3" Exhaust on K20 powered cars?

[spetz]

Hi guys,

Is there a reason why the K20a responds so well to such huge exhausts?
I remember a few years ago 3" exhausts were for high powered turbo cars, and now on NA 2.0L cars

[lil_foy]

Offtopic but damn you make a lot of threads with questions. Legit so many!

[spetz]

Curiosity gets the better of me...

[mrwho]

It’s not just Honda/K20a engines that respond better to larger exhausts…

The header and collector are one of the most important parts of an exhaust system and is where the majority of power is made. After that, you’d want an exhaust system that is as free flowing as possible.

However, people tend to see a drop in torque with large exhaust systems, well, without a tune... This is due to a drop in exhaust velocity which actually creates back pressure for the engine to resist. So, there is a limit to how big you’d want an exhaust system to be. Not to mention the added sound/noise pollution…

[Snoop_gee]

With reponses like this
k20 2.5" or 3" exhaust!!

Its clearly 3" is the choice for many
But your right i have often thought with like Naturally Aspirated cars that 3" is more of a turbo thing and not for N/A.

But after ..

Trial and error with different diameter piping is great, but understanding this from a scientific perspective will give you the knowledge to do what is right.

Larger diameter piping allows exhaust gasses expand and cool as they travel their path
Cool exhaust gasses move slower than hot light dense gas pulses
Keeping the piping diameter smaller will allow the gas to stay compact and thus retaining its ideal properties
The overall design of the exhaust system can also hinder and help as well
gutting cats and running test pipes and open pipes only helps so minimally its barley worth it
N/A 4bangers shouldn't require piping in the 3'' realm
But the 3inch diameter piping with carefully calculated bends will yield the best results and the dyno graphs prove this.

[GSi_PSi]

Green was 2.5 Inch , Red 3 inch exhaust

as you can see, awesome torque and kw gains in the midrange

[dougie_504]

Wow the 3" really shines in that 5-6,000rpm range!

[CRXDEL501]

No replacement for displacement

Let it breatheeeeeeee baby lol

[EKVTIR-T]

How come when my friend put 3" on his dc5 it felt like less midrange after?

Made it feel shit actually

[Snoop_gee]

^ maybe its cause its not tuned properly.
what ECU is it using?

[EKVTIR-T]

^ maybe its cause its not tuned properly.
what ECU is it using?

It was tuned with piggyback

[Benson]

piggyback is the problem. Get a proper ECU in there and he would yield better gains