A friend of mine has a 95 that I've been doing a lot of work on and the next step is to try and quiet it down inside. It's putting down 550 hp at the wheels and is ungodly loud inside. So loud you can't really hear anything else. Part of the problem is he has a 4" exhaust with aan N1 muffler and a titanium exhaust.
Right now the tranny is out and we'll be coating the underside in quiet kote but I doubt it will help a lot. I've tried to convince him to put some baffling in the exhaust but he doesn't want to lose any hp. It's kind of annoying trying to convince him of things sometimes. My other thought was to coat the exhaust with something (ceramic?) to give it more mass along with quiet koting the entire interior. He wanted to put in a partition between the cabin and the trunk made out of lexan but I don't see that working, it would also be a bitch to build and make look good.
I need to know if you guys have any other ideas on either coatings, treatments or anything else that can be done to help. He is weird about getting/keeping every hp. The car is a daily driver for him even with as loud as it is. Thanks for any help you can give me.

 

Not sure what its called but I remember seeing some kind of trunk lining that was supposed to help muffle a sun woofer. I don't know what it can withstand but maybe worth taking a look.

 

That is what the quiet kote is supposed to do but I'm just not sure it will be enough.

 

What the hell do you/he expect from a 4" straight pipe rotary? It's gonna be loud and ******* obnoxious. He's either gonna need to buck up and deal with it or compromise a little power.

Gut the interior, lay **** loads of dynamat, reinstall interior. Besides that, there's not a whole lot you can do without choking some power via exhaust. A resonator or 2 won't hurt too bad. Turn up the boost 1 or 2 psi and make up for what power you lost. Also, if the wastegate is dumped, rerouting into the downpipe makes a significant difference. W/G won't be quite as responsive but it's a hell of a lot quieter.

 

He does also have an open wg dump which I know doesn't help. I may be able to get him to plumb that back in. I'm just trying to convince him the partition is a dumb idea.

 

If you want quiet, you have to sacrifice flow for quieter sound.

 

A rerouted wastegate is less of an issue with a full 4" exhaust. If done properly, it should make little difference. Dumping is all relative to pipe diameter.

As others mentioned, the interior sound deadening will help for cabin noise.

He can also consider incorporating another muffler in the midpipe. A quality straight through design will not effect flow but will reduce resonance.

 

Not only is it retarded, it wouldn't help at all. The loudest noise is going to be the wastegate dump, which is right at the passenger footwell/floorboard (in front of partition). Route that back into the exhaust and tell him it won't sacrifice any power. He won't notice a difference whether it does or not. Again, 4" straight pipe is your enemy almost as much as the dump. You could coat the undercarriage with an inch of that junk and put 5 layers of dynamat inside, it's probably still gonna be considered loud.

I know exactly what you're dealing with as I have a 4" straight pipe, dumped w/g FD. I honestly feel bad for my neighbors when I start it and pull in/out of my 'hood. Just gotta deal with it.

 

one thing that I dont think was elaborated on was when the car was loud ? high way loud ? or full throttle loud . if he's ok with the car being loud and obnoxious when hes flooring it and the waste gate opens up to dump the excess ,

OR is it when hes cruising. , because re routing the waste gate dump wont make a huge difference when its closed .

Also isn't wrapping the Exhaust in Fiberglass supposed to quiet it down some?

 

One or more high-quality straight-through mufflers like the Borla XR-1's should knock some db's off with little or nor effect on power.

 

The car is loud all the time, cruising and obviously WOT. I know there is nothing that will make the car anything close to quiet but I need ideas on how to get it better. I also know there is no one thing that will do it but a combination of different things. Does anyone think the partition behind the seat idea will make any difference?

 

I just changed a car from 3" with a single resonator, open dump and a straight through muffler to this:

All 3", Recirc WG at 30 degrees 24" from the turbo, immediately into a cat (later changed out for a BHR res), then into a dynomax super turbo 16" muffler, then a vibrant performance 14" resonator, mandrel bends to the final muffler by the fuel tank, which is another dynomax superturbo, 20" (dodge durango application). I know two of the same muffler in series isn't the best, but they are different size, hopefully reducing the intensity of different frequencies.

The thing has the typical rotary snappy notes at idle, but it is so quiet you can hear every rattle and bump and whisper of any wind noise. Cut the noise by at least 60-70%. The dynomax mufflers are published at 700 SCFM, but will need to be repacked with stainless packing material once I burn all the fiberglass out in a few months/weeks.

4 inch straight pipe and dump... um, throw that away unless you want to wear earplugs while driving

If you search, this has been discussed a LOT BTW, lots of other ideas out there. I gladly traded a little flow for a quieter more enjoyable car.

 

BURNS STAINLESS mufflers have proven the be the quietest, and make the most power.... and they are most expensive. onlything close in the no power loss department was a supertrap,

 

Thanks for all the help. I'll sit down with him and go over the options. Anyone think the partition will do anything but look ugly and weight a ton?

 

banana in the tailpipe

ok... a stack of bananas

 

It'll help, but not much. A couple resonators will do more, won't look like ***, and he will end up with as good or better hp/weight ratio. HP really isn't important. It is the hp/weight ratio and he should be looking at that instead of just HP.