Ok, so I was already to go out and get the standard JDM 4-1 DC header and Carsound 2.5 inch cat setup to bolt up to my Greddy EVO exhaust. Now I have read a bit about people second guessing this setup due to the smaller diameter of the EVO exhaust. My major mods are CAI, cams, cams gears, ITR valve springs, Apexi V-AFC, and eventually this exhaust system. Is there a better exhaust set-up for this strata of horse power and cat-back combo or will I not notice a big difference with the JDM/Carsound setup once I get everything tuned? I've read a lot on this but I have not found conclusive evidence either way.

 

bump bump bump

 

Go with the JDM 4-1 and the carsound, but get a custom 2.5" catback. If you have a lot of dough, get a hytech or smsp, if your on a budget (most of us are) pm user kteller8. He was selling custom mandrel bent 2.5" and 3" catback systems for a really good price a while back in the F/I section.

 

from what ive heard...unless ur pushin an a real big am't of horsepower...the bottleneck caused by the EVO from 2.5 down to 2.36 shouldnt be a big deal, however once you start gettin into higher modifications youll feel the difference if you upgrade the piping...this is my concern right now too...however i plan on goin turbo anyway so i gotta upgrade the piping...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by marltonteg &raquo;</TD></TR><TR><TD CLASS="quote">from what ive heard...unless ur pushin an a real big am't of horsepower...the bottleneck caused by the EVO from 2.5 down to 2.36 shouldnt be a big deal, however once you start gettin into higher modifications youll feel the difference if you upgrade the piping...this is my concern right now too...however i plan on goin turbo anyway so i gotta upgrade the piping...</TD></TR></TABLE>

i was just going to say what he said. i also have the evo, and am planning to do the same thing as you guys. there is a "bottleneck" from going from 2.5" to 2.36", but you dont want your exhaust to be too large if you arent making enough power (there is a thread i read very recently about this, im sure you can find it somewhere). unless you are going to make &gt;230 N/A whp, then you will be fine with the 2.36 exhaust. besides, the way i think of it, is getting the JDM ITR header with the 2.5" collector and and 2.5" high flow cat is better than either getting a header with a 2.25" collector (reg DC sports that most people get, i think falls under this category), or a cat that goes from 2.5" to 2.25" (therefore making your system go from 2.5 to 2.25 to 2.36)

 

Your defeating the purpose of the exhaust system if you do a step down like that. Its backpressure city.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">http://www.team-integra.net/sections...p?ArticleID=48

The 2 goals of a header-cat-exhaust system (notice I didn't just say exhaust only) is to:

a) to efficiently remove as much of the combusted inert exhaust gases out of the cylinder.

Remember that burnt exhaust gas is inert or does not combust twice (EGR & fuel economy is another story) and therefore cannot make power if it is in the cylinder...it takes up space in the cylinder and prevents fresh air and fuel from coming into the combustion chamber to make power.

b) to keep the velocity or speed of the exhaust gas leaving very high.

When high exhaust gas speeds are reached, a wake is created from an exhaust pulse leaving the cylinder head (see SurferX's exhaust article here for some nice pics of this wake or pulse). Following behind this wake is a low pressure pulse that acts like a vacuum is created. This vacuum literally sucks in more fresh air and fuel at cam overlap, when the intake valve is just starting to open and the exhaust valve is almost about to close. Since both the intake & exhaust valves are partially open at this time of cam overlap, the header is actually "connected" to the intake manifold & intake port for a brief period. The exiting exhaust gas helps pull in the next fresh intake air & fuel. This is called scavenging. And scavenging is what helps draw in more oxygen and fuel for combustion.
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A mismatched exhaust system will create unessiary backpressure or poor exhaust velocity and you will not get any scavenging.

Stop thinking about exhaust systems are parts performing their own function, instead think of them working together as a system.

Have you done any tests that prove a 2.5" collector to a 2.5" cat, to a 2.36" catback is going to perform better than a 2" collector, to a 2.25" (or 60mm) cat & catback on a bolton B18C1?

Are you aware that slowly increasing the diameter as you get further away from the engine is a method to prevent exhaust reversion and thus increasing exhaust velocity?

 

So if this down-size in exhaust diameter will create back pressure, considering my strata of horsepower, I don't think it would be advantagous to go to a full 2.5 inch system. Is there a different header/cat combo that will work better with the EVO?

 

yeah im aware of all of that...and ive read most of the articles on TI, its where i learn everything, so yeah im thinking 2.25 header for me for now, although im havin trouble finding one...atleast a good affordable or maybe used one...all i was saying is i dont think the bottleneck being a little over a 1/10 of an inch is gonna make much reversion and a significant am't less scavenging...maybe im wrong, and trust me StyleTeg i know u know a lot more than i do, if this is completely off the mark ill delete it...

 

The numbers seam very insignificant, but they really do make a huge difference

consider this

the difference between 2.25 and 2.36 (60mm) in terms of capability of NA HP, before the exhaust becomes inadequate for scavanging is

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
2-1/4" up to 210HP @ the flywheel (about 180-185 whp)

2-3/8" (60mm) up to 235HP @ the flywheel (about 200-207 whp)
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.11 inches and the difference is 20 - 22whp.