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Discussion Starter #1
Okay so I am looking for exhaust options for my NA. I have heard though that NA cars need a certain amount of backpressure for the upgrade to be worth it. I am not sure what the stock exhaust size is, but I know that 2.5 to 3.0inches is an upgrade from stock. I haven't seen too many exhausts for these cars that are NAs and was just wondering which size should I go for. Originally I was looking at the HKS Super Dragger which is 3 inches, but would that eliminate the backpressure that I need? Also please lemme know your results if you have an aftermarket exhaust on your NA.
 

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Piyaud-Baka
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I got the HKS sport Catback, 2.5 inches, looks stock, but its just right, I think 3 inchs is overkill on a N/A unless your gonna swap to turbo
 

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Deffinately dont go over 2.5 in. Anything more is overkill. Your options are HKS sport, Pacesetter Monza, or a custom made one. However any of the Cat backs for the turbo model will work however I wouldnt recomend them cause they are 3in or bigger. The HKS is now getting hard to come by as HKS discontinued that exhaust. I personally have the Pacesetter one and love it. It looks stock, sounds nice, pretty cheap, and gets the job done. Anyhow thats just my .02 cents. Good luck and do it right.
 

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Discussion Starter #4
Are there any options that have a single tip exhaust? I kinda don't like the look of dual tips.
 

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AlexSmith said:
Are there any options that have a single tip exhaust? I kinda don't like the look of dual tips.
someone correct me if im wrong but I believe the HKS sport has dual tips. I know the pic they show is single but thats a general pic. I know that the Pace setter one is dual because I have it on my ride. I think if you want single your best bet would be to custom make one which isnt really hard. Or you can go with one of the turbo model exhausts but as said before those are bigger than 3". Anybody else have any ideas for this guy or have I pretty much covered every option?
 

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i put 3" on my my na with a sort of generic dual tip muffler. never had any problems with back pressure. i plan on doing a turbo swap, thats why i went so big though. sounds great though.
 

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Discussion Starter #7
stiles87 said:
i put 3" on my my na with a sort of generic dual tip muffler. never had any problems with back pressure. i plan on doing a turbo swap, thats why i went so big though. sounds great though.
Do you notice a good gain in power with that exhaust setup, also is that a catback or entire system from headers?
 

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Hardcore Night Warrior
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From an "old" engine builder I was once aquainted with on a forum I was once on, his knowledge never ceases to run out.

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

http://victorylibrary.com/mopar/header-tech-c.htm


http://www.burnsstainless.com/TechArticles/Theory/theory.html

http://grapeaperacing.com/GrapeApeRacing/tech/exhaustheaders.cfm
the short answer is ANY BACK PRESSURE IS BAD!
what your trying to do with a correctly designed exhaust is to have the majority of the exhaust system act like extended collectors on the headers, in effect useing the inertia of the hot exhaust pulses from each cylinder to cause a cyclic low pressure wave to be timed to assist the next firing cylinders to scavage the cylinders

heres the info you need,
http://www.enjoythedrive.org/content/?ID=26046

http://www.enjoythedrive.org/content/?id=10185


http://victorylibrary.com/mopar/header-tech-c.htm


to adjust for your altitude
http://rshelq.home.sprynet.com/density_altitude.htm

and if you want to get it perfect you should usr your DYNAMIC COMPRESSION RATIO VOLUME in the formula at the rpms for peak hp that your engine makes

http://cochise.uia.net/pkelley2/DynamicCR.html
most of the time that comes out close to the same as the static cylinder volume at the peak torque f.y.i.

LET ME ASK THIS QUESTION?
WHATS THE FIRST THING YOU DO AT THE TRACK TO YOUR EXHAUST SYSTEM?
you open the headers to have less back pressure correct!!
BACK PRESSURE IS BAD, BAD,BAD, the idea has gotten around that you need back pressure to build torque, FALSE!!!!!! that IDEA was prevalent because if you stick too large of an exhaust pipe on a low rpm engine it loses the ability to scavage the cylinders with the exhaust gas pulse in the exhaust with stock exhaust manifolds, some how the old wifes tale got around that you needed back pressure...FALSE.. what you need was EFFECTIVE CYLINDER SCAVAGEING which the smaller tail pipe dia. was provideing by acting like the collector on a set of headers!if you have headers , especially full length headers with a merge type collector you can,t make the exhaust too large,THINK ABOUT IT! the first thing you do at the track is un-cork your headers....why? because YEARS OF TESTING PROVES, less BACK PRESSURE MAKES MORE HP WITH HEADERS!!!! now some one is saying yeah but thats at the track and your running the engine at 5000rpm-6500rpm , well true and a good point because we typically only run 1000rpm-3000rpm on the street what it shows clearly is the collector on a low rpm engine needs to be about 10ft long for max effect so you need an exhaust that works with a collector thats about 20" long at 6000rpm and one 10 feet long at idle, THATS WHERE THE IDEA OF TOO LARGE A EXHAUST comes from but as long as you follow these rules youll be fine, READ THIS,

