What about aftermarket resonators? Will imstill be losing 14 lb ft of torque?

 

The expense, in my opinion, is wholly worthless. The factory one is completely pass-through and stainless steel. There is no power gain to be found with replacing it. I suppose if you wanted to make the stock muffler sound better you could try it, but with the results I just got, the factory resonator would be the last place I looked for anything performance related were I to do it over. And the stock exhaust tips are not as aesthetically pleasing to me as something with a bit more heft.

I did consider doing an aftermarket one, hoping maybe I`d keep some of the throaty sound while still eliminating the raspiness, but in the end I figured the Borla exhaust sounds great on it`s own. Not to mention that an inexpensive resonator will be mild steel, not stainless, and it`ll rust...fast.


I go back to saying that Mazda did a damn fine job engineering parts and hardware for this car.

 

Thanks for the response... i am now a bit worried, i did the muffler delete, didnt feel any difference when accelerating but it sounds sooooo good. Curious about if the muffler delete gains or loses hp/tq.

 

Lost 14ft/lbs!!! Yeah, it picked up 3hp and moved the whole power band up (a lot), but it lost torque across the entire rpm range, and given torque is what actually gets the car moving, and it`s hard enough to get torque out of a 2 liter engine, I had the resonator reinstalled right away. Guess, what? The torque is back.


The point and conclusion? Keep the resonator, keep the torque. Yes, it sounds louder and throatier without it, but the performance suffers. I wouldn`t have believed it made such a difference if I didn`t have real world proof with my own vehicle.

Yep, what you did was change the design of the system. In doing so, you changed the flow characteristics. Probably the pulse timing went to hell, and with it any of the scavenging effect that gets you that bit of power.

 

Thanks voodoojef .... I've been reading/following several of your experiment threads and you time and effort really helps the rest of us that can't.

I'm sure I speak for at least a couple of members when I say THANKS!

 

^^^ Ahh man, just passing along my own experiences. I was really hoping to be able to jump on here and say "Hey, look what I did! And it turned out really great!" LOL. But nope, I tried something and it sucked so I figured I`d pass it along.

There`s a lot of utter bulls*it out there that folks just literally make up about modifying cars. It`s presented in a convincing enough manner that other people might believe it, then they blow hard earned money on whatever it is and it turns out like crap, and they end up having to somehow justify their decision by inventing some false positive about whatever. Instead of saying "I lopped off the resonator and picked up 4hp!" I tried to be very clear that the story was really "I lopped off the resonator and it drove like ass, and here`s real proof of why".

Glad to be of help. Here`s to whatever the next experiment may be :-D

 

I replaced my stock resonator with a smaller vibrant one and didn't feel any loss in power on my 2.5 but gained a slightly louder and deeper tone compared to stock.

 

That option was definitely on the radar. If the shop had already discarded my factory resonator, that`s what I would have done.

I have to admit, it sounded badass without it. Almost had an F1 car tone out of the Borla, just the slightest hint of raspiness that a smaller aftermarket resonator would have probably eliminated. But given the work we`ve put into the tune and the rest of the mods I was definitely not OK with giving up 14ft/lbs of torque. An aftermarket resonator may have a lesser effect on it, but that`s a test for someone else to pay for :grin2:

 

Just shows how much Mazda did on Skyactiv R&D.

 

Well on turbocharged engine it would help to remove all possible restrictions to exhaust gases, but seems Skyactive being naturally aspirated needs some "backpressure" to provide its power..

 

To get all overly technical and unnecessarily detailed, backpressure is never a good thing. It`s a myth propagated by the misunderstanding of what happens when too big a pipe is used for exhaust. What is really happening is the loss of "low pressure side vacuum scavenging". Exhaust gas velocity slows, which limits or eliminates the area of vacuum behind each pulse. Without it, the engine is left to simply push the gasses out as they come vs the flow very literally helping suck the next exhaust pulse out, keeping exhaust velocity high, keeping low pressure side vacuum high, keeping exhaust velocity high (and so on).

Imagine an engine spinning at 2400 rpm. That`s 400 cycles PER SECOND. The minute change in exhaust gas flow characteristics might not add up to much when it happens once, but when it`s happening hundreds of times per second, it can be enormous.

 

I always find that amusing as well. I'm no tuning guru, but backed up anything in not good. Having the exhaust system tuned to actually help the engine evacuate burnt fuel (via that vacuum/scavenging) and maintaining velocity is what you want to strive for.

 

Again, Mazda seems to have this 1 figured out. I've seen a few attempts to make a "better" header to replace the stock 1....only to see trouble & losses instead of gains.

