3" to much for KA?

[esoj1987]

hiim new to the tuner scene and ive been wanting to put a 3" catback exhaust on my 1991 s13 but i heard that 3" is too much and that it would loose power instead of vise versa. is this true. i just got the car so its completly stock. i whant the exhaust more because of sound than performance. i whant it to sound deep and throughty. strong. NOT like the half car half lawnmower hondas at my school.what size of exhoust will give me the performance and the deep rich sound i am looking for.Also what kinda muffler should i get?

-newbee

[DRFT24O]

youll definetly loose low end torque but your up top power will get better. If your gonna stick to n/a i would go 2.5".

[Axel Grungy]

2.25 or 2.5 for n/a ka

[InsanityInc]

so much misinformation.

3" seems to be the best for KA. No losses, big gains (10+ whp).

Dyno:http://forums.freshalloy.com/u...&vc=1

I swear I answer this question every other day.

[nismofly]

and youre also the only one that ever says that...

for the sound youre looking for go with a either a 2.25 or 2.5 inch brm catback.

check out the sound of 2.25 with a few other mods someone put on posted here:

http://www.midwestfbodymeet.com/adams240.html

[InsanityInc]

Seems I have facts to back what I say up. What do you have? Oh, hearsay and no dyno? Well, I stand corrected.

[robbbby]

Must... Resist... Urge... To... Stab....

[TrunkMonkey]

and youre also the only one that ever says that...

actually, i stopped saying it a long time ago since no one seemed to listen.

as far as the original poster is concerned, if you're looking for the best sound then go for the 2.5". unless you add a good resonator, anything bigger is going to be VERY loud. even more so if you decide to install an aftermarket header too.

-demetrius

[jmauld]

youll definetly loose low end torque but your up top power will get better. If your gonna stick to n/a i would go 2.5".

This isn't true, I actually have a completely stock dyno, versus a dyno with 3" exhaust, intake, and pullies, and I didn't lose torque anywhere. In fact it was a healthy gain across the rpm range.

And it's not even very loud, but that's subjective.

[toptechracing]

Have you got those Dyno sheets. I would really like to see them as a comparison if you wouldn't mind sharing.

[nismofly]

i see one dyno, and people on there even were saying one dyno vs. another and one exhaust vs. another can net totally different results. imo its not the numbers themselves but consistency of the numbers, with different exhausts, different mods other than the exhaust, and different dyno runs in different conditions. i know thats a lot, but theres another person on there that had an apexi n1 and lost 5hp from stock, and another that had apexi gt spec that didnt have numbers but said it accelerated real well. its not always the same result by any means...i trust demcj more but i still say consistency wins. if you can consistently prove the gains, and not over stock, but over a 2.5 in exhaust, then i will admit im wrong and shut up

[toptechracing]

Quote »Seems I have facts to back what I say up. What do you have? Oh, hearsay and no dyno? Well, I stand corrected.[/quote]I see a single Dyno sheet that shows a gain over stock. I see nothing that makes a proper comparison to the other sizes mentioned.

[jmauld]

Have you got those Dyno sheets. I would really like to see them as a comparison if you wouldn't mind sharing.

The newest one is at work, I will look for the old one tomorrow.

[toptechracing]

Cool Thanks. I am going to be doing a bunch of dyno work this winter (I hope) on both a 3 valve and 4 valve and it is nice to have other reference data.

[nismofly]

you dont by any chance have a dyno with a 2.5 inch do you? im not saying a 3 inch wont net gains by any means, what i was talking about is i think you can get a bit more from a 2.5 inch than you can from a 3 inch. this is what im wondering...

[jmauld]

No, but if someone wants to send me a 2.5" & 3" exhaust that are otherwise identical, then I'll dyno them. IMO, that would be the best way to figure it out, but even then, the data would only apply to someone who has a car that is set up similarly to mine.

[EstoMax]

just to chime in, i have a 3 inch stainless steel catback with a high flow cat and yes it is loud, but i like it and i think its sounds fine. although im not sure i will get a header because the noise will go up a LOT with that.

loud is debatable though, so depends on your taste. but trust me neighbors will hate you if you have to turn your car on early in the morning. i can easily hear my car idle from my room which is on the opposite side of the house from the carport

max

[nismofly]

No, but if someone wants to send me a 2.5" & 3" exhaust that are otherwise identical, then I'll dyno them. IMO, that would be the best way to figure it out, but even then, the data would only apply to someone who has a car that is set up similarly to mine.

i wonder has greg done this for brm? i havent seen any brm dynos but i know they make like the best exhausts, and they make 2.25, 2.5, and 3 inch exhausts. i wouldnt mind the other stuff on the car, its the difference between a 2.5 and a 3 inch system on a na ka engine that i would like to see. and seeing as it would be on the same car with an identical setup aside from exhaust, on the same dyno, on the same day even, that would satisfy my needs.

interesting well definately have to look into doing something like this...

