Dave, what's NVH?

 

The vibrations are not from pipe hitting the chassis, and flex joints are used to relieve binding in an exhaust system - it allows a certain amount of travel for the exhaust as to not break headers/manifolds or CATS, etc, that are in a fixed installation.

Most all aftermarket systems are made far more stout than a factory system, thereby not requiring flex joints, as long as the jigs are made properly and to tolerance, there will be no binding in the system and the rubber mounts will provide the needed flexibility under general driving conditions as heat expands the system and tolerances get even closer.

Rick

 

Nissan uses flex joints as their exhaust system is made to Zero tolerance specifications. Therefore flex joints are needed to allow some play in the system, otherwise they would be replacing manifolds and CATS due to the stress relief need, for expansion due to excessive heat, over time.

This has nothing to do with Noise, Vibration for Harshness, other than a testing phase to measure how much NVH is being experienced and where it being produced from. Most NVH is from vibration characteristics and resonance from drivetrain components, hence the reason there is so much padding and rubber all over your cars, inside and out. It's a large reason there is a double wall of steel between you and your engine compartment. Perhaps an industrial level flex vibration dampener joint will help, if the system itself was actually vibrating and rubbing somewhere, but your typical flex/expansion joint for exhaust systems is made differently and used for a different purpose altogether, as above.

The only way to reduce drone, is to augment flow and/or change pulse reflection and absorption characteristics of a system. Typically the quieter the system, the less efficient, and thus, seemingly at least, the louder the exhaust the better performance you'll get.

WITH THAT SAID THOUGH - louder isn't necessarily better and quieter isn't necessarily less performing. High quality components and technology design and testing, can end up with the best of both worlds - which is usually the system your car came with!

If you want more performance, you will end up with a louder car exhaust, to some degree at least, and sound is completely objective. What's loud and drone to one, is perfect to others. If you want to increase sound outside your car though, expect to hear it inside as well. I know people who think the stock sound is too loud, and then try to quiet further

Drone - is not sound coming from the back of the car and bleeding into the interior either. Drone is when those low tones escape poorly constructed mufflers and other exhaust components, hit the ground, and then bounce back up into the chassis and thus into the cabin. The result of the leak-back into the car from low tones coming from the rear of the exhaust, totally resembles drone, but the lack of trunk and back-half car insulation, is mostly what causes the sound leak back into the cabin. I've dynamatted, 2 layers, everywhere in the back of my car, as during R&D a few years ago, the drone was horrible in test systems, and I found that I could get rid of 1/2 of it with a few layers of Dynamat Extreme.

Rick

 

^^^Thanks Rick for the very informative post.

Like you, I used Dynamat extreme on my entire rear/trunk panels. However, I barely noticed a difference in the drone inside my cabin. I think the noise in the back seats are worse than the noise in the front.

Sometimes, I love how loud my exhuast gets but when I have friends in the car, I get complaints

Anyway, thanks for the info!

 

No problem. I have dynamatted my car from head to toe. The floorboards, firewall and whole trunk are all 2X layered with it. Only the roof and doors have a single layer. Remember, and metal surface, technically, that does not have it installed, will continue to resonate. So inside of doors as well, complete trunk floor, 1/4 panel interior, rear deck, seat mounts/floorboard etc., rear interior panels and all.

We completely stripped the car out, Dynamatted, and put it all back together one week. The only downside is the weight ;-)

 

I have heard and driven Gary's ride and it is quite loud inside and the car plastic rattles. Same as mine.
I have a dual custom exhaust using magnaflow mufflers sebring tuning tips(4) and the same size resonators as Gary's my piping is regular exhaust pipe nothing fancy. I think that the pipe where my H pipe is and the 4 tips is the only difference from Gary's and we are about or close to the same with drone. He has a 05 I have a 03 both A/T. It took a while to get use to but now its ok. I'm thinking about changing a few things up in the future.

Gary and I have same engine mods and he dyno'd 1 hp more than me...

 

Just to add, with my "silencer gasket" added there is no vibration. It's clear now that the vibration is directly associated with the very low sound frequency & high volume of this exhaust

Can't wait for my exhaust control valve

 

Anyone think about wrapping the rear mufflers and X-pipe muffler with an exhaust blanket? I would think the resonance would be muted if the muffler casing is vibration dampened...

 

Yea, actually, Lawrence's car drones at <1k rpm, then it seems to quiet down a lot. In my car, it drones from 2k - 2.7k. Outside of those rpms, you mainly hear the exhaust note on the outside.

I'm thinking about dynomatting the floor....would that help?

 

Keep in mind - the low volume is coming from the rear of the car (out the tailpipes), not under it, so the mufflers etc. are not leaking the pulse, the pulse is leaking into teh cabin from the rear of the car. Wrapping htem would do nothing for this.

If the mufflers were leaking the low pulse directly, then wrapping could help.

Rick

 

Does dynomat add a bunch of weight? or not enough to matter.

 

I completely disagree, Rick. The stock exhaust is far more "stout" than any aftermarket exhaust. Take note of the tubing wall thickness compared to that any aftermarket exhaust. The thickness and weight are far greater with the stock exhaust. The stock exhaust uses a lower grade heavy stainless steel which will show some surface rust in certain areas, but will last probably a lifetime. The thick walls deaden exhaust noise and retain exhaust heat to keep the exhaust velocity high.

