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Discussion Starter #1 (Edited)
As most of you already know, we are proud to announce our biggest, most demanding financial and knowledge product so far that will be released publicly, later in autumn this year.

It will be a completely new exhaust system, designed completely from scratch. TIG handwelded by the best welder I know. Idea was to offer the best, yet affordable exhaust available on the market for our beloved 4C. We did our best and I believe we succeeded. Dyno graphs, weighs and other specs will be revealed soon.
Before releasing this product to the market I would like to share a few facts about the stock exhaust system, to better understand the goal of our project.

1.) Stock downpipe with catalytic converter (cat):

When you look at the picture of stock 4C cat, you quickly notice a strange, unappealing design. Now there is always a bragging about how good the aftermarket part is over stock part, but there are few things we need to know and respect.

By more and more demanding ecology standards, there is no secret that today’s cars are taxed according to the emissions they produce and manufacturers struggle to get the best performance with least possible emissions and ecological impact. Between these two factors, there is always a tradeoff. It's either performance or ecology.

Stock downpipe with cat on 4C is deigned in a way to be the bottleneck. It is right on a turbo, as close to the engine head exhaust outlet as possible and with curves, tight as possible. This causes very high temperatures which means the best possible performance of the cat, that means the least possible emissions. When you start your 4C you can hear a deep, loud sound from rough running caused by extremely high advanced ignition timing, to make the cat heat up as fast as possible. In a minute or so the cat almost glows and the emissions are as low as possible. The factory has succeeded here for sure.

From performance point of view, the stock cat design is as bad as it gets. High velocity exhaust gases exiting the turbo hit the 90° cat band right away. After that, the 800 cell mesh even further blocks the flow and by now you have killed pretty much all the flow and performance and temperatures are as high as possible. Backpressure is immense. With a basic remap you can already hear the turbo fluttering that is caused by the backpressure. Pumping in even more air is simply rising the temperatures in the head, the pistons, the exhaust system in the intercooler and complete engine bay. Regardless the intercooler you put on, the engine map, the turbo you put on, the factory exhaust system simply won't provide nearly enough flow for anything above 230hp, yet it is perfect for stock engine if low emissions are the main goal.

That is the first chapter. More to follow...
 

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As most of you already know, we are proud to announce our biggest, most demanding financial and knowledge product so far that will be released publicly, later in autumn this year.

It will be a completely new exhaust system, designed completely from scratch. TIG handwelded by the best welder I know. Idea was to offer the best, yet affordable exhaust available on the market for our beloved 4C. We did our best and I believe we succeeded. Dyno graphs, weighs and other specs will be revealed soon.
Before releasing this product to the market I would like to share a few facts about the stock exhaust system, to better understand the goal of our project.

1.) Stock downpipe with catalytic converter (cat):

When you look at the picture of stock 4C cat, you quickly notice a strange, unappealing design. Now there is always a bragging about how good the aftermarket part is over stock part, but there are few things we need to know and respect.

By more and more demanding ecology standards, there is no secret that today’s cars are taxed according to the emissions they produce and manufacturers struggle to get the best performance with least possible emissions and ecological impact. Between these two factors, there is always a tradeoff. It's either performance or ecology.

Stock downpipe with cat on 4C is deigned in a way to be the bottleneck. It is right on a turbo, as close to the engine head exhaust outlet as possible and with curves, tight as possible. This causes very high temperatures which means the best possible performance of the cat, that means the least possible emissions. When you start your 4C you can hear a deep, loud sound from rough running caused by extremely high advanced ignition timing, to make the cat heat up as fast as possible. In a minute or so the cat almost glows and the emissions are as low as possible. The factory has succeeded here for sure.

From performance point of view, the stock cat design is as bad as it gets. High velocity exhaust gases exiting the turbo hit the 90° cat band right away. After that, the 800 cell mesh even further blocks the flow and by now you have killed pretty much all the flow and performance and temperatures are as high as possible. Backpressure is immense. With a basic remap you can already hear the turbo fluttering that is caused by the backpressure. Pumping in even more air is simply rising the temperatures in the head, the pistons, the exhaust system in the intercooler and complete engine bay. Regardless the intercooler you put on, the engine map, the turbo you put on, the factory exhaust system simply won't provide nearly enough flow for anything above 230hp, yet it is perfect for stock engine if low emissions are the main goal.

