some say 2.5 is perfect and 3" is too big. can anyone post a dyno showing how putting 3" hurts/betters a motor. please dont just post what you think or heard. i want FACTS from engine builders who have hands on experiance or people running 3" on their car. all my previous searches yield 900+ fs threads. thanks guys.

 

try doing a search on only the all motor forum. That will limit your results to what you want to see.

In a nut shell I haven't ever seen a dyno on here that I can recall, where a 3" exhaust made less power than a 2.5" on any setup. If you're really serious about this, do some searching, limiting the parameters so you get more specific information. The next step would be to dyno each exhaust on your car and report back as to what worked best for you, then sell the one you don't want.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 00Red_SiR &raquo;</TD></TR><TR><TD CLASS="quote">
In a nut shell I haven't ever seen a dyno on here that I can recall, where a 3" exhaust made less power than a 2.5" on any setup. </TD></TR></TABLE>

/thread

 

doood, if i had the resources (both exhaust,dyno time, tuning time and a six pack of carona), i would do the comparison in a heart beat to prove/disprove this debate. i have searched this on more than one occasion with no real answer. is there not a tuner out there with the above mentioned resources who can provide us with some sort of proof worthy of a place in the faq section?

 

both me and 00Red_Sir are saying that a 3" exhaust will make more power on almost every setup. I have never, ever seen a dyno to show a loss of HP going from 2.5 to 3" exhaust.

From what I understand everything past your header is just restriction.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2LEM1 &raquo;</TD></TR><TR><TD CLASS="quote">both me and 00Red_Sir are saying that a 3" exhaust will make more power on almost every setup. I have never, ever seen a dyno to show a loss of HP going from 2.5 to 3" exhaust.

From what I understand everything past your header is just restriction.</TD></TR></TABLE>


Exactly....and the only way to know what kind of difference it will make on YOUR car is to do the comparison. It sounds expensive until you realize that you will sell one of the two exhausts and only end up paying for one in the end.

 

good points guys. so why does everyone say 3" is over kill if it offers less restriction? is this just a case of "well i heard 2.5 is best so it must be true" without ever receiving proof. ive also heard of loss of back pressure??????? when i was open header for a day, im 100 positive that my car reved/ pulled harder than with exhaust. you would think that 3" exhaust is as close to open header as possible maening it should rev faster. CAN ANYONE RUNNING 3" VOUCH FOR ANTHING THAT IM SAYING? thanks for the replies.

 

why would you want backpressure?

open header DOES give more performance.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ivan93egreppin210 &raquo;</TD></TR><TR><TD CLASS="quote"> when i was open header for a day, im 100 positive that my car reved/ pulled harder than with exhaust. </TD></TR></TABLE>

Really? 100 % positive huh? What did the dyno numbers or track times say then?

 

i'm seriously sure i've posted this at least 10 times... this is my 1.8L lsvtec with pr3 pistons. Open header hit 236, 2.5" exhaust with test pipe hit 228, the green graph is a 2.25 exhaust with 2.5" carsound.

In my experience, as you can see, 2.5" hangs with open header until after 7k rpm; which is when the s2s2 cams start to pull. so FOR MY SETUP, i regret not moving to the 3" system. If you had ITR cams or some bc3's i'm sure it wouldnt make as much of a difference.

all 3 setups were tuned by Todd at CAT. once again.. this is a 1.8L, 81x89mm, oem pistons, toda header

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Combustion Contraption &raquo;</TD></TR><TR><TD CLASS="quote">

Really? 100 % positive huh? What did the dyno numbers or track times say then?</TD></TR></TABLE>

give me a break man. i know my car and i know if its pulling harder so yes i am 100% sure i was faster. my dyno that day was a 1000 hp give or take a hp j/k back on topic..... here is a little thread i came across during a search.


https://honda-tech.com/zerothread?id=2077910

its about back pressure


Modified by ivan93egreppin210 at 9:30 PM 5/13/2008


Modified by ivan93egreppin210 at 9:31 PM 5/13/2008

 

I ran 3" exhaust on a JDM b16a. I run 3" a b18cXX both motors made/make good power. Search on here for my dyno post.

IMO, 3" exhaust is the way to go.

 

the added db's of the 3" is enough for me to just stay with a true mandrel bent 2.5" system

 

One last thing, running too big or too small of a header can hurt power. But I would say running 3" on NA 4 cylinder motor would never hurt power.

 

my personal preference is 3" on 2.0L and up.. i think it is a bit over kill on a b16.. but then again it all depends on the motor and specs of it.. but i see a lot of people making great power with the buddy club spec 2 exhaust and that is 2.5 i believe..

 

a properly tuned setup will "make good power" on a 2.5" however that doesnt mean you're getting "max" power

 

http://bbmoto.net/wiki/index.php?ExhaustTheory

 

cookie cookie cookie

 

98vtec, that is good stuff. so why isnt there something in the FAQ section that shows all this great info you guys are posting? can we add this thread to the FAQ so we can start changing the myth........

 

2nd link under h22..

 

to be honest man i never bothered to look there due to the fact that i dont have an h22.(wish i did) . that thread seems to be geared toward h22 more than anything. might i suggest moving it to the exhaust section along with this thread. the exhaust section only consists of a thread about posting race headers. there is useful info there but what about links for the rest of the exhaust system aside from the header. considering that exhaust plays a large role in an N/A build, i think the exhaust section is very little help in the FAQ section. thanks

 

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
Smaller diameter piping with carefully calculated bends will yield the best results in our situation

Heat soak, air densities, inlet air temp, altitude, humidity, type of driving are all things to consider when choosing an exhaust system

Back pressure yields torque figures (especially in the lower band) and allows the exhaust pulses to pull them selves through the exhaust piping instead of your engine compensating and wasting energy pushing them through, it may be minimal but its less than ideal

max cfm is the ideal goal, since engines are sophisticated air pumps work towards this and you'll make the power your looking for, now ask how much can i spend



Modified by elwuudz2 at 11:48 PM 5/14/2008

 

The science behind it sounds nice, but i think especially built motors will benefit from a 3inch exhaust. A proper header for the setup is even more important

 

science is not fact.

in middle school, everyone learned that science is forever changing. A theory of two weeks ago could be slandered by a theory of tomorrow.

 

you need the back pressure for something called the savaging effect...