Hi guys,

Currently my car is stock as can be, from the factory stock. No intake or anything, i will be picking up a oem full stock exhaust + oem header next week hopefully. My plan at present is gut my primary cats and replace the stock secondary cats with a straight pipe while also changing the resonator + mufflers (to play around and find a sound im happy with.

I will try and document this process as thorough as possible for anyone else thinking of going the same route. I've briefly read through the this thread which gave me extra motivation
https://www.clublexus.com/forums/is-...me-soon-6.html

I will be do a before and after dyno after the above changes, once i decide on which exhaust shop to carry out the work, currently interviewing a couple and getting their opinions on the above.

What i would like to know from the all wise forum members is the following:

1) Do you foresee an CEL errors ? if so, whats the best way to remove those?
2) Are there any special request, things that guys would like me to measure, keep track of, take pics of, make videos of?

****All criticism as well as tips are welcome...****.

The only thing i have my mind set on is the tail pieces Its 101mm angled tailpieces, i actually want the burnt tip look but no garages over here stock them, might need to experiment on one and see what can be done to stainless steel to get that blue burnt tip look [See image below]



Here's a pic of a cat of another car in one of the workshops i visited,
I tried looking through it, could barely see any light on the other end of without holding at a ridiculous angle, can see why these are so restrictive.

 

Wow those cats really do look insanely restrictive! Im thinking about doing mine as well. Which cats are the ones your going to be deleting? I dont know which ones to do because I know some of them have sensors on them and really dont want to be having a stupid check system light on. Also I hope deleting them gives me some poping when i downshift =D

 

Yep, and that was only a half a piece and i could barely see light through while shining a torch on it...I plan to delete both primary (the ones on the header) and secondary (the ones in the mid pipe). Not sure whether you will get the downshift poping, i have a manual transmission as i prefer being in control of the revs myself.

Here's some pics to get an idea:
Primary


Secondary



Here's a pic of the two O2 sensors after the Primary Cats, these two need to be fooled once the Primary cats are knocked out. still deciding on how to go about doing this.

 

Keep us updated. It looks hood so far.

 

So im thinking about replacing the two secondary cats with just a stright pipe. Will this make any lights go on my dash board? The last thing i want is a check engine light.

 

Replacing the two secondary cats shouldn't raise any Cel errors as far as i understand as they are situtated after the second set of sensors so the ecu wont even know they missing...I was planning on doing the same, however i want to try an squeeze out as much power as possible

 

By default cats are not restrictive. They do not hinder air flow at all. The car also requires a certain ammount of back pressure to maintaine proper performance. Take for instance their pipes everyone buys. They keep the same overall pipe size but reduce the length of both the secondary cats and resonator. On my car I deleted the secondary cats and installed a magnaflow resonator. No CEl's,light smell, decent amount of popping on down shifts.
Everything I've read hadn't pointed me in going true duels or increasing pipe size. The motor simply wouldn't do much more. Thankfully a good friend owns a muffler shop and built my system. Drone isn't bad but I would like louder at some point.

 

I'm sorry but that part in bold is simply not true! How did you come to that conclusion? it doesn't take a rocket scientist to tell you that an exhaust without cats will almost always make more power than an exhaust with cats due to having better flow...look at the picture of the cat i posted above? and tell me how can having a blockage like that not restrict exhaust flow, the whole point of the catalytic converters is to ensure is has a very large surface area to force the flow of exhaust gases into every inch of the cat to perform oxidation and make the exhaust gases less toxic.
I do agree that certain motors do require a certain amount of back pressure to perform, but those are mainly smaller capacity engines, the is250 does not fall into this category.

 

While I dig up some older articles I'll leave you with this. Every motor needs back pressure. Take a small 6cyl motor like this one and remove all the back pressure. I'll be back with some good reads that might shed some light on this. Happy kwanza

 

I agree that all cars need SOME level of back pressure.

Why not just run an electric cut out?

 

In regards to the OP's search for "burnt" exhaust tips, I'd suggest getting some titanium exhaust tips and doing this:

http://my350z.com/forum/body-interio...-titanium.html

 

Okay sure, I'm always open to a good read....but my logic is this: Removing all the cats will not drop the back pressure to 0, the flow and design of the stock header will still provide some back pressure, i doubt it will be noticeable enough to change the way the car drives under normal driving conditions.
In addition if back pressure is that important, lets use the ppe tuned headers as an example, these have no cats and better flow to allow the gases to escape faster from the motor?

Let's say hypothetically we could remove all back pressure by not bolting on a header or exhaust or anything, i have no doubt that the motor would run like crap. So don't get me wrong, i do agree with you to a certain extent. However saying that the cats are not restrictive at all is untrue, overtime the cats become less efficient and even clogged in some instances causing a blockage.

 

Electric cut outs is a not a bad idea...however i don't like the part with the moving parts, a motor, switch and wiring. Just leave you open to more issues down the line. might start leaking, motor might stop working, switch might fail. the more pieces there is, the greater the chance of something in the system failing. so i'd rather opt for some R&D and get an exhaust note thats not too loud and not too soft for everyday driving that will still yield some power.

 

Thanks for this, i've seen this before while searching for ideas....however i couldn't find a titanium exhaust tip that was of similar quality as the stainless tip in my first post. My only options for titanium is to import them, and without seeing what the quality is like up close, i wouldn't risk it. Since my first post i haven't had much time to research it but from some brief reading it would appear that it cannot be done on stainless steel. same so i might have to abandon the burnt tip idea for now until i came across a similar looking titanium tip locally.

 

Headers are another animal. Let's not get these confused. They make power by generally having equal length runners to an overall larger collector. If you have a header system that's bigger then allowed say 3" over a 2.5" it will not allow for back pressure.
Now what I'm trying to convay is that the minimal amount of removing cats really won't amount to anything. Personal on my 350 I've removed the secondary cats. No dyno numbers but honestly other then a little more noise no real world gains.

I'm still hunting for the article I read a number of years ago on motortrend. In short it was about high flow cats vs no cats vs California's restrictions. They had some bench tests and what not.