I know, lots of talk about exhaust drone, but I have a question I haven't seen asked(or couldn't find via search). First, the setup. '96 LT1, 3.07 gears, all stock engine, stock exhaust except the mufflers. I picked up the Magnaflow axle-back mufflers, as people seemed to really like them, and I got them for $250 shipped. They sound great! However, the drone from about 1300-1900RPM's makes me wish I didn't have ears. It's unbearable, and vibrates the whole damn car. It's especially bad going uphill and in city driving. They sound perfect outside of that rev range. Oh, and I know people will say to just get a Corsa exhaust, but I'm not going to spend that much money, when all I want is a sound and cosmetic change.

So, the question is, has anyone added an h-pipe to address the drone issue? I was thinking of having a shop add one just after the diff, just forward of the spare tire carrier.

 

In my experience you get what you pay for. When related to exhaust systems is usually in drone and fitment. Corsa's have zero drone, but you could buy 5 Magnaflow set ups for the price of a Corsa.

Saw the Same thing between Flowmaster and Borla on the SN197 Mustangs. Both sounded great when sing the throttle, both well built... but DRONE was significantly different.


Drone doesn't bother a lot of people on weekend cars.

Mustang in example had an H-Pipe with both sets of mufflers. Possibly an X pipe would help more?

 

I don't really don't think it's so much a cost issue, as it is a tuning issue. Heck, those muffs have a list price of around $600, and people were happy to get them for $350. Any car can end up with drone, but the C4 seems especially sensitive to this issue. I've had super cheap mufflers on past vehicles, with no drone issues. The Saab 9-3 I had and this C4 seem to really not like aftermarket mufflers, lol. I figured I was rolling the dice, and didn't find any drone complaints about the axle back Magnaflows, looks like I lost anyways. Seems like more people don't mind drone than do.

Anyways, I figure either an x or h-pipe just might kill the drone. I'd hate to ditch the resonator for an x-pipe though, especially if it ends up not ending the drone. Don't really want it any louder either.

 

Exactly, and R&D cost money. The Corsa is a better engineered product.

Yes, which is why I chose the particular mustang I did as an example. The mufflers are right at the end of the system, just like the C4. Fox body Stangs were not as sensitive as the S197's because of muffler location... and the S197 and C4s are very similar in this aspect.

I haven't had multiple arrangements of exhaust systems on C4's. I am just sharing my experiences.

 

I knew that, excuse my Monday morning fog brain, lol! For sure Corsa is the better engineered product. I wonder if other manufactures even ride in the cars that they test fit these systems to. I think they just focus on looks and sound, and couldn't care less about what it's like in the car.

 

This is a "technology" issue you are fighting. The MF muffler uses "sound absorption" as the method and OEM and Corsa both use "Pressure wave cancelation." Pressure wave cancellation cost WAY more in design, engineering and test so the engine sound is constant throughout the RPM range.

You won't be able to get a MF to behave like a Corsa. Your best bet for sound is to run as straight and free flowing pipes as you can from the manifolds and put a pair of OEM mufflers on the back.

Peppy and Cheap.

 

I'm in California, can't touch the exhaust until after the catalytic converters. No headers, high flow cats, or removal of cats.

 

Better check your laws again.... it's more than just pollution now. If an officer subjectively says your car is too loud, you get a ticket(fine).

Exhaust Law Summary

You are basically rolling the dice on if you can accurately judge how a cop will feel about it. Yes, you may beat it after lost time (not sure how much your time is worth to you), potential court costs, and potential legal fees. Depending on who you talk to, that could many any exhaust modification could be deemed illegal.

In an LT1 car, the exhaust is not a restriction on engine output. Stock Mufflers are fine. All you are getting is a different sound to your preference.

 

A large portion of their customer base doesn't care either. Especially on cars out of the age of being common daily drivers.

 

I know about the sound ordinance stuff. Stock Mustangs are louder than this car is with the axle back, and cops in the areas where I drive don't care. It's not until the third offence that you get bent over a barrel anyways.

And yeah, all I'm going for is sound and looks, not chasing power here. I've got a few things I can try to lower the drone. The stock muffler hangers are hard as a rock, so that's not helping matters any. Time to get some fresh rubber in there. Next, will be to mass load and dampen the rear tub, which was in the works anyways, as I already have a bunch of left over materials. Those two things should take the edge off at the minimum. Next will likely be an h-pipe, or just save up for a Corsa, lol. I'd really like to make these work though, as they sound so damn good, and even at WOT they aren't obnoxiously loud.

