust is definitely more beneficial. Less back pressure/restriction allows the turbine to spool freely = more power. With a naturally aspirated engine, however, a slight amount of back pressure is desired or you can actually lose a bit of power. If I remember correctly it's the exhaust stroke where a NA engine needs it the most, with a spooling turbo the engine itself doesn't need to put a whole lot of effort into evacuating exhaust gases from the cylinders since the turbine is already taking care of that by design.
7. .....Oh boy. LOL. Let me put it this way..... lots of people have had great experiences with SFR and lots have had great experiences with BTR - and the same can be said for those haven't. If you're in any of the Facebook groups I would try to avoid taking some of the "opinions" you'll come across there very seriously - check out the different companies websites, look at dyno sheets for different tunes, search through the threads on here.
8. Unless you're already tuned, say, for a cat-back and then you throw on an 02 housing, no, you wouldn't have to re-tune just for exhaust changes. The ECU's are very good at adapting to minor changes like bolt ons - typically disconnecting your battery for 30 mins or so will re-set the memory and once you hook it back up it the ECU will "re-learn" and adapt to the modification. Anything that affects performance of a vehicle in a major way - like a turbo - needs a re-tune or you'll run into trouble. Air-fuel ratio is a major thing to consider - lean out a cylinder with too much air and not enough fuel and you might end up with a hole in your block.
9. The amount of boost that can be safely be run depends alot on how strong your internals are and the compression ratio of your engine. GDI engines in particular run higher compression than engines built for boost like the 2.0t Theta. I would say 8-9 Psi for a 3.8 is a safe number - too much boost and of course you'll blow your engine. I'm sure there's a calculation that tuners make to determine what a safe number is.

I hope that helps you a little bit, if you haven't found it already check out the "Gencoupegeek's newbie guide to modding" - there's an incredible amount of knowledge to be found in there and he covers pretty much anything you can think of. Good luck!
 
#22 · (Edited)
With a naturally aspirated engine, however, a slight amount of back pressure is desired or you can actually lose a bit of power.

I see this pop up all over car sites from time to time, and its incorrect. What you think is helping isn't back pressure, its exactly the opposite - its exhaust velocity.

Before I explain this, think of trying to drink through a straw. You need the right diameter straw or you're going to get frustrated pretty fast. Too much diameter, you can't get enough suction to pull the fluid mass up the straw. Too narrow, you can't get enough volume to make the work you're putting in worthwhile. Keep that in mind.

Consider a vehicle running "open head". Not "open headers" but open head. No exhaust manifolds at all. They run like crap. Even a leaky gasket or a few broken bolts on an otherwise proper exhaust manifold will ruin an engine's performance. People who have no experience in fluid dynamics look at that and say "aha! you have to have an exhaust, which is by its very nature more restrictive than running an open head, therefore 'some back pressure' is needed!"

Nope. No way. A proper exhaust doesn't add back pressure, it adds discharge velocity by offering the spent gases a path.

When you design an exhaust system, you have to consider the discharge mass/volume at the peak power rpm desired, and then have the precise tubing interior diameter (I.D.) tuned to assist those gases into making the fastest exit possible. Spent gases released to ambient simply expand until they lose all their energy. Direct those gases into a path - like a tube - and now you give those gases a mission. The exhaust pulse follows the pipe and creates a suction behind it. The faster the gas moves the more suction it develops. The suction actually pulls the next exhaust pulse along with it, which pulls the next pulse and so on. It creates what you might consider a siphoning effect, a continuous negative pressure stream coming off the cylinder and heading out to those burnt titanium tips on your exhaust. This stream effect causes the scavenging of further spent gases from each cylinder joined to the exhaust system.

Now, if the exhaust pipe has too large of an I.D. for the application, it allows the gas to expand farther before following the pipe. Energy is lost and with it goes cylinder scavenging. If the pipe is too tight for the application, the exhaust pulse will back up and somewhat prevent scavenging, and ultimately induce reversion, which is where the pressure wave starts to back up into the intake manifold. Avoid that.

I suppose you could state that the initial pulses meet back pressure in the form of the exhaust path, which forces the gases to head down that path and create suction, but that doesn't mean the back pressure is intrinsically good - its simply a necessary condition of forcing the gases in the first place.

So, no amount of back pressure is ever a good thing. Unfortunately a lot of misinformation goes on about this, and the worst culprits outside of the internet are exhaust shop employees, who continuously spout this "fact" without a shred of proof. The best designed exhaust for ANY application always has the least back pressure at the design rpm, while it has the proper tube I.D. to create the maximum scavenging and the proper length to tune the exhaust pulse for best torque area and desired peak.