That is the first chapter. More to follow...
The stock downpipe/cat does look like a piss poor design, so I don’t understand why we are not seeing much improvement with aftermarket DP’s.
 

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The stock downpipe/cat does look like a piss poor design, so I don’t understand why we are not seeing much improvement with aftermarket DP’s.
Everything has to be working as a package. Just adding a different exhaust, down pipe, etc. won't do much without adjusting the overall tune to take advantage of that. That means both the ECU and the TCU have to work in concert. The newer race version ECUs address that somewhat as they can be tuned to match other changes.
I wouldn't be so quick to knock the stock setup....you have to remember that it was designed to meet smog regulations, provide exhaust scavenging, fuel mileage, long life, and the short distance from the turbo was designed to get the CAT as hot as it needs to be as quickly as possible to minimize pollution in the cold cycle. That is at odds with perfomance mods usually.
 

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Everything has to be working as a package. Just adding a different exhaust, down pipe, etc. won't do much without adjusting the overall tune to take advantage of that. That means both the ECU and the TCU have to work in concert. The newer race version ECUs address that somewhat as they can be tuned to match other changes.
I wouldn't be so quick to knock the stock setup....you have to remember that it was designed to meet smog regulations, provide exhaust scavenging, fuel mileage, long life, and the short distance from the turbo was designed to get the CAT as hot as it needs to be as quickly as possible to minimize pollution in the cold cycle. That is at odds with perfomance mods usually.
True. Had a chat with alfa1105 the other day and one of the things he remarked upon was the reduction in heat in the engine bay with his new 3” exhaust system fitted compared to stock...Refer to the ‘Next level’ thread.
Keeping it on-topic, looking forward to seeing the performance improvement with the new exhaust. Is there a matching tune to be developed for the exhaust work?
 

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Discussion Starter #10
Well said RKBerta.

Like already mentioned from a performance point of view and from the build quality aswell, stock exhaust system is quite poor (poor welding, cracking on the Y, pipe, random bends), but very efficient from an ecology aspect (heat). End tips look somewhat cheap Chinese tuning if you ask me, but that's just my personal opinion.

Correct. The true gains will come from a tune, but one very important fact that we have seen lately must not be forgotten. On a completly stock engine, we are already loosing power due to ignition retarding caused by heat soak. Remaped engine gets far worse. With high flow 3'' ehxuast, even with a stock ECU, the HP should be far more stable, and on tuned ECU even more. We will look into the ECU later aswell...

However, I did some fast road driving today. I could definately feel better top end, quicker spool and much less engine bay heat once I came back. I had my exhaust wrapped aswell to keep the temps down. This will be an additional option upon an order for those who don't want to get their hands dirty and full of glass spikes. :D
 

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With upgraded downpipe we can win around 5hp and a bit better engine response. If the tune is pushed more the car actually becomes slower on the street or racetrack due to heat soak (less power on the dyno after a few runs).
Sometimes, from a given engine and turbo it's not much you can ask.
 

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With upgraded downpipe we can win around 5hp and a bit better engine response. If the tune is pushed more the car actually becomes slower on the street or racetrack due to heat soak (less power on the dyno after a few runs).
Sometimes, from a given engine and turbo it's not much you can ask.
And some weight reduction.
 

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With upgraded downpipe we can win around 5hp and a bit better engine response. If the tune is pushed more the car actually becomes slower on the street or racetrack due to heat soak (less power on the dyno after a few runs).
Sometimes, from a given engine and turbo it's not much you can ask.
This is what I was referring to, not a full exhaust with tune. Adding a catless or Hi Flow Cat to the equation will reward you with an additional single digit gain. Hardly seems worth it.
 