[i2ice4m3]

This isn't true, I actually have a completely stock dyno, versus a dyno with 3" exhaust, intake, and pullies, and I didn't lose torque anywhere. In fact it was a healthy gain across the rpm range.

And it's not even very loud, but that's subjective.

so you have a stock dyno versus a dyno with all those parts installed, or a stock dyno vs 3" exhaust, stock dyno vs intake, and stock dyno vs pullies?

[jmauld]

two dyno's:one stockone with those parts

Yes I know it's not exactly a fair comparison, but good enough to make the point that I didn't "lose" torque by picking a 3" over the stock exhaust.

I think most of the local guys all have 3" exhausts on SR's, so I don't think I could find anyone locally to let me borrow a 2.5"er, to do a direct comparison.

[InsanityInc]

i see one dyno, and people on there even were saying one dyno vs. another and one exhaust vs. another can net totally different results. imo its not the numbers themselves but consistency of the numbers, with different exhausts, different mods other than the exhaust, and different dyno runs in different conditions. i know thats a lot, but theres another person on there that had an apexi n1 and lost 5hp from stock, and another that had apexi gt spec that didnt have numbers but said it accelerated real well. its not always the same result by any means...i trust demcj more but i still say consistency wins. if you can consistently prove the gains, and not over stock, but over a 2.5 in exhaust, then i will admit im wrong and shut up

Funny part is, they actually tried the 3" because they saw that a magazine made 15rwhp with a 3" exhaust on a KA (he makes mention of it in his post). Also, if you go to OTHER forums, you can find a number of KAs using 3" to great effect. Also, there is no possible way that going to a 3" pipe will make you lose 5 horsepower, unless there's some massive defect in the pipe

[TrunkMonkey]

if you can consistently prove the gains, and not over stock, but over a 2.5 in exhaust, then i will admit im wrong and shut up

i believe you will see a slightly better torque curve with the 2.5" (emphasis on slightly). imo, it won't be enough to say the the 2.5" is ultimately better. personally, i'd rather give up a few ft-lbs down low in order to gain several hp up top. imo, there's waaay too much emphasis placed on torque when it comes to the KA.

i just think that the biggest point that needs to be clarified is that someone who is going from stock exhaust system to 3" won't automatically lose low end power.

-demetrius

[jmauld]

i just think that the biggest point that needs to be clarified is that someone who is going from stock exhaust system to 3" won't automatically lose low end power.

-demetrius

YES!

I still think it would be a good comparison to do a stock vs 2.5" vs 3" dyno on the same car on the same day.

[nismofly]

yes because top end power is not my worry at all, its low end torque that im worried about, because i will be running autocross and limited road racing, and driving on the street you really dont have to worry about top end power as much as you need to worry about the lower end...

i never said you would lose anything with the 3" if you look at my posts, i said the 2.5" would be better for street driving, where im really not going to use the top end power as much, but a little low end would be nice sometimes.

to the original poster - you said you were worried more about sound than performance...to answer your question, a 3" would not lose any power necessarily, but depending on the exhaust, it will be loud. seeing as you live in cali, you might have to use a silencer, which would eliminate the purpose, and you might as well get a slightly smaller pipe anyway. like i said go to that link i first posted, thats the brm exhaust. if you want something very loud, youre not worried about getting in trouble, then you can get the 3", but from what ive heard most systems that big and bigger you can forget about stuff like talking when your on the highway, and youll be waking people up at night with some systems. if none of this worries you go ahead, because the power loss is nothing to worry about, and as you can see nobody can say what the exact difference will be between a 2.5" and 3" in power...

[jmauld]

yes because top end power is not my worry at all, its low end torque that im worried about, because i will be running autocross and limited road racing, and driving on the street you really dont have to worry about top end power as much as you need to worry about the lower end...

Why are you willing to give up high-end power? At an autocross, you are in higher rpm at least as much as you are in lower rpm ranges, and at a HPDE you are hardly ever below 4K.

For autocross, I'd look for a system that provides the most gain across the entire rpm range, with a focus on high rpm. But I wouldn't be willing to give up much low rpm power to get it.