http://victorylibrary.com/mopar/header-tech-c.htm


btw Im writeing this like this to get you guys to think about it then we will look into the answers of how to get both ends of the rpm range covered and yes Im leaveing out some info on purpose





is exhaust back pressure killing performance ?
its a fast easy test that needs to be done and more than a few cars running older cats are having a restricted exhaust thats hurting your performance badly, and because the problem tends to build up slowly many people don,t notice the gradual power loss
first thing youll need to realize is that the TEST POINT needs to be after the header collector and in front of the CAT AND MUFFLERS. next thing you need to know is that to get a valid answer youll need to have a long connector hose so someone in the pass seat can CLOSELY WATCH the gauge as you accelerate under load (FLOOR THE CAR THRU THE FIRST 1-2 GEARS and watch the pressure surge. readings above 1psi mean somethings partly restricted, readings above 3psi are hurting your performance BADLY
the test kit is about $50.00
http://www.jdsdiagnostic.com/eptspage.htm

ITS NOT RARE TO LOOSE 20% or more of your hp to a restricted cat
your unlikely to lose much if any hp especially if you install an (H) pipe just before the reduction in tail pipe dia. and use a gradual reducer to change from 3' to 2.5" mostly because the exhaust gases have cooled a great deal by the time they reach that point in your exhaust system and with that heat loss a reduction in voluum and potential back pressure



http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1313&prmenbr=361


http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1306&prmenbr=361
now the thing that most people overlook is the TIME BETWEEN PULSES and the DISTANCE THOSE PULSES CAN TRAVEL BEFORE THE NEXT TIME THE EXHAUST VALVE OPENS and the necessity to time the returning negative wave to be at the exhaust valve for the following exhaust pulse, first read this http://www.geocities.com/MotorCity/Track/6992/vizard.html
http://www.burnsstainless.com/TechArticles/Theory/theory.html
 

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AlexSmith said:
Do you notice a good gain in power with that exhaust setup, also is that a catback or entire system from headers?
noticed a good power gain. its just from the cat back becuase i plan on swaping in a 7mgte and it would have to be replaced so there is no point.
 

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Discussion Starter #10
Holy information Batman!
 

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I noticed a good gain on my NA when I put doug thorley headers and a monza 2 1/2in catback on. Kept good response down low and it opens up nice higher in the rev range.
I did have a straight through muffler on once and aside from being too loud it seemed to make it sluggish at low revs. I am changing to a 3in system now though as I have a GTE to go in. NA exhaust is for sale soon....
 

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don't go over 2.5 if you're not planning with the turbo, and make sure u have the cat converter in place, i have 2.5" exhaust i took the cat off and car lost torque had to put it back in, then i added a silencer into the muffler and pickup was even better, so yeah the N/A does need backpressure
 

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just make sure you do a FULL system rather than just a cat-back. Remember, you want the same diameter (or as close as you can and keep it legal) the whole way through for proper scavenging.

If you do happen to go with a cat-back that was for a turbo, leave the silencer in and see how you like it. I noticed a considerable loss in low end throttle response after I removed it.
 

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Hardcore Night Warrior
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maciejk said:
don't go over 2.5 if you're not planning with the turbo, and make sure u have the cat converter in place, i have 2.5" exhaust i took the cat off and car lost torque had to put it back in, then i added a silencer into the muffler and pickup was even better, so yeah the N/A does need backpressure

Did you bother reading any of the information I supplied? :scratch:
 

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chevydude said:
From an "old" engine builder I was once aquainted with on a forum I was once on, his knowledge never ceases to run out.

Holy crap that's detailed. Up until you posted that, I've always heard and believed the old backpressure myth you referred to...I'm not smart enough to understand all those fancy words, anyone translate? :)
 

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More info for my NA homies.

Grunt, grunt, back pressure bad. Remove exhaust gasses effectively (cylinder scavenging) good grunt, grunt. :)

During the exhaust stroke, a good way for an engine to lose power is through back pressure. The exhaust valve opens at the beginning of the exhaust stroke, and then the piston pushes the exhaust gases out of the cylinder. If there is any amount of resistance that the piston has to push against to force the exhaust gases out, power is wasted.

In a normal engine, once the exhaust gases exit the cylinder they end up in the exhaust manifold. From the manifold, the exhaust gases flow into one pipe toward the catalytic converter and the muffler. It turns out that the manifold can be an important source of back pressure because exhaust gases from one cylinder build up pressure in the manifold that affects the next cylinder that uses the manifold.

