Starting on the muffler fabrication.

Well, I managed to get a few of the main projects done so far this winter, and the next ones are the aluminum radiator support and the new muffler (singular). It seems to me one big muffler ought to weigh less than two medium size mufflers, so I thought I'd give it a try. My exhaust system has about a three foot "X-pipe" running under the passenger seat, and this is where I was going to place the muffler. Current configuration:



I'm going to cut a section out and install the new muffler there. I made some measurements to see what will fit, and then got some sheetmetal bent up at a friend's welding shop. Here's the main body of the muffler:



I'm going to start cutting some end pieces and a top cover this week. Initially I am going to make the cover removable as I expect to be making some tweaks to the internal baffling and routing depending on noise levels and backpressure readings (I'll have an O2 sensor fitting just upstream of the muffler, and can use this fitting to screw in a pressure gauge line.)

My goal is to reduce the total exhaust system weight, and also be able to place that (muffler) weight where I want it, just in front of the right rear tire.
I've got a few ideas on the internal construction, consisting of some surge volume and sound dampening material. I want this muffler to flow well, but I don't want something that sounds like a big tin can.

that looks like mild steel. How about titanium to save weight. http://www.onlinemetals.com/merchant.cfm?pid=7851&step=4&showunits=inches&id=322&top_cat=131 You could make something adjustable as different tracks have different sound regs.

You could build an internal divertor controllable from the cockpit.

rodeck350 said:

that looks like mild steel. How about titanium to save weight. http://www.onlinemetals.com/merchant.cfm?pid=7851&step=4&showunits=inches&id=322&top_cat=131 You could make something adjustable as different tracks have different sound regs.

You could build an internal divertor controllable from the cockpit.

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Mild steel is for the prototype. Once I'm happy with the performance (sound/backpressure) of the thing, I was going to look into lighter weight options. (I've never welded titanium, so I don't know if I'm talented enough to do it.) I am going to put a thermocouple in the muffler to check on how hot things get. If the temps are reasonable enough downstream there, perhaps an aluminum housing would work. (I know how to weld that.)

I have kicked around the cockpit adjustable idea a few times. I'll know more of how much adjustability I'll need once I find out how the prototype works.

Thanks for your input!

Brings back smiles.....a dash operated cutout.....back 50 years ago, a older friend had that on his Ford.....

and a friend in college had welded in some water pipe to his exhaust system....we drove through the farm lands nearby, and come up on some cow in the field....downshift and bang hell outta that thing, the cow would TAKE off running......:bounce::bump:

makes me want to go back again, and put dash operated cutouts on this vette, just to annoy hell outta the neighbors.....

:bounce::bounce::cussing:

Got a bit of sheetmetal work done on the muffler ends and the removable top cover, and am kicking around ideas for the internal structure.



I need to get some 3 1/2 inch exhaust tubing to make the inlets, and then the internal routing will be sheetmetal strips and some perforated material to allow gas crossflow in some areas while still containing the dampening material (SS wool and fiberglass) in the surge volume areas.



So far the weight looks like I'll be able to meet the target of 15 pounds when complete. This weight will primarily be on the right rear tire. I'm estimating (until I remove the present rear mufflers for weighing) that this setup will remove 5-10 pounds off the car, along with a slight reduction of the polar moment of inertia.

Ron Covell sells an advanced TIG welding DVD that covers titanium.
IAW the DVD, titanium welds like mild steel. The big difference is titanium
requires the weldament(sp)to be in a tent filled with shielding gas.
Of course you must use titanium welding rods.

You can weld ti with a normal gas shield, just have to turn it up and use a wide nozzle, if it turns brownish you have an inadequate shield

Are you going to use the perforated metal for the sides of the "path" through the muffler?

BBShark said:

Are you going to use the perforated metal for the sides of the "path" through the muffler?

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I'm going to somewhat alternate the use of regular sheetmetal strips and lengths of the perforated material depending on what the expected comparative pressure levels are at that position and if the gas flow has to change direction. I'm trying to get some exhaust gas "shunt" flow through some SS mesh to quiet things down, and I'm hoping to get some of the curves to produce localized high and low pressure areas to facilitate this flow through the mesh. I'm also going to try to put some fiberglass insulation around several internal walls in an attempt to increase the dampening and also keep this thing from sounding like a tin can. I had a well known muffler brand on my Corvette several years ago. After spending a good chunk of my weekend welding tubing and elbows to the mufflers to fit them in the back there, I took it out for a test drive. Eleven miles later the car was back in the garage and I was taking them out. It was too loud and they sounded like crap. I then spent the next weekend welding in a set of turbo type mufflers. I love the sound of the present system, but this exercise is mainly a weight reduction issue, but hopefully not at the expense of a nice exhaust note. The muffler housing cover will be removable so I can get in there and re-do/re-route the exhaust flow and/or dampening material. Once I'm happy with things I'll weld it closed.

Have you considered trying to keep some of the parallel reflective surfaces from promoting standing waves? The shorter parallel surfaces (the depth of the muffler, top to bottom) could create standing waves that might make the muffler sound pretty harsh or drone at a specific frequency.

