The TRUTH about aftermarket exhaust drone

F.I. Inc. · 09-19-2013, 11:48 PM

Quote:

Originally Posted by ped

Other manufacturers are probably guilty of this as well, but FI is the one I (now) have experience with, so unfortunately I have to pick on them. I just had a FI catback with 18" resonators installed two days ago. Despite claims all over this forum this system has drone and a lot of it. 7AT drivers who leave it in D will find themselves in the tallest gear most of time - pressing the accelerator in this situation (but not enough to force a downshift) will bring on drone like crazy, turning the interior of the car into a low-frequency resonance chamber! Some people may not care about this, but the fact remains that all the claims of "no drone" are not true, and I wish someone had made this more clear around this forum - it would have saved me a lot of wasted money. So new people researching an exhaust for your 370Z and considering Fast Intentions consider yourselves warned.

For those who care or later find themselves in the same position, I want to let you know the answer to this problem is that Fast Intentions (and possibly other manufacturers) are building their exhausts minus a very important item - a Helmholtz resonator. This type of resonator attaches to the main pipes at a 90-degree angle, and is capped on the end. The shape doesn't matter (J shaped, etc) as long as it's the proper length - basically what you need is to know the frequency of greatest drone (say 120 Hz for example) and then shoot for a resonator that is 1100 feet / frequency / 4 in length which gets you a tube length which will have a natural resonance 1/4 of the wavelength of the worst drone. Since this tube is closed on the end that doesn't attach to the exhaust pipe no exhaust really flows into/through it, rather a standing wave is established (like when you blow over the top of a Coke bottle) which cancels much (or all) of the drone. Similar to noise-canceling headphones in concept.

Why FI and possibly others are leaving this out? I'd guess it's the inability to determine the proper frequencies needed since the catback may eventually be combined with other items like an HFC, different exhaust header, etc. Thus what would work with stock cats and headers wouldn't necessarily work (at least as well) with aftermarket replacements of these items.

My beef isn't so much that they leave them out, it is that so many fans of FI in this forum make FI exhausts out to have NO DRONE which is absolutely nonsense as I can tell from having it installed two days ago. At a minimum people need to have REAL information before blowing 1100-1200 dollars on an exhaust that can induce headaches or at a minimum be highly annoying. I'll probably get flamed for this since FI seems to be so well regarded here but I wish someone would have warned me before I wasted money having this installed and now will be paying labor charges again to have the stock system put back on (or to have Helmholtz resonators welded on) plus loss for restocking fee since the exhaust can't be sold as new anymore.

For the curious who want to see the outcome of the calculation above, for a drone that is worst at 120 Hz here is how to get the length resonator needed to counteract it:

1100 / 120 / 4

= 9.16667 / 4

= 2.29167 feet

(times 12 for inches)

= 27.5 inches for the length of he Helmholtz resonator tubes

Ped,

First and foremost let me be the first to apologize if you are unhappy with the result of your purchase. That being said I feel that the tittle of your thread is misleading and unfair. You need to understand that sound is subjective and everyone perceives it differently. What may be loud and have drone to one person may not be loud nor have drone to another! Not anywhere on my website page do I state the exhaust system has NO DRONE. I state that it has no rasp and that may actually be a little misleading. I should state that certain combinations have no rasp! I will be sure to change that shortly.

Now let it be known to everyone who reads this that you DID NOT purchase our exhaust through us. You purchased it through a third party vendor and I have no control how the purchasing process took place. I have no control how you were informed or educated on the options available.

I can tell you that every single one of my systems that I sell, I take the time to go over every option with each individual customer. I have been doing this a long time and have sold nearly 900 units for this car. For you come up with a thread like this now is a little unwarranted and ridiculous in my opinion. You are clearly have a bad taste in your mouth over your buying experience with the vendor and are directing it at us, NOT COOL! You should of resolved this with them in a private manner opposed to attacking us on a subject where subjectiveness of sound plays the main factor.

There are 100's of reviews out there. Here on the forum, on our website, YouTube, ect... I have hundreds of satisfied customers running different combinations for this car. Are there unhappy people out there who may have buyers remorse, sure but that has happened to all of us at one point or anther in life. You cannot make every single person happy however we try. At the end of the day I know our satisfaction rate is in the high 90 percentile.

Now you emailed me Tuesday 9/17 and stated that you were "regretting" your purchase. I took the time out of a courtesy to email you back in detail in response. Now I could of just told you to deal with the shop you purchased it through because you were not my customer. However, I took the time to go back and forth in emails with you answering all of the questions you had for me. After all, it is my product. I explained to you much of what I wrote above and that the interior sound should dissipate roughly 10% once the resonators broke in and had some mileage put on them. You emailed me back stating that the combination you purchased was our quietest however not quiet enough. You asked if I had a quieter muffler to interchange. I responded with saying that unfortunately we do not have a quieter option than what you purchased and every once and a while our quietest option is just not quiet enough for some. I closed by saying the best thing to do moving forward was to contact the shop you purchased our exhaust through. Again, I will state if you feel like you were mislead than I do apologize. Not at any point did it come from me nor anyone from Fast Intentions, Inc. You can ask anyone who has dealt with me or my company. We take the time to make sure every single customer is satisfied and comfortable with their purchase!

All of this being said, I am more than willing to take time out of my schedule to talk with you over the phone. Even though you are not directly my customer, I would like to hear your side of the issue one on one and see if there is anyway I can help.

Thank you for your time.

Tony

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