The idea behind an exhaust header is to eliminate the manifold's back pressure. Instead of a common manifold that all of the cylinders share, each cylinder gets its own exhaust pipe. These pipes come together in a larger pipe called the collector. The individual pipes are cut and bent so that each one is the same length as the others. By making them the same length, it guarantees that each cylinder's exhaust gases arrive in the collector spaced out equally so there is no back pressure generated by the cylinders sharing the collector.
This help?
 

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I think im going to continue to believe my "myth". Im not ready to jump on some guys bandwagon just because he has a descent point. Thats the only time Ive heard something like that in my life. Im going to need some solid advice from an expert to believe that. I ran my car for awhile with a 3in exhaust and it felt horible in the low end and deffinately was loud as hell. As soon as I put the 2.5in on it was great all through the RPM range. To me that means more than something Ive read from someone I dont even know. So to the person who started this thread ill tell you what you try both and pick what works best. Im just telling you what worked best for me.
 

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Discussion Starter #18
wusaint36 said:
So to the person who started this thread ill tell you what you try both and pick what works best. Im just telling you what worked best for me.
Hiya! I started this thread looking for just some good ADVICE and EVIDENCE from those that have tried both. There is no way that I will pay to test both options now. My car is NA, and from the looks of things, may stay that way for awhile. I was definitely NOT looking to make some people upset or anything. Anyway, what are anyone else's takes on the subject.

P.S. is this sticky worthy, though it's not for turbos? :scratch:
 

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AlexSmith said:
Hiya! I started this thread looking for just some good ADVICE and EVIDENCE from those that have tried both. There is no way that I will pay to test both options now. My car is NA, and from the looks of things, may stay that way for awhile. I was definitely NOT looking to make some people upset or anything. Anyway, what are anyone else's takes on the subject.

P.S. is this sticky worthy, though it's not for turbos? :scratch:
Ahh nobody in here is really angry. If i came off that way sorry. Anyhow if we could get some more input with everyones opinions I think its deffinately sticky worthy.
 

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First let me say this, a stock exhaust manifold and a header are not one in the same. They may do the same basic job, but they work totall different on how they route exhuast gasses. Second, the shorter piece of info is from howstuffworks. The large post was from a retired Mech Eng who's been building engines for like 30 years already. This info has been around for a long time though, the only thing is that we've been beaten to death with this back pressure myth that it's hard to believe anything else, especially when people put large exhaust piping on a car with a stock exhaust manifold. What happens in a stock manifold is that these exhaust gasses are all colliding with each other and aren't getting expelled at an effective rate causing back pressure. Slowing down your exhaust gasses reduces power simple as that.

Now a header is designed in such a way that each exhaust pulse travels in it's own pipe to avoid collision with other exhaust gasses. These headers are also designed to expel the ehxuast in sequence one after another instead of colliding all together at once like a stock manifold so that they arrive at the collector so they don't collide and create unwanted perf robbing back pressure. This is the reason why headers have all those bends and sometimes loops in them so that they exhaust evenly with out collison.

Stock exhaust manifolds DON'T have equal length exhaust pipes and your header collector either and when your exhaust gas get's exhausted they all collide with each other in the manifold creating unwanted back pressure. Because of the fact that your mani doesn't have equal length piping and a collector you will put 2.5" piping that ACTS as a collector and equal length piping in order to create quasi-effective cylinder scavenging, instead of a truly effective cylinder scavening that you would have with a header. When you put a 3inch diameter pipe on a stock exhaust manifold you lose that quasi-effective cylinder scavenging effect you had with the 2.5" piping. This in turn makes people think they are losing backpressure and losing performance, wrong, you are losing "effective" cylinder scavening and performance.


Situation 1.) A good way to try and understand this concept is that you have 100 people in a room thats on fire and all of them trying to get out of it at the same time (exhaust gasses are the people and getting people out of the room is effective cylinder scavenging ). The only way out to get out of the room is through one door (stock exhaust manifold). It doesn't take an Einsten to figure out people are going to be running into each other and have trouble getting out of this one door (back pressure). Now in this same room their are a few windows, and in order to try to get more people out of the room they climb through windows (people climing through windows are the quasi-effective cylinder scavenging like mentioned above). Obviously climing through windows or running towards one door isn't an effective way of getting out of a room that's on fire.

Situation 2.) Now, let's switch this up a bit. You still have 100 people in a room that's on fire and all of them are trying to get out (again, people are the gasses and getting people out of the room is cylinder scavenging). Instead of getting out through one door and a few windows we now have 100 doors for all 100 people (100 doors are the headers which allow effective cylinder scavenging). I don't know about you, but I think situation two is the most logical way to get out of a room that's on fire.
 
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