Cat Delete Good or Bad?

[240sR4drifting]

Well i'm looking at a car and i just noticed there is a cat delete... Now i don't know much about cars but i'm pretty sure that means they took out the catalytic converter... For reasons i don't know... but it also says it has a full 3'' exhaust?... i'm not sure what that is (full flow 3inch exhaust?) but i live in Ohio where there are no emissions so don't say its illegal... i'm just wanting to know if its a good idea to put the cat converter back in (would that help the performance?) or just leave it as is? It has a stock ka24de in it and if i get it i'd save up for a few months and get an sr20det... So please just lend me some advice!

-Thanks for your time!

[booey13]

It's strictly for emissions. It will be quieter with a cat, but it won't affect anything. And a full 3in exhaust have proven dyno results on the ka motor. They like to breathe.

[ixfxi]

It's strictly for emissions. It will be quieter with a cat, but it won't affect anything. And a full 3in exhaust have proven dyno results on the ka motor. They like to breathe.

call me stupid, but you have no idea what you're talking about

a 3" exhaust is WAY too large for an NA 2.4L... motor doesnt flow nearly enough to fill that up.. you'll end up with huge lack of back-pressure and lots of rasp.

a 2.5" exhaust w/ cat is the way to go for a street car.

[pacotaco345]

3 inch straight pipe fed with 3 ebay headers and a cat delete on a N/A ka w complete emissions delete and a cone filter FTW!! thats what i have but in all honesty its a bit overkill..

[$nicklefritz]

call me stupid, but you have no idea what you're talking about

a 3" exhaust is WAY too large for an NA 2.4L... motor doesnt flow nearly enough to fill that up.. you'll end up with huge lack of back-pressure and lots of rasp.

a 2.5" exhaust w/ cat is the way to go for a street car.

ok yur stupid ... back pressure ie. restriction of exhaust flow is like shoving a rock in yur ass , no need 4 it

[Kevin_S14]

im liking where this thread is going...
but anyways i would just leave the exhaust the way it is since you plan on getting the SR motor in the future.

[WINTERS14]

ok yur stupid ... back pressure ie. restriction of exhaust flow is like shoving a rock in yur ass , no need 4 it

A certain amount of back pressure is good... Without it you lose low-end torque.

[nate1]

no cat is fine it will free up more power high up. if u put a cat on it will lose some top end but gain more in the mid. cat will also help keep the noise down. 3inch is fine most of the big name companys like apexi ect use a larger than 2.5 for there n/a ka24de exhausts any way so it wont kill your power. ka's dont really respond to bolt ons any way so you will be hard pressed to see and feel the difference between 2.75 and a 3. also if your going sr down the road 3 is what u will want anyway.

[4DOOR_LIFE]

3 inch straight pipe fed with 3 ebay headers and a cat delete on a N/A ka w complete emissions delete and a cone filter FTW!! thats what i have but in all honesty its a bit overkill..

your age reflects what you've done to your car. lol

[Sad s13]

^ so true.
if you dont mind the noise then leave the 3in

[chituntang]

Well i'm looking at a car and i just noticed there is a cat delete... Now i don't know much about cars but i'm pretty sure that means they took out the catalytic converter... For reasons i don't know... but it also says it has a full 3'' exhaust?... i'm not sure what that is (full flow 3inch exhaust?) but i live in Ohio where there are no emissions so don't say its illegal... i'm just wanting to know if its a good idea to put the cat converter back in (would that help the performance?) or just leave it as is? It has a stock ka24de in it and if i get it i'd save up for a few months and get an sr20det... So please just lend me some advice!

-Thanks for your time!

1. 3in is the diameter of the piping. You can get a 3in cat and you will still have a 3in header back exhaust.
2. Just because there is no emission where you live, it does not mean it is legal to remove the cat from the car. If there is no regulation on emissions, no car manufacturer will put a cat on any car because they are pretty expensive.
3. For the KA motor, if you have been on this site long enough, you should know that it has been dyno proven that a 3in exhaust on the motor will gain power on the entire powerband.
4. SR, on the other hand, with a fmic, 3in turbo back exhaust, and boost turn up to 11psi will yield ~210whp.

But modding a stock KA motor with intake and exhaust makes no sense. Power gain is there, but no enough to make a difference in the real world. Its for the look...

