3 in cat back, is it to much??

[s13rb25det]

hey I have a bone stock 91 240sx with a bone stock ka24de! I am looking at turbocharging it some time but right now the exhaust system is falling apart! so I want to upgrade it to like a 3in catback I am just wondering if this is to wide for a NA four cylinder?? it would be perfect when I TURBO CHARGE my car but will I lose power untill then!? what are you guys using? thanks oh, also what is a good catback for s13s? for power and low noise!!! no rice sound! thanks Roger Larson

[EstoMax]

3 inch has been dyno proven to not lose power with ka24de's , they like big exhausts : )

~10whp max gain on it

so go for it.. i have one.. its kinda loud and my friends hate it but who cares

[ddgsxr504]

No offense to you (sr13rb25det) but before this thread starts WW III up in this bisch "again" MODS please lock this F'n thread!

Dude I know you are new so I will tell you what to do! Please don't take this as me being an A hole but I see this same question at least once a week from some one who just bought a 240 and asks the same question you just did. Use the search button on the top right or even go back a few pages on this forum and you will find at least 3 other posts just like yours. The reason I say this is because last time someone asked this question the whole damn NICO community almost had a civil war over this subject. You can read all about it when you find the thread! Good luck!

[Dattebayo]

No reason to lock this thread.

It has been proven that 3" exhausts will improve your overall power, but they are LOUD and there will be a loss of torque (comparibly to stock) throughout your lower (2K-4K) powerband.

Its not the end of the world, but some of those Hondas that you may want to smoke will get the goat on you early if you do this mod.

I hope that InsanityInc posts in this thread...

[lrb_2000]

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

[hek1620]

3 inches it is.

[InsanityInc]

No reason to lock this thread.

It has been proven that 3" exhausts will improve your overall power, but they are LOUD and there will be a loss of torque (comparibly to stock) throughout your lower (2K-4K) powerband.

Its not the end of the world, but some of those Hondas that you may want to smoke will get the goat on you early if you do this mod.

I hope that InsanityInc posts in this thread...

Well, you get your wish, but you're blatantly wrong. Since you have apparently missed the dyno graph every time it's been posted showing that there are NO losses anywhere in the powerband compared to stock, here it is again:

[Ni2s4s0aSnX]

3 inch is good. You won't loose anything from it before you get the turbo, and you'll need to have at least a 3 inch when you put the turbo on it. But if you're one of those people who think that you can just pop a turbo on a stock 240 and call it good, you're wrong. There are more mods that you'll need or else the engine won't be able to handle the turbo as well. You'll need at least a performance clutch and flywheel. But companies that make good exhausts for the 240sx are GReddy, APEXi, HKS, etc.

[lrb_2000]

basically any 3" mandrel bent straight-through exhaust is going to show the same gains. .. you don't have to necessarily get a name brand... I have Megan Racing 3" Catback, and it sounds nice N/A, very good quality, installed in like 10 minutes, and only $365 shipped.

[Dattebayo]

I was drinking when I wrote that, so let me clean this up a bit

Yeah, they are good and the pdrop I was talking about is that annoying drop in torque from 2K-4K in the dyno graph. Somebody find a dyno graph of a 2.5 inch pipe and the curve is much smoother rather than coming on strong and losing power, then re-gaining it again starting at like 3.5K.

This is what I mean comparibly to stock. Not that it is worse, but I seem to get my self mis-understood every time...

[ddgsxr504]

And so it starts....

[InsanityInc]

I was drinking when I wrote that, so let me clean this up a bit

Yeah, they are good and the pdrop I was talking about is that annoying drop in torque from 2K-4K in the dyno graph. Somebody find a dyno graph of a 2.5 inch pipe and the curve is much smoother rather than coming on strong and losing power, then re-gaining it again starting at like 3.5K.

This is what I mean comparibly to stock. Not that it is worse, but I seem to get my self mis-understood every time...

That same thing happens in the stock graph, and on all KAs pretty much. It has nothing to do with the exhaust system, and everything to do with the intake system. I mean, just look at the graph, the 3" exhaust made absolutely no change in how the power dropped or when.

[s13rb25det]

cool, looks like I will go with a 3 in cat back. also what ones do you guys like? I have had a ssautochrome.com catback on my last 240 (with the rb25det!) and it sounded nice and was built pretty good too. but it was loud!!! any one know a company that has a reasonable low noise catback? thanks

[AmoebAssassin]

BRM or RS*R Exmag

[Riley2.4L]

I asked the same question and started the same war not too long ago. heres the summary: if you get a 3 inch now with the stock KA you'll gain power in the high end and lose power in the bottom ( in other words the horse power will be there but your acceleration will suck.) if you got 2.5 in the power gain would be more towards the mid range. So unless you plan on getting a rather big turbo and running your car at 100mph alot, you're better off getting a 2.5 inch exhaust with a quick spooling turbo

[Bigvinnie]

3" cat back systems will be fine for temporary power gains, but once you add headers and even a 3" high flow cat you will lose power.This one guy used his stock cat, then took it out for straight 2.5" test pipe, he actually lost 2HP and claims that it was due to less scavaging( other wise known as back pressure).
Modified by Bigvinnie at 5:15 PM 9/22/2005

[InsanityInc]

I asked the same question and started the same war not too long ago. heres the summary: if you get a 3 inch now with the stock KA you'll gain power in the high end and lose power in the bottom ( in other words the horse power will be there but your acceleration will suck.)

