Both Milltek and mqubed/mariokart catless downpipes seem to be pretty popular. Are there any significant differences between them? I understand that both will throw CEL that can be tuned out. I believe both have good fitment and welds. So for a seemingly unsophisticated piece of metal, does it matter which one I choose?

 

paying for name and price, only difference.

 

But lots of experience in catted and catless downpipes. For catless, unless there is a major kink or turn in one, or a bad weld, walls - their performance should be indistinguishable. Just removing any air restrictions is the big gain. Catted is a whole new game though

 

so what’s the best catted / decatted on the market today?

 

"Best" is really a function of what you are looking for ....

Could be reducing pressure loss in a Forced Induction application, not throwing a CEL, being quiet as stock, passing emissions in CA .... all depends.

For one of my applications - I went with the Miltek catted. It greatly reduced pressure loss, was not significantly louder, was a drop in, paired well with a borla exhaust and passed the smog requirements where it is lic'd ( NC ). I did need to tune out the CEL though ( don't confuse the physical part of emissions testing ).

I used to do a lots of forced induction in early gen Miata's - in that case, I went with home built catless - as there were not bends. I replaced with a short resonator - so actually looked like a thin cat. Still passed smog and was a little quieter than an open pipe ... or at least deeper and not raspy.

One of my friends, Corky Bell who is an OG F/I guru told me the best thing you can do is to run a 0.5 - 1.0 inch diameter bigger cat then what you have. This really minimizes pressure loss - but you need to have room to do it. He has even run 2 race cats in parallel.

 

Would love to hear from the man himself @MarioKart

 

And see if he responds to your question

 

Or I can ask in a public forum so that information is available for the next person that has a similar question?

 

Pretty sure Mario will say his is best....

 

im sure he will. I’m hoping to hear if there are any real benefits to going with his. I came across an old comment of his saying his new DPs don’t throw a CEL like his old ones did. My brain tells me it’s the tuning but his post read as if it had to do with the hardware itself.

 

That is assuming he sees the thread .....

 

did you see where I tagged him?

 

How are folks getting their high flow cats to pass when tunning them out? Don't your states emissions just pull OBDII data? To tune out the CEL, the downstream O2 sensor basically has to stay in "ready" mode. Here in Arizona, this will not pass emission, trust me, I've tried.

I am trying to find a high flow cat that will still pass the OBDII test and it seems maybe this isn't a reality.

 

Here is what some have tried:

https://www.northamericanmotoring.co...cel-6-fix.html

And I believe Mario has adjusted/angled the second 02 sensor on his downpipe to avoid CEL ( don't take this as fact though ... - you should reach out to him )

 

Put your stock one back on for emissions and switch back once passed, did this for years with my Sentra. My R53 is catless and no resonator, I have a spark plug anti Fowler drilled out for my bottom 02, no cel and it’s not tuned out, but different engine.

 

I would like to avoid having the swap it out once a year if possible. Although it looks quite a bit easier to do on this car than most others I've worked on over the years. Turbo studs are prone to getting brittle and snapping them makes for a bad day. The defouler method is usually a solid play, I may just give this a try.

 

I’m pretty sure the only way is a stock downpipe. Even with a sports cat, I’m pretty sure it’s going to throw a code, unless it’s tuned out. I have the w11 so, like I said before totally different engine. I had a n14 and I’m pretty sure with the 3 years of researching I had done, while owning it, there was no way to turn the light off other than a tune, hence why I went with a catless one. We don’t have an emissions check in Cincinnati, so I wasn’t to worried about it, the r53 was picked up with intention of keeping it the way it was, however a blow stock header just below pre cat, made me go a different route. I had a catted header on order, but was on back order for 2 months, which led me down the catless route with a drilled out Fowler. It did pop a p0420 when i was stuck in some nasty traffic, but I cleared it and haven’t seen it since. But supercharged vs turbo.