[$nicklefritz]

A certain amount of back pressure is good... Without it you lose low-end torque.
Back pressure is detrimental to combustion engine operation efficiency so in affect you take 3 steps back and 1 step forward when adding a cat or skinny exhaust,

[WINTERS14]

Back pressure is detrimental to combustion engine operation efficiency so in affect you take 3 steps back and 1 step forward when adding a cat or skinny exhaust,

Yes. ADDING a cat or skinny exhaust will decrease exhaust flow and decrease power. But removing the stock cat that was designed and tested by Nissan engineers causes a loss of low end power. It helps top end and makes an especially big difference in turbo cars, buy in N/A it doesn't do a whole lot.

[RB180sxChris]

call me stupid, but you have no idea what you're talking about

a 3" exhaust is WAY too large for an NA 2.4L... motor doesnt flow nearly enough to fill that up.. you'll end up with huge lack of back-pressure and lots of rasp.

a 2.5" exhaust w/ cat is the way to go for a street car.


Agreed I had a testpipe on my s14 NA KA got a gain in hp but lost in torque. The pick up sucked nd my car was retarded loud like a civic loud as fuck but not going anywhere lmao! But now I got a catco cat on my car its some what quieter nd I got back pressure again so I got my lost torque back

[DxZoo]

A certain amount of back pressure is good... Without it you lose low-end torque.

this is true, when i bought my sohc it had a full 3inch and it feels a bit gutless below 3k and these motors are supposed to be decently torquey from what ive read. Need to get my buddy to fab up a full 2.5 one of these days

[Matej]

My catback has 3" piping, but I am using an OEM (2.5") gasket in it.
Not sure if that does anything. :)

[Kevin_S14]

OP plans on going SR20det. just keep the catless for now and use it for the new swap.

[ILoveMyRHS13]

I have a 3" straight pipe with a punched out cat on my KA. Yeah, I don't have much under 3k, but that allows me to drive slow enough around town but I still have good top end for the track.

[EDacIouSX]

do you guys realize you are all arguing over 10 hp?

[towlie]

Cats are for hippies

[camaro379ss]

A certain amount of back pressure is good... Without it you lose low-end torque.

This is correct they teach you this in trade school and nissan factory school if you are lucky enough to go like me. N/A engines need some back pressure hints the smaller exhausts and such. Where as turbo'd cars do not becuase the turbine itself creates enough backpressure for the system. The cats are there for emissions yes and the vehicle has been designed with that in mind. If the car absolutely needed a bigger exhaust I'd like to think the engineers would be smart enough to put it on there. I have had the chance to be around some engineers from nissan (for altima coolant problems on 03-06 body) but they didn't speak english very well thats why they came with a translator.

Like previously stated, is 3" ok on a N/A motor, yes and with the cat delete you will lose torque, see very minimal if any hp gains with more noise. Nothing more nothing less.

[booey13]

^^most cars weren't designed with performance in mind. Which is why they rolled out of the factory with restrictive exhausts and emissions. It's been stated plenty of times on this thread...a full 3in exhaust will yield hp gains throughout the powerband on an NA KA.

call me stupid, but you have no idea what you're talking about

a 3" exhaust is WAY too large for an NA 2.4L... motor doesnt flow nearly enough to fill that up.. you'll end up with huge lack of back-pressure and lots of rasp.

a 2.5" exhaust w/ cat is the way to go for a street car.

I'm not going to call you stupid because you said to call you stupid. I'm going to call you stupid because well...you're stupid.

[pacotaco345]

your age reflects what you've done to your car. lol

lol I said it was a bit overkill, I got the whole exhaust for 120 bucks so I can't complain. But anyways, if I told you I did a 5 spd swap in my garage, an engine swap after that, and base/clear'd my car all on my own would that reflect my age too? I love how people judge... To get back on topic if the cat is already gone and you don't have emissions standards where you live its not really worth it to go get another one.

[240sR4drifting]

lol I said it was a bit overkill, I got the whole exhaust for 120 bucks so I can't complain. But anyways, if I told you I did a 5 spd swap in my garage, an engine swap after that, and base/clear'd my car all on my own would that reflect my age too? I love how people judge... To get back on topic if the cat is already gone and you don't have emissions standards where you live its not really worth it to go get another one.

