baulum

Hi everyone,i have a ek3 sedan with d15z4 non vtec engine and have just done few mods like cylinder head shaved by 0.030'',sport air intake system,oil catch tank,4-2-1 manifold outlet 2'',custom muffler but exhaust piping remain stock with an additional resonator,actually there are two resonators.

Well i think that the stock piping is 1.50'' or 1.75'' and i want to know if i must change the piping to 2'' as i have just removed the stock header and replaced a 4-2-1 header.Thanks in advance.

300whpej

a 2" exhaust is fairly close to a factory 1.75. go to 2.5" if you really want to notice the gains of your motor. dont expect huge gains with simple bolt-on's though. i say you gain roughly 7-10 hp with all the work you've done, with out a street/dyno tune

baulum

I fear that the 2.5'' might be too big for the little d motor,i can lose power.With a 2.5'' also it'll be very loud,what do you think about a 2.25''?Here in my country we do not have dyno for proper tuning,thats why i keep asking from Honda-Tech.

300whpej

2.25 is fine, but 2 will still be slightly restrictive

supra-n-civic

2 1/4 wodl be nice. no bigger if you are staying all motor single cam. if you go to a dual cam ever id say 2.5 would be nice. boosted id say no less than 2.5 but even 3 would be ideal for the street

Rok_Stok

It depends where you want your power. The larger piping you go with, the higher in the powerband your power will be distributed. This is because every RPM has an ideal exhaust diameter for maximum exhaust velocity.

At low RPMs, exhaust velocity is highest with smaller diameter piping, giving you great off the line acceleration and low end grunt for around town.

At high RPMs, exhaust velocity is highest with larger diameter piping, giving you more power up high, but your low end power will be sacrificed.

I stick with stock exhaust piping because I don't race, and if I feel like letting lose on the highway, it does just fine. But having sufficient power for driving around town, and maintaining good mpg, is what I need most. Plus I like the way it sounds.

I've had all kinds of exhaust setups on my B16A. I had the lowest amount of low end power when I had a 4-1 header with a 2.5" collector, a 2.5" test pipe, and 60mm exhaust. The top end was great, but how often are you going to be maxing your engine out on local roads? To me, it's not worth the risk, it's not worth it to your engine, and it's loud. Switching back to stock was so nice because my car sounded good again, and I could just drive it normally without worrying how loud it was, and it takes no effort to get up to speed now.

Your engine has even less torque than mine, so you'll need all the low end power you can get, and if you got big exhaust, it's not like it would be fast. But it's your call, I see people with D15s with header and exhaust all the time.

baulum

I can understand the reason of using big piping.Probably i'll change it to 2.25 as there will be few mods later but not bigger.Thank you all for these info.

Rok_Stok

2.25" is a great size, you'll feel more top end for sure, and low end won't be affected too much. You'll actually pick up some midrange torque.

kmeister

i think id stick with the 2.25 myself.

newtron63h

gotta throw this in there. dont pour money into a d15(except maybe a d15b) at minimum get a d16z6 or d16y8. none of these engines really have much potential without a turbo or MAJOR money in a N/A build.

i think 2" is plenty enough for light mods if you MUST go up in size. 2.25" might be a bit too big and 2.5" is definitely too big for a stockish d15.

newtron63h

thank you for having another way to explain this........ive been trying to get people to understand the velocity vs volume concept for years and very few understand.

Rok_Stok

One good thing about a D15 is the mpg. That's always FTW.

mikej94civex

i run 2.5" on my d16z6 with an apexi resonator and oem non high flow cat, and it's fine!