This statement is a logical contradiction. If you make more power, you accelerate faster.

Also, look at the ****ing graph. There is no loss anywhere compared to stock.

[InsanityInc]

3" cat back systems will be fine for temporary power gains, but once you add headers and even a 3" high flow cat you will lose power.This one guy used his stock cat, then took it out for straight 2.5" test pipe, he actually lost 2HP and claims that it was due to less scavaging( other wise known as back pressure).

Modified by Bigvinnie at 12:54 PM 9/22/2005

First, backpressure and scavenging are NOT THE SAME THING. How many ****ing times do I have to tell you this? Scavenging is releasing the inert exhaust from the cylinder. Backpressure is a positive pressure in the exhaust pipe, which ALWAYS inhibits scavenging.

Second, I'd bet money on the reason for his power loss being a bad install or bad test pipe which resulted in an exhaust leak.

[Bigvinnie]

First, backpressure and scavenging are NOT THE SAME THING. How many ****ing times do I have to tell you this? Scavenging is releasing the inert exhaust from the cylinder. Backpressure is a positive pressure in the exhaust pipe, which ALWAYS inhibits scavenging.

FACT:They both work in conjunction as one. You simply cannot have back pressure with out scavaging. Well atleast for N/A the whole dynamic changes once you go F/I. and NO there was no exhaust leak, those were facts, I can get you the forum link if you would like and you can rebuddle with him..........

[s13rb25det]

all right!!!!! sorry to have started this up again!! I will go with a 3 in catback and I am pretty sure I will lose some low end torque untill I turbo it! but I would not go with any thing smaller than 3 in on a turbod car, so I will just deal with thhauste power loss until then. my main concern is quility and noise, I dont want it rusting out in a few years and I CANT STAND loud exhausts!! I know by switching to a wider exhaust it will be somewhat louder but some of noise coming from these cars are just plain stupid!! o.k. thank you for all the info! you guys are great!!

[Riley2.4L]

This statement is a logical contradiction. If you make more power, you accelerate faster.

Also, look at the ****ing graph. There is no loss anywhere compared to stock.

actuallly thats not true. If your power band is shifted upward then your going to have the most power in the higher revs and you'll lag at the lower revs. Not to mention the dyno shows a 3 in. exhaust compared to stock. of course the 3 is going to make more power. its like putting a little league base ball player against Ken Griffey junior. Show me a dyno of a 3 in. vs a 2.5in and I'll show you exactley what I mean

[ddgsxr504]

No reason to lock this thread.

Yeah good call on that one!

See no one wants to F***ing listen to me but oh well have it your way. Like I said in the other million posts just like this one, get WTF YOU want and call it a day. Between 2.5" and 3" there is no noticable damn difference! Lose a few gain a few blah blah, it's not like a hp here or a hp there is going to make a F***. Just get what you want and stop posting these stupid a$$ exhaust questions!!!

[InsanityInc]

actuallly thats not true. If your power band is shifted upward then your going to have the most power in the higher revs and you'll lag at the lower revs. Not to mention the dyno shows a 3 in. exhaust compared to stock. of course the 3 is going to make more power. its like putting a little league base ball player against Ken Griffey junior. Show me a dyno of a 3 in. vs a 2.5in and I'll show you exactley what I mean

Look at the ****ing graph. Look at it. There is more power and torque everywhere. There is no way you can "lag" when you have more power. You are a blind idiot.

also, YOU said:

Quote »if you get a 3 inch now with the stock KA you'll gain power in the high end and lose power in the bottom[/quote]Which is false. You don't lose anything.

[InsanityInc]

Quote »FACT:They both work in conjunction as one. You simply cannot have back pressure with out scavaging. Well atleast for N/A the whole dynamic changes once you go F/I.and NO there was no exhaust leak, those were facts, I can get you the forum link if you would like and you can rebuddle with him..........[/quote]Honestly, every time you label something as a fact, it's really a stupid myth based on half science. Have you ever been right about anything?

Also, you are right that you can't have backpressure without scavenging, but that doesn't mean anything. Scavenging is the act of removing exhaust from the cylinder. The only way you're not scavenging is if the car is off, and obviously if there's no exhaust going through your pipe, there can't be any backpressure.