The purpose of the flex sections is to reduce NVH (primarily vibration and harshness) and to let the exhaust move freely instead of torquing the exhaust manifolds and cats. The flex section removes vibration by letting the engine move more freely from the exhaust. The flex sections along with the exhaust hangers and engine mounts dissipate vibration. When you remove the flex sections, you'll get more vibration. It's really that simple. I've installed numerous exhausts on my last three car. I quickly learned the value of the flex sections and I should have known better prior to buying the Borla system, but I was too dumb and believed what I read on this site from those saying it didn't cause any additional NVH. It was quite obvious after installing the Borla TD that it was creating a lot of vibration. You could literally see the pipes vibrating at idle and you could feel heavy vibration through the muffler. Under load, the increased vibration was pretty apparent. In a 350Z, it would be fairly acceptable, in a G35 is seemed a bit too much.

Years ago a had a Stillen y-pipe for my 96 Maxima. The flex sections on the y-pipe were about 50% shorter than OEM and the increase in vibration was noticeable. 2 year later the flex sections failed and I replaced the y-pipe with one from Warpspeed which had flex sections the same length as OEM. The vibration was majorly reduced.

 

It depends on how much you do, but yes it does.

A standard trunk kit is about 14lbs., but to do an effective job on our cars, you almost need two.

It's easier to buy it in the bulk paks. You'll save money in the long run.

When we did my whole car, it added 240lbs - and that's 2 layers almost everywhere. The car is as quiet as a Mercedes 500 SEL (this was done the 2nd week I owned the car), however, after a blower, headers and exhaust ands more - it got a 'bit' louder...though I can't imagine what it would be like without the Dynamat.

Rick

 

DaveB -

There's no arguing between us here. Stock systems are stout, sure they are, but have you seen how much they do move? Try moving the tip around on a stock exhaust, then try that with the FI system, or most other dual systems for that fact...you really can't move them at all - they are more stout in many cases.

There is much debate on the usefulness and need for flex joints. Do they help with vibration, sure they do, because they 'flex' and limit the total amount of 'wiggle' while driving around, and in some cases allow it to wiggle as needed. It is for a vibration issue, but not one that creates drone or related issues that are on topic from the OP here. It's the vibration issue that causes related components to break, if the flex isn't there. That's what you get from a factory zero tolerance system. This is where the aftermarket systems without flex joints discussion never ends.

It's believed by some, that without flex joints, you'll crack manifolds and CAT housings...sure, if the system is not made right and binds on those parts. If you look at the systems that do have flex joints, you'll notice they are 2 1/4" systems or single systems, or systems with thin 18gauge pipe, like the Borla. That's one reason the Borla drones..thin wall pipe and components that actually do drone - and release pulse through their walls. The FI systems have 16 Gauge SS and 14 Gauge aluminized, and stock is 14gauge. Weight-wise, the SS system is 7lbs lighter than the stock system and the and the Aluminized is about 5-6 lbs heavier...and this is for 2X the pipe and components. The other lighter systems use very thin wall tubing and usually 2 1/4" pipe as well.

Now, for the OP where vibration is concerned, he is noting that the vibration is from the amount of drone, not components vibrating against the car and resonating. CAN flex joints help that...hmm..don't know for sure, but doubt it. The industrial vibration control flex joints are a different story. They are also built differently, but I doubt any significant change would be noticed as the systems really don't move at all. Also, most systems are made with slip joints and clamps, the FI system and HKS as well, are made with flanges..and that is why they are just as stout as the factory system..as it is made with flanges as well.

Now - lets go this route. If the flex joint is that imperative for sound, then why don't all the single exhaust cars who only use a new Y-pipe without flex joints, have this problem? Not to challenge you, but to make a point from what you wrote earlier, simply removing the flex joints should cause noise, but instead, removing them allows for better flow and performance.

The first configuration I tested, when I tested a few years ago on these cars, was to install 3 different Y pipes and see the result. Very subtle noise change, due to an increase in flow from the more efficient Y pipe, and about 3 HP at best. When we got to creating and testing the FI system, we tried flex joints, just to appease those who may have this argument, and found Zero change in the tone, vibration or any other part of the design. We then decided to save customers about $120 for parts they wouldn't need.

The vibration you felt through the muffler, was the pulse leaking through the muffler itself...otherwise known as drone. The bouncing of the system is how many clamped systems work, unfortunately. The Borla is my favorite system out there, next to FI, of course So I'm not bashing anyone here.

Installing a larger flex joint will stop more vibration..that's pretty obvious, if the vibration is there to begin with. The Maxima's have a lot of engine and chassis torquing from the 90's, and the mounts weren't the best. There are a lot of aftermarket bushings and mounts available for those cars, as it is a major problem to begin with. I don't want to go into the Stillen Y pipe, etc..there are much better parts out there to go into it deeper.

Anyways - there are several angles to take on this - I really don't think any one is right or wrong as we really are stating similar things and have some different takes and experiences as well.

Item 1 though - adding flex joints to the FI exhaust will not change anything - we've been there and done that, so save your money.

Rick

 

So just an update, 3 days ago I installed electronically controlled exhaust gates inline with my FI exhaust. So far these things are awesome, when closed they provide enough flow but very low noise (an aggressive stock tone), I can open them up 10, 20 30, % etc. I’m driving around now with them open roughly 65 % and I’m loving it., the car pulls like mad, not insanely loud and sometimes I open %100.to scare the neighbors or to go all out. So far these things have brought back my G love.