Biggest restriction in oem exhaust ?

[Brichinelo]

I’ve read multiple threads and still can’t quite get a definitive clear answer. On the stock exhaust is the biggest restriction the primary downpipes , secondary downpipes or mufflers? I’m torn between ultimate performance downpipe midpipe combo and just getting Jun bl downpipes and calling it a day. I hear the ultimate performance kit provides significant increases as opposed to stock cats and downpipes . I know with the up kit overboost will be an issue so before I did that I would get an aftermarket tune. Anybody with the ultimate performance downpipe midpipe can provide some insights ? Thanks and appreciate all input and feedback .

 

[Daniel @ K8 Stinger Store]

You will get the most gains by swapping out the primaries which is why I tend to suggest the Ultimate Performance Downpipe Combo Kit (click HERE) when someone is looking to maximize performance. As long as you have a Jb4 or equivalent you will be fine running this kit.

 

[oddball]

The "biggest" restriction is the primary cats. But you're probably asking the wrong question.

The replacement process really should be from back to front: muffler, THEN secondary cat, THEN primary cat.

Replacing the primary, besides physically difficult, has other complications. Just read here about overboost codes.

Just replacing the mufflers is quick, easy, and has a hilariously large impact (25hp?).

 

[G70LEbyAdoom]

The "biggest" restriction is the primary cats. But you're probably asking the wrong question.

The replacement process really should be from back to front: muffler, THEN secondary cat, THEN primary cat.

Replacing the primary, besides physically difficult, has other complications. Just read here about overboost codes.

Just replacing the mufflers is quick, easy, and has a hilariously large impact (25hp?).

This is an understatement. When I replaced the OEM catback with my megan racing catback, which still has a pretty big muffler on it compared to other exhaust options for the stinger, I could physically feel the extra power because of how less restricted it was. It makes me very excited to install the downpipe/midpipe combo I have.

 

[Brichinelo]

The "biggest" restriction is the primary cats. But you're probably asking the wrong question.

The replacement process really should be from back to front: muffler, THEN secondary cat, THEN primary cat.

Replacing the primary, besides physically difficult, has other complications. Just read here about overboost codes.

Just replacing the mufflers is quick, easy, and has a hilariously large impact (25hp?).

Just deleting the mufflers ? 25hp ? I’ve heard bad drone with that . To each his own as far the replacement of the exhaust.

 

[Brichinelo]

This is an understatement. When I replaced the OEM catback with my megan racing catback, which still has a pretty big muffler on it compared to other exhaust options for the stinger, I could physically feel the extra power because of how less restricted it was. It makes me very excited to install the downpipe/midpipe combo I have.

We spoke bro. I’m excited for you as I want to follow your route and we both have the Megan Catback

 

[G70LEbyAdoom]

We spoke bro. I’m excited for you as I want to follow your route and we both have the Megan Catback

Welp, i was told yesterday that all the parts are now in, so my car should be done by the end of next week hopefully.

 

[Brichinelo]

Welp, i was told yesterday that all the parts are now in, so my car should be done by the end of next week hopefully.

Sweet. If you can bro provide some sound clips of that combo up kit and Megan Catback .

 

[NYBIOMED]

Really wish Megan Racing would make a catback for the 2.5T. I don't get it, no one else really has an affordable catback yet for the 2.5T, so the opportunity is there. With such a nice refresh of the 2022 GT-Line, I think its selling pretty well, as It has has narrowed the gap with the 3.3TT and is a bargain at $38k and $42k with AWD and the S&S package. The only thing I desire from the 3.3TT trims are those damn sexy Brembos and I'm working on that! LOL.

 

[oddball]

Just deleting the mufflers ? 25hp ? I’ve heard bad drone with that . To each his own as far the replacement of the exhaust.

That's not what I said. Replace them with a catback from your favorite vendor.

 

[1st sting]

Really wish Megan Racing would make a catback for the 2.5T. I don't get it, no one else really has an affordable catback yet for the 2.5T, so the opportunity is there. With such a nice refresh of the 2022 GT-Line, I think its selling pretty well, as It has has narrowed the gap with the 3.3TT and is a bargain at $38k and $42k with AWD and the S&S package. The only thing I desire from the 3.3TT trims are those damn sexy Brembos and I'm working on that! LOL.

