Catless/ strait pipe vs. cat effect on mpg?
 

Hey guys, like quite a few other people on here I have a catless midpipe, and like everyone else it throws a code so the engines in limp mode.

My question is, how much of a difference in mpg would there be with a good cat not throwing a code vs the catless midpipe throwing one? would the better flow increase it at all?

sounds like you have a failure of a front o2 sensor. So it's not the catless midpipe it's the faulty sensor causing the car to go into limp mode.

https://www.rx8club.com/series-i-trouble-shooting-95/o2-sensor-failure-front-rear-192278/

funny, I've never heard of a bad O2 sensor or catless midpipe causing the PCM into limp mode

funny, i have

yeah, you and everyone else I suppose

too funny, actually ...

Okkkkkkkk so regardless of how funnny it is, a gutted cat throws a code for most of us.... aaanyyy word on the mpg effects?

it throws a code and indicates this with a check engine light, but it does not make the PCM go into "limp" mode. The engine will continue to operate normally in spite of the code. If you want to get rid of the CEL/code you will either need to install a cat converter or cheat the system by blocking the code with a Cobb Accessport. MPG just depends on how you drive or what cat you may or may not have. Some high end racing cats will flow the same as a cat-less midpipe.

If the Engine light is on, chances are it will not go in open loop, meaning it wont ajust for the best performance/economy it will stay with the base maping, where it is important to get flashed if your are to modify anyting on the engine to put this ''limp mode'' values where you want them to be... even cancel your MIL light for these normal occurances (having not cat)

So even if your just running a less restrictive exhaust and intake, its a good idea to get a COBB ? Or did i misinterpret?

you didn't misinterpret, but he doesn't have any clue what he's talking about and is wrong

Ive searched around, how exactly do you get a Cobb Accessport, I just got an agency midpipe off rotary to complete my exhaust and I'm sure it will throw a CEL

you can order it from www.mazdamaniac.com

When I had my high flow cat and throttle coolant bypass I did notice the secondary air pump running all the time (high pitch wine during start up). Meaning it was trying to warm up the car/cat faster (open loop) and dumping more fuel. Ever since I put stock cat back for smog and undid the throttle bypass, I got way better gas mileage about 20-50 miles more on a full gas tank, but I did lose bottom/mid end power. Also my exhaust tip started to melt my shroud due to the excess heat :(.

searched around, as in glancing quickly over your shoulder? :rolleyes:

the results will vary greatly depending on the cat converter being used and the tune

no

to the op-
if you like the sound you will keep your foot in it more causing you less mpg. if you dont like the sound you will put your foot in it less, causing better mpg.

Having a midpipe will not throw your car into limp mode :), just cause you to fail smog emissions with a static CEL. Blinking CEL will throw your car into limp home mode (something mechanically wrong). With that said, when i get my RB dual resonated midpipe I am removing my secondary air pump :). power > mpg, gotta pay to play. I didn't expect good mileage when I decided to get a sports car.

drove a few hundred miles with agency midpipe, no CEL. thus thankfully no expensive cobb, i get roughly 300 miles to the tank on average I'd say the full exhuast helped out quite a bit, of course on the weekends.. it drops severely ;)

Nah that can't be, really???
I'm not saying you're wrong I just can't see the connection.

1) The secondary air pump has no way of knowing the Catalytic temperature. It comes on when the car is cold and runs until a certain engine temperature not catalytic temperature.

2) The engine is NOT in Open Loop when trying to warm up the car/cat faster. I don't know where you got that idea.

3) The Throttle Body bypass you undid it? Huh you mean you put it back to stock? Anyways I still can't see the connection on the secondary air pump.

I honestly don't think the the TB bypass and the cat delete will largely impact the time for a vehicle to warm-up.
Maybe it was just colder when you had the mods vs stock setup?

Just say'n -- if you have more details I would like to here them. I'm ready to be convinced.

A blinking CEL doesn't always put your car in to limp mode. Most times it's indicating a misfire.
It's not really relevant whether the CEL is on or flashing the code that is important.
For example you may have a Failed OMP which should put your car in to limp mode and throw a CEL (solid check engine light).

I can't think of a flashing cel that will put your car in to limp mode, maybe a misfire or knock event.

@wcs

My car still has mods, only difference is the coolant bypass and the cat delete were removed. I'm thinking the reason I used more fuel was because more cold air was going through the engine, and colder air is more dense than warmer air, meaning dump more fuel, you are right on the money sir. And I realized there are other sensors mainly temp that determines open loop/close loop. I think the secondary air pump was going crazy since there was no cat? (maybe the ecu is triggering the pump to turn on to increase oxidation since o2 sensor is detecting alot of emissions, dunno just a speculation).

You are right with the flashing CEL, most of the time its a misfire, and the computer can try to adjust. I just remember my buddies truck who had a bad MAF and he kept getting misfires/weird fuel trim data and no power. Thing was the MAF code never popped up, it gave us a run for our money.

Just thinking out loud here,
The IAT is before the TB so it's curious how this mod effects things both with the Stock setup and the bypass setup.
(FYI I'm using the bypass setup, I'm also boosted just so you understand my perspective on rolling this around in my noodle)

Actually IIRC temperature has nothing to do with OL or CL.
There are two parameters:
1) Load
2) RPM

The vehicle is always in CL until the engine load limit or the RPM limit is reached.

Could be, I don't know what all effects the Secondary Air pump. <shrug>


LOL
We've also completely hi-jacked this thread but oh well, it really wasn't a good thread topic anyway.

/start full thread jack mode

To the OP,
When you put a midpipe on the car, you reduce backpressure and the car will want to run leaner. The O2 sensor will detect this and the ecu will compensate to bring the car back into it's assigned operating perimeters. Without changing these settings in the ecu, you may gain a little horsepower, a lot more sound and little else. You have to tune the ecu to run leaner to get better fuel economy.
For many it's easier and cheaper to modify their driving habits.

to be honest, your description fits pretty nicely haha anyway is there a midpipe that wont make the car sound ricey..? I like the agency but dang it makes the exhaust hella loud.. I dont know what people are talking about, i haven't gotten any CEL's with the cat off.. limp mode sounds like a personal problem to me

I have seen a couple 2004's that did not get a cel from removing the cat, I am not sure why. IMO loud exhaust does not = rice. A rotary engine has a distinct sound, nothing like a 1.6 d series Honda with a coffee can strapped to the back. If you do not want the car louder put the cat back on.

It's threads like this that make me realize humanity is ultimately doomed

Loud does not = Rice

Rasp at any volume = Rice

Just my 2:o: