When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I took a look at my 78 and it looks like an 18 would fit, but it would be very close. With a 71 you may have a little more give since the tips come straight out rather than having to take an angle and sneak out under the bottom of the bumper. Like Belgian said, angling the can down a bit would help as well, albeit expose more of the muffler body.
I used dynamat on the floor and rear wall of the luggage area behind the seats.
I also glued acoustic foam on the top panel facing down to help absorb noise that makes it thru the dynamat. It seamed to help, but I can't give you a direct comparison. Figure every bit helps, and it doesn't weight hardly anything unlike the dynamat I used. With the front trim panel attached, you can't even see it.
Last edited by Jason Staley; Jul 19, 2016 at 07:57 PM.
I also have 3" Exhaust and I am also running the longest Muffler (Borla) I could fit under there. Actually a bit longer than what would fit. The Inlet of the Muffler was cut off and the Mandrel bend is welded directly to it. Same for the Tail Pipes. This put the Muffler in the way of the Rear Tire as You pointed out so a Notch was cut out of the corner. If there is a will, (HP) there's a way ( Quiet). All it takes is more work.
A question : is this sound waves bouncing back off the ground and back to the body or is this eminating from the pipes themselves;
BTW : my mufflers are 14" ones. which were the max I could comfortably fit under the car in the rear.
You are talking about resonance, or "drone" & it's more prevalent with some mufflers than others. First off, there are several factors here that are making it a challenge to tame the exhaust on your ride. 3" dual exhaust is considerably louder than 2.5" exhaust. 304 stainless pipes have more of a "ring" to them than aluminized mild steel pipes - so that is a factor. Are you running a crossover somewhere? That will help - either an H or an X. Personally, I prefer a good old H-pipe. The other thing to consider is the diameter of your system. Unless you are in the vicinity of 500+ HP, you do not need a dual 3" system. If you are over 500 HP & the car is a street car, 2.5" exhaust will be fine for street use & occasional WOT blasts. If the car is wild & you have a monster motor & you want max performance at the expense of decibels, then run the 3" system. Dynomax Bullets will reduce noise very minimally - they are small bodied glasspacks with not very dense packing material inside of them, so they do not absorb & cancel sound very well. You may want to consider going to a non straight-through pair of mufflers in the rear as well, but I would not recommend using Flowmasters - they are probably the worst offenders of producing resonance. Anyway, food for thought.
I'm in the 500 hp range and yes I need the 3" pipes.
Last trip I made with my 2.25" pipes and a WOT blast ended in a blown up muffler. Even the 2.25" was not what I would consider as quiet and that was a turbo type muffler with chambers.
Larger mufflers will help bring the volume of your exhaust down, and laying dynamat, or another sound insulator will help reduce cabin noise. In our experience, placing the sound deadening behind the seats and in the trunk was most effective, though some people go as far as doing the entire body.
Have you messured the loss in dB after soundproofing? I used antivibrating mats, and sound deadeners on the whole trunk part (except the top) and I do not see much improvement.
What is the average idle volume (in dB) messured in a C3 with Corvette Central Magnaflow (2"), mine's 91 and it seems a lot to me.
Not the most popular option but, this worked for me.
I just installed a cam-ed engine in my 81. MUCH louder then my earlier engine.
I have headers with 2.5 inch dual exhaust & straight through MagnaFlow mufflers.
Solution, I added two High Flow catalytic converters, just after transmission.
- Brought the volume down (not quiet, just much quieter)
- Still very low rumble
- Garage doesn't stink of unburned fuel (wife stopped complaining)
However, some of my friends think I killed performance (unconfirmed affect on performance, car still goes well,,, I am not a racer).
I like it, and I no longer worry when passing the police (81 not e-tested here. I bought car without cats).
Last edited by Diablozx9; May 16, 2017 at 01:36 PM.
Not all sound deadeners are created equal; there are HUGE differences between the different materials.
The really serious sound deadening uses 3 different materials; you've got your Dynamat category which is for vibration absorption, the middle layers I understand the least but most of the kits only do mild noise absorption and are mostly focused on heat insulation, and then a top layer proper, thick sound absorption layer using something like Ensolite.
My recommendation is: 1. Generic Dynamat in the storage area 2. typical kit insulation (cheapo foil stuff), 3. Ensolite.
If you've got the X-pipe you've probably already addressed the general exhaust resonating frequency / drone stuff, so it seems like you just need / want good-ole fashioned noise cancelling.
You could go nuts and do the Lizard Skin spray-on stuff under the car, too; but from what I remember it is messy and can add weight in a hurry.
- Garage doesn't stink of unburned fuel (wife stopped complaining)
Wow. Yea, I have that problem right now, too.
My solution is to caulk where the drywall meets the garage floor to have less smell make it into the basement & to hope that my efi conversion thins out the idle a bit more so there's less total smell.