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@Gale I really like your approach. Taking the time to explain the benefits and drawbacks of the stock system and your system really sets you apart. I'm looking forward to reading about your approach to the rest of the exhaust.

Sent from my Pixel 2 XL using Tapatalk
 

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+3

I love the sound and functionality of the Akrapovic (sound really, I never actually drive in N so functionality doesnt matter much, lol). I wouldn't want to lose the titanium shriek of the Akrapovic. I had a LE with race exhaust and the Akrapovic is infinitely better sounding IMHO. It also is better sounding than some of the aftermarket units that I have heard, though I haven't heard them all and it's really just because it's titanium.

I would love for someone to design something that corrects the down pipe design and keeps the Akrapovic. I guess the first question is really is it worth it if youre going to keep the Akrapovic, though I suspect it is because I think it's 2.5" and I doubt that is really the limitation of the system.
 

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Discussion Starter #18
This is what I was referring to, not a full exhaust with tune. Adding a catless or Hi Flow Cat to the equation will reward you with an additional single digit gain. Hardly seems worth it.
I think 275HP with stock ECU AW remap or 290 HP with AW Race ECU, the numbers are rather good for 1.75l, bone stock engine. The 3'' exhaust or 3'' CAT alone won't give much without tune in terms of max HP, sure. But if the HP and torque curve stay stable for longer due to less heat soak, and I suspect the power curve has moved a bit to the upper range of RPM. If the engine breathes (flows) better with less backpressure so the turbo doesn't have to work so hard and if the exhaust system weighs less than stock, then there is nothing but benefit.

And for users running modified turbos (hybrids etc.) and remaps, proper high flow exhaust is basically a must, because this is where all of the heat generates from. Only after you get your engine breath (flow) properly, then you should go for remap, bigger turbos, more efficient IC systems etc., otherwise you're just chasing your tail. Remember it is the engine flow that reflects the performance, not the amount of boost. Stock 4C is already heavily boosted, let alone the remapped versions. Of course, you can run higher boost, bigger IC, bigger turbos, yet you heat the air more and the result is unstable engine that looks promising on the dyno but it is actually quite poor on the track. It is a huge difference wheatear you have 290 HP on a dyno for single run, or you can actually maintain 290HP on the track on long straights. A huge difference between "dyno queen" car and track car.

It is like running slicks on a stock car with too soft suspension, improper alignment etc. Slick tires will genereate more grip than street tires, sure. But yet far less than they could with proper alignment and suspension. You do benefit, but nowhere near what you could have with a smart approach. It is the same with the engine.

Let's wait for dyno runs, shall we?
 

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@Gale I really like your approach. Taking the time to explain the benefits and drawbacks of the stock system and your system really sets you apart. I'm looking forward to reading about your approach to the rest of the exhaust.

Sent from my Pixel 2 XL using Tapatalk
That exactly how I learned to know Rudi in real life! He is caring, takes his time for your opinion. I hope he succeeds in his project, and if so, will gladly follow him!
 

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Let's wait for dyno runs, shall we?
Excellent approach, let numbers do the talking. And you are looking at why OEM design is like it is, not bashing it. A lot of aftermarket suppliers do this, and it in fact shows a lack of knowledge/understanding. And sometimes, it shows that OEM wasn't that bad after all, or better, than aftermarket. I saw some of that on my previous car. And if they managed to exceed OEM, a lot was done to hide the secrets, and disrespecting others who went down the same path.

A guy with your approach, drove that community single handed forward by think, share, try - over and over. Presenting numbers why he think like he did. Usually, he had the best suggestion, but sometimes other members had improvements/suggestions he followed. An example to follow.

And mentioning this, he discovered that relatively modest differences in tubing, and modifications regarding turbine back pressure, could give more positive gain than might expected. And the slogan; Everything affects everything. For example turbine pressure ratio; after experimenting with different exhaust setups, to get PR down the last bit he desired, he went for another intercooler with less pressure drop. This resulted in turbine had to do a bit less work, lowering PR to more healthy level. If you can ever call turboing a rotary engine healthy....
 
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