Also, this is why performance exhaust mods should always start at the exhaust manifold and work towards the back - catalytic converter restriction notwithstanding - and the more radical you get with engine mods, the more you have to consider exhaust diameter. Increase the air volume, increase the compression, increase overlap, increase the rpm range/move the power band up the dial, or any combination of these things, you have to take a serious look at your exhaust diameter. But change out your back box to help your growing list of performance mods? Its a waste of time. Do it for sound, but don't kid yourself into thinking you'll pull major power out of it. Even if you're going for sound, pull the cat(s) first, before you do anything else. Converters stifle exhaust sound, dampening the tone and reducing resonance. With modern cell cats its far better now than in the days of the old pellet boxes or even the monolithic types, but those cells still crush the sound somewhat. Pull the cats, bolt in some test pipes, and go from there.
 
#6 ·
Nope, the OP had it right.
Not trying to be an a$$, from the way you have it an axleback bolts on to a testpipe/secondary cat. Lol
 
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#8 ·
Thank you, everyone, for the clarifications so far. It's also my understanding that the textbook definition of a down pipe is the first tubing that immediately mates to the turbo on an FI car. But the GC 3.8 isn't FI. So that leads me to two followup questions:

1) On exhausts that claim to include "down pipes" for the 3.8, don't they really mean replacements for the "front pipes" from the GC 3.8 service book? The OEM part numbers are 286102M750 and 286112M750. These are the pipes that run between the primary cat and the secondary cat, as far as I can tell.

2) If that's true, then have I made an accurate diagram of the Genesis Coupe 3.8 (2013+) exhaust? https://i.imgur.com/dmeY3Hr.png

3) And there's no O2 housing because it's not the 2.0T?
 
#9 ·
1. Yes aftermarket are called downpipes
2. make your manifolds and primary cats one piece as they are not seperate
3. Correct
 
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#11 ·
Classifieds here? FB GC pages? Ebay is a long shot
 
#14 ·
Good news. I was able to install the R2C CAI successfully a few weeks back. Took way longer than it should as I am still a noob and fitment was extremely finicky, but everything is a-ok nearly a month on! No idiot lights from the engine, no bizarre rattling, and the butt dyno seems to feel an improvement.

Next up: exhaust!
 
#15 ·
BTR tune, Ive had both. SFR tune i kept having issues with and it would take weeks to get a response, plus the BTR feels better, havent dynod it yet to compare to the sfr, but im happier with it
 
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#17 ·
For exhaust I always end up doing hours of research searching all the different mufflers, pipes, and settups. Not only on my car (being the most important tho) but on similar cars as well. Don't be bogged down to just what the "genesis" community is putting on their cars, there's a ton of different things you can do that will sound and look amazing.

Next once you find what you want, I would buy the parts separately (mufflers, test pipes, headers) then take it to a good shop and have them weld it up the way you want, it will generally be WAY cheaper, aND you can have it the way you want. See how other exhaust setups are set up as well, since sometimes even the bends can make a unique sound.

I have a video a coupe posts down, but I went with test pipes and an old ferrari muffler and it turned out fantastic! Couple other you tube videos have a similar settup and sound fantastic
 
#18 ·
I definitely would look into Jesse's exhaust setup with the Ferrari muffler. The videos sound pretty damned amazing, and if I didn't already have the Ark GRiP I'd consider going that route.
 
#20 ·
Feel Free to reach out to me dude. I'm in Georgetown, we're practically neighbors. I'm happy to help install stuff or whatever.
 
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#24 ·
if you are looking for a deeper exhaust note than larger id piping will be louder and deeper but will generally have more exhaust drone than a smaller id piping. drone can be eliminated with certain resonators and mufflers for example the hks hi power muffler for the old sti's. i used to have the carbon fiber one on my 2.0t (which btw drones like im about to be bombed...) and it eliminated the drone (i have since taken it off in favor of a straight pipe). if you go f/i than you could use whatever size ID that youd like. im pretty sure apexi made a 3.5 pipe kit for the 2.0t but that might be something thatd be custom for the 3.8 guys. somebeody correct me if that last statement is wrong. im considering a 3.5" pipe on my 2.0t as i installed one on my eclipse and it made a world of difference to the tone.

sum it up to say that an n/a exhaust with a deep tone and no drone should have a good resonator (to eliminate drone and hi pitched noise) 3" piping since it will have a minimal effect on bottom end power but will sound much deeper, and if your using a muffler its personal preference but i liked my hks. you could use the 4th gen eclipse gt as a comparison since it sounds very close to the 3.8 genesis with the same muffler.
 
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