Help me design a muffler for 3.6 varioram

[jmz]

Hi all,

Getting closer to driving my 3.6 varioram swap. The car will be an RSR IROC tribute so I need the exhaust spacing to resemble that. …no GT3 mufflers etc.

I am running a set of headers …William Knight style with v-band connectors.

I have an excellent fabricator that can make whatever I want.

Anyone have a good top notch suggestion?

I will run in this configuration for about a year. I plan on putting a built 3.5 in the future.

Thanks,
Jay

[Duc Hunter]

I am sure Bill V will chime in here. He has made several posts on his opinions on 3.6 conversation mufflers.

I have gone round and around and I’m currently running Rothsport headers that look similar to what you have in your picture. I currently have a GT3 muffler and for my mission it’s entirely too loud at 86+ decibels on the freeway at 75 miles an hour. Yes, that’s on the quiet side of the muffler.

My question for you is what is the mission for the car? Is it going to be a street car? Is it going to be taking long road trips? Is it going to be a track rat? Is it only for weekend enjoyment closer to home? That will have a lot of impact on exhaust choices.

i’ve tried lots of different styles of exhaust on mine, including various headers and various mufflers, including the GT3, some Flowmaster configurations, etc. Originally I was also looking for RSR style outlets (and may go back to that). What I would say is the first challenge for you would be how far towards the rear of the car or the collectors. If they’re very far back, it makes it hard for you to design a intake pipe for the muffler that will make the 90° turn to go parallel to the muffler, well turn upward to get them up high to flow into the muffler. Because the RSR style outlets you want are narrow compared to something like a 3.2’s, you probably want to have the outlets of the muffler on the bottom, and they would turn 90° inside of where your collectors are to point towards the rear of the car. between the collectors, where the muffler has to sit vertically, where the rear body is, etc.… There’s not a lot of space back there.,

For me personally, my car is a street car, one that gets a reasonable amount of use and takes long road trips to various car shows. I was thinking about putting some muffler packing in the quiet side of the GT3 muffler to make it more tolerable under normal street conditions. In looking at the GT3 muffler internals, I’m not sure that’s possible. So my next step will probably be to do what Bill often recommends, get a Fabspeed dual in/out muffler for a 964, run both outlets, and put a valve on one of the two outlets. That will reduce any droning and give me a nice sound that’s not too loud for cruising down the freeway, and I’ll be able to open it up when it’s above 4500 RPM. (When my valves open automatically). I could even put a switch in to open them manually when I want it loud.

Just some thoughts.

[Jjm4life]

I have a William knight 3.5 with his headers and a gt3 muffler Setup. Sounds great but I agree it can be too loud at times. But at full chat it sounds awesome. I might try attempt to move it wiring rk extend the exhaust tips a bit in an effort to get it from under the car to further out and away if that makes sense

[jmz]

This will be a multi purpose car. It will still be used on the street but also somewhat track optimized. I plan on using it on both. ...I'd like to be able to run Laguna Seca and not get flagged for being too loud otherwise I don't mind a little bark in the exhaust. I have looked at the flowmaster/dynomax option and that looks reasonable but if I am going to pay the money for fabwork I want to make sure it is done right. I've considered modding the intake onto a bannana muffler but worry that may choke the engine too much

Originally Posted by Duc Hunter

I am sure Bill V will chime in here. He has made several posts on his opinions on 3.6 conversation mufflers.

I have gone round and around and I’m currently running Rothsport headers that look similar to what you have in your picture. I currently have a GT3 muffler and for my mission it’s entirely too loud at 86+ decibels on the freeway at 75 miles an hour. Yes, that’s on the quiet side of the muffler.

