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Dual Exhaust...... For all those who told me NO! Bite ME!


2geepfinder
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FYI dual 2.25" tubes are way bigger than a single 2.5" or 3" pipe

 

cross sectional area of 2.25" pipe (inside) = 3.5466 sq. in

 

cross sectional area of 2.5" pipe (inside) = 4.4301 sq. in

 

cross sectional area of 3" pipe (inside) = 6.4918 sq. in

 

do the math:

3.547 x 2 = 7.094 ie dual 2.25" pipes will flow more than a single 2.5" or 3"

 

There is such thing as too much exhaust pipe. Too big of a pipe hurts scavenging, which counteracts the work you did in the first place. That much pipe, you should be running a HUGE supercharger or turbo for there to be a need. I remember SCC making an article on this before and if I remember correctly N/A engine displacement/exhaust size describes these engines to run best with 2.25 and possibly 2.5" pipe. That setup is overkill on even a V8 engine.

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I've tried many diamters and settled with 2"-2.25" myself. I thought the combination of 2.5" and headers was just too much and when I reduced it I felt a little improvement in my low rpm range and no differance in the other ranges.

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  • 2 months later...
I wanna see your dyno results, when you going!?

Also, did you wind up putting the o2 sensor after the cat?

 

Works had me tied up for the past couple months, I'm now back in Burlington, WA I look for a local dyno here and get back with some results.

 

Yeah, the O2 sensor had to be installed after the cats cause there just wasn't any room to install the x-pipes pre-cats.

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I like it!!

I have to question your driver's seat dyno though. I'm kinda with GG on this one, for $1300 I'm sure I could pull out more ponies than dual exhaust. :shrug:

Your math is impeccable...

DUDE, it's a friggin 3.0 liter motor that tops out before 6k RPM!!!

Unless you have done something significant to the intake (and cams?) more than 2.5" is probably just a waste of metal.

You can hang 6" HVAC ducting and a fart can if it makes you happy, I just won't believe it runs better. :shrug:

 

B

[/quote

 

You have to tell the whole story if your going to tell it at all............. so lets start from the top shall we....

 

Our 3.0L motors have an intake area of 9.6211 sq. in. and an exhaust outlet area of 10.6028 sq. in. (6 outlets 1.5" dia. each with a area of 1.7271 sq.in.). The stock manifolds only have a 2" dia outlet at 3.1416 sq.in. per side which is:

=>(1-(6.2832/10.6028))*100%)) = 40% restriction of flow just at the manifolds. Both then flow into 2" pipes then are collected into a single 2" pipe which is:

=>((1-(3.1416/6.2832))*100%) 50% restriction.

Overall our factory exhausts restricts flow by at least ((1-(3.1416/10.60280)*100%)= 70%. Pre cat and Muffler, so lets assume that they'll add another 10% when their new.

 

So, right off the factory floor say ~ 80% restriction.

 

Let's break it down into 3 options;

 

1) 2.5" Single Pipe system

 

Assumptions;

Pacesetter Headers 2†collectors into 2 -- 2" pipes into 1 -- 2.5" pipe

All calculations pre cat & muffler

 

Calculations;

[(1-(4.9087 sq.in./10.6028 sq.in.))*100] = 53.7%

 

70% - 53.7% = 16.3% increase in flow……..Not bad!

 

2) 3" Single pipe system

 

Assumptions;

Pacesetter Headers 2†collectors into 2 -- 2" pipes into 1 -- 3" pipe

All calculations pre cat & muffler

 

Calculations:

((1-(7.0686/10.6028))*100%) = 33.33%

 

70% - 33.33% = 36.67% increase in flow……Better!….

 

3) 2.25†Dual pipe system

 

Assumptions:

Pacesetter Headers 2.25†collectors into 2.25†pipes

All calculations pre cats & mufflers

 

Calculation:

((1-(3.976/10.6028))*100%) = 25%

 

70% - 25% = 45% increase in flow…….Damn good!

 

 

A couple of things to note the 2.25" Dual system is 2.25" front to back no reduction anywhere. As tight as the 2.25" pipe is I'd imagine it would be difficult to install the 2.5" or 3" without some reductions or additional bends not required with the 2.25" Dual set-up.

 

I'd like to see some photos of the 2.5" and 3" single systems, if anyone has some post them up.

Edited by 2geepfinder
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your equations show your dedication but I think you missed something;

when you open up diameters to "increase flow" the gasses travel thru the pipes at a lower velocity becuse there is more room for them if the velocity is too low it can create turbulance within the pipes and combined with the fact that being able to expand into that area makes the gasses cool faster making them create more tubulance. this turbulace, if present, will disrupt the scavenging process(which heplps draw more air/ fuel into the engine) untill you reach a hig enough rpm to create enough exhaust to rise the velocty to a point where it clears the turbulance.

that being said I'm not going to disprove you results, just providing some for thought. honesly noting speaks better that actual numbers and charts. I had my vg30i on a dyno and I will post my sheet for comparison when you get yours up here. MY low tq band is very flat (desireable) and my hp also is low.

I assume you will show MUCH HIGER HP and higher peak TQ @ a higer RPM but with a steeper TQ curve to go with it.

 

In the end and everyone should agree; you do what makes you happy. And it seems this mod made you happy so enjoi it reguardless of what others say.

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dammit i wish I would have understood my thermal fluids class a little bit more...but I guess depending on your assumptions you could determine if it was turbulant or laminar flow but I think the only accurate way to determine the results is either by doing it and testing (which seems to be in progress) or using software simulations like flowworks to study the flow path

 

you do what makes you happy

 

100% agree b/c i've been semi-flamed on several boards for putting the 94-95 dash/emissions in my 87 and granted i've run into every problem there is but it'll be complete some day and she'll ride like the best of'em and I like to be unique...no matter how many folks don't like it or think its stupid or a waste of time and $ theres always a few that will enjoy it and follow in the footsteps which is kinda the reason we're all here b/c if we were all into ricing out civics we'd be on a different board...

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100% agree b/c i've been semi-flamed on several boards for putting the 94-95 dash/emissions in my 87 and granted i've run into every problem there is but it'll be complete some day and she'll ride like the best of'em and I like to be unique...

thats the curvy dash right? kool. takes allot of determination to do someting like that.

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In the end and everyone should agree; you do what makes you happy. And it seems this mod made you happy so enjoi it reguardless of what others say.

 

There is truth to that, but when you share, you open yourself up for anything that comes.

 

Our 3.0L motors have an intake area of 9.6211 sq. in.

 

So is that figure pre-filter, at the MAF, or at the heads?

 

 

Unless the exhaust is smaller than the MAF opening, there is no "restriction" on the exhaust side.

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thats the curvy dash right? kool. takes allot of determination to do someting like that.

 

eh no determination at all...just engineering experience in the automotive world...granted i've run into every road block and problem there is but it will be complete sometime.

 

I think this exhaust routing would take more determination...

Edited by unccpathfinder
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eh no determination at all...just engineering experience in the automotive world...granted i've run into every road block and problem there is but it will be complete sometime.

one thing to remember when doing all these calcs on area and whatnot.... at any given time only one cylinder is firing, and the exhaust is not a constant flow, it is a series of pulses so regular flow formula's do not apply. thats why an engine with smaller exhaust pipes and a tuned tri-y header will out perform and engine with a huge exhaust and plain headers..... and on another note, if you headers that have the right size primary tubes and are the correct length what you bolt up to them from their doesnt matter unless it is excessively restrictive. the scavenging effect should take place in the header and not in the exhaust pipe

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