Did your plenum spacer change your exhaust sound?

I installed the Motordyne 3/8" spacer this last weekend and am very pleased. I'm trying to decide if I'm imagining that my exhaust sounds different. I have the orginal Stillen which can resonate in the cabin under specific load conditions. I swear it is less resonant now. It's just not happening as often or with the same intensity. My ECU has had plenty of time to learn about its new mod as I took a 400 mile road trip after install. I kinda noticed it on freeway travel but it's when I got back to town it was more apparent because you have a lot of acceleration/deceleration sequences.

It's kinda like the exhaust note has moved farther back too. Whereas exhaust sounded like it was in back seat before and a resonating under load, it is now sounding like it is coming out the exhaust tips. Am I crazy? Is there a technical explanantion?

 

I have the 1/2" spacer and original Stillen exhaust as well... My impressions are that the engine is a little louder now... not in a bad way. If this is true for you too, it may be that you are hearing the motor roar more now and thus the exhaust isn’t as noticeable - giving the illusion that the exhaust is tamer?... Not sure but that's what I found on mine.

Additionally (I thought of this after the fact) - depending on how long you've had you exhaust, or how many miles you've put on it, the exhaust very well may be mellowing out a bit. I found that to happen on mine after about 500-800 miles or so. Being as you have the original version (not the new quieter one) you have probably had it for a while... If that's the case I'm sure it has already mellowed as much as it's going to.

 

I think my Stillen was done mellowing 15K ago. : )

I will give your theory a shot in the coming days as well as trying to determine if I'm imagining things. More likely there is a simpler explanation like the high 90 degree temps in Oregon or me losing my hearing.

I'm not complaining. Everything sounds great as far as I'm concerned. It would be nice if the resonance zone was diminished but I've always liked the Stillen under hard acceleration and higher RPMs regardless. Mean and aggressive. I can live with the occassional sonic intrusion for all the times it sounds great.

 

Not to be a bore, but I feel compelled to relay... I originally set out to buy a true sports car - test drove RX8 (always loved the late version RX7), version 8 was weak... drove the 350Z, LOVED IT!, probably the most fun to drive car I have experienced!, but cabin wasn't quite right... Drove the G coupe and it was pretty much the right mix...

Then the dreaded occupational consideration. When I first sought to buy I was unconcerned about anything but performance and a little comfort… during my shopping I was offered a position (occupation) that required long computes and 2-3 client capacity > No-brainer = G35 sedan AT. Done deal. Happy with the decision until...

Currently NO long commutes (unless I choose a road trip), NO client need (but might change) - so I have been on a quest to make my (overlooked semi-luxury sedan) perform like the car I sought out to buy.

Moral of the story?... My car must perform. Period. Thus, Tony's spacer, Stillen's exhaust and CAI, and future headers will have to be tolerated by any corporate schmuck that sits in my car in the future. All my little extras shouldn’t be audibly noticed to a casual or business rider.

That was a little more than a little off-topic, but since sound of exhaust was an issue, I had to convey the reason behind my madness... now what coupe wants to race me?!!!??? J/K (sort of)

 

My experience and opinion:

Changing inlet air flow rate and/or air flow distribution by adding CAI's, plenums, plenum spacers, etc. also changes exhaust gas flow and thus sound. Exhaust note changes are more noticable with most aftermarket exhaust systems. Stillen's may be the most pronounced due to the x-pipe's exhaust gas scavanging/cylinder charging characteristics.

 

Appreciate the input all. I went out last night after changing my oil and tooled around. I'm still thinking it's not quite as intrusive as before. I keep accelerating and waiting for that few seconds of resonance in the 2-3K RPM range and it doesn't seem like it's as intense. I concede the "ear dyno" might not be all that scientific but, intuitively, it makes sense that modifications to the air flow system would change the tone characteristics.

My theory: formerly exhaust gases moved through the system at a different rate (presumably slower). At some point in the exhaust system the turbulent gases became "stuck" and tumbled about at the "resonance point" until they air flow increased enough to pass through this stage. With the spacer, air flow is increased from the get go. Exhaust gases stay in the resonance zone for a shorter period of time due to the increased air flow. Possibly they do not even reach the former air flow rate which caused the more intense resonance.

This is my English/Journalism major theorem so big grain of salt.

 

OCG35: I can relate to your story. I have a couple kids so the sedan was the obvious choice. At the time we had another sedan which was smaller (Volvo S40) so the G was to be the road trip and family hauling car when necessary plus my own ride. A few months later we traded that Volvo for a new 4Runner. The T4R immediately took over all the family duties. I use my car for work and my thing. 90% of the time I'm solo in the G. I could have easily gotten a coupe and lived with it. Not sure I would have though. Something about the coupe's rear end doesn't do it for me. I really enjoy my sedan and it's performing very well. Ultimate stealth!