Exhaust size?

[ON3_T1M3]

I finally scrapped some money together after getting my 240 fixed, i have a friend with a 350z, and he has gotten sponsered by a local performance garage, i went out there the other day to see their dyno in action at an event they were holding, got to talking to one of the owners and he said that they could do a full custom exhaust with a magnaflow muffler for 250-300 bux, have over 600 saved up and a paycheck coming i was all for it. the only question remains 2.5" or 3" ??? not sure which way to go yet, ne ideas/opinions

i'm also looking into a header seeing as though i still will have money left over, any advice on brands that make a good header for the KA? thanx for the help:)

[214kka-et240sx]

hotshot headers are the best IMO, as for piping i think, 2.5 would be better i dont think 3' for a n/a engine is good

[240DRFT]

go with 2.5"...you can check ebay for some headers, but hotshot is good

[xekushnr]

n/a cars have a louder exhaust note than turbo cars do. unless you plan on putting down more than 300rwhp, 3" will not be necessary. in fact, it would be overkill.

[biggie]

3" is fine on an NA KA. It has been dyno proven that you get HP gains and no torque loss.

[ON3_T1M3]

but how is 3" gonna sound on an N/A? i want the performance but i also don't want it to sound like complete ****, or totally ricey u know.

[ForsakenTH]

i would still go with 2.5"...while 3" might gain hp...its all at the top so you never really get to it...2.5" wont increase your top end much but it will bring up the bottom end...the end you use more.

[naed240sx]

Where are these dyno graphs? I have not seen anything like this, and everybody who knows what they are talking about says go 2.25 or 2.5. Not to be an *** or anything, but if all the turbo guys are going 3 ", why do you think that a NA car should use 3" as well?. Remember, its exhaust velocity, not backpressure that has a direct effect upon efficiency and horsepower. 3" piping is too large for a 2.4 NA motor. Backpressure will be low, but because of overly large piping, exhaust velocity will be lower. to answer the question posed by the creater of this post... yes, 2.5 sounds good- hope it turns out well.

[mrflip69]

UGH

You're the guy that rubbed gasoline on your paint... and now you're telling people about 2.5 exhausts. That's funny, you almost have the right idea, but you flip it around at the end.



There you have it, 3" is NOT overkill for the KA24DE. Maybe other N/A engines, but because of the size of its displacement, it is not a factor.

Here is the original thread:

http://forums.freshalloy.com/u...art=1

This info should be stickied somewhere because people continue to spread around misinformation, even though it has already been proven. Show me a dyno of a 3"+ exhaust causing a substantial loss in hp/torque.

[JimmyMethod]

Anybody have a dyno of their car without headers? THAT would REALLY solve this issue.I don't know about the KA, but I've seen several cars that HAVE lost power with a massive exhaust system or no system at all.Now, I don't know if that's true for the KA, and that dyno graph seems to suggest it isn't, but, looking at that dyno, the temp was about 5 degrees off, and althought that should make it move in the other direction, I'd like to see a dyno sheet with more closely controlled conditions.

[ON3_T1M3]

I just got contacted by the guys at the shop they can get me a header for a good price, so i think i'm just gonna do everything threw them, (at least the header and exhaust) as for the exhaust, i've been thinking about going with the 2.5, i have no plans (aka no funds) for forced induction, right now i'm leaning to the 2.5 but it could change i haven't set nething in stone yet, ? does ne1 know how the KA N/A sounds with a header and a 2.5 or 3" exhaust? if the 3" sounds ridiculuous i won't even consider it, but i'm thinking it won't be too huge of a diff.

[naed240sx]

Thanks for the dyno graph.Referencing sport compact car's article , 3" sounds huge. 2.4 liter = 2,400 cc, so scc reccomends 2.25" diameter piping. I just have a hard time believing that all of the exhausts designed for turbo 240s are only 3", if 3" is the best for NA.SCC's claims seem to be conflicting in our two references. Their article is listed below:http://sportcompactcarweb.com/...part2/

And as far as the gas on paint, you need to stop dwelling on that post. This was a solution that worked for me, and did not strip or damage any of my paint. I was simply trying to be helpful and posted the truth about my situation, so please don't reference to that post in an effort to prove that I know nothing about cars.

Thanks

[ON3_T1M3]

well thanx for all the input i'm still not positive which way to go, but it's looking more like 2.5" hopefully i will get it all installed ina couple weeks, and have some dyno results to,

[biggie]

Mrflip, thanks for looking that up.

And as for the sound its gonna depend on the exhaust system used. I have a Tanabe SMR, its very deep and loud (without scilencer), sounds very good. My old HKS 2.5 Hyper sounded about the same, just not quite as loud (but that was on a different car, etc).

As a note, it may occur that magazines may not know everything, especially SCC.

[240marcuSX]

of course the bigger the piping the more gains, to a point.

but trust me, 3" on NA sounds like crap, and would suck for daily driving, i had a 3.25" exhaust on mine for about a week, and had to take it off and sell it because it was ridiculous.

