For those of you who have added sound insulation (Dynamat, etc.), did it make a difference?

Sound deading the floor. The best and honestly biggest PITA option is to derivit the bottom sheet metal panel and fill the interstitial space with foam sheet. Between the metal pan and fiberglass floor it's a big drum. Would require being vigilant on checking the underside rubber grommets periodically to keep water ingress away.
Also found that an engine tray that closes off the underside also reduces some road noise.
Next biggest is the wheel wells, tires fling rocks and fiberglass tubs.. Very noisy. Modern vehicles use a felt lining there to reduce road noise.

 

Not theoretically perfect, but certainly not "bad". One only needs to look at the exhaust system of a modern Porsche 911 or Cayman to see that they point the output of opposing cylinder banks directly at each other on some versions, and they don't seem to be having any performance issues of consequence.

If you want to worry about something, you can worry about the very unequal length of the headers between the cylinder banks.

I might generalize by saying while a non restrictive flow path is desirable in an exhaust system, the primary driver of flow is the huge pressure differential between the exhaust system and atmosphere.

 

Interesting your refer to Porsche engines....I found the below pic on the web:

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and lots of other variations for a 911 exhaust. I guess the "X" in the middle is pretty much what the Magnaflow and Borla dual exhaust would be doing.

So...maybe its not that bad as you say....

This one seems to have a resonator or something on only one side...interesting.

 

Going off memory, there's a good 1.5"-2" between them.

 

@ChevyDave SIMPATICO my brother

 

Seeing the Ansa that was repaired above, There could be a much easier and significantly less expensive option - go to your exhaust guy - have them open it up and pack it full of fiberglass and weld it back up. I would think that would quiet it down. along with some sound deadening...

 

I think the 308 is geared perfectly. I've accidentally implied that the 308 needs different gearing. I facetiously suggested that if you wanted to convert it to a commuter car, it probably would benefit from a taller 5th gear. Sorry 'bout that.

I have driven my 308 many miles on the back roads of California, highway 88 and highway 4 for example from Virginia City NV or Lake Tahoe back to the San Francisco Bay Area.

I would hate to have to drive the 308 down that soul-sucking Interstate 5 through the San Joaquin Valley to Los Angeles. It would hurt my brain listening to the engine scream along like that in a steady state.

 

Since Mr Maxwell (the OP) has a single-outlet exhaust, and he's looking to quiet the exhaust note, I'm curious if anyone's cut open a factory single-outlet exhaust to see:
A) What the flow path looks like.
B) How it dampens the sound.
C) Why the dam thing weigh so much?
- Dave

 

This seems like an excellent idea .... I will look into this option... I can do welding myself and Amazon sells the packing material...

 

Agreed, 3x8s are perfectly geared for the job they are designed to do - which is not big highway cruises.

 

It never occurred to me to insulate for sound in my GTS. However insulating against heat (side sills, center tunnel) is something I've considered.

 

45 lbs. for the muffler alone

 

I did a full 5mm insulation and it was a total waste of time and money. It did absolutely nothing but be a pain in the a$$. I totally regret doing it and wound NEVER do it agian. To be specific, it made no difference in sound, temp or vibration. Don't bother.
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Impressive job, nonetheless!

 

If all that dynamat makes no difference, it tells us that the floor is not a meaningful source of road noise, as that butyl rubber does block some sound, any dense rubber/vinyl material is a sound blocker. Reflected sound is controlled by lighter weight foam or felt.

Small amounts of dynamat are all that is necessary to reduce the tinny type of vibration noise on a given metal panel. Like a one foot square on each floor zone would be enough.

 

For those of you considering this for heat, it definitely isn't worth your time. However, I will share this. A few years ago I gave the car to my dad to drive around and he got to tinkering. He concocted this wind deflector for the targa grove above the windshield. I thought he was crazy at the time but after driving it around and testing it myself, it's the single biggest improvement I've seen to reduce the inside temps. It made a huge difference. Here is the thread: https://www.ferrarichat.com/forum/threads/radiator-heat-dissipation.573126/#post-145917203