[nismofly]

actually thats what i thought was that you would be in higher rpms, but from what read low end torque is a lot more helpful because the turns are so tight, thats why the jwt autocross cams focus on improving torque, not the top end. i havent run one yet, but people like axel grungy up there have, he helped me and other people a lot with autocross questions, he might be able to help more.

[TravisD]

I actually have a completely stock dyno, versus a dyno with 3" exhaust, intake, and pullies, and I didn't lose torque anywhere. In fact it was a healthy gain across the rpm range.

...good enough to make the point that I didn't "lose" torque by picking a 3" over the stock exhaust.

I dunno...your experiment kinda throws the bird up to the scientific method. I mean, how do you know those other mods don't compensate for a loss, and add up to a net gain; one that would be higher with different sized pipes? You would need:A) a control: bone stock B)experimental set 1: stock + 2.5" pipesandC)experimental set 2: stock + 3.0" pipes

I would go so far as to say the aftermarket systems would need to be of the same manufacturer and type, to allow for the possibility that muffler design could affect performance.

Also, the Nismo catback system is 3.0", and I would guess it was put together with the JDM engine in mind, as that is the majority of their market. The SR20 of course has less low end power, so they probably wouldn't want to sacrifice any (driving on twisty mountain roads would kinda suck with no low end). That is, if they had performance as the key goal during design or even cared.

Oh, yeah, we're talking about for n/a, so the 3.0" Nismo system may be a moot point if I assumed correctly. Wild guess: 2.25-2.5" for n/a (season to taste), 3" for f/i. Stock is like 1.8".
Modified by TravisD at 7:39 PM 11/22/2004

[jmauld]

I dunno...your experiment kinda throws the bird up to the scientific method. I mean, how do you know those other mods don't compensate for a loss, and add up to a net gain; one that would be higher with different sized pipes? You would need:A) a control: bone stock B)experimental set 1: stock + 2.5" pipesandC)experimental set 2: stock + 3.0" pipes

I agree with that, except that doing the experiment on a completely stock car is only part of the equation. The experiment should also be done on a car that's equipped with "common" mods, in addition to a stock car. Again, I have both a completely stock car and a lightly modified car sitting in the garage and I'm willing to donate the time, if I can collect/find the exhausts locally.

My whole point was that this statement is incorrect.Quote »youll definetly loose low end torque but your up top power will get better. [/quote]You "may" lose low end torque, but making a blanket statement like that is just wrong without knowing all of the other variables. Which brings up another issue, any dyno testing will only apply to the type of muffler that was tested. Different muffler types may produce different results with the varying pipe sizes. *edit: just saw that you said that before.

I found my dyno sheet at work, and tried to scan it, but the lines were too light to show up. I've got an email out to the guy at the shop to try to get the file from him.

[AustinSilvia]

hey anyone ever seen the picture with the retarded kid and the special olympics... comparing it to arguing on the internet...

well anyway so all this arguing over cat back exhaust... WOW.

you know depending on the condition of your cat (if it's the original 1991 cat) those gains will be minimal at best. who gives a damn about 5 hp? if you're thinking about buying a cat back exhaust for $500-600 why don't you save yourself some money and weight and just build your own and replace that damn old cat while you're down there. you'll end up spending a fraction of the cost and have a high flow cat that will give you more gains than some "specialty" cat back exhaust that has a name printed on it. you also learn how to weld in the process, unless you have someone else do it for you... welding thin metal is kind of hard if you have no welding experience... but then again if you've got the money to piss away on a special cat back then go you (but i'm assuming you don't because you're asking about this kind of thing here)... you then have an exhaust that does nothing but make noise (however nice it may be the fact is that you will be paying for noise... and $500 is a lot for some damn noise... why dont you drop that $500 into a stereo instead? better sounding noise i think). personally i would save that money for a turbo or something else, but hey that's me.

by the way i built my full turbo back exhaust with 2.5" straight and mandrel bent tubing (most of which i purchased on ebay, except the straight pipes cause i got them at a muffler shop so i didn't have to pay shipping), a high flow cat and a carbon n1 style muffler. good luck. any other questions just ask.

[aznyo15]

Wow this is one of the longer posts I've seen of the 2.5" vs 3" exhaust in a while. I would think people would stop arguing about it after reading the entire FA thread from last year. A 3" is good for the KA24DE and provides gains in hp and torque all across. The dyno was done once with minimal mods and stock exhaust and then with the exhaust replaced with the Pro Racer.

So basically you're looking at 2.5" for sound reasons and 3" if you care more about the gains in power over the sound level. 3" exhaust isn't too loud really, I live in Los Angeles and have never been pulled over for my exhaust. (just don't floor it )