Problem is, that means absolutely nothing. Backpressure is AWLAYS detrimental to scavenging, end of story. If anyone tells you otherwise, they are wrong. Just ****ing think about it for christ's sake. You are trying to blow something through a tube, if there is a pressure blowing the opposite direction on the other side of the tube do you think it's going to be EASIER or HARDER to blow air through the tube? It's pretty goddamn simple, it's going to be harder.

The reason why a smaller exhaust CAN perform better for an engine is due to exhaust VELOCITY, which has NOTHING, I repeat, NOTHING to do with backpressure. In fact, velocity REMOVES backpressure because the reason you want velocity is due to the bernoulli effect, which states that as a fluid (gases are fluids) increases in velocity, the pressure across that fluid drops.

reference:

http://en.wikipedia.org/wiki/Bernoulli_effect

It's used all over the place in cars.

Take a ****ing physics class before you try to form a hackneyed argument against me again please. I'm tired of being an ad hoc teacher.

[Riley2.4L]

Insanityinc listen to what I'm saying and stop rampaging like a freaking moron. the dyno graph shows a 3 in exhaust vs. a stock exhaust. No matter what the 3 in. is going to do better it's aftermarket. if you had an aftermarket 2.5 in exhaust vs. a 3 in exhaust in the dyno then you would see the lower rev power drop in comparison to the smoother transistion of torque using a 2.5. Thats what I'm saying. You'r getting angry and ignoring the key points of what I'm saying because you don't want to see the truth. I mean c'mon a guy just recently posted a thread about how he bought a 3 in exhaust and experienced lagging in the lower revs

[Kenrik]

FACT:They both work in conjunction as one. You simply cannot have back pressure with out scavaging. Well atleast for N/A the whole dynamic changes once you go F/I. and NO there was no exhaust leak, those were facts, I can get you the forum link if you would like and you can rebuddle with him..........

Exactly Backpresure is the wrong word... Backpressure is air trying to move the other way... BUT Pressure which creates VELOCITY because there is more air comming out of the engine then can fit in the pipe is required!! I think 3in is to big for NA...

[InsanityInc]

Insanityinc listen to what I'm saying and stop rampaging like a freaking moron. the dyno graph shows a 3 in exhaust vs. a stock exhaust. No matter what the 3 in. is going to do better it's aftermarket. if you had an aftermarket 2.5 in exhaust vs. a 3 in exhaust in the dyno then you would see the lower rev power drop in comparison to the smoother transistion of torque using a 2.5. Thats what I'm saying. You'r getting angry and ignoring the key points of what I'm saying because you don't want to see the truth. I mean c'mon a guy just recently posted a thread about how he bought a 3 in exhaust and experienced lagging in the lower revs

I have a 3" catback on my car, there is no lagging, and like I said, if you're LAGGING IN THE LOW RPMS COMPARED TO STOCK YOU HAVE TO HAVE LESS POWER COMPARED TO STOCK. You claim I'm putting words in your mouth, but yet you keep saying those words.

Also, show me a 2.5" dyno. I very severely doubt it will see anywhere near the gains of the 3". There's 6 or 7 ft-lbs over stock coming off IDLE with the 3".

[Kenrik]

I have a 3" catback on my car, there is no lagging, and like I said, if you're LAGGING IN THE LOW RPMS COMPARED TO STOCK YOU HAVE TO HAVE LESS POWER COMPARED TO STOCK. You claim I'm putting words in your mouth, but yet you keep saying those words.

Also, show me a 2.5" dyno. I very severely doubt it will see anywhere near the gains of the 3". There's 6 or 7 ft-lbs over stock coming off IDLE with the 3".

Pass the Amunition buds... the Civil war begins now...

2 2 2

[Riley2.4L]

ok well how would you know insanity if you've never seen a dyno of a 2.5 vs. a 3? your' entire argument is based off of speculation as opposed to fact. I'm not saying 3 in. sucks or anything you do gain power. it increases the power band high end wise which is gonna give you lag in the lower revs. I mean this is logic it's known round the world. I learned it when I posted a similar thread not long ago and you rampaged through that thread too lol

[InsanityInc]

ok well how would you know insanity if you've never seen a dyno of a 2.5 vs. a 3? your' entire argument is based off of speculation as opposed to fact.

And your's isn't? At least I have a dyno of the 3" and a reasonable thought process to tell me that a 2.5in system isn't going to do better than 6-7ftlbs off idle on an mostly stock engine with only a CAI.

Quote » I'm not saying 3 in. sucks or anything you do gain power. it increases the power band high end wise which is gonna give you lag in the lower revs. I mean this is logic it's known round the world. I learned it when I posted a similar thread not long ago and you rampaged through that thread too lol [/quote]Look at the graph. If you don't "lag" at lower RPM stock, then how are you going to "lag" at lower RPM with the 3" when you're making more power? It makes NO SENSE AT ALL.