gnode

Been searching for anyone who has actually done a cutout on the IS350, but have not had good luck on this board.

Does anyone here actually have a cut out? If so, where is it/are they installed? Do you have after market headers?

I am not looking for speculation or incorrect theories about whether or not a cut out will yield gains.

The fact is that other than O2 sensors feeding information back to the engine which automatically adjusts its tune based on what the sensors tell it, a cutout will increase power. Cats, mufflers, and pipes, no matter how well engineered by Toyota have to meet emissions requirements and sound goals. The further upstream you can install the cut out, the more performance will be gained. You will gain more performance than you would with an aftermarket exhaust that involves mid pipe and beyond (headers will still offer gains). If anyone here says a cut out will not improve performance, you are also saying that an aftermarket exhaust will not improve performance.

However, if installing the cut out causes problems related to the O2 sensors and creates a CEL, that in itself may (likely) negate any performance gain if the error it causes triggers the ECU to pull timing and "limp".



So, does anyone here actually have a cut out installed? If so, what kind of performance gain have you experienced? Are you getting any problems such as a CEL? If so, how did you overcome it?

Kurtz

iTrader: (1)

Despite the fact you immediately then go into your own incorrect theory on why it will do so...

The "fact" is you have no grasp of exhaust velocities, and why they're important to making power. Nor any concept of exhaust scavenging either.

Otherwise prior to O2 sensors and cats (ie most of the history of cars) why wouldn't everyone just run open headers to make the "most" power if your theory made any sense?

For that matter, why wouldn't headers with 5" tubes make more power than headers with 2" tubes on any car you picked?

For that matter why doesn't a 5" cat-back exhaust make more power on a car than a 2.5" one does in every single case?

No, they're saying that exhaust sizing is a complex science, and that there's more to it than your incredibly simplistic understanding of the situation. A lot more.

gnode

Open headers make the most power, thanks.

The only times it does not is when the ECU is self tuning and reads input from O2 sensors etc and has to meet other requirements, such as emissions.

Anyway, you obviously don't have the information I am looking for.


Another reason people don't run open headers is safety for the driver and passengers. You don't want to suck in exhaust through the AC or any parts of the body that are not air tight.

You would also go deaf. Have you ever actually driven a car with open headers or just a down pipe and no other exhaust piping installed? It is like firing a weapon without ear protection.

Why do top fuel dragsters use open headers?


As for your other questions:
5" header tubes would not fit, and "more than necessary" is not necessary. If the volume of exhaust gas produced per RPM is less than the volume of the corresponding section of pipe, then the pipe is sufficiently sized. You do want that section of pipe shaped in a way that minimizes chaos (this is where equal length headers and xpipes can help, if needed). Then you want the exhaust let out ASAP. For a front engine car, that happens to be the rear of the car to avoid killing the driver, and thus, the long exhaust system is born.

A 5" cat back would not gain significant power because it is after the 2.5" bottleneck higher up in the exhaust stream. The only gain you would experience are other bottlenecks reduced or eliminated by the new pipe design. The diameter itself is not a major consideration at that point. But if the pipe eliminates a bend or obstruction, you will get a gain on that merit.


Alternate question for you:
Why stop your exhaust system at the end of the car if piping can magically add performance? Why don't we see anyone make exhaust systems that go longer, with a dozen cross pipes and sexy curves? Why don't top fuel dragsters have extra long pipes?

The key to exhaust performance is to eliminate as many bottle necks as possible. Therefore, you want a system that meets these goals:
As short as possible meeting safety requirements
As few bends as possible
As few obstructions as possible (cats and type of cats, mufflers)

Just about anything else serves a purpose other than performance. Cut outs achieve the above goals, as long as they do not sabotage the computer system which can negate the gains.

Kurtz

iTrader: (1)

You're wrong.. and welcome! If the car isn't meant to be run that way, the headers aren't designed to be run that way (proper size and length for correct exhaust scavenging), and the type of engine won't benefit from a rightward rpm shift in the power band, suddenly you're potentially slowing down the car.

I'm gonna steal an explanation of some of this from an F-body guy at the end of the post

Because they are designed to. The engine is built with that in mind, the header/collector size and length is designed with exactly that in mind.

That's exactly why assuming that removing everything past the headers on a car not designed to do that will always make power is a really dumb idea.


That's a key to it. By no means the only one... and ignoring the others in favor of that one is a terribly bad idea.


Now, read this thread:
http://www.fbody.com/anything/950661

specifically the deep explanation of exhaust waves and scavenging.

The 2IS is not designed to run open headers. If you remove everything past them (taking the O2s out of the equation for the moment) you are not automatically going to make more power. You might well make less.

Now, if you could tune the engine (which you can't) and you could design your own headers that had -exactly- the correct size and length for the engine to optimize exhaust pulses and scavenging, and for the tuned power band you plan to run it in, then adding more exhaust parts after those headers would lose you power across the board.

But that's not the case.

Exhausts are different sizes on different cars for a reason. Same reason intake manifolds aren't all the same size/length.

gnode

So you basically wasted a lot of time considering I said they need to be big enough for the volume of the exhaust per RPM.



You are going to have to be more specific regarding the link you provided. Much of what they are talking about applies to engines that don't have a computer to control AFR or timing.



His discussion about low end torque is somewhat wrong headed. Uneducated folks in the turbo world often have the same misconception: back pressure helps turbos spool faster. Sure it does, and makes the car slower at the same time. In a turbo application, the backpressure increases load > increases exhaust output > spools the turbo faster > gets torque earlier in RPM. However, the car is slower because it goes through the RPMs slower. If it takes you more real time to go from 1000 RPM to 3000 RPM, then it frankly does not matter that you had faster spool: you were slower. This is very deceptive if you only look at a dyno based on RPM. The guy on the fbody forum at least does admit that the car is faster with open headers.