 

Do you think resetting the computer would have maybe made a difference? I'm genuinely asking.

 

I do not. I am actually right in the middle of the ECU tune process (well, nearly done anyway) and I emailed OVT about compensating for the loss with some tuning calibration. Mat didn`t communicate it had anything to do with it nor would it solve anything so I am left to surmise It was isolated to the hardware.

 

Finally an answer that has been tested and can be proved with evidence! Thanks!

 

Interesting find there VoodooJef, thank you for sharing that. Never would have thought there would be such a performance decrease from removing the resonator. I wonder if the effect is even greater on the 2.5 L engines.

Makes me wonder now if need any supporting modifications before getting the tune. Always thought people with the best results from tuning are those who have the full straight through cat back exhaust (eg. from corksport where it removes the second cat and resonator).

Since there isn't much else we can do (intake, exhaust, maybe headers), would the best tune results be achieved from just an otherwise stock car? You said you gained quite a bit of power from your tune process, what other modifications did you have?

 

Mazda spend a great deal of time and money engineering the Sky Activ cars for optimal performance. One of the systems that they did well is apparently the exhaust. The header is a tri-y 4-2-1 pipe that is extremely efficient at scavenging spent gases from the combustion chamber. When you change things downstream, ie remove or change the pipe and resonator, you change the way the engine performs. The entire exhaust system is tuned to draw the spend gases away from the engine. Pulse timing is critical here. Altering pipe size changes flow velocity, and changing flow velocity changes pulse timing. When the pulse timing is off, exhaust scavenging stops working and you end up with spent residuals in the combustion chamber instead of fuel charge, so you lose power. This is apparently pretty important to how SkyActiv technology works, as valve overlap can be considerable at certain throttle settings.

 

I`ve got a Corksport intake and Borla exhaust. In my OVT tune thread I mentioned that in my first dyno session we also tested the stock airbox against the Corksport and it gave a rock solid 7hp at the wheels.

Here`s one caveat: I cannot tell you what diameter pipe the muffler shop used. I assumed they just welded in a section of 2" to match what`s there, but if they just welded up a piece that was 2.25" then there`s another factor. I`ve never seen dyno results from the full CS catback (or any exhaust, for that matter LOL). If they`ll send me one (just a mid pipe) I`ll throw it on and test it. I bet if it proved effective there would be a handful of folks right here that would buy one. Hell, I`d even send it back to them if they wanted it (or buy it if I really liked it), but I`m done cutting up my exhaust so unless someone hands me some bolt on components my exhaust research is complete there.

I bet if a slightly smaller pipe was used (48mm, maybe 45?) it would maintain torque and still support max HP.

EDIT: Just took a look. The CS cat back has a resonator. That`s very telling.

 

Yes you are right I totally missed that the corksport midpipe has a resonator, what I meant was that it removed the second cat which some people believe helps, don't know if that's true or not.

The only thing I worry about is the effect of increasing the pipe diameter to larger than stock. When I had an Ultimate Racing exhaust installed I had the shop add a 2.5 inch pipe right after the stock resonator up to the axle back and right away I noticed a loss in acceleration vs stock. Unfortunately I can't isolate if its the larger pipe or the actual muffler, or both. I switched it back to stock asap. Now I'm iffy about messing around with different exhausts/ mid pipes, too much work, time and money experimenting, though fun.

Good to know that the intake can definitely show real performance increase, though I think people were always worried about heat soak in the hot months. What are your thoughts on that?

 

I noticed a subtle increase when I put my Borla axle back on there, so I bet it was the pipe diameter. I am coming to learn that the skyactive system is very sensitive to change (for the better in some ways I`m sure).

**SO FAR** I am of the opinion that intake heat soak is utter bupkis. I ran some data logs for intake air charge temp with both systems. Average was roughly the same with both, and air intake temp was LOWER at WOT with the SRI (and it was 95 degrees that day). I`m guessing the the volume and velocity of air being pulled in at WOT with the short ram has the effect of rolling the windows down. The air itself is not any cooler at all, but more of it flowing wicks heat from the sensor (our skin, in the case of the open window analogy).

Think of this (again, getting more technical than necessary LOL): The air inlet for the factory airbox is where it is, then there is the air pathway to the actual box itself, which sits in the engine bay. The filter is between the box and the throttle body, and the filter more than likely can`t flow enough air to empty the box faster than it can fill, so **some** air hangs out in the airbox, doing what? Warming up to engine bay temps.