Looking for a nice cat back for my K5GT. Only have the midpipe available so far. New platforms are annoying in that respect.

 

[keplaffintech]

Replace them with a catback from your favorite vendor.

A catback alone is not going to make any power gain. As you said, the primaries are the bottleneck in the system. If the primaries are still there you're not going to get any change in flow restriction. In addition, the only way to get more power from the stock setup is to increase boost, lower intake temperatures without decreasing boost, or advance timing.

There's no secret math there, if you expect to reduce back-pressure by removing stock mufflers in the hope of increasing boost, the ECU will compensate and cancel out any effect. If you remove primaries (which actually reduces back-pressure) the ECU will detect the boost spike and go into limp mode.

Even if you lower intake temps, the stock ECU will adjust boost to compensate (reduce boost).

You need a tune/piggyback in order to make more power from bolt-ons, as this will adjust boost and timing.

 

[Brichinelo]

This is an understatement. When I replaced the OEM catback with my megan racing catback, which still has a pretty big muffler on it compared to other exhaust options for the stinger, I could physically feel the extra power because of how less restricted it was. It makes me very excited to install the downpipe/midpipe combo I have.

You get that downpipe midpipe combo on
Your ride yet ?

 

[G70LEbyAdoom]

You get that downpipe midpipe combo on
Your ride yet ?

I dont even have my car back from the dealer yet lol, Hopefully either today or tomorrow it will be ready, then I have Logging I have to do for Lozic, Then I have to find time to put the pipes on. They probably wont be on till the end of april/start of may

 

[oddball]

A catback alone is not going to make any power gain. As you said, the primaries are the bottleneck in the system. If the primaries are still there you're not going to get any change in flow restriction. In addition, the only way to get more power from the stock setup is to increase boost, lower intake temperatures without decreasing boost, or advance timing.

Just about any other car I'd agree with you.
HOWEVER, it's been shown that just installing a cat-back on the stinger 3.3 DOES result in higher HP on a dyno. It's simply shocking, but still true. Usually muffler kits are snake-oil (in the performance department) but not this time. I didn't cut open Kia's mufflers to see WTF they did, but, well, they did something.

That explanation of tuning and power is a little too simplistic. Engines are not digital, and the ECU doesn't have *THAT* precise of control. Any improvement in exhaust flow, even way down at the end, will change the engine's dynamics, and in our case will result in higher power. It's not just about back pressure. The fluid dynamics of intake and exhaust are really f'n complicated.
One way to think about it is the ECU is trying to create a certain type of combustion event at any given moment. What actually happens is something completely different, and the power derived from that event can be different than the ECU expects. The ECU, effectively, has a model of the complete powertrain in its tables and uses that to make decisions. Change anything in reality, and the ECU won't know. Might cause the reality version to "perform" better than the model, might now.

That was one nice thing about carbs. It was clear that we were trying to play a piano with a sledgehammer. Tuning was very imprecise so you made decisions based on outcome. I think we're at a mid-point now where there's a ton more sensors and data, but modeling hasn't caught up. We've just gotten better at knowing the conditions, but not necessarily complete understanding.

 

[Brichinelo]

All good keep the forum posted

I dont even have my car back from the dealer yet lol, Hopefully either today or tomorrow it will be ready, then I have Logging I have to do for Lozic, Then I have to find time to put the pipes on. They probably wont be on till the end of april/start of may

 

[G70LEbyAdoom]

All good keep the forum posted

Thats the plan

 

[keplaffintech]

it's been shown that just installing a cat-back on the stinger 3.3 DOES result in higher HP on a dyno.

I question those tests. Often they're done by the manufacturers of the parts themselves. Here's an example of blatant lies stating that swapping out the secondary cats can give you +30whp, it's just impossible:

If you've got an example of a back-to-back test done by an independent tester I'd be keen to see it.

and the power derived from that event can be different than the ECU expects.

Power is a function of many variables, but unexplainable fluid dynamics in the cat-back, after the stock cat itself, just isn't one of them.

The ECU certainly will react to keep boost at target. So any gains you think you can make by making the car 'breathe easier', the ECU will just adjust the wastegate to ensure that boost stays exactly where it wants it.

This is how tunes make power, they change the target boost and timing so that the ECU will keep the wastegate closed for longer, and the turbo boosts higher. It can do this on the stock exhaust no problem.