Kurtz

iTrader: (1)

No, I really didn't.

I did try to explain to you why removing everything past the header/exhaust manifolds can hurt performance though, especially on a car not designed to be run that way.

Do you have some data to demonstrate the 2IS is designed to run that way? It certainly sounds like it since you insist that O2 issues aside the car must perform better with open headers in 100% of cases, which is simply wrong.

Maybe you'll actually listen to some science if a pretty girl explains it to you- try this link:

http://www.motoiq.com/MagazineArticl...Ask-Sarah.aspx



Notice how she agrees open headers would be great on a car with optimized headers... and not so great on a car without them? Like say a 2IS?

Notice how the answer she is giving is in answer to a guy who asked why a friend lost HP on a dyno with open headers?
Something you claim is UNPOSSIBLE!!!

The article explains why it is possible in a bit more depth that I'm sure you'll continue to ignore, as well as linking to 2 other header articles she wrote that go much more in depth than that, and also explain why you're wrong in your thinking that "big enough to let all the exhaust out" is the only consideration in the size of header pipes, and why smaller pipes can be better in some cases.

gnode

I wonder why I asked about headers...............

And placement of the cutout..................

Anyway, talking to you on this subject is a waste of time.




Back to the original questions:
1. Does anyone here have a cutout?
2. If so, where did you put it, and what were the results?
3. If so, do you have any aftermarket headers?
4. Did you have to do anything regarding the sensors?


Read the article you linked. All it does is support eliminating back pressure being good and points out that bad headers are bad.

What I am talking about doing is placing a cutout after the headers, probably at the very beginning of the mid pipe. Now, if you have any science that proves that is wrong, or actual evidence from someone else who has actually done it with an IS350, I don't think you can contribute to this thread.

iSuxeL

iTrader: (21)

You might want to PM t0e, I think he had them but don't quote me on that.

And just to join the festivities, our car is very different gnode. I will have to agree with Kurtz, he's a long time member and knows his stuff just like lobuxracer. Sorry I can't help much.

gnode

The fact that aftermarket exhaust improves our performance is evidence that a cutout will also improve performance, as long as it does not cause computer problems.

Aftermarket exhaust primarily improves performance by reducing back pressure through the elimination of bottlenecks.

If I can eliminate the bottle neck of the mid pipe and beyond for $200 instead of $1500+ while remaining quiet during cruising but much louder when I want to go fast, that is the best. For $300, I could do intake and cutout and be right up there with those who spend $3000+ on a full exhaust system without the headache of emissions testing problems.

Kurtz

iTrader: (1)

That makes as much sense as saying if a 2.5" inch exhaust improves performance than a 5" one will improve it more. That is, no sense at all.

If the cutout ruins exhaust scavenging and/or kills exhaust velocity you'll lose power, just like that mustang did on the dyno with open headers in the link I gave you.

and by maintaining optimal exhaust velocity throughout the system... which is why "eliminating restriction" isn't the only goal.


Where do you get $3000+ for a full exhaust? The Joe Z race exhaust is $1500.

But if you're trying to save money, instead of $300 for cutouts/intake you can spend $400 on a used tanabe and $100 on a Joe Z. It'll be (relatively) quiet all the time, and you'll gain ~12 rwhp, versus the 13-15 that a "full exhaust" gives you, and even better, the car will be legal. (which cutouts aren't of course since they bypass emissions parts)

Plus, you'll be using a solution actually engineered for the car by people who understand how exhaust flow works.

lobuxracer

iTrader: (2)

I read this:
And concluded this:
You have no idea what you're doing and even less of a clue what might happen when you take a well engineered exhaust and arbitrarily modify it in a way quite certain to remove all the "well" from the engineered.

Good luck with your project. When your car runs slower, you'll know we were pretty confident it would before you did anything.

And please do measure real world performance before and after this mod using a watch and a measured course so you don't confuse "louder" with "more power."

gnode

Neither of you know what you are talking about.

Yes, if a 2.5" exhaust improves performance, a 5" exhaust will not hurt. You may not gain anything, but you will not lose anything, either.

Anyway, I have much more experience with actually fast cars than either of you.

If someone has actual experience with cutouts on IS350s, I appreciate your input.

Kurts: Full exhaust includes headers.
People who produce cutouts, and then others who know where to put them, are the ones who truly understand exhaust. I doubt any honest vendor here who produces exhaust would claim they can beat a cut out. I invite any vendor to contradict me. On the contrary, they produce a product that produces a great sound and also has great "always on" performance, while in some cases, meets emissions requirements.

I live in DFW. They don't check under your car. With the cutoff turned off, the exhaust is stock and will pass any inspection.




Guess I am burning bridges pretty quick here. I just don't tolerate false speculations, regardless of post count. I am looking to modify my expensive car, and don't want to do something that will mess it up or not yield results. If no one really has real experience with cutouts here, then I will give it a try and post the results. But I would prefer someone else be the guinea pig!

t0e

iTrader: (1)

I don't have cut-outs, although I did buy the equipment to install one.

But there was no room to install it properly and get correct flow, so I scratched that project and went with a full custom setup.
This is how I had it planned out..


All aftermarket exhaust re-install the o/2 sensor in the same place and no errors are given. So, I would recommend you install it behind the o/2 sensors and you should be fine.

As for power, only a dyno can prove it, I'm sure you might loose a bit of low end power and gain high end. I have run 3 different set-ups all with different results. I like my last one best : )

ElitistK

iTrader: (4)

Cutouts are only useful if you're boosted and you want to by-pass the cat under scramble boost. On an normal NA engine it's pretty useless unless you're in it for the ricer factor.

btwanky

look below.. my is-f with them