00EckoSI

i did my research on this and i just want peoples opinions that have b16 and b18s that run 2.5 or 3" exhausts on a N/A engine..what do they like and what dont they like, and what the advantages and disadvantages are of the exhaust.

EKb20p8r

I have a b20 and run a 2.5" exhaust. It's probably overkill based on the motor's estimated 170 bhp. I would say a 2.5" exhaust is appropriate for 200 bhp, and 3" for like 250+. A b16 would never flow enough NA to see any significant gain from 3". LS-VTEC, maybe.

PROs: sounds deep with a resonator and a large chamber-type muffler.
CONs: loud. Going too big just makes it louder, and worst case creates turbulence in the exhaust stream, hurting power.

madjdmyo217

aw man that means when i get my motor built i have to get rid of my apex ws?

300whpej

all motor applications, turbo builds and supercharged setups would benefit from a 3" exhaust, but anyone not looking to make high hp (280-300whp) will do just fine with a 2.5" exhaust.

ChokolAwt

iTrader: (1)

think of it like open headers. an exhaust thats too big for the setup sacrifices low end torque in exchange for top end hp.

Matt93eg

I'd like to know what B20 you have.

My piping is 2 1/4" mandrel bent to a 2.5" Vibrant. I still have the 2 1/4" piping because that's what my Apexi N1 came with. I just hacked off the canister muffler and welded in the Vibrant.

blkcivic310

im running a b18C1 to a 2.25 muffler shop piping to a 2.25 magnaflow and it sound pretty deep and screams when OT

98civdx

2.5'' will work, 3'' is too big.

Sr420Det

Yeah 2.5 inch would be fine to 250 hp anything more I'd run a 3'. There is a exhaust theory that no back pressure will hurt power (so theoritically u could make more power with the 2.5) at different rpms. I say the less back pressure the better. 3' is hard to make fit right, it can b done but 2.5 is easier

96romaEK

I've got a 2.25" mandrel system now and will be keeping it when I turbo this summer. Should be fine for 180-200whp.

Schister66

As has been said several times over, you do not need a 3" for your setup. I would go with a 2.5" at most...

00EckoSI

bump

DVDr

iTrader: (2)

2.25 to 2.5 .

If you are running a good catalytic converter then a 2.5 will work great.

I tried a 3" exhaust once on a 1.6 ( left from a turbo setup ) , and that thing felt horrible.

Tons of noise, revved quick to redline, but car wouldnt move. I felt it lost alot of midrange torque.

I have a 2.5" setup with cat and chambered muffler. and feels great and dont think im loosing anypower compared to running straight pipe ( maybe 1% )

burnykawizzle

dude honestly ive had a 3inch exhaust and its just too loud. i now have a 2.5 and im happy with it since its not as loud cat converter and mufflers do matter a bit when it comes to sound and power lose so stick with a high flow cat converter

azandford

my d series budie all run 3inch exhausts...they sound like crap and there always trying to convince me that 2.5 is to small.... there pushin 220 and i got about 300... When would a 3 inch exhaust become beneficial?

Matt93eg

I actually got to experiment with this on a Dirt Bike I had. I know its not a car but exhaust theories are the same. The bike had an aftermarket exhaust which was a brand called Super-Trapp. The end of the muffler was closed off and it used a Disc configuration.

The exhaust gases vented out of the muffler through the discs. The more discs, the more flow, less discs equaled less flow. The instructions said you could run a maximum of 12 discs and a minimum of 4. I played around with it, with 4 on there it had quite alot more low end and midrange but seemed to choke up after that. With 12 on there it lost quite alot of lowend power and grunt but really woke up in the midrange and up through the top of the RPM range.

It was neat to be able to play around with it and it allowed me to kinda move the Power band around where I needed it depending on the track.

boxeocampeon

run 2.5 at the most for NA

Sr420Det

Exactly, kinda just a tuning tool but i say that when ur racing a honda car, u will always b up top in the rpm's, so u might as well improve this area the most cause thats where u will b if u wanna go fast. Basically if u want to accent ur power band up top than run a 3inch, if u want to improve it down low run2.25. I wonder where diminshing returns comes into play on either side of the spectrum. I dont think it can b "too big", a straight pipe dumping out the bottom, I guess is the least amount of back pressure u can achieve or maybe 4 big single runners dumping out the bottom lol. Whats to little?, if tuned right could probably make a ton of torque on a small as exhaust

EKb20p8r

I have a B20Z with p8r head, Crower 402s, and Hondata S300.

