Exhaust Theory Question: Quiet with good flow?

[85 Cutlass Brougham]

I am trying to take my overall lack of funds time and putting it to good use by planning for the future. That being said, I am thinking about a new exhaust for my Cutlass. I want it to be almost stock like quiet with no drone, but still flow well. So, my idea is to use a 2.5 in system with an X pipe, 2 mufflers under the seat, and the Walker Dynomax X crossover muffler between the axle and gas tank (dual in, dual out), in the stock position for a V6 car. This would all terminate in 2.5 in dual tailpipes. What mufflers would you recommend for my need for quiet and low backpressure? Anyone have any other ideas as to how to achieve these seemingly contradictory ends?

(If you are wondering why I want to do this, I have a medical condition called Tinnitus, where your ears ring all the time and loud noise makes it worse. It is essentially hearing damage caused by too much loud noise. I really don't want to make it worse. I even wear hearing protection to run a sander, or mow my lawn to avoid the escalation of the problem.)

 

[Tony_SS]

The new GTO use a a true dual resonator right after the trans, but I would go one step further and use this: an x-pipe muffler, where the xpipe should be, then use 2 mufflers of your choice after that - and nothing chambered - they are designed to make noise, no reduce it.

 

[shotgun]

First ,do you need headers?
They are a big source of sound/noise. Again I am limited since I bleed Pontiac blue,but aren't there cast headers for sbc ( sanderson?).
Also how about Vette Rams horns?
Don't know how they would work in your chassis.

After that get the thickest wall exhaust tubing you can get.
Run an x or a H at minimum.

Tony SS idea is something I thought of also,just don't think there is room for it.

Pick 2 mufflers that have the opposite sounds.
Glass pack type kill low end sounds and let highs and crackle threw.
Turbo types make low mellow sound and kill the high crackles.

I like the second set behind the axle idea.

I did something similar on a customers cars. We installed a Pypes crossflow muffler in a TA in the loud position>they are reversible.

Anyway it was too loud for the guy. But it was all welded up.

I picked up a set of Moroso Spiralflow mufflers and installed them inline where you normally mount the mufflers,under the seat area.Lost very little ground clearance.

Sounded great.

I would use the smallest tubing size you can use without hurting power,install an x, use the smallest diameter but largest case Dynomax super turbo you can use,then install 2 Spiral Flows behind the axle in place of the crossflow muffler,last have your exhaust shooting straight out the rear.

 

[85 Cutlass Brougham]

The muffler Tony SS pictured is the one I want to use after the axle. I agree about chambered mufflers being too loud. I have dual 2.5 in Flowmasters on my AMC and they can wake the dead from two counties away. I currently have a Dynomax cat back on the Cutlass now with Edelbrock headers and it is pretty quiet. Even with no sound deadener and the car gutted, I really can't hear the exhaust at speed. I just think it is a flow restriction because it has a terrible Y pipe design, and necks down to a single 2.5 in pipe before Y ing into 2 2.25 in pipes. I also wonder if using 2.5 in pipes and mufflers for improved volume would work well with 2.25 in tailpipes, the smaller tailpipes being used for less resonance. Is there a mathematical formula for determining the size of exhaust that is needed for a given engine? I also wonder what math is available to determine resonance frequencies, etc. in exhaust systems. Also, if I plan on a small nitrous system, like a 125 shot, would I also need a larger exhaust to support it?

 

[dan2286]

That x-pype muffler looks like a cool idea. Does anyone know if that is more or less efficient than a real x-pype?

 

[Vern]

Its merely another marketing gimic and does not work like a real x pipe at all. A properly designed x pipe has the sides of each exhaust pipe flow hit the other. Each bank in a v8 has pulses that are oppsite of the other bank so as one bank pulses the pulse as it travels thru the x is moveing faster than the exhaust in the other side of the x and it drags or pushes the exhaust on the other side along a little faster, then the other bank pulses and it does it in return. The net effect is that it helps keep the exhaust velocity and also even helps to scavange or pull exhaust out of the other heads recently fired cylinder. A quiet near zero loss exhaust system has been done before but it is not in practice eazy much in the same way a person that knows how to port brand x head might not get the best results the first time he ports heads for y. It also balances the exhaust pressure.

 

[shotgun]

Gotta go with Vern on this one!

That muffler is good for trucks where the exhaust has to run down one side of the chassis.

Assuming it is mounted in a transverse position,the exhaust pulse would be hitting almost dead on in the x portion. That would kill lots of sound as well as HP.

Add to that fact you are planning an X upstream,the exhaust flow "should" be more constant,making it even worse!

If you are dead set on using it, use an H pipe up front,spiral flows,then
that muffler.The idea here to keep the pulses so atleast they don't "hit" dead on in that muffler.

Another option is improving the insulation in the car.
How about using some Dynomat type product.
I have also use a foil/bubble type insulation from Home Depot with success.
May not work as well as Dynomat but it is lighter.

 

[Vern]

I went to delete a word i double posted and this thing showed up. Beats me.

 

[85 Cutlass Brougham]

The car will have a Dynamat like product applied to the whole interior, plus it will use the jute mat type of sound deadening in a larger amount than GM used when the car was new. It won't be as quiet as a good new car, like a BMW, which has better aerodynamics (especially in the side windows!), but I am trying to avoid as much as possible. I have even increased the sound deadening in my otherwise stock beater pickup truck to cut down interior noise.