Hey I'm actually only 14... but most people wouldn't help out if i told them that... "because they have better things to do then help me out"

[towlie]

Hey I'm actually only 14

http://1.bp.blogspot.com/_ALgJmZKXivs/TIFpSbtM3LI/AAAAAAAAHFg/vxGujGAZm_c/s1600/Chris+Hansen+Child+Molestation+Fake+Issue.jpg

[Nick_04K]

do you guys realize you are all arguing over 10 hp?

Hilarious. Maybe search for some KA24DE dynos. It's like 3whp difference between the most and least restrictive aftermarket exhausts available.

Everyone in this thread will find that a 3 inch performs best on average for a KA though. Removal of the stock exhaust manifold and cat are the only places your losing power down low.

This topic has been covered, and beat like a dead horse. Please search guys

[Perfect Balance]

Not going to go too in depth, since it's somewhat off topic, but no, cars don't need backpressure. People think this because they put a 2.5 inch exhaust on their 1.6 sohc liter Civic, and it lost power everywhere except 6,000rpm +. The reason it loses power at low rpm is because the engine doesn't produce enough exhaust gases to maintain a high velocity of exhaust flow, which in turn doesn't make for much of a scavenging effect and overall exhaust flow out of the engine is worsened.

By putting on say, a 2.25 inch mandrel bend exhaust, the engine still doesn't produce enough gas for this size to be restrictive, but the velocity of exhaust flow is improved, scavenging effect is improved and in a best case scenario, exhaust gases are actually pulled out of the cylinders instead of being pushed out by them. With some adjustable cam gears to control valve overlap, you can really see some power gains.

People then see this as "smaller exhaust = more power" and "smaller exhaust = more restriction/backpressure" and end up at "backpressure = more power", which isn't the case. If you take that same exhaust and put a crappy muffler on it with pinch bent piping, you will still see a power loss, despite the smaller piping diameter.

The only exception is if the factory ecu doesn't have enough adjustment and you end up running lean and burning up valves or something, but this usually isn't the case with simple bolt ons, but if you start running cams and stuff, this could be an issue.

Here's a great article by Mike Kojima.
http://www.motoiq.com/MagazineArticles/tabid/59/articleType/ArticleView/articleId/900/How-to-Make-your-Own-Effective-Exhaust-System.aspx

[camaro379ss]

^^most cars weren't designed with performance in mind. Which is why they rolled out of the factory with restrictive exhausts and emissions. It's been stated plenty of times on this thread...a full 3in exhaust will yield hp gains throughout the powerband on an NA KA.



I'm not going to call you stupid because you said to call you stupid. I'm going to call you stupid because well...you're stupid.

Cars are most definitely designed with performance in mind. Except its the performance of what the economy demands = MPG not HP.

[joeapple8]

I think my 2.5 piping to a resonator from cat back does me fine, if you're driving a KA why bother with horse power?

[yetijeff]

ok yur stupid ... back pressure ie. restriction of exhaust flow is like shoving a rock in yur ass , no need 4 it

with and n/a car u need back pressure. u lose alotta low end torque with no no back pressure. if it was boosted thats a different story. the turbo is the back pressure. but i too have 3" straight pipe, n/a ka and its loud as fuck and i love it FTW!!

[mxexux]

Not going to go too in depth, since it's somewhat off topic, but no, cars don't need backpressure. People think this because they put a 2.5 inch exhaust on their 1.6 sohc liter Civic, and it lost power everywhere except 6,000rpm +. The reason it loses power at low rpm is because the engine doesn't produce enough exhaust gases to maintain a high velocity of exhaust flow, which in turn doesn't make for much of a scavenging effect and overall exhaust flow out of the engine is worsened.

By putting on say, a 2.25 inch mandrel bend exhaust, the engine still doesn't produce enough gas for this size to be restrictive, but the velocity of exhaust flow is improved, scavenging effect is improved and in a best case scenario, exhaust gases are actually pulled out of the cylinders instead of being pushed out by them. With some adjustable cam gears to control valve overlap, you can really see some power gains.

People then see this as "smaller exhaust = more power" and "smaller exhaust = more restriction/backpressure" and end up at "backpressure = more power", which isn't the case. If you take that same exhaust and put a crappy muffler on it with pinch bent piping, you will still see a power loss, despite the smaller piping diameter.

