No Cat midpipe for NC

v67gsr · Post by **v67gsr** » Wed Jan 03, 2007 11:37 pm

Hi Brian.

Any idea if there will be, when will be, midpipe with no cat for NC?

I don't like RB one cause of the pipe size. Your midpipe (with cat) size just perfect to me ut I don't want any cat in my car, at all.

Post by **Brian** » Thu Jan 04, 2007 8:58 am

Why do you want it with no cat at all, what do you think will be gained?

v67gsr · Post by **v67gsr** » Thu Jan 04, 2007 9:46 am

Brian wrote:Why do you want it with no cat at all, what do you think will be gained?

Because I aleady have a target set for my engine. Bring it up to 8000 ~8300 rpm redline range. It is no point for me to put parts that will later generate restriction into the whole system and need to be change again. Plus I prefer buy OTS products instead of custom made. I like your midpipe cause it meet all the spec I seek for except the cat part.

Post by **Brian** » Thu Jan 04, 2007 9:58 am

It is an unusual single biscuit spun cat...you can't measure the restriction with stock redline though I suppose you might measure some at 8000rpms. We include it for several reasons.

Those wanting to add the race header (or our coming header) can easily mount their O2 sensors either side of this little cat (our pipe is threaded already) and avoid codes. They also avoid that nasty smell of unburnt hydrocarbons at stop lights that comes with having no cat in a drop top Miata. It is the least restrictive cat we could put in there and still have a cat...and we went with the spun design because the addition to weight is the lowest possible.

That very small cat also makes a great resonator. Did some experimenting with cats of different sizes to kill that 3000 rpm DRONE/ BOOM that this motor really wants to make on decel when uncorked. The extra short chambered cat did the best job on that...

Thus, sorry, we won't be making a version without the cat...

v67gsr · Post by **v67gsr** » Thu Jan 04, 2007 10:07 am

Brian wrote:It is an unusual single biscuit spun cat...you can't measure the restriction with stock redline though I suppose you might measure some at 8000rpms. We include it for several reasons.

Those wanting to add the race header (or our coming header) can easily mount their O2 sensors either side of this little cat (our pipe is threaded already) and avoid codes. They also avoid that nasty smell of unburnt hydrocarbons at stop lights that comes with having no cat in a drop top Miata. It is the least restrictive cat we could put in there and still have a cat...and we went with the spun design because the addition to weight is the lowest possible.

That very small cat also makes a great resonator. Did some experimenting with cats of different sizes to kill that 3000 rpm DRONE/ BOOM that this motor really wants to make on decel when uncorked. The extra short chambered cat did the best job on that...

Thus, sorry, we won't be making a version without the cat...

Oh, so it is a single biscuit type. Sound good. I will do more research then.

I have the Club Race exhaust right now and love it. Only problem is the pipe is still a little smaller than my ideal size, and the location of the exhaust outlet make it fairly loud to general public (music to me but my passenger all sufffer). However, I got someone willing to pay reasonable good $ for my Club Race exhaust so I am looking for alternative system.

Post by **Brian** » Thu Jan 04, 2007 10:15 am

I see...if you like it on the louder side (yet not as loud as the cup exhaust) consider our RACE RoadsterSport with the new midpipe which will give you 2.5 inches of flow all the way.

v67gsr · Post by **v67gsr** » Thu Jan 04, 2007 11:05 am

Brian wrote:I see...if you like it on the louder side (yet not as loud as the cup exhaust) consider our RACE RoadsterSport with the new midpipe which will give you 2.5 inches of flow all the way.

I think the problem with Club Race exhaust being that loud is due to the location (right under the trunk) and position (pointing downward at angle) of the exhaust outlet. Much of the sound wave end up bouncing back to the trunk area and transfer into the cockpit.

I do suspect DC/Mazdamotorsport do that in purpose to lower the sound volumn measure from outside (may be to meet exhaust volumn rules) yet to keep the maximum flow speed and volumn.

miataman · Post by **miataman** » Wed Jan 17, 2007 10:17 pm

Would you expect significant gains from removing the stock cat from the midpipe?
I am talking about in comparisson to the stock midpipe.

I am considering as a next step to delete the second cat (The first was deleted with the installation of the header) and use some sort of by-pass of the 2nd O2 sensor with a simulation or something similar.

Post by **Brian** » Wed Jan 17, 2007 11:19 pm

Nope, these modern cats are not very restrictive. It is all about total flow through the midpipe and you need the diameter for that. Simply pulling that second cat but keeping the same diameter tubing won't change the flow significantly...

miataman · Post by **miataman** » Thu Jan 18, 2007 8:39 am

Thank you Brian!
My problem is that I am experiencing some pretty nasty drone from the exhaust in the 3-4k rpm region and I am considering ways to solve it.
In addition to that I have found laptimes to drop mainly from 'driver improment' and secondary from setup changes (and good tires of course) and good brakes.

So I was considering deleting the cat and perhaps the resonator from the stock midpipe and use the stock back-box.
This way the car would look stock too and wouldn't attract attention like it does now.

What would you suggest?