full 3" exhaust system getting blow back
 

Hi guys,
ok, let's start with the "WTF happened here"

1) got Mangok's custom made single output exhaust system from header back. 3" all the way, using a magnaflow high flow cat i believe, + 1 resonator, then ending with a single output magnaflow muffler. Loud as shit, but i feel a difference with the car breathing better..

2) out of curiosity, I wanted to know if it will pass Emissions testing in Ontario,Canada (laugh right now) and when I tested, epic fail. No worries, I have 5 months to decide to slap on the old exhaust before i need a sticker.. so anyway..

3) the results are.. quite shocking. on Stock exhaust, my car did pretty well on a previous e-test. (was worried since it's rotary, could have been an emissions nightmare, but the stock catalytic actually hides more than you know) passed with flying colours. this time, i'm looking at the hydrocarbon content and it's skyrocket to around 298 I think (pass is 63). Everything was just not reading to passing levels, they're ramped past and blew the limit out of the water.

4) i'm curious as to why i get popping when I drive every now and then (usually staying in gear without acceleration to slow, i hear a pop) and looking around the thread realize this is unused fuel blowing up.

5) with Mazdamaniac's tune on stock exhaust, car runs amazing. with new exhaust, has the pop every now and then, some compromise on the mileage, (used to hit 400km, now close to 380)

The mechanic who did the test says I'm running too rich.

Plugged the COBB in, monitor what's going on, on WOT I see it go to 12-13 on AFR, when on cruise, I'm at 14.5-15, almost always trying to hit 14.7, when I let go of the throttle, i see the number spike up to 20.4 or so until it calms down.

Looking at previous threads
https://www.rx8club.com/series-i-aftermarket-performance-modifications-23/question-going-catless-accessport-164776/
this states that the optimum AFR is 14.7, and Mazdamaniac states power gain should have AFR around 13.

Initial threads about the COBB state that it doesn't really matter what you're blowing out, so exhaust system shouldn't play a big part on this (I do read too much and get my info mixed up.. if this is incorrect, let me know)

my issue - 1) want to get rid of that popping if possible, and 2) I know WCS said just slap on the old exhaust system and test, but I seriously think that there's a better way to tweak this new system so it's not as rich, bring back the small MPG gain, and even out the new breathability of the car..

Essentially, I think I need Jeff's help to re-tune, but want to see if anyone had a similar setup and tested with a COBB to see if this is normal?

I wish I had it plugged in and monitor before I changed the exhaust system up to compare numbers. Not sure if Jeff made it more lean than stock to get the HP gains.. but I do remember him telling me to get rid of the catalytic if I want to free up more HP, and this new system looks like it did (high flow cat is tiny compared to the stock cat.. don't tell me it's restricting the same amount of air)

Ok.. done with the rant. Let the counter posts begin!

Thoughts? have you got your 3" exhaust setup pass Drive Clean emissions? :)

No CAT...NO PASS :)

Very simple :)

If you don't want the pops , put the CAT back in also.....

Otherwise...live with the pops...your AFR sounds normal....14.7-14.9 cruise is OK..and high 12-13.s is fine NA for WOT without a cat

has the "high flow cat".. does it count?

Not always...I had three fail on my car in short order.....

Put the stock CAT and catback on for emissions...;)

Live with the pops...cause sometimes they are flames :) and thats cool :) when you have the midpipe on

wow.. yes, thanks for the insight.. makes me want to think about slapping the old one back and having them re jig the whole exhaust.. may need to get a local shop here to make a new setup with the stock cat. sucks though! really like the setup, but I guess one day this will fail.

Boo-urns!

Cat-back will have no impact on emissions, cat will. Do you know what brand/model of hi-flow you have? Just curious for comparisons. I want to try an e-test with the BHR catted pipe.

I wouldn't consider what you are running to be "too" rich. Tuned by Jeff, my car hits about 11.8-11.9 at WOT near the redline. It is richer than most cars run, but then again they shouldn't be redlining it for an e-test. ;)

Get them to weld in the Davesport 100CPI cat.
http://www.davesport.com/cgi-bin/davesport/DCAT100.html

May not meet E-test standards but it's middle ground between stock and nothing

For clarity, perfect, perfect, perfect.
Unless I missed it in a previous post, you will always see large AFR's when coming off the throttle. This in NORMAL behavior.

Hey DB, I can't wait to get an e-test done on the Davidsport cat .... should be interesting to see what we get.

Scott you getting it done? Let me know how it turns out please!

I wish I had a picture of it before I had it installed (yes I know, could have done myself, but I was sick that time).. I don't know actual part from Magnaflow but looks like the standard (small) high flow cat that they offer.

yes, curious to see how this turns out..

I'm ready to return back to stock cat eventually (was told that one day, this setup will fail.. soon! ) and if that's the case, the other alternative is to get that back on and find a catback setup.

if we can find the "best" solution for better air flow + emissions qualifying, I'm game for it!

you can find pics of the exhaust I got from this thread

https://www.rx8club.com/rx-8-parts-sale-wanted-44/3-custom-exhaust-magnaflow-single-exit-197983/

You can always try the HJS cat. 200cpi core, ~$500. Should last longer and clean better than the davesport

Why did his efficiency (km/l) decrease?

don't know what it was but I think I'm hovering close to 400 again. So yeah, aside from go emissions pass, life is good.

bumping this up! Scott did you ever do the e-test on the Davesport cat?

Nah not yet.
We have the Davesport cat however.
Warren is working on getting someone to fabricate it in to the spare RP Supercat midpipe I have.

Will post result as soon as it's completed.

I'm going over to his place tonight sooo I'll put the bug in his ear again.

The pipe is at the shop... I need to go check on this... it's been there a while :(

BHR is now offering the Davesport super cat on there pipe so they must know something.