[ON3_T1M3]

thanx alot, i just talked to the guys at the garage and will be heading over there hopefully within a week for a downpayment. i discussed this with them and we decided on the 2.5, cutsom made mandrel bent, with a magnaflow muffler, i'll try and get pics, and some dyno results up ASAP

[All_Motor_KA]

of course the bigger the piping the more gains, to a point.

but trust me, 3" on NA sounds like crap, and would suck for daily driving, i had a 3.25" exhaust on mine for about a week, and had to take it off and sell it because it was ridiculous.

3.25" is different then 3". My friend has a N/A s14 with a 3" and it's the nices sounding 240 I've heard. Get a good muffler and you will be fine.

[mrflip69]

Thanks for the dyno graph.Referencing sport compact car's article , 3" sounds huge. 2.4 liter = 2,400 cc, so scc reccomends 2.25" diameter piping. I just have a hard time believing that all of the exhausts designed for turbo 240s are only 3", if 3" is the best for NA.SCC's claims seem to be conflicting in our two references. Their article is listed below:http://sportcompactcarweb.com/...part2/

And as far as the gas on paint, you need to stop dwelling on that post. This was a solution that worked for me, and did not strip or damage any of my paint. I was simply trying to be helpful and posted the truth about my situation, so please don't reference to that post in an effort to prove that I know nothing about cars.

Thanks

Sorry, I meant no offense by my post. It just irritates the hell out of me when speculation is taken into account over cold hard facts. The SCC article just lists generalizations as a rule of thumb, and does not even back up its claims. We can argue all day about exhaust THEORY, but in the end, the dynos always come out on top.

Again, my apologies for coming off so harsh and bringing up another thread. I took it quite condescendingly when you "called out" the dyno graphs proving 3" exhausts on a KA.

Of all the exhaust threads I've read, everybody who installs a 3"+ system on their cars seem to think they've lost low end torque, perhaps this is just a case of mind over matter, being intimidated by such large piping.

I digress. For the particular author of this thread, he has made a wise choice in sticking with 2.5". Yes, 3" would probably yield the same gains, but if he's not looking for more and is concerned about cost and noise, then he's better off with 2.5".

Good luck with the exhaust. Try comparing the cost of the custom system to that of AZHitman's BRM before you finalize any purchases.

[ON3_T1M3]

it's a local shop which i like alot better than shipping, ( i have had some BAD ebay expiriences not with car parts but just in general) quoted at 250 bux and they can get me a header for 200, so i'm prolly gonna do it threw them, if my parents don't go totally anal on me,

[dfw240_EE]

Mrflip, your dyno graphs compare two cars, one (the dark blue hp line) with 3". The green HP line, is that a car with the AEM cas with stock exhaust or 2.5"? I would also like to see a similar dyno of 3" vs 2.5" if you might have one.

However, I am surprised that the 3" doesn't shift the peak any at all.

[mrflip69]

It's the exact same car. Green is stock exhaust. Yeah, I kinda got confused a bit when I first read the original thread, until he bishez at some guy for interpreting "baseline" as something other than stock. Baseline is relative anyway

[dfw240_EE]

Well, if I make it big, I will get both a 3" and 2.5" BRM for my car, and dyno both

[InsanityInc]

I have a 3" BRM system, and while it's fairly loud, it's not the kind of loud you get a ticket for. Also, there is definitely no torque loss, I have to drive up some steep hills every day.

[nismofly]

either way the power difference on an NA car will be nothing you could tell with a butt dyno, therefore the 2.5" which is quieter would probably be the better idea

[dfw240_EE]

I suspect that if anyone did a comparison between a 2.5" and a 3" system on a dyno, there would be negligible difference. That is just instinct talking though.

[cyrus240sx]

maybe i should dyno my car... because right now i have a gt spec exhaust on an N/A motor, and thats like 3 3/4 inch piping!

[masticatingcow]

I'll go to bat for big stinkin' exhausts. I'm running the A'pexi N1 Dual catback. From the cat, exhaust runs into a 3" collector pipe, and a couple inches back, splits into two 2.5" pipes all the way back to the canisters. A crosssection of my pipes has an area of about 9.8 in^2, where as the 3" collector has an area of around 7.8 in^2. Assuming an exhaust system flows only as well as it's most restrictive part, we'll say that my exhaust is a 3" system.

Not only did the top end open WAY the hell up, but I got some definate GAINS in the low end. There are hills around here that I could not accelerate up in 5th before I got the exhaust. Now, at about 2500rpm, I'm able to charge up those same hills with a little more authority in the same gear.

Just my $0.02, but I don't believe the KA suffers AT ALL with a larger exhaust.

Believe what you like, though.

[nismofly]

that exhaust is meant for the exact purpose you described it for though...

the smaller piping diameter improves on the low end and the higher flow from having two pipes improves the upper rpm range

[masticatingcow]

Okay, I understand that increase the surface area of the pipe relative to the volume of air increases friction, and therefore backpressure. But how effective can that theory be when each pipe on my exhaust is flowing about half the volume that a single pipe 2.5" catback does? It doesn't make sense.

The only explanation is that the 3" collector allows the KA to flow enough gas into the twin pipes to make the theory effective, which means the KA flows enough gas to make a lone 2.5" pipe too restrictive.