Hi, new member here. I just bought my first Vette a week ago. The exhaust was loud on the car when I bought it so I replaced the mufflers with a pair of Quiet Flow mufflers from summit. At the same time I hollowed out the cat. Before.and after the work the exhaust drone at 35 to 40 mph is maddening. Any tips?

 

Welcome to the forum!

Is it a manual or automatic? A lot of the drone is RPM-specific, so if you're in a manual I'd just try changing the RPM range you're driving in by shifting differently. In an automatic, I'm not sure how feasible that is. I've found that on both my Vettes the 1700 RPM range is obnoxious, no matter which muffler I've had on.

Additionally, lots of guys like to insulate the interior. This is going to add some weight, so if you're making a track car you should be aware of that. It's also a good bit of a job, as you'll have to remove the carpet and door panels. There are all kinds of sound insulation products for cars, and they're all expensive. I've found that Frost King A/C insulation from Lowe's works really well and is considerably cheaper (it's the self-adhesive kind with aluminum backing). You pull out the seats, carpet, and interior panels, and put a layer or two of the Frost King on everything then re-install. It's not terribly thick so it doesn't add much, but be careful in places where panels meet or something where clearance may cause a problem. Not only does this insulate against the outside sounds, but it also dampens vibrations in the car's body as well which helps to eliminate a lot of rattles that these cars are just prone to. It won't completely fix it, but it should really help with some of the drone.

 

Thanks!

Its an automatic, all stock as far as I can tell. it runs great and shifts good. .

Honestly I'm not worried about weight. Its not going to be anything but a nice weather cruiser. I'll definitely check out that insulation, also is there anything that I could wrap the pipes and mufflers with to tone it down?

 

Not that I can think of. You're better off with different mufflers than doing that.

Watch the RPM range, I'd bet you're hitting 1700 RPMs. Not much you can do about that in an automatic, but at least you know.

The insulation will help, ESPECIALLY in the rear cargo area. I'd put at least two layers there. It doesn't add a LOT of weight, nothing to be concerned with, but it's not negligible if you're trying to get every ounce of performance out of the car.

These cars just have a lot of rattle, and by dampening that down you reduce the noise considerably. I don't think it will ever be gone, but it helps.

EDIT: I did this to my first vette but now that I'm thinking about it, I might do it to my newer one as well. It just made the whole car feel a little...sturdier? Because it eliminated much of the rattling.

As a thought, you might get under the car and check things like bearings, bushings, suspension, u-joints, etc are all tight. It could be something besides the exhaust that's making noise. Want to make sure you don't have a bad bearing or something.

 

I will definitely give the underside another look over. I already changed the shocks and tires, and I may need tie rod ends. The car pulls a little bit to the right constantly. Since it has 127k on it there may be more.that needs changed.

 

I have had good success eliminating road noise using Block it pads in the hatch area, door sound proofing insulation, and fresh window seals. I even think the window tint I recently added removed a few decibels. I wish now I had taken some before measurements to quantify what I think I am hearing.

On exhaust, my 89 6 speed is all stock except for empty cats. It has a nice mild rumble now but I would say there is no drone. I suppose that's subjective.

 

Check out heimholtz resonators for exhausts, I believe it has been covered in the forum before.

 

I'm not saying there's a problem, but just to double check If there's a bad wheel bearing or something you'll want to know.

Dynamat is the more 'professional' soundproofing material. It's considerably more expensive but from my understanding does a better job. I've never used it but some people swear by it.

Anything that reduces road noise will help with drone, but one of the reasons to do the soundproofing stuff is that it dampens the body vibrations. That's what causes the 'drone' effect-the exhaust sound resonating through the body. You'll never completely get rid of it but insulation definitely helps.

 

If you want to quiet your car down, there are proven methods from the car audio world. But you can't just blanket you car with dynamat and expect good results. Actually dynamat will do little to help with the exhaust drone. You need a product that will add mass between you and the thing producing the sound. While dynamat can do that, there are other products that will do it better and for less money. The common material used for this is Mass Loaded Vinyl (MLV). This is why everyone recommends the mass backed carpet - same principle. Also this is the approach that the block-it product uses too, but with a multi-layered isolating mat. There are lots of products available, but I'd recommend reading up on sounddeadenershowdown.com. Don, the site's owner, has been there and done that with anything you can think about that claims to be a sound deadening/blocking product. He's got a great method for quieting cars down and top notch products.

 

That guy knows his stuff but MAN is it expensive...

 

His prices are fair when you consider the knowledge that comes with it and the fact that he has put the research into providing the best possible products to work together to you - as he states "OEM quality materials". That being said, if nothing else it is a valuable site because it explains how to actually block noise. You can get MLV, CLD and CCF on amazon and get great results using his methods. I just like promoting his site because he is literally "the little guy". Watched him go from a hobbyist who was trying to quiet his car down and was dissatisfied with the results to a person with a wealth of knowledge on the topic through his own research that was able to turn that into a nice small business. For those that don't know, he originally ran a comparison site for all of the different sound deadeners available on the market (hence the name - sound deadener showdown). He would acquire samples and then measure them dimensionaly, test them in extreme situations, and rank them based on their effectiveness and price. It was an awesome service for which he got no return. His research lead him away from the norm in car audio which was just layer after layer after layer of CLD to what we have today as a standard CLD to control vibration, CCF to decouple surfaces, MLV block sound.

 

Has anyone applied materials to the front fire wall foot wells and kick panels? Did it make a noticeable difference? On my 89, this sounds to be the last remaining area that transfers noise -- specifically tire noise. My tires are BFGOODRICH G-FORCE SPORT COMP-2 and although great handling tires, they are noisy to me.

 

I run the (dreaded) OBX exhaust. It's droned some down low.
I lined the rear with sound deadening when I re-carpeted. It helped, for sure.
The biggest thing I did to kill the drone? Changed from the 2.59's to the 3.54's in the rear end. HUGE difference bringing the cruise R's up some. Not cheap though.

 

An out-of the box solution but it goes back to RPM and exhaust-these cars usually have an RPM range that makes the exhaust drone something awful.

Please don't get me wrong-not saying he's wrong or that his prices are unfair, just expensive. Turns it from a small, cheap project to a much more involved one. If you're going to do it, though-might as well do it right.

 

Your best option to remove resonance is really to change the cruising RPM via a gear swap. If that is all youre doing with the car, not drag racing or anything, then it would be fine. Normally I would not recommend it for folks with an 84.

I've heard of people plugging an exhaust tip with brilo pads or other steel wool, dynamat/sound deadener, and adding crossover pipes (Xpipe or H-pipe) in the catback. All do help to some degree, but it is the big resonant sound chamber behind you and the RPM youre running that makes it maddening. I also would not have hollowed out the cat, that is making it worse.

 

Thank you for all of the info guys. For now I'm going to try the frost king insulation. I bought 3 rolls so I will see how it works.

 

Would love to see some pics from your installation if you think about it!

 

Is the exhaust system loud because it is modified? If so, you might have to go back to stock if you want it quiet. I went to Borla and it is a nasty loud one. Unfortunately it is too good to just toss and buy a Corsa to get rid of some of the drone.

 

BFenty, Is this the stuff you used? Might get some and see what it does since it's so cheap. Pulling out the carpets to do a good clean anyway, can't hurt to spend a few bucks for a little more comfort.

https://www.lowes.com/pd/Frost-King-...lation/1081449