Exhaust size

[BryanGrigsby]

I have a na ka24de now, but want a cat back that will flow nicely with a turbo set up further down the road, possibly a ways down the road. How big in diameter should get in piping now? Will too big eliminate too much back pressure and cause a loss in torque?

[XcreatureX]

yes...but i had a 3" na and didnt really notice it..

[BryanGrigsby]

Is 95mm too big? Or should I go for something in the 75-85mm range?

[XcreatureX]

isnt 80 = to 3" i wouldnt go bigger then that

Seth

[BryanGrigsby]

76mm is exactly 3 inches.

[hysteria]

basically what i gathered from reading some research an engineering student did on the subject was that (this is in the simplist way i can put it) it boils down to you do not want back pressure. you want the exhaust to be sized such each exhaust pulse will actually flow through the runners with so little turbulence that they will create a vacuum like state inside the exhaust, effectively pulling on each pulse following it (kind of so the exhaust gases have to work as little as possible to escape).

just get a 3 inch exhaust if you are going to add a turbo later, because turbo's rely on the pressure differential between the manifold and the exhaust in order to spool... the larger the difference the faster the spool. the best setup would be to have no exhaust at all but it's not possible.

[TheOne]

actually its been proven that 3" does not loose power or torque, but increases the hp as much as 15rwhp(seen on dyno sheets), but most people don't get it on n/a cause it just sounds too much(depending on muffler choice and resonator), i'd still get 3" though cause a turbo will like to have free flowing exhaust.

[HolyShiznit]

^^^Thank you for that I was about to say something. Our cars LIKE TO BREATHE. I fyou are going turbo get the biggest you can get, it's not going to hurt it. Honestly.

[hannibal]

95mm is pretty big. IS that the Apex GT Spec. THats the only exhaust Ive seen that big.

Go with the 3" (75-80mm). THere was a huge debate over 3" vs 2.5". As TheOne said, its been shown the 3" is good for NA. If you want to go turbo eventually, I wouldnt go any smaller.

[Checkered-Member]

First lets understand how the turbine works, there are many forces at work, one of them is the fact that inside the turbo manifold pressure is higher then outside, so pressurized air (exhaust) wants to go down its concentration gradient which lies outside of the turbine, this force drives the turbine.

So lets say we had no down pipe, the turbine will work at maximum efficiency, however that’s impractical, the more restriction we put on the turbine the less efficient it will be, so the down pipe needs to be as big as possible, so there is a nice difference in pressure between the inside and outside of the manifold.

The rest however, for street use, meaning that at idle it doesn’t sound like a 420 V8 I would stick to 2.5 so it’s not ultra loud

On a side note: there is a turbo kit out for a 2001-2005 Honda civic, the guy who made it, made a special downpipe for customers in California, there is a cat in the down pipe, guess how much power the turbo kit makes? 30 hp over stock @8 psi, you can get that with Bolt-ons…lol

[nissanfanatic]

backpressure=badexhaust velocity=good.

Exhaust sizing is equally important on turbocharged cars as well as NA cars. The better you maintain exhaust velocity throughout the exhasut system, the more power you make. 3" is perfect size for a mild-medium turboed KA.

Exhaust theory

[Nismo_Freak]

Wow I'm amazed.

For once there aren't 15 idiots putting up stupid commentary that was old hot rod wives tales.

A turbine with a downpipe actually would probably see greater mass flow, mainly because of the seperation of the flows and the postponement of the exhaust condensation. It's beneficial to have some exhaust piping to mainting fluidity.

[crzycav86]

Wow I'm amazed.

For once there aren't 15 idiots putting up stupid commentary that was old hot rod wives tales.

I was thinking the EXACT same thing, and I was considering posting something like that. For once there's an exhaust thread without typical spreading of misinformation. GO NICO!

[Craving4Boost]

ive heard 2.5" can do 300hp just fine

[sunnys14]

2.5" can do 300hp fine but 3" would do even better. If your gonna stay NA for awhile the quietest exhaust ive heard is the Apexi N1, theyre SUPEr quiet on the KA compared to my Blitz NUR spec R. Both my friends have the N1, SOHC s13 and DOHC s14

[GEO]

I ahve an N1 and its quiet. VERY quiet at idle, but once you open it up, ****.... haha

[XcreatureX]

rs*r exmag

[Jookmasta]

BRM with no resonator.......................the hotness (both when i was NA and now)

[HolyShiznit]

I guess it's different for me I plan on running 25+psi so I want big and I do agree about the exhaust velocity, that's why I have an equal length manifold.