Have you considered a vacuum actuator for flow diversion? I think the Z06 has this, not sure.

BBShark said:

Have you considered trying to keep some of the parallel reflective surfaces from promoting standing waves? The shorter parallel surfaces (the depth of the muffler, top to bottom) could create standing waves that might make the muffler sound pretty harsh or drone at a specific frequency. Yep. I've got dampening material in all directions with the exception of the portion of the two horizontal surfaces that actually comprise the flow path. Although desirable I don't have the vertical space to allow adding material above and below the main flow path, other than some minor insulation on the top surface to keep from heating the floorboard too much. I'm still doing some calculations regarding the speed of sound at high temps versus the "cavity width" to see what frequency things would try to resonate at. My first thought is that this frequency will be much higher than the resonant frequency of the floorboard/rear storage area floor. (But hey, I could be flat out wrong. It happens to me on a semi-regular basis. :amused: ) Have you considered a vacuum actuator for flow diversion? I think the Z06 has this, not sure.

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Thought about it quite a bit. I don't know at this point if it's needed or desired, though. I have several vacuum/pneumatic and electrical actuators on the shelf if I go that direction. I'm just holding off getting fancy at the moment until I see what my noise/backpressure baseline is with this muffler.
I appreciate your interest in the technical aspects of this. :thumbs:

QUOTE:...parallel reflective surfaces from promoting standing waves? The shorter parallel surfaces (the depth of the muffler, top to bottom) could create standing waves that might make the muffler sound pretty harsh or drone at a specific frequency. UNQUOTE

Is that what is going on in the SPIN-TECH? Also just womndering if that approach would be easier to fabricate and test modifications? Seems like they use a series of curves inside a simple shaped "container" almost like beer cans welded in to "turbulate" and attenuate.? Any thoughs?

http://www.drgas.com/spin_tech_mufflers.htm

Interested in finding a similar solution. Will watch closely as you build/test.

51 days or so..

Cheers - Jim

If you plan on using a "fiberglass" packing I suggest you contact Kerry Bryant @ http://areapnolimits.com/home.html.
Kerry uses a very hi quality light weight packing in the exhaust canisters he builds.
I don't know if you have ever heard of Kerry or not. He was the VP at Jardine and Doug Thorley before setting out on his own.

Made a little more progress today. Got the muffler housing installed up in the exhaust pipe. This is the first trial fit. I made a bit of progress since and have the rear pipe mocked up too, ready to put some tack welds on it prior to removal. Once I get the tack welds done I can make some quick progress doing the seam welds and placing some internal baffling in the housing.



Once I get the muffler "permanently" installed I need to weld some pipes from the "Y" under the camber strut bracket up to the tips.

that looks really nice. I didn't think it would look that good.

Can't wait to hear it.

Thanks for the kind words, Turtle.

Made a little more progress today. I got all the box seams welded, along with the inlet and outlet tubes. This is a picture while I was tack welding the outlet tube. (Pardon the dark picture. I had some momentary flash issues.)



I'm pretty close to starting to cut and bend the internal routing baffles. I'll just be putting intermittent type welds in there in case I need to take them out to re-route stuff.
I still need to get some exhaust elbows to weld up the rear muffler replacement pipes.

Made a little progress the last couple days bending up stuff for the internal routing walls. Here's things roughly mocked up to show the general routing, with solid walls for flow direction, and some perforated areas for gas/pressure flow into the dampening materials. I've got a lot of stainless steel mesh left over from a motorcycle muffler I modified years ago, but I still need to get some 'glass type material for extra dampening.



I still need to bend up additional tabs to help keep the flow where I want it.
I ordered some exhaust pipe elbows today from Summit to weld up the pipes to the under-bumper area, and I still need to check a couple local muffler shops for some (304?) stainless steel tubing scraps to form the "chrome" tips.

I have been following your thread on this Mike and find it very interesting. What are the chances of getting some sound clips when you start on the tuning of the new exhaust? I think it would be very interesting to see and hear the changes that you make

SCCA VETTE said:

I have been following your thread on this Mike and find it very interesting. What are the chances of getting some sound clips when you start on the tuning of the new exhaust? I think it would be very interesting to see and hear the changes that you make

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I've never done a sound clip before, and I'll confess I haven't a clue what's required to do it. Any helpful hints are welcomed.

(On a side note I'm trying to make sure all the new projects on the '69 are small "quick" items so that the car isn't torn apart when events start up again at Grissom this spring. I had one mile on the engine when I came up for last fall's events, and it's just too frustrating towing all the way up there when I'm not sure I've got all the bugs worked out of the "last" modification.)

BBShark said:

Have you considered a vacuum actuator for flow diversion? I think the Z06 has this, not sure.

Click to expand...

I think it's called the NPP option. Don't know what NPP stands for. It's available on all C6's I believe. I have a base engine model with it. It is used to bypass the muffler. When you have the muffler bypassed, the cat reactor provides some muffling. I usually drive withe muffler in the exhaust circuit, since there's a noticeable droning sound without the muffler. Bypassing the muffler adds 6 hp to the engine.