 

An H pipe has worked both poorly and well for me, depending on the location. The rearward installation placements I did were just a waste of my time. The forward placement (at the header reducers) made a noticeable reduction in bodywork drone. The farther forward you can place the crossover, the better the effectiveness/efficiency.

 

Fascinating, I though the forward location was more for performance reasons than anything. I thought for killing drone it wouldn't matter, but clearly it does. I guess some of the frequency tuning must occur before the mufflers in these cars.

Bodywork drone is the perfect description. I can tell the rear tub is acting like a passive radiator and booming away into the cabin, hence my desire to mass load the bugger(and reduce road noise a bit).

 

Look up 1/4 wave resonators

 

That is going to have a lot to do with Harmonics as well. Certain frequencies will resonate/amplify more than others... in which case the H-Pipe may fix that portion of it.

I am curious what you mean by mass loading. Is that what you call using material like Dynomat?

I can tell you this, I have seen this a lot of times... we get caught spending more time and money trying to make a cheaper product work instead of paying upfront (and not just with cars) for better Engineered/Quality Products. We have all been there, but it sounds like you want what a Borla or Corsa system promises.

 

Already did, not really much room on these cars for that, and that could get pricey quick.

I'm not spending a bunch of money to make these work, for the very reasons you stated. The only cost items will be the hangers(should be done anyways, regardless of what exhaust I run), and an h-pipe, which should be pretty cheap. Beyond that, no more cash trying to make these work.

Dynomat is one way to mass load, but effectiveness can vary, at least in my experience. Mass loading is usually done in layers, typically you'll have a dense foam layer, and a thinner rubber or vinyl layer. Second Skin Audio makes some good, but pricey stuff. I layered the rear trunk area in my Volt with it, and it killed all the road noise that was coming from that area. I've got some left over, plus a Dynomat equivalent, so that was paid for last year. Basically it's eliminating the surface's resonant frequency, and performing some general sound deadening at the same time. I was going to do this anyways for road noise, so it should help a bit, but it won't solve the issue.

 

I have a C4 Coupe with a Cat-Back Chambered exhaust and it does not drone.
It is connected to an aftermarket Hi flow catalytic converter. I still have the original front Y pipe.

My catalytic back system was available in different metals. I chose the standard out of aluminized steel. It is over 20 years old and still on the Corvette. I paid less than $500 for my cat back, they are not that expensive. You should not have to insulate the bottom of the entire Corvette to eliminate "drone". With the chambered pipes you eliminate the big ugly mufflers, Instead you have a great sound and less weight.

On my 1988 C4 the Corvette gained almost 14 hp from the replacement of the Original Catalytic converter to a High Flow aftermarket unit and the chambered pipes. Then one day I am cruising along at 60 mph with the cruise on and then the dashboard indicates I am getting better than 30 mpg on the highway and I have the 3.07 gears as well on my 1988. I also had the A/C running while I did it going down I-95 from Baltimore to Washington D.C..

I like the sound the chambered pipes make I actually have them on both of my Corvettes. They sound good on the L98 or the BB 427 and both of them have been there for 20 plus years. I use Allen's Stainless Exhaust in Indiana.

Best regards,
Chris

 

I have the same issue but maybe slightly less so with my '93 LT1. Just recently returned from a 1600km tour and the most annoying problem was the drone. It disappears at 2000 rpm, the system is a 3" stainless steel cat back one that was fitted to the car when I got it, don't know what brand it is but looks similar to a Billy Boat one.
I'm thinking a Helmholtz resonator will likely fix the issue but so far I haven't found anyone that has fitted one to an LT1 C4.

 

What do the tips look like? It's likely either the Magnaflow or Borla cat-back. I think 3" pipes are too big for these cars(in stock form), and contributes to drone.

There is one person here that did the Helmholtz on his exhaust, but I can't find the thread now. Basically added a long curved and capped off pipe just before the mufflers. The pipes were very visible from the back of the car. He did a good job on it, but I didn't care for the look. I'd rather just pay for the Corsa at that point, lol.

 

Hi these are the pipes fitted, can you id them?


'93 vette exhaust

'93 vette exhaust 2

'93 vette exhaust 3

 

Looks like B&B mufflers to me, not sure about the rest though.

I also see what looks like soot where they clamp on. Try tightening the clamps up a bit, as leaks can cause unbelievable drone.