It isn't about backpressure. It's about attached flow versus turbulent flow. An open header is fine and dandy because the exhaust is able to exit quickly with no restriction. A 3" exhaust, or 4", or whatever, is no good because the motor is trying to push all that volume of gas down the pipe, which is moving too slowly and is no longer flowing right (it's tumbling and swirling around all the way down the pipe). Having a properly sized exhaust can actually outperform an open header because the flow down the pipe creates a sort of venturi or siphoning effect which pulls gas out of the headers.

For a b16 I would estimate 2.25" would be all you would need. Turbo is a totally different concept. The majority of restriction or backpressure is right at the turbine. Creating the largest pressure difference between the header side and the downpipe side becomes the goal, so a larger exhaust is always better (because the siphoning effect is negligible compared to the power the turbo gives you).

Avistar23

2.5 should be more than enough, the only time i have used 3 inch is on high horsepower b20 builds (im talking all motor here) but i still dont know how muhc difference it really boils down to.

Sr420Det

[QUOTE=EKb20p8r;42024973]I have a B20Z with p8r head, Crower 402s, and Hondata S300.

Having a properly sized exhaust can actually outperform an open header because the flow down the pipe creates a sort of venturi or siphoning effect which pulls gas out of the headers.

QUOTE]

So u think u would still make more peak power (up top) with a properly sized exhaust. I understand the concept not much different from sizing ur thorttle body accordingly. The air moves faster when its going through a smaller hole, moves slower through a larger hole but ur getting much more volumn. I still dont know, maybe on a very low power motor. Im sure fading in and out of 90% (whatever ur motor is at its peak) volumetric effiecency has a lot to do with the proper sizing of the tb, exhaust, and even the lenth of the intake. U cant go wrong with a stupid short intake, properly sized tb, and a 3" exhaust on a honda motor. Throw in some short intake mani runners while ur at it and ur peak power will reward u.

Im not one of those people who praise low end torque. I think torque is what women and regular americans think is fast. U know y everyone thinks four cylinders are slow, cause they never rev them high enough and they make no torque generally. Dont bash me saying torque is the true measure of power cause i already know that. Hp is the description of the torque curve and honda motors r pretty flat and pretty long. Keep the hp up and u keep ur torque curve longer, granted it may start later but remember were trying to go fast so we wont be any lower than peak torque anyways. prob wont even c it when u shift to the next gear

EKb20p8r

I'm sorry you have had bad experiences with torque. I understand what you're saying about maximizing top-end power for racing purposes; as long as you have a close-ratio transmission and stay in the powerband then yes, it doesn't matter what torque is below, say, 5000 RPM.

However, a 3-inch exhaust is ridiculously oversized for 90% of the NA motors on here. Since some people are just saying "it couldn't hurt" without having any actual reason to say so, I looked something up.

"As far as ability of an exhaust system to flow enough air for a given amount of horsepower without causing significant back pressure, this is from one of David Vizard's books:

1. For avoiding significant restriction from back pressure, the pipe should flow at least 2.2CFM per horsepower produced.

2. A straight pipe will flow ~115CFM per square inch of area (using inside diameter of the pipe)"

I did the math: According to the formula, a 2.25" pipe would be good for a max of 208 BHP, a a 2.5" is good for a max of 256 BHP, and a 3" pipe is good for a max of 370 BHP. Assuming 15% drivetrain loss, unless you've got over 215 WHP N/A, 3" is oversized and is probably not doing anything but being loud and losing torque. Hope this answers the question.

realis9

Anything after the collector is a restriction. So 3" will be fine.

EKb20p8r

Oh, thanks for simplifying that, I don't know why I bothered to do all that math. However, have you considered that cold, turbulent air is also a restriction? 3" will be LOUD and unnecessary for anything under 200 WHP.

Using your logic, 3.5" would be fine, too, except that the car would drag *** until it burst forth in a magnificent 150 dB roar for the last 300 RPM on the tach.

gibsanez

Lots of K and H builds are doing great with 3" exhaust N/A. Did anyone realize you actually create back pressure when moving to too large of an exhaust for your engine?