jledford

iTrader: (1)

I went to a local event over the weekend for the inaugural shakedown run on my STU prepped HR 350Z and got dinged for sound. I ended up blowing a 96.6db, on a 96db limit. The sound meter was a little farther than SCCA normally puts it, at 65ft instead of 50ft, perpendicular to the finish straight. I was between 5000 and 5500 rpm crossing the sound line and didn't got much higher as it was right on the finish gate.

As far as engine mods I only have an Injen CAI and a Tomei cat-back exhaust. I'm running stock exhaust manifolds, stock cats, and stock y-pipe. All this still on a stock tune. I also had a modified silencer installed in the Tomei cat-back where I had drilled a bunch of 5/16" holes around the outside of the center piece trying to make for a bit better flow but still reduce the sound.

I had to swap to a second non-modified silencer for the exhaust and still was in the 94db range. I'm worried that if I go back to this site and they have a faster course and I get in the 6000 to 7000rpm range I'll exceed the sound limit again, even with the unmodified silencer.

I know titanium is louder than stainless which is part of my problem. I love the way the exhaust sounds but don't want to be a guy that gets a local site lost or is always right at the limit, possibly getting hit for sound when atmospheric conditions change.

Is there a quieter 3" single exit that would allow me to not worry about sound as much but still save a good bit of weight over the stock cat-back exhaust?

I've seen an ISR and AAM 3" single exit that are both stainless and both look to have either a large resonator or extra muffler under the car. I could sell my Tomei and swap to either of these and possibly have money left over:

ISR:
https://conceptzperformance.com/isis...33_p_18179.php

AAM:
https://conceptzperformance.com/aam-...fs3_p_2122.php

Any opinions on these? Any others to consider?

The final thing I have to consider is that in the future I want to put PPE headers on the car and high flow cats. At that point I might have to just get a custom cat-back made to get the sound down enough while still keeping 3" back and low restriction.

dkmura

iTrader: (64)

Consider having a 90 degree turndown built for your exhaust. Road racers use them to direct sound away from the sound meter without resorting to building a new exhaust.

03threefiftyz

iTrader: (25)

That seems really loud with stock cats/manifolds/ypipe....

...but yeah a turndown will help.

jledford

iTrader: (1)

A turn down is always on the list for a temporary solution, there are a few people doing this at that site already. I was just hoping for something more permanent solution as there's no reason I shouldn't be able to make the same power at a lower db. I realize I'll have to compromise on the weight of the exhaust a bit but that weight is down low so it's not a terrible spot to have a little extra weight.

SilverGLE

iTrader: (3)

AAM should be much quieter. Or, have a resonator welded in your exhaust, somewhere. a 12" Vibrant should do it. If you don't want to hack up the Tomei, get the Motordyne XYZ with the resonator.

I have a custom exhaust with a 3" Greddy RS (inlet) single muffler and a Motordyne resonated XYZ pipe. No complaints with sound, thus far!

jledford

iTrader: (1)

Well the Tomei is titanium so welding isn't the easiest. I know a guy that could weld it but would need a titanium resonator (and the Tomei already comes with one in it).

I'm going to look into the AAM.

Also as stated above I'll be going with PPE headers and hi-flow cats. To be STU legal the cats have to be directly after the headers, I've been told PPE makes custom y-pipes for this exact STU application so most likely will be going with them.

SilverGLE

iTrader: (3)

Does PPE make the y-pipe, or is it completely custom? If PPE does it, they may be able to stick a resonator in after the merge, depending on its design. I've not seen pics of a custom y-pipe with cats in it.

jledford

iTrader: (1)

I've been told that PPE makes the y-pipe, just have to call them about it. Anyone that is running PPE headers in STU has to have some sort of custom y-pipe with cats in it or else they aren't legal for the class.

SilverGLE

iTrader: (3)

Gotcha. Right, I'm aware of the cat replacement rule in STU.

Man those PPEs sound so smooth...

jledford

iTrader: (1)

I hope to get a set of PPE headers over the winter and have them on the car for next season, along with the catted y-pipe. Those are about the last power item I can add so that part will be done once it's tuned.

Anyways I talked with Z1 about my issue and they said the AAM is about the quietest you can make a 3" single exit so I got a quote and ordered one up. It's drop shipping from AAM and I will install as soon as it arrives. Hopefully before Oct 23rd so I can go back to the same venue with the new exhaust and see what I register on sound.

Glenn350zHR

iTrader: (5)

i ended up building a stainless steel catback with burns race mufflers in line that weighs somewhere between 15-18lbs. its quiet and makes power. might have it for sale in the coming months along with the PPE long tubes and ypipe that we talked about. that Tomei is insanely loud. its a thin-walled titanium which just acts an amplifier. i couldnt take it anymore. i was packing a turndown with steel wool last year at nats killing power. not worth the 5lb savings imo.

jledford

iTrader: (1)

I know we've already talked via PM about some things but please keep me in mind.

Glenn350zHR

iTrader: (5)

let me know how the AAM works out for you.


Heres mine

jledford

iTrader: (1)

That sounds great! I can tell is quieter than my current setup. Have you looked at any sound logs from national events to know what db range is normal for you car?

As soon as the AAM comes in I'll get it put on and to an event. Not all events down here have sound but we have events scheduled all the way through December so I should know in the next couple of months if for some reason it's not hear before the Oct 23rd event.

jledford

iTrader: (1)

The AAM arrived on Saturday and I put it on the car yesterday. It is much quieter inside the car and I believe should be good to keep me below almost any sound level. The way it sounds is ok but not nearly as nice sounding as the Tomei to me.

The fit on it is not as good as the Tomei. It seems like the pipes are about 1" to 2" too long and the muffler is ever so slightly touching the bumper cover. I'm not sure what I'll be doing about that yet but will need to find a solution. It also felt very twisted (for lack of a better term) when getting it on the hangers and trying to line up the flanges. Everything looked better with the bolts installed but loose but once tightened it pulled and twisted on the hanger rubbers pretty good. The closest clearance is near the W-brace, it start at about 1/2" clearance when fitting and is down to less than a 1/4" once tightened down.

Finally according to my step-on / step-off bathroom scale holding each exhaust the AAM is 26.5lbs while the Tomei was 14.5lbs so I gained 12lbs on the car.

Glenn350zHR

iTrader: (5)

As long as its not rattling against anything fitment wise all the exhausts seem to fit tight. The back bumper tho will melt if the muffler is touching. It should be quieter than the Tomei being stainless. Stainless is going to weigh more than titanium. My custom exhaust is light only because of the Burns race mufflers used.

GodISmE

I was told that these aftermarket exhausts make you lose a few HP/Nm and that the best option for HR is to leave the stock exhaust and just get rid of cats. Is that true?

dkmura

iTrader: (64)

The HR stock exhaust is simply too heavy. You can save 35# right there by going with a 3" single with a small muffler at the back. UpRev did recommend going to test pipes for a full race vehicle and my Touring class Z usually stays below sound limits at all the race tracks I've been to.

GodISmE

Test pipes resonated and / or with reflective mufflers or not? 2,5'' into 2,5'' Y pipe into 3'' till the end?

dkmura

iTrader: (64)

Probably better to start a separate thread to ask these kind of questions. Don't want to hijack this one and take it too far OT...