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Well, my neighbor, several houses down, who I've never spoken to in 10 years expressed some strong displeasure towards me today.

My car is admittedly loud but I'm not sure what to do to quiet it. I'm running a 4 into 1 with a cat about a foot off the collector. I have a 2.5" I/o 4.5" diameter flowmaster between the rear wheels with a 90 degree turn pointed straight out the back.

I'm currently looking at a vibrant ultra quiet resonator in place of the flowmaster. I have tried a baffle and it significantly altered the afrs to the point where the car was bucking all over the place.

Any ideas before I buy the vibrant?

I would try and track down the original matching motorcycle muffler. Then make it fit. The factory mufflers are very efficient and quiet.

Graham

The "bucking" with the baffle added was probably some reversion from adding back pressure to the exhaust combined with using a sport bike motor (cams) with too little gear (that is why standard class bikes with less aggressive cams make better street driven becs). You can add anti-reversion cones/lips to the system. Bucking is not normally caused by rich mixtures from more back pressure with the same fueling.

I've never had much interest in the concerns of neighbors, but based on your description, that would be a very LOUD system. A reasonably quiet/socially responsible system will need a retune and will be slower/less responsive, but well worth it imho if you drive on the street.

The "muffler" described must be a "flowmaster outlaw series race muffler". There is a 7 inch and an 11 inch long version. Neither makes an effective muffler nor does the vibrant.

I suggest the Walker $31 #18426. 2.5 /2.13 in-out, 13 long x 4.25 thick x 8.8 wide. 17.75 long over all with the pipes but you can trim those down if needed. Probably need to run it straight back versus side ways or consider diagonal with 45 degree mandrel bends. This is a replacement muffler for 5.0L v8 and 4.2L L6 jeeps but it will not sound like a jeep. For $31, consider trying it.
https://www.summitracing.com/parts/wlk-18426

I second using the oem bike muffler at the rear which should work ok for most neighbors.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

OEM silencers are going to be very difficult to fit as they are strange dimensions. That walker is going to be even harder to fit.

I'm currently using this:
https://www.amazon.com/Flowmaster-71416 ... 156&sr=8-5

Can't see (no pics) why the walker would be harder to fit. The connecting pipes on the walker can be shortened and butt welded like headers for close to the same 14 inch length, it is the same thickness, and while it is wider, it could be rotated. Again, can't see the issue without pics but an effective muffler needs some volume. There is hardly any additional volume to a straight pipe with the one you are using and any other round design with more volume would need to be longer and/or thicker.

Flowmaster 71416 is listed as 14" case, 4" thick, 20" long, making it longer than the walker but slightly thinner.
https://www.summitracing.com/parts/flo-71416

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

It looks like you ran parallel to the outer frame rail all the way back, through the fender, then turned 90 after the rear kick up in the rail.

I see something forward of the muffler. Looks like a gusset and a heat shield for the fuel tank. I would use the stainless flowmaster version of the walker since it will be partially visible, make room with 2-1/2 more inches of clearance forward of your existing muffler and let the other 2-1/2 extend to the rear.

https://www.summitracing.com/parts/flo-71226?rrec=true

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

It is a heat shield for the fuel tank. https://photos.app.goo.gl/uKurT8U9hMdX1nDA8


https://www.summitracing.com/parts/wlk-21762
I may be able to fit this with the majority of the muffler going vertical behind the rear panel. I would then 90 the upper port towards the floor and 90 again out the back. A new heatshield would need to be fabbed as I'd be within 5 or so inches of the fuel tank at this point.

Thoughts?

I think you mean forward of the rear panel versus behind but yes, that sounds like a good plan and a very effective muffler. Since the muffler would be in a pocket with little airflow, a good heat shield to block the heat rise would be important. The fiero places the muffler in a similar config and has a blower motor in the trunk with blast tubes to circulate the air, along with a spaced heat shield on the trunk. Two steel .050" sheets, spaced an inch apart and airflow between them would be very effective between the tank and muffler. Venting the rear panel or fitting mesh inserts could work well too. Make a cardboard muffler to test fit before buying.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Appreciate the help! I'll post an update when done.