thought I would share pix of my new exhaust. I'm a 335 but I thought you guys might also be interested. I bought the exhaust from a local guy in Maryland. He had had it made by a company in Elkridge called Benchmade Proper. It's a 3" downpipe back exhaust with vibrant cylinder resonators and vibrant oval resonators. It has quad tips that are amazing. Everything is 304 stainless and tig welded by the owners, Joe and Brian. I took the exhaust to them after a day of trying to hang it on jackstands with a torn rotator cuff. I just couldn't pull it off and I also wanted to develop a relationship with them as I may expected to have the exhaust modified to my specs should there be drone or poor fitment, etc. I went to BMP on a Saturday morning and had the exhaust hung and the bumper cut.
Benchmade Proper is really small shop and just starting out but they are starting for the right reasons. They don't cut corners or overpromise. The materials are quality and they're willing to accommodate all requests. Their workmanship speaks for itself. I'm really happy with how it turned out. Joe cut my stock bumper and it looks great. I expected to end up buying an Mtech if this didn't work out but I'm completely satisfied.

The exhaust is pretty boomy - lol at that description given my screenname but that's the first word that came to mind - at 2000 rpm. It was obtrusive at first but seems to have mellowed a bit. I will ultimately install downpipes though and am concerned about drone as my car is an automatic. I've been researching like hell about side branch resonators, aka helmholtz resonators, aka anti drone canisters, and would appreciate any and all advice. Essentially the side branch resonator is a capped tube that T's into the exhaust and adds 1/4 wavelength of the offending resonance frequency. My question is how to calculate that length. My car is an inline 6 and the peak drone is at 2000 rpm.

This is one of the more helpful things I've found.
6 cylinders @ 2000 RPM (250 deg F)
CFR = (2000/120) = 16.67 Hz
EFR = 6(CFR) = 100 Hz
c = 49.03(460+250)e0.5 = 1306.4 ft/sec
lCFR = 1306.4/15 = 87.09 ft
lEFR = 1306.4/100 = 13.06 ft
Tail Pipe Length = 13.06/4 = 3.26 ft (or 9.79 ft)

CFR = Cylinder Firing Rate
CFR = RPM/120 for 4-cycle engines
EFR = Engine Firing Rate
EFR = N(CFR) where N = # cylinders

What this tells me is that I need a 40" side branch resonator added to each pipe. That's fine except everything else I've read said that 26-28" did the trick. I don't really trust my calculations here but don't want an exhaust shop spending ALL day playing with pipe length to get things right. Has anyone had any experience with side branch resonators?
Enough with the typing...




















The exhaust gets obtrusive around 2300 rpm but only under load in 6th. It doesn't drone it more like booms. I'm considering adding sound canisters (similar to what's used on a G37) in the near future. Joe knew exactly what I was talking about when I talked with him. In fact, he was doing that exact same thing for an RSX later today.

I'm very pleased. The quality, fitment, and attention to detail that Benchmade delivers is awesome.

 

Nice work!

 

Branchmade proper ftmfw!!!!!!!

 

I've heard great things about this shop. Gojira had it's exhaust done there.

 

I was thinking about getting an exhaust made there also...they've never done Pcars so they are looking into mine as a shop promo car to get them into the Pcar market...

they do nice quality stuff for sure...

 

That is a great looking exhaust.

I might have to get them to fabricate some headers for me

 

Really impressive quality work. Thanks for sharing.

 

There is a quicker, easier and more accurate way to figure out the length needed for a side-branch tube to counteract exhaust resonance.

You need to take a Real Time Analyzer with you in the car. You can get apps for the iPhone & iPad. Using the RTA drive your car until you hit the resonant frequency then look at the RTA to determine the peak frequency. Now all you need to do is use a closed tube calculator to determine the length of pipe needed to create that resonant frequency. Using the same diameter tube as the exhaust cut a hole in the existing system before the resonator/muffler then weld your closed end side-branch tube to the system. Bingo - resonance gone

There are many closed tube calculators available on the internet.

 

That is very nice work. I opted to dump the exhaust all together and just resonate. Love it.

 

Not knowing the proper length for that 1/4 wave reflection, fabricate your resonators as long as you can with a stainless rod with disc (piston) attached, inside cap end of the resonator(s). The rod will exit through a hole at the center of the end cap and will have a small bend to use as a handle for adjusting the functional length of the resonator internally. Then 'lock in' the desired length after testing with an external set screw (stainless) at the weld beaded neck of the rod exit. You probably will have 2 or 3 short trips for testing till the rod freezes up.