The only exception is if the factory ecu doesn't have enough adjustment and you end up running lean and burning up valves or something, but this usually isn't the case with simple bolt ons, but if you start running cams and stuff, this could be an issue.

Here's a great article by Mike Kojima.
How to Make your Own Effective Exhaust System > MotoIQ > Magazine Articles (http://www.motoiq.com/MagazineArticles/tabid/59/articleType/ArticleView/articleId/900/How-to-Make-your-Own-Effective-Exhaust-System.aspx)

Finally, somebody with some intellect. People need to put an end to the idea that some back pressure is good. That whole idea is just a bunch of BS passed down from the old hot rod days when people didn't understand how exhaust pulses worked. We should be smarter now take a closer look at how these things really work....:2c:

[two40guy]

i got three inch pipe from my exhaust manifold back on my ka. and i dont know my car is too loud for me sometimes but it doesnt effect power much. i was sideways all day yesterday at the track and it sounded cool just not so much on the street gets you a lot of unwanted attention

[soreballz]

Not going to go too in depth, since it's somewhat off topic, but no, cars don't need backpressure. People think this because they put a 2.5 inch exhaust on their 1.6 sohc liter Civic, and it lost power everywhere except 6,000rpm +. The reason it loses power at low rpm is because the engine doesn't produce enough exhaust gases to maintain a high velocity of exhaust flow, which in turn doesn't make for much of a scavenging effect and overall exhaust flow out of the engine is worsened.

By putting on say, a 2.25 inch mandrel bend exhaust, the engine still doesn't produce enough gas for this size to be restrictive, but the velocity of exhaust flow is improved, scavenging effect is improved and in a best case scenario, exhaust gases are actually pulled out of the cylinders instead of being pushed out by them. With some adjustable cam gears to control valve overlap, you can really see some power gains.

People then see this as "smaller exhaust = more power" and "smaller exhaust = more restriction/backpressure" and end up at "backpressure = more power", which isn't the case. If you take that same exhaust and put a crappy muffler on it with pinch bent piping, you will still see a power loss, despite the smaller piping diameter.

The only exception is if the factory ecu doesn't have enough adjustment and you end up running lean and burning up valves or something, but this usually isn't the case with simple bolt ons, but if you start running cams and stuff, this could be an issue.

Here's a great article by Mike Kojima.
How to Make your Own Effective Exhaust System > MotoIQ > Magazine Articles (http://www.motoiq.com/MagazineArticles/tabid/59/articleType/ArticleView/articleId/900/How-to-Make-your-Own-Effective-Exhaust-System.aspx)
Thank you for not being dumb.

with and n/a car u need back pressure. u lose alotta low end torque with no back pressure.
Read the quoted post above.


For the simpletons: Back-pressure bad. Exhaust velocity good. Too big a pipe = less velocity.

Here is a VERY basic example.
Think of air as a fluid. Imagine a water pipe. How effectively could your kitchen sink faucet pump water though a drinking straw? Not very well. On the other end of the spectrum, how effectively could that same faucet pump water through a fire hose? Not very well.
But a garden hose? That'll do. That's velocity.
Any kind of blockage in that hose will slow the water down. Kinks, stones, whatever. That is back-pressure, and that is never good.


This is hardly an issue on an N/A KA, as they love to breathe. Sure, you lose a little low end torque, but the horsepower gains up top make up for it.


Back on topic:
If if doesn't have a cat already, and you don't NEED a cat where you live, fuck it. Leave it as is.

[booey13]

Cars are most definitely designed with performance in mind. Except its the performance of what the economy demands = MPG not HP.

We're using the same word different ways. Yes most cars are designed to "perform" efficiently. However, there are fewer cars designed with "performance" in mind, meaning sports cars. MPG=economy car. HP=performance car

[allntrlundrgrnd]

3" is better for N/A AND turbo on the KA.

I had the dyno sheets saved somewhere.

I can't believe this is still under debate!

[Bushido]

yeah for real.

ka with 3in pipe is dyno proven to net a bigger gain than 2.25 and 2.5

freshalloy circa 2002

[dreadedfist]

Anecdotal evidence time:

On my RB20, I swap the cat on for emissions testing. I usually leave it on for a few months because I notice slightly better low rpm torque that makes daily driving easier, namely starting on hills. There are other reasons why I remove it again, however.

1) With the cat, the exhaust is significantly quieter, with less "bass" (I guess you'd call that drone). I only have a rear muffler, no resonators. With the test pipe in place, the exhaust is much more droney on the highway, but sounds better in and outside.

2) With the test pipe in place, lower rpm pickup is weak. Yeah yeah, it's an RB20, don't expect anything below 3000rpm, I know. But the engine came stock in my car and I love it for it's snappy nature. Higher rpms are where the catless setup shines.

3) My experience tells me that driveability with no cat is dramatically increased (you actually see the full benefits of a catless setup) with a tune. My anecdotal evidence tells me that when I put the test pipe on, it runs much, much richer. Leaning out the rich points will make good power gains.

What I'm saying is if you plan on running catless, tune the car for that setup. So yes, there is a big difference on turbocharged cars between cat-equipped and cat-less, when setup properly. If you're on the stock ECU, I guess go catless if you want to shoot flames. Bitches love flames. If you're running an NA setup, the difference is probably neglegible, but I have no experience so I can't comment.

[ixfxi]

i love how you guys are arguing about the most inconsequential shit.


KA24E or DE.. whatever NA motor you have. You guys think that adding these bullshit bolt-ons: 3" exhaust, headers, delete cat, delete EGR... etc etc.. like you're unleashing the horsepower on your magic beast. wow, feel the power that your massive stock compression 2.4L will now put down at the wheels.

calm down buddy, we're gonna need some slicks!!!

seriously... you guys are a bunch of fucking poseurs. unless i hear about adding more fuel, and adding more air, and thereby doing something to increase your compression, by pistons or forced induction.... whatever. do that, and then you can talk.

in the meantime, all i'm hearing is a bunch of 17-20 year old bitches talk about how much theoretical power they're attempting to unleash, and in reality they're doing NOTHING.

reminds me of that part in "old school" where will ferrell is unleashing the power from the beast... haha what a great scene

[yomisiu]

cool your jets, pal.

[booey13]

i love how you guys are arguing about the most inconsequential shit.


KA24E or DE.. whatever NA motor you have. You guys think that adding these bullshit bolt-ons: 3" exhaust, headers, delete cat, delete EGR... etc etc.. like you're unleashing the horsepower on your magic beast. wow, feel the power that your massive stock compression 2.4L will now put down at the wheels.

calm down buddy, we're gonna need some slicks!!!

seriously... you guys are a bunch of fucking poseurs. unless i hear about adding more fuel, and adding more air, and thereby doing something to increase your compression, by pistons or forced induction.... whatever. do that, and then you can talk.

in the meantime, all i'm hearing is a bunch of 17-20 year old bitches talk about how much theoretical power they're attempting to unleash, and in reality they're doing NOTHING.

reminds me of that part in "old school" where will ferrell is unleashing the power from the beast... haha what a great scene

Who in here said by doing those mods there is shit tons of power to be had? Don't be butt hurt because everyone else knows that there are power gains from running a 3in exhaust on an NA KA. No one said anything about unleashing any sort of beast. OP asked if there were benefits of running said exhaust on said motor and the question was answered. You on the other hand are in here talking shit just like you do in every other thread you comment in. So STFU and come to terms with yourself that you're wrong on this one and quit trying to cover it up by calling everyone else names...we're all posers until you HEAR us talk about more air/fuel? If anyone is a poser its you...coming in hear and acting like you know what you're saying. Do everyone a favor and stay out of the thread...

[Nick_04K]

call me stupid, but you have no idea what you're talking about

a 3" exhaust is WAY too large for an NA 2.4L... motor doesnt flow nearly enough to fill that up.. you'll end up with huge lack of back-pressure and lots of rasp.

a 2.5" exhaust w/ cat is the way to go for a street car.

i love how you guys are arguing about the most inconsequential shit.


KA24E or DE.. whatever NA motor you have. You guys think that adding these bullshit bolt-ons: 3" exhaust, headers, delete cat, delete EGR... etc etc.. like you're unleashing the horsepower on your magic beast. wow, feel the power that your massive stock compression 2.4L will now put down at the wheels.

calm down buddy, we're gonna need some slicks!!!

seriously... you guys are a bunch of fucking poseurs. unless i hear about adding more fuel, and adding more air, and thereby doing something to increase your compression, by pistons or forced induction.... whatever. do that, and then you can talk.


