mawfuqqa
mawfuqqa New Reader
11/4/20 9:52 p.m.

Lexus ISF 5.0 V8 with Xforce catback but 3.5" muffler delete quad tips at the flanged axleback. The hotdog/bottle resonators still there.

Considering a single Spintech Sportsman 3000 XLP (8 spin traps with packing) or RV 8000 (10 spintraps no packing) 2.5 dual in/out where the current bottle resonators are.

Conclusions from what I've experimented/experienced and read/heard 

- Mufflers: Overall sound reduction but perhaps not much for actual DRONE. May change the exhaust note/frequency and exhaust scavenging characteristics depending on what is inside. i.e.) Chambered/spin traps/baffled str8 etc.

- Resonators: Do very minimal in over all sound and drone change. May change the exhaust note/frequency

- Drone tube/Quarterwave length tube: Has to be measured out quite accurately to affect a drone range i.e.) I've read of a owner that two 27" long at 1.75" piping got rid of much of the troublesome drone of the ISF low range. These tubes can possibly have steel wool packing before welding up.

- Helmholtz chamber: Affects wider drone range than a quarterwave tube and no need to be as accurate in dialing in measurements as a drone tube.

 

I still want very audible exterior note, currently with the 3.5" muffler deletes it's actually very pleasing on the ears with a distinct lumpy rumble and NO drone under regular cruising at any gear especially freeway. The problem is any time I am opening up the throttle lightly (extremely bad if left in D)  it drones SUPER bad. My teeth closed I can feel the loud droning vibrations shaking and rattling my teeth causing my teeth to cause a buzzing drone of itself!

I fear the 3000 XLP maybe too quiet but still potentially have a light drone (ok) if a heavy drone and I add a helmholtz chamber or drone tube the car may then be way too quiet.

Perhaps I can leave the exhaust as is and maybe will add two helmholtz chambers and the two 1.75" drone pipes at 27" length?? On that note, I need to figure out where to be helmholtz canisters or just turn some old mufflers into some.

akylekoz
akylekoz SuperDork
11/5/20 6:48 a.m.

There have been some discussions on this topic here and lots of info elsewhere also.   

I've always wanted to experiment with a Helmhotz, but sold the droning car.   From what I under tand the best way to start is with a calculator to determine the length needed based on cylinder count rpm and other factors then make a trombone system for tuning.  Once you find the sweet spot or best compromise you make a permanent one or just make the adjustable one fixed.

 

cyow5
cyow5 New Reader
11/5/20 7:32 a.m.

There are several types of "drone" that I've seen people use confusingly interchangeably:

1) a particular rpm excites a harmonic with the exhaust and is louder than the neighboring rpm ranges

2) the interior of the car resonates at a particular rpm that coincides with a specific rpm

3) cruising rpm happens to be an irritating frequency (to use a tired stereotype, "my wife drones on and on" would be using "drone" in this same sense)

4) cylinder deactivation

#1 can be addressed by some combo of the devices you mentioned, but #2 will always exist until you change the interior volume of the car. From what I can tell, they'll seem very similar except #2 won't improve unless you can *dull* the exhaust at that particular rpm while #1 tries to avoid *exciting* it. #3's solution is like #2. #4 is an interesting one my wife's G8 GT suffers from- the cylinder pressure doubles and the exhaust decibels jump by about ten while the rpm cuts in half. This sounds like you excited the problem in #2 but just can't be avoided while retaining cylinder deactivation. Her exhaust has helmhotz chambers, but you can't tune it out because that's just the nature of the beast. This may not apply to you, just mentioning it because it fits my list. 

 

Ian F (Forum Supporter)
Ian F (Forum Supporter) MegaDork
11/5/20 7:39 a.m.

I've seen/read about such a system on an R53 MINI many moons ago.  The owner wanted a R56-esque straight exhaust (he relocated the battery and cut out the rear battery box), but without the turbo of the R56 engine, the drone was unbearable. So he added a Helmholtz chamber to tune out the drone.  He said it did eventually work, but it took a lot of trial and error welding.  Im sure there are audio modeling programs out there that would reduce the amount of welding, but my guess is the learning curve of the software would probably take as long or longer than changing the exhaust in real time.

frenchyd
frenchyd PowerDork
11/5/20 8:15 a.m.

In reply to Ian F (Forum Supporter) :

The sound varies depending on the camshaft. You tune the exhaust like you tune the intake and both need to work to optimize power. It's a function of exhaust diameter primary length and secondary length. 
   When you get it right it's beautiful to feel and hear. 

mawfuqqa
mawfuqqa New Reader
11/8/20 5:07 p.m.

@aky yes but the info is kind of all over the place throughout the internet, I figure will condense this into a mother thread of sorts

@cyow wow, that cylinder deactivation drone sounds like nails on a chalkboard x50000000 except it's constant.

1) a particular rpm excites a harmonic with the exhaust and is louder than the neighboring rpm ranges: Especially nuts at 1.8-3k range when under load

2) the interior of the car resonates at a particular rpm that coincides with a specific rpm: see #2

3) cruising rpm happens to be an irritating frequency (to use a tired stereotype, "my wife drones on and on" would be using "drone" in this same sense): Cruising is FANTASTIC in the ISF! Much better than WITH the xforce mufflers. EXCEPT throttling up around town or low rpms or basically anytime except at cruising causes my entire body to vibrate into a drone of it's own through my bones and teeth.

4) cylinder deactivation: I do not think any of my cars have this and good thing they don't.

@Ian part of my response to you is below in the main body

@French agreed, but can be hard to achieve for certain individuals. I am especially a bit nuts when it comes to this. A full headerback is not entirely satisfying enough due to some nuances here and there and I must frankenstein the unit for the past 13 years it seems 

The learning curve is probably why there are a low number of systems with an actual canister.

Would a canister have to be made? I'm having an extremely difficult time finding a canister like this side branched one. I've throughout the years have turned existing mufflers and resonators into a helmholtz chamber by capping off the outlet or inlet (depending which way I've flipped it) but I don't believe it works the same as a full on empty canister or a empty can with packing. 

Amuse Helmholtz resonator dimensions - Page 10 - S2KI Honda S2000 Forums

 

I go through a few systems and frankenstein my exhaust PER car at least 2-4 times and I've gone through over a dozen cars. Eventually I get tired of throwing money and I just rip my hair out or wear noise canceling headphones.

I'm considering buying like 3 huge drinking thermos and welding them all together or something... and capping the big mouth port with a flat sheet of metal.

Decided to buy a spintech 3000 XLP sportsman in place of the two Xforce hotdog resonators for my ISF. I may get rubber exhaust vibration dampeners welded along the pipes are random sections. If the end outcome is still more drone than i'd want I will repurpose the hotdogs along the piping and cap it off.

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