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Discussion Starter · #1 ·
I have pretty much all access to a dyno shop, so when it comes to testing things for power I can get more than butt-dyno confirmation almost instantly. Yesterday I had the muffler shop cut out the resonator in my `16 2.0 and run a straight segment of pipe. Figured "eh, the resonator is completely pass through anyway, might as well open up the sound a little". Well, it felt a little doggish when I left the muffler shop, but I chalked it up to being tired (me, no the car). Drove it around a bit last night, still felt lame. Ran it on the dyno today.....

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.

It might not make a difference on an un-tuned car. On mine, with roughly 29ft/lbs more than stock, it was a kick in the balls.

Years ago Stillen built an 1100hp 300ZX that was loaded with all this high rpm HP stuff. Steve got in it and drove it, and said it was nearly undriveable when he got back. It made such little torque that it could hardly get itself moving. Of course once it got to 6K rpm it hauled ass LOL.

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.
 

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Discussion Starter · #3 ·
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.
 

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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.
 

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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.
 

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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!
 

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Discussion Starter · #7 ·
^^^ 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
 

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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.
 

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Discussion Starter · #9 ·
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:
 

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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..
 

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Discussion Starter · #12 ·
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.
 

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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.
 

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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.
 

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Discussion Starter · #16 ·
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.
 

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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?
 

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Discussion Starter · #19 · (Edited)
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.
 

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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?
 
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