The only real difference we`d see is with a cold air intake, and even then the entire airflow pathway runs through the engine bay regardless, so I doubt we`d see a lot of difference. With that said, I do agree and have seen personally the difference it can make when an engine is making significantly more power. No matter how you shake it, it takes X amount of fuel and air to make Y horsepower, and with 300+hp worth of air passing through and wicking heat vs less than 200 it makes for a better argument, but even then you`re looking at a 3 or 4 hp difference.

Ultimately it comes down to getting the volume of air necessary into the motor. Otherwise you`d see 10,000hp funny cars running complicated systems to cool the incoming air. Believe me, the air scoop inlet on one of those engines is fully heat soaked. They don`t even have coolant passages in the block. I could go into why F1 cars have the inlets where they do but that leads to an entirely new discussion on aerodynamics, under car vacuum and low pressure trailing side vacuum.

 

And I just heard back from Mat at OVT. I sent him a data log I took without the resonator just to see what the numbers looked like. He said everything looks great, and the timing looked better than average so if anyone needed any further evidence that the colossal torque loss was related to anything other than the resonator, there it is

 

Got a little confused reading this, you're saying the data log looks good without the resonator but wasn't the whole point of this thread to explain that you should keep the resonator?? LOL do I have the wrong understanding here?

 

So... no before / after dyno results from the OP? Just butt dyno measurements and "supposed" actual dyno runs but no posted proof?

I replaced mine with a Vibrant bottle style resonator and haven't looked back.

Sorry OP, I need proof.

 

I really don`t give a damn what you need. FWIW, yes, I did run by the dyno shop the day after after leaving the muffler shop (thought I said that earlier, you know...in the very first post). I didn`t pull the figure 14ft/lbs out of my %$#. I don`t snapshot every dyno session. My bad. Didn`t realize I`d let you down, you being the only one who gives a @#$%. I do what I do as a courtesy to others who might have similar plans, it just so happens I have access to a dyno at nearly any time of any day, given I`ve known the owner of the shop for 17 years. I`ve posted snapshots of my dyno pulls all along the way in my tune thread, the last of which is scheduled for tomorrow morning to get a final figure. I`ll be sure to have a notary on hand to verify the results for you. :rolleyes 1::001_rolleyes:

 

OK Lets tone it down a bit. Play nice or somebodys going to time out

:rulez2:​

 

Ok, ok....maybe I overreacted. LOL. I`m normally the level headed one. Doesn`t mean I don`t mean exactly what I said, only that I could have been more delicate in my response.

I suppose it just pushed a button to come on and say "Hey guys, I spent money to try something, and it turned out for the worse so I spent more money to undo it" and have someone puff up about it. There is absolutely no glory in admitting something didn`t work, so if anything I threw myself under the bus. Meh, it`s only monday.

 

We all appreciate everything you've shared, @VoodooJef. Thanks....Let's all just chill.

 

Yeah...how do we even know you really own a mazda...haven't seen it with my own eyes...maybe you need to post your registration

Seriously, when a guy says I changed my oil and I can feel the car is faster, we all call bs. But when someone says I changed x, the car felt slower, and so I dynoed it and saw the results.....thats good enough for me.

And vodoo didn't say changing the res to another brand did it, he said removing it all together. So for those that replaced theirs with an aftermarket...you probably can never look back.

But to think that some modification can't actually hurt performance is stupid.

 

It`s all good. What irritated me was the fact that I`ve been excruciatingly thorough with my tune report and dyno numbers, going so far as to post screenshots of the dyno graph and video of my car doing a full pull strapped to the dyno from every session and I post up the results from a very simple procedure that I never intended to actually test anyway and someone tries to call me out on it?

Like I said, I really don`t care who believes what. It`s not like having an extra few hp ( or a few less, in this particular case) makes me some kind of legend. I just happen to have access to things other folks might not, and given that we all work hard for our money I figured it would be cool if I could report back on the actual, real results from various mods so anyone else thinking about the same thing can see what effect it actually has, and can judge whether or not it`s worth their money. The tune has kicked booty, and I`m headed to the shop in about 2 hours to get the final figures. Cutting the resonator out did NOT kick anything but rocks LOL.

 

I'm not sure why you took it so personal. It's just, if you managed to make a discovery regarding that back pressure from the resonator, don't you think that would be big news? We surely need more back to back testing to confirm your finding.

Had you have some actual data to back up your claim, that would have been a major leap forward. I wasn't trying to be negative at all. I guess I could have worded my post a bit differently... my apologies.