LOL @ you always being such a prick! Your first post is comical because you always hold yourself so high and act like you've been around the block so many times that you know EVERYTHING! Even myself, at sixteen whopping years old understand exhaust scavenging and pressure vs. velocity.

And about your "adding air and fuel" comment.... Your an idiot.

Adding things like a header, intake, and three inch exhaust are precisely to allow air into and out of the motor more efficiently. And on the fuel side of things, most KA are running rich still even after NA mods. Adding more fuel is unnecessary most of the time.

[WERDdabuilder]

http://kpnv.files.wordpress.com/2009/07/mj_popcorn.gif?w=200&h=136

[ayuaddict]

Stock everything + light flywheel > whatever awesome exhaust/cat/intake you can throw at a KA.

[towlie]

This thread makes me lol

[Kevin_S14]

i haz 3" catback on me KA. me want SR20...

[ixfxi]

Who in here said by doing those mods there is shit tons of power to be had? Don't be butt hurt because everyone else knows that there are power gains from running a 3in exhaust on an NA KA. No one said anything about unleashing any sort of beast. OP asked if there were benefits of running said exhaust on said motor and the question was answered. You on the other hand are in here talking shit just like you do in every other thread you comment in. So STFU and come to terms with yourself that you're wrong on this one and quit trying to cover it up by calling everyone else names...we're all posers until you HEAR us talk about more air/fuel? If anyone is a poser its you...coming in hear and acting like you know what you're saying. Do everyone a favor and stay out of the thread...

LOL @ you always being such a prick! Your first post is comical because you always hold yourself so high and act like you've been around the block so many times that you know EVERYTHING! Even myself, at sixteen whopping years old understand exhaust scavenging and pressure vs. velocity.

And about your "adding air and fuel" comment.... Your an idiot.

Adding things like a header, intake, and three inch exhaust are precisely to allow air into and out of the motor more efficiently. And on the fuel side of things, most KA are running rich still even after NA mods. Adding more fuel is unnecessary most of the time.

i love when i get tag-teamed by a pair of n00bs.. i feel like peter north doing a session with a couple of bitches

do you guys have any factual data to backup your bullshit claims, or do you just like spouting your mouth to make you feel better about driving a piece of shit, neglected 20 year old car with a fucking NUISANCE exhaust setup and lack of emissions which is federally required.

you guys may not like my lack of bullshit tone, and unfortunately it stems from listening to 20 year old fuck-tards claiming to preach the benefit of running an over-sized exhaust and lack of cat.

edit: i just realized one of you fruitcakes is 16? what is this, your fisher-price 240sx? my first car? grow some, read a book, then come back and talk.

[booey13]

Id say you're more like Ron Jeremy since you're so seasoned and know everything.

[camaro379ss]

I found this explaination and it makes complete sense. Just thought it would be interestingto add. I dunno I see both sides now...


Back pressure being an essential part of a good exhaust system is a myth. It is more correct to say that a perfectly stock engine that cannot adjust its fuel delivery needs back pressure to work correctly.As with all myths, however, there is a hint of fact with this one. Particularly, some people equate back pressure with torque, and others fear that too little back pressure will lead to valve burning.

One misconception is that an increase in back pressure will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that back pressure produces more torque. The increase in torque is not due to back pressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

Another misconception is that back pressure can result in burned valves. This is believed by some after they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. While the valve burning has occurred as a result of the exhaust mods, it wasn't merely due to a lack of back pressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well. Valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc.), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

The reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in back pressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that back pressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced back pressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if back pressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

Modern vehicles are generally exempt from the effects of a decrease in back pressure. Because the computer that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing back pressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the computer's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust back pressure reduction, these limits won't be reached.


I also seem to be soon relizing that this is more of an arguement over flow velocities more than anything......just saying. I myself got really caught up in just the arguement side of it and I just sort of realized it.

[ixfxi]

^ well thank you bill nye, the science guy. but last i checked, this isnt a website of tech talk and intellect. this is zilvia. so take all this science engineering talk and fuckoff. thanks. :-)



Id say you're more like Ron Jeremy since you're so seasoned and know everything.

you give me too much credit

ron can suck himself off

i'm not nearly that flexible



anymore

[camaro379ss]

^^^just trying to help out. For me it makes alot of sense because all of my professors were heavy hot-rodding type people and that's all they ever talked about. That's how they passed down the backpressure is necessary thing to me.

I dont know I guess I would rather just know the truth rather than get defensive and type trash talk on the internet(General statement not directed at anyone).....Typing Tough Guy:rl:

[nismoracingsx]

you give me too much credit

ron can suck himself off

i'm not nearly that flexible

...anymore

lawlz :keke:

I'm lovin' it :cj:

[Matej]

Stock everything + light flywheel > whatever awesome exhaust/cat/intake you can throw at a KA.
Also, lightweight driveshaft and pulleys.
The three best stock KA mods, as far as fun gained per money spent.


Of course, exhaust/header/intake and such will not hurt, but everyone should be aware that any gains are minimal at best.
I confess that even knowing so, over time I have acquired all of the above mentioned parts. I am having fun collecting every bolt-on mod possible and trying to get the most out of an n/a KA, even if it is silly. :)

[slomar91]

Been there, done that. Had a brand new 3 inch exhaust on my single cam. Traded it for a rusty stock exhaust. Maybe you idiots enjoy driving around an annoyingly loud car with no power. I don't know the logistics of back pressure or all that bs, but I know damn well my car had more torque with the stock exhaust, not to mention i could rev it above 4k rpm without alerting every cop within a 1 mile radius. Enjoy your PLUS 2 HORSEPOWER for your "freeway pulls"

[lflkajfj12123]

easily the worst thread on zilvia in a while

[DRIFTO16]

I think the 3 inch is a little over kill
but its no biggie if u dnt mind the noise
if u do buy a dam stock exhaust and throw the dam thing in
....if u dnt understand what the effects of not having a cat
r then maybe buying an sr in a few months isnt a good idea
good luck with finding your answer =]

[usdm180sx]

Since your state has no emissions leave it as it is. You also have a good base setup for the sr. On a ka a cat delete and a 3" exhaust will shift the power and torque curve up. You'll get more high end (5500 rpm) but will lose low end torque.

[nomoremk2]

How many of you guys are gonna keep saying the same thing that's been stated and argued over the past two pages? Did either of you even read the thread before posting?

[usdm180sx]

i love when i get tag-teamed by a pair of n00bs.. i feel like peter north doing a session with a couple of bitches.

Haha another classic from one of the original kings of old skool

[Mishkin_707]

ok yur stupid ... back pressure ie. restriction of exhaust flow is like shoving a rock in yur ass , no need 4 it


:rofl: no this shit made me laugh!!


to the op, just keep it the way it is due to you going SR, if you're worried about back pressure like every other person in here just poke a couple holes in a potato and shove it in the muffler, you'll get you low end torque back so these idiots stop fighting about it and everywhere you go it will smell like french fries.

[240sR4drifting]

http://1.bp.blogspot.com/_ALgJmZKXivs/TIFpSbtM3LI/AAAAAAAAHFg/vxGujGAZm_c/s1600/Chris+Hansen+Child+Molestation+Fake+Issue.jpg
nevermind... i was trying to get to the fact that any one can be smart with cars regardless of their age!

[BoostSlideWayz]

I had on my ka24e when i first had it with ebay headers and 3.5" cat delete and cat back but WAYYYY to ricey sounding .... now that its boosted it sounds alot better.. but for daily driving i say keep the cat.. Or just hollow it out i heard that makes it not as raspy.

[Corbic]

do you guys realize you are all arguing over 10 hp?

10 fly-wheel horsepower.


People need to get over the idea that Exhausts add any real horsepower in stock-applications and just except it's for looks and sound.

You'll feel like your making more power cause your be loud and raspy.

[gearhead55]

i think its funny that this thread has made it to 3 pages.

Anyway, my two cents is that with most engine setups the exhaust is all about the sound you want, not about the power it adds. If you want a loud ass setup that pisses grandmas and downers off then run a straight through setup. If you want to avoid attention then run a quiet exhaust. The power difference will be minimal. Personally i like my shit loud, cause i'm a rat rodder at heart...

[ixfxi]

Also, lightweight driveshaft and pulleys.
The three best stock KA mods, as far as fun gained per money spent.

hopefully not the under-crank pulley. those billet crank pulleys are non-dampening pieces of shit and good for nothing.


just adding a new tangent to rant on