My question for you is what is the mission for the car? Is it going to be a street car? Is it going to be taking long road trips? Is it going to be a track rat? Is it only for weekend enjoyment closer to home? That will have a lot of impact on exhaust choices.

i’ve tried lots of different styles of exhaust on mine, including various headers and various mufflers, including the GT3, some Flowmaster configurations, etc. Originally I was also looking for RSR style outlets (and may go back to that). What I would say is the first challenge for you would be how far towards the rear of the car or the collectors. If they’re very far back, it makes it hard for you to design a intake pipe for the muffler that will make the 90° turn to go parallel to the muffler, well turn upward to get them up high to flow into the muffler. Because the RSR style outlets you want are narrow compared to something like a 3.2’s, you probably want to have the outlets of the muffler on the bottom, and they would turn 90° inside of where your collectors are to point towards the rear of the car. between the collectors, where the muffler has to sit vertically, where the rear body is, etc.… There’s not a lot of space back there.,

For me personally, my car is a street car, one that gets a reasonable amount of use and takes long road trips to various car shows. I was thinking about putting some muffler packing in the quiet side of the GT3 muffler to make it more tolerable under normal street conditions. In looking at the GT3 muffler internals, I’m not sure that’s possible. So my next step will probably be to do what Bill often recommends, get a Fabspeed dual in/out muffler for a 964, run both outlets, and put a valve on one of the two outlets. That will reduce any droning and give me a nice sound that’s not too loud for cruising down the freeway, and I’ll be able to open it up when it’s above 4500 RPM. (When my valves open automatically). I could even put a switch in to open them manually when I want it loud.

Just some thoughts.

[jmz]

Originally Posted by Jjm4life

I have a William knight 3.5 with his headers and a gt3 muffler Setup. Sounds great but I agree it can be too loud at times. But at full chat it sounds awesome. I might try attempt to move it wiring rk extend the exhaust tips a bit in an effort to get it from under the car to further out and away if that makes sense

I would very much like to hear about your 3.5. Did William build and design or just design? fuel injected or carbs? THanks!

[Duc Hunter]

If you ahve not read these, check them out. ESP comments from Bill V. He has forgotten more about these things than most of us ever knew.

Thread 1

Thread 2 - Longer and better one

[Bill Verburg]

Budget and material availability will be the issues, besides fab skills
here are some best practices
The bananas are great because they have max volume and wall stiffness, they use the entre volume between the bumper and the chassis end

Here is a stock and modified banana, I like the lower rear inlets, they would need to be wider apart for modern 3.6 headers, The domed ends and curved lateral walls stiffen the case and reduce sound transmission as does the heave gauge steel. Outlets vary but I like the stock left exit mirrored on the right. The inlets open into mirrored large chambers, this reflects a useful acoustic signal back up the pipes, The now expanded gasses then flow to the central chambers where the bulk of the sound deadening wrap will be, the transfer tubes on the right have bell shaped ends that facilitate flow, I'd like to see more perforated and wrapped pipe here.


Thats what the factory did on the 954(964RS/LW muffler




993 side mufflers are pretty good too, won't fit a 911 because of the oil tank but the construction is informative, inlets are the straight end pipes, again domed ends and oval walls, heavy gauge steel, bell l shaped exit into a large cavity to generate the acoustic return signal, wrapped perforated pipe, the interior cross pipe size tunes sound volume, bigger is louder smaller is quieter.

a better flowing version is the turbo version of this


modified n/a


actual tt


all the perf. pipe is wrapped

GT3



Note the case stiffening
upper is quiet lower is loud
That arched pipe connecting the 2 outlets does nothing to muffle the noise, eliminate it, put a perforated divider shelf ala the oe banana w/ wrap or ss scrubble between the 2 inner bulkheads.

[Duc Hunter]

Bill, I have often wondered if packing the chambers either side of the center would help reduce (significantly) the quiet side of a GT3 muffler, without of course changing the louder side (since it would be out f the loop). My impression from seeing the exploded views like your picture tell me that packing anything would mean ass must flow through the packing material, which is a no go obviously. So by design, there is no way to cut open a GT3 muffler and make the quiet side more quiet. Seem right?

In previous threads you have talked about the Fabspeed muffler as a really good option. Have an exploded views of one of them?

[Jjm4life]

Originally Posted by jmz

I would very much like to hear about your 3.5. Did William build and design or just design? fuel injected or carbs? THanks!

Bought the car off another member with a rasant itb/ecu/cop setup. never ran right. William designed the motor and I had the itbs swapped out for ATpower ones. William iwasn’t doing motor builds (is he now?) at the time, so mine was assembled at his direction by will Pyle at fairwinds in Delaware. that was the closest shop to me
That he was essentially willing to trust to build it. Exhaust, tuning and the last 10% was done closer to home at ace performance in Tewksbury ma and they have been maintaining and further modifying it since .

Shoot me a DM if you have any specific questions. Happy to talk about my experience

[jmz]

I have access to very good fabricators. …not a money no object project, but I am willing to spend for a good outcome. If I use the banana it will be close to RSR style with input and output almost being a straight through shot. I am afraid this
may be too loud.

I am searching for the best 2 in 2 out to adapt. …either that or run 2 independent mufflers but fabrication gets much trickier that way.

Any words of wisdom or advice?

Originally Posted by Bill Verburg

Budget and material availability will be the issues, besides fab skills
here are some best practices
The bananas are great because they have max volume and wall stiffness, they use the entre volume between the bumper and the chassis end

Here is a stock and modified banana, I like the lower rear inlets, they would need to be wider apart for modern 3.6 headers, The domed ends and curved lateral walls stiffen the case and reduce sound transmission as does the heave gauge steel. Outlets vary but I like the stock left exit mirrored on the right. The inlets open into mirrored large chambers, this reflects a useful acoustic signal back up the pipes, The now expanded gasses then flow to the central chambers where the bulk of the sound deadening wrap will be, the transfer tubes on the right have bell shaped ends that facilitate flow, I'd like to see more perforated and wrapped pipe here.


Thats what the factory did on the 954(964RS/LW muffler




993 side mufflers are pretty good too, won't fit a 911 because of the oil tank but the construction is informative, inlets are the straight end pipes, again domed ends and oval walls, heavy gauge steel, bell l shaped exit into a large cavity to generate the acoustic return signal, wrapped perforated pipe, the interior cross pipe size tunes sound volume, bigger is louder smaller is quieter.

a better flowing version is the turbo version of this


modified n/a


actual tt


all the perf. pipe is wrapped

GT3



Note the case stiffening
upper is quiet lower is loud
That arched pipe connecting the 2 outlets does nothing to muffle the noise, eliminate it, put a perforated divider shelf ala the oe banana w/ wrap or ss scrubble between the 2 inner bulkheads.

[David]

I'm working with Jay on this and the engineer in me wants it to be as good as possible with no regard for Jay's budget

The real limiting factor on this muffler is that the center to center dimension of the headers left to right is the same as the IROC bumper exit dimension. Since the IROC had straight pipes off the headers, this makes perfect sense but trying to fit a muffler in there while maintaining the same center to center dimension is difficult.

I'm not a fan of the banana muffler because the inlet will line up with the outlet and I don't think the exhaust expanding in the banana muffler and then going right back out will muffle much.

I've taken a stab at designing a muffler with off the shelf 304 stainless bends and mufflers.

Here's my first take designing a muffler using a Borla dual 2.5" inlet/outlet with a X cross internal configuration:



After reading Bill's comments on one of the linked threads, I see that the X cross inside the muffler is not going to help flow so here's my second design using a dual 2.5" inlet/outlet with each side having a straight through design. I'd like Bill's take on this since there would still be some mixing of the flows inside the muffler even though each has their own perforated tube passage.

[jmz]

Glad you chimed in.

[Duc Hunter]

Great drawings! What about your design, but a wider can left/right. then have the input and put put weld in like they would on a banana, and use internal chambers/baffles, to prevents the straight through run?

Hopefully Bill will chime in soon!

[David]

Originally Posted by Duc Hunter

Great drawings! What about your design, but a wider can left/right. then have the input and put put weld in like they would on a banana, and use internal chambers/baffles, to prevents the straight through run?

Hopefully Bill will chime in soon!

I thought about that and even started sketching up some designs and reading some papers on muffler design. Problem is, once you start talking baffles, you're into a lot of trial and error testing to find what works and that's not in the cards for this project.

Here's a 3rd design using even more of Jay's money: it uses two $750 2-stage Burns Stainless mufflers. The mufflers could even be offset left and right to improve tubing position.

[Bill Verburg]

Originally Posted by David

I thought about that and even started sketching up some designs and reading some papers on muffler design. Problem is, once you start talking baffles, you're into a lot of trial and error testing to find what works and that's not in the cards for this project.

Here's a 3rd design using even more of Jay's money: it uses two $750 2-stage Burns Stainless mufflers. The mufflers could even be offset left and right to improve tubing position.

pluses and minuses of that design;

Pluses: sides are kept separate, there is only one step at the exit, and it's a big one which sends the strongest possible return signal that can be used by cams w/ a decent amount of TDC compression overlap. There is a minimum of bends.

Minuses the longer the muffler the better for noise suppression, there is a lot of wasted territory where the external tubes bend around

[Bill Verburg]

Originally Posted by David

I'm working with Jay on this and the engineer in me wants it to be as good as possible with no regard for Jay's budget

The real limiting factor on this muffler is that the center to center dimension of the headers left to right is the same as the IROC bumper exit dimension. Since the IROC had straight pipes off the headers, this makes perfect sense but trying to fit a muffler in there while maintaining the same center to center dimension is difficult.

I'm not a fan of the banana muffler because the inlet will line up with the outlet and I don't think the exhaust expanding in the banana muffler and then going right back out will muffle much.

I've taken a stab at designing a muffler with off the shelf 304 stainless bends and mufflers.

Here's my first take designing a muffler using a Borla dual 2.5" inlet/outlet with a X cross internal configuration:



After reading Bill's comments on one of the linked threads, I see that the X cross inside the muffler is not going to help flow so here's my second design using a dual 2.5" inlet/outlet with each side having a straight through design. I'd like Bill's take on this since there would still be some mixing of the flows inside the muffler even though each has their own perforated tube passage.

again, pluses and minuses.
I'd need to see the internals to know what pluses there are

minuses, as w/ the other design lots of waste volume where the external pipes bend around,

In general you want the largest possible internal volume, you want as large a cavity for expansion as possible where the first step transition is, perforated, wrapped pipe is the next best thing to straight pipe and adds sound suppression, keep the sides separated until after as much gas expansion as is possible has occurred

look at the banana and GT3 and 993 side mufflers for examples

here are other factory internals the later they are the more efficient and better balance between muffling and power, though I see tweaks for all of them that would be beneficial.


here's what you are dealing w/ internally

[David]

Bill, this design uses a straight through muffler from Stainless Bros. They say each side is straight though with no crossing in the middle like Borla or Magnaflow. Of course the construction is a little more difficult since the left and right side inlet/outlet tubing/bends aren't mirror images. Any concern with one side being a longer run than the other?

[skinnerd]

I had a twin pipe Monty that we modified the inlets.
It had a good deep tone but was not loud at all.
Not sure where you'd buy this muffler any more.

[skinnerd]

Perhaps something like this could be modified to go with your V-band setup??

https://patrickmotorsports.com/products/exh911rsrsmsspms?srsltid=AfmBOopA1IaYhXFA0Tez4MHGz eK3PymWcUtnUdzKc_RSDQWW73tzfk2i

[3rd_gear_Ted]

I have a Dynaflow design very similar to top drawing. The muffler weight support use the two lower case studs. Muffler has a mount bracket